Reactive nitrogen chemistry in aerosol water as a source of sulfate during haze events in China-Kebin HVIP专享VIP免费

下载本文档

阅读 323
格式 pdf
大小 490.9 KB
约11页
2023-04-20
收藏
点赞(0)
海报
举报

ENVIRONMENTAL SCIENCE 2016 © The Authors,

some rights reserved;

exclusive licensee

American Association

for the Advancement

of Science. Distributed

under a Creative

Commons Attribution

License 4.0 (CC BY).

Reactive nitrogen chemistry in aerosol water as a

source of sulfate during haze events in China

Yafang Cheng,

†

Guangjie Zheng,

1,2

* Chao Wei,

Qing Mu,

Bo Zheng,

Zhibin Wang,

Meng Gao,

3,4

Qiang Zhang,

Kebin He,

2†

Gregory Carmichael,

3,4

Ulrich Pöschl,

1†

Hang Su

6,1†

Fine-particle pollution associated with winter haze threatens the health of more than 400 million people in the North

China Plain. Sulfate is a major component of fine haze particles. Record sulfate concentrations of up to ~300 mgm

−3

were observed during the January 2013 winter haze event in Beijing. State-of-the-art air quality models that rely on

sulfate production mechanisms requiring photochemical oxidants cannot predict these high levels because of the

weak photochemistry activity during haze events. We find that the missing source of sulfate and particulate matter

can be explained by reactive nitrogen chemistry in aerosol water. The aerosol water serves as a reactor, where the

alkaline aerosol components trap SO

, which is oxidized by NO

to form sulfate, whereby high reaction rates are sus-

tained by the high neutralizing capacity of the atmosphere in northern China. This mechanism is self-amplifying be-

cause higher aerosol mass concentration corresponds to higher aerosol water content, leading to faster sulfate

production and more severe haze pollution.

INTRODUCTION

Persistent haze shrouding Beijing and the North China Plain (NCP) dur-

ing cold winter periods threatens the health of ~400 million people living

in a region of ~300,000 km

. Characteristic features of the winter haze in

northern China include stagnant meteorological conditions with low

mixing heights, high relative humidity (RH), large emissions of primary

air pollutants, and fast production of secondary inorganic aerosols, espe-

cially sulfate (see section M1) (1–5). Analyzing surface-based observa-

tions at a site in Beijing during January 2013 (see section M2) and

using concentration ratios of sulfate to sulfur dioxide ([SO

42−

]/[SO

])

as a proxy for the sulfate production rate (5), we find that sulfate pro-

duction increases as PM

2.5

(particulate matter with a diameter of less

than 2.5 mm) levels increase (Fig. 1A). Ratios are six times higher during

the most polluted periods (PM

2.5

> 300 mgm

−3

) than during clean to

moderately polluted conditions (ratios of 0.1 when PM

2.5

<50mgm

−3

Traditional air quality models, however, fail to capture this key feature

of NCP winter haze events even after accounting for aerosol-radiation-

meteorology feedback (see sections M2 and M3) (6–8). The chemical

mechanisms used in these models usually comprise gas-phase oxidation

of sulfur dioxide by OH radicals and aqueous-phase reaction pathways

in cloud water, involving H

and O

, resulting in sulfate production

rates that scale with the intensity of solar ultraviolet (UV) radiation

(9,10). During NCP haze days, UV radiation is significantly reduced

because of the aerosol dimming effect, resulting in a decrease of most

oxidant concentrations (5). Figure 1B shows that the midday O

values

drop from ~22 parts per billion (ppb) under clean conditions to ~1 ppb

duringthehazeperiod(andalsolosetheir typical diurnal variation, fig.

S1). The reduced oxidant levels and increased sulfate production suggest

the existence of a missing sulfate production pathway. Even after consid-

ering the gas phase and cloud/fog chemistry, there is still a large gap

between modeled and observed sulfate (Fig. 1C). Adding an apparent

heterogeneous process with sulfate production rates that scale with

aerosol surface area and RH can greatly improve model predictions

(see sections M3 to M5) (7), but the chemical mechanism of the missing

sulfate production pathway has not yet been identified.

RESULTS AND DISCUSSION

We find that reactive nitrogen chemistry in aerosol water can explain

the missing source of sulfate in NCP winter haze. Aerosol water is a

key component of atmospheric aerosols, which serves as a medium

that enables aqueous-phase reactions (11–13). The aerosol water con-

tent (AWC) in Beijing, calculated using measurements of RH and

aerosol composition and the ISORROPIA-II thermodynamic equilib-

rium model (see section M6) (14–16), is well correlated with the

missing sulfate content, the difference between measured and modeled

sulfate (D[SO

42−

]) (Fig. 1C) (see sections M2 to M4), suggesting its

involvement in the sulfate production. Note that because of the salt-

induced freezing point depression (17), aerosol water will not freeze

for a winter temperature of ~271 K in Beijing.

Taking the impact of mass transfer and ion strength into account,

we make a conservative estimation of sulfate production rate for dif-

ferent reactions in the aerosol water under relevant atmospheric trace

species concentration conditions (see sections M4 and M7 to M9) and

find NO

to be the most important oxidant in Beijing during haze

periods (Fig. 2B). In the presence of aerosol water, gas-phase NO

can partition into the condensed phase, react with SO

dissolved in

the aqueous phase, and produce sulfate as well as nitrite (R1) (18).

2NO

2ðaqÞþHSO3ðaqÞþH2OðaqÞ→3H

þðaqÞ

þ2NO

2ðaqÞþSO42ðaqÞðR1Þ

Under heavy haze conditions (PM

2.5

≥300 mgm

−3

), the sulfate pro-

duction rates of the NO

reaction pathway (R1) are ~1 to 7 mgm

−3

−1

much higher than the reaction rates involving other important aqueous

oxidants such as O

and H

. According to Zheng et al.(7), an ad-

ditional sulfate production of ~3 mgm

−3

−1

is needed to explain the

Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128,

Germany.

State Key Joint Laboratory of Environment Simulation and Pollution Control,

School of Environment, Tsinghua University, Beijing 100084, China.

College of Engi-

neering, University of Iowa, Iowa City, IA 52242, USA.

Center for Global and Regional

Environmental Research, University of Iowa, Iowa City, IA 52242, USA.

Center for Earth

System Science, Tsinghua University, Beijing 100084, China.

Institute for

Environmental and Climate Research, Jinan University, Guangzhou 511443, China.

*These authors contributed equally to this work.

†Corresponding author. Email: yafang.cheng@mpic.de (Y.C.); hekb@tsinghua.edu.

cn (K.H.); u.poschl@mpic.de (U.P.); h.su@mpic.de (H.S.)

SCIENCE ADVANCES |RESEARCH ARTICLE

Cheng et al.Sci. Adv. 2016; 2: e1601530 21 December 2016 1of11

observations in the severe winter haze periods of Beijing (see section

M9), which falls right into the range of production rates from the chem-

ical reaction mechanism we proposed (R1). As illustrated in Fig. 2, sul-

fate production in aerosol water underhazeconditionsdiffersfromthat

in cloud droplets, where the major oxidation pathways are reactions

with H

and O

,andNO

playsonlyaminorrole(12,19). Thus,

traditional air quality models usually include only the H

and O

re-

action pathways of sulfate production in the aqueous phase, whereas the

reaction pathway is neglected (7,20).

The AWC is typically three to five orders of magnitude lower than

the water content of cloud or fog (21). On this basis, how can the NO

reaction pathway become important in such tiny amounts of water?

The increased importance is due to the relatively high aerosol pH and

elevated NO

concentrations in Beijing and the NCP during haze

periods. As shown in Fig. 2, aqueous oxidation rates of S(IV) by

and O

are strongly pH-dependent. High pH increases the sol-

ubility and the effective Henry’s law constant of SO

, pulling more

into the aerosol water and thus increasing the reaction rate. When

pH increases by one unit, the reaction rates increase by one and two

orders of magnitude for NO

and O

, respectively. The H

reaction

does not show a strong dependence because high pH reduces its reac-

tion rate coefficient, which offsets the effect of increased solubility.

Compared with North America and Europe, aerosols in the NCP

are more neutralized (22), as shown by a higher cation-to-anion ratio

(Fig. 1D). This neutralized featureisalsowelldocumentedandisthe

reason that acid rain rarely occurs in northern China (see section

M10) (22). Using the ISORROPIA-II thermodynamic equilibrium

model (see section M6) (14–16) and in situ aerosol bulk composition

measurements, we obtain average pH values of 5.4 to 6.2 for aerosol

water under NCP haze conditions (see sections M6 and M9). Similar

calculations based on size-segregated aerosol composition measure-

ments even show a higher effective pH and sulfate production rates

(fig. S2).

Elevated NO

is another key factor that leads to fast sulfate forma-

tion. Substantial amounts of NO

come from direct emission of NO

(= NO + NO

). Although the NO

-to-NO

ratios were reduced be-

cause of weak photochemistry during the haze event, the stagnant

weather trapped more NO

near the surface, resulting in elevated

concentrations that were, on average, three times higher than

those under clean conditions (~66 ppb, Fig. 1B). These periods of

highest NO

levels occurred when the concentrations of other photo-

chemical oxidants that can produce sulfate (H

,andOH)were

low (Fig. 1B and fig. S1). Changes in pH and precursor concentrations

together lead to the transition from an H

-dominated regime of

aqueous sulfate production in cloud droplets to an NO

-dominated

regime of aqueous sulfate production in haze (Fig. 2). Earlier studies

had already suggested that the NO

reaction pathway may contribute

to sulfate formation in fogs under polluted conditions (23,24), but

NO2 (ppb)

0–50

50–100

100–300

>300

PM2.5 (µg m–3

)

Midday O3 (ppb)

O3NO2

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0.0

[SO4

2–] / [SO2]

0–50

50–100

100–300

>300

PM2.5 (µg m–3

)

300

250

200

150

100

SO4

2–

(obs. - model, µg m–3)

12008004000

Aerosol droplet solution (µg m–3)

4002000

AWC (µg m–3)

Europe

East Asia

North America

2.42.01.61.20.80.40.0

Anions (µmol m–3)

2.4

2.0

1.6

1.2

0.8

0.4

0.0

Cations (µmol m–3)

Fig. 1. Characteristic featuresof a major haze event in Beijing, China(January 2013). (A) Sulfate/sulfur dioxide ratio ([SO

42−

]/[SO

]) and (B)middayozone(O

) concentrations

(10:00 to 15:00 local time) and nitrogen dioxide (NO

) concentrations at different fine-particle (PM

2.5

) concentration levels. (C) Correlation of the unexplained sulfate concentration

(DSO

42−

= observation −model) (see sections M2 and M3) with aerosol droplet solution and AWC (color-coded). (D) Anion-to-cation ratio in PM

2.5

as observed in Beijing (solid

symbols)andinotherstudiesinnorthernChina(opensymbols)(tableS1)compared to the characteristic ratios reported for aircraft measurements in the Arctic of outflow from

East Asia, Europe, and North America (solid red, blue, and green lines; here, only NH

,NO

−

,andSO

42−

were considered) (87).

SCIENCE ADVANCES |RESEARCH ARTICLE

Cheng et al.Sci. Adv. 2016; 2: e1601530 21 December 2016 2of11

during the Beijing haze event of January 2013, fog was not observed

and sulfate production by NO

occurred in aerosol water instead.

Sulfate production rates from the NO

reaction pathway (R1)

calculated on the basis of measurement data (hourly concentrations

of NO

,SO

,PM

2.5

, and RH; sections M2 and M4) show a positive

dependence on the PM

2.5

concentration, varying from 0.01 mgm

−3

−1

under relatively clean conditions to nearly 10 mgm

−3

−1

in the most

polluted periods (pink circles in Fig. 3). These reaction rates can account

for the systematic underprediction of models and explain the large

missing source of sulfate in the Beijing haze (black diamonds in Fig. 3).

Under clean conditions, the OH reaction (green crosses in Fig. 3) dom-

inates the oxidation pathways of SO

. As particle concentrations increase

and more sulfate is produced, the photochemistry slows down, leading to

less OH, and sulfate production via this pathway decreases. From this

aspect, the OH reaction has a negative feedback, which is self-buffered

against heavy pollution. As PM

2.5

concentrations and RH increase simul-

taneously [a special feature of haze events in NCP (5)], the OH reaction

becomes weaker, whereas the aqueous-phase reaction of NO

starts to

play a more important role. For the January 2013 conditions at PM

2.5

~100 to 200 mgm

−3

, the aqueous-phase reaction becomes the dominant

oxidation pathway (Fig. 3). In contrast to the OH reaction, the NO

re-

action shows a positive feedback mechanism, where higher particle mat-

ter levels lead to more aerosol water, which accelerates sulfate production

and further increases the aerosol concentration. This positive feedback

intensifies the PM

2.5

levels during haze periods, resulting in a series of

record-breaking pollution events.

The NO

reaction with SO

in aerosol water produces not only sul-

fate but also nitrite (R1), which may undergo subsequent oxidation or

disproportionation reactions forming nitrate. This is consistent with the

high nitrate concentrations observed during the haze event, which are of

similar magnitude to the sulfate concentrations (up to ~160 mgm

−3

)(5)

and have also not yet been explained by air quality models (7). Depend-

ing on the pH value of the haze droplets, nitrite can also form nitrous

acid (HONO) and undergo reversible partitioning with the gas phase

(25,26). Moreover, the release of HONO removes H

,whichmayhelp

to sustain the droplet acidity and efficient sulfate production (27,28).

For the same haze periods, record high aerosol nitrite concentrations of

up to ~12 mgm

−3

were observed in Shandong, northern China, with

nitrite concentrations well correlated with NO

at high RH (>50%)

(25). The nitrite-to-HONO molar ratio of ~3 in Shandong is a hundred

times higher than the ratio observed during a pollution event in

Nanjing, Yangtze River Delta of China, where only trace amounts of

nitrite were detected in the aerosol phase (up to ~0.4 mgm

−3

), and

the aerosol water there was more acidic (pH ~4) (24,25). This further

confirms the more neutralized feature of aerosol particle composition

and haze in northern China.

Our study unfolds a new and more comprehensive conceptual

model of sulfate formation in NCP haze events, including not only

the traditional OH, H

, and O

reaction pathways in atmospheric

gas phase and cloud chemistry but also the NO

reaction pathway in

aerosol water (Fig. 4). The NO

pathway may not be limited to winter

haze because it may also be important at night and during fog events in

polluted regions with high boundary layer concentrations of PM

2.5

and

andelevatedRH(23,24).Theimportanceofmultiphasechemistry

holds for a wide range of aerosol pH. When aerosols become more acid-

ic, the sulfate production can be maintained at a high rate through TMI

reactions (Fig. 2B). The important role of aerosol pH in the multiphase

reaction pathway highlights the need to better understand the sources of

ammonia and alkaline aerosol components from natural and anthropo-

genic emissions (soil dust, seawater, agriculture, energy, industrial, and

8765432

10–7

10–6

10–5

10–4

10–3

10–2

10–1

100

101

102

103

Beijing haze

H2O2 O3 TMI NO2

8765432

10–5

10–4

10–3

10–2

10–1

100

101

102

103

104

105

d [SO4

2–] / dt (µg m–3

h–1

)

Cloud droplets

Fig. 2. Aqueous-phase sulfate production by sulfur dioxide oxidation under

characteristic conditions. Sulfate production rates for (A) cloud droplets and (B)Beijing

haze plotted against pH value. Light blue–and gray-shaded areas indicate characteristic

pH ranges for cloud water under clean to moderately polluted conditions and aerosol

water during severe haze episodes in Beijing, respectively. The colored lines represent

sulfate production rates calculated for different aqueous-phase reaction pathways with

oxidants: hydrogen peroxide (H

), ozone (O

), transition metal ions (TMIs), and nitro-

gen dioxide (NO

). Characteristic reactant concentrations and model calculations for

clouds and haze are taken from the literature and observations, and specified in Materials

and Methods (see sections M7 to M9) (12,21).

10–3

10–2

10–1

100

101

d [SO4

2–] / dt (µg m–3

h–1

)

8006004002000

PM2.5 (µg m–3)

NO2 reaction

OH reaction

Missing source

Fig. 3. Importance of the NO

reaction pathway for sulfate production in the

Beijing haze (January 2013). Sulfate production rates calculated for the aqueous-

phase NO

reaction pathway (pH 5.8) and the gas-phase OH reaction pathway

compared to the missing source of sulfate. Crosses and circles represent hourly

production rates calculated on the basis of measurement data, and the diamonds

represent the average missing source (arithmetic mean ± SD) (see sections M3 to

M5) (7). The pink-shaded area shows the maximum and minimum sulfate produc-

tion rates by the NO

reaction pathway bounded by the aerosol water pH ranging

from 5.4 to 6.2 during haze periods.

SCIENCE ADVANCES |RESEARCH ARTICLE

Cheng et al.Sci. Adv. 2016; 2: e1601530 21 December 2016 3of11

/11

下载本文档

文本预览下载提示常见问题

ENVIRONMENTALSCIENCE2016©TheAuthors,somerightsreserved;exclusivelicenseeAmericanAssociationfortheAdvancementofScience.DistributedunderaCreativeCommonsAttributionLicense4.0(CCBY).ReactivenitrogenchemistryinaerosolwaterasasourceofsulfateduringhazeeventsinChinaYafangCheng,1†GuangjieZheng,1,2ChaoWei,1QingMu,1BoZheng,2ZhibinWang,1MengGao,3,4QiangZhang,5KebinHe,2†GregoryCarmichael,3,4UlrichPöschl,1†HangSu6,1†Fine-particlepollutionassociatedwithwinterhazethreatensthehealthofmorethan400millionpeopleintheNorthChinaPlain.Sulfateisamajorcomponentoffinehazeparticles.Recordsulfateconcentrationsofupto~300mgm−3wereobservedduringtheJanuary2013winterhazeeventinBeijing.State-of-the-artairqualitymodelsthatrelyonsulfateproductionmechanismsrequiringphotochemicaloxidantscannotpredictthesehighlevelsbecauseoftheweakphotochemistryactivityduringhazeevents.Wefindthatthemissingsourceofsulfateandparticulatemattercanbeexplainedbyreactivenitrogenchemistryinaerosolwater.Theaerosolwaterservesasareactor,wherethealkalineaerosolcomponentstrapSO2,whichisoxidizedbyNO2toformsulfate,wherebyhighreactionratesaresus-tainedbythehighneutralizingcapacityoftheatmosphereinnorthernChina.Thismechanismisself-amplifyingbe-causehigheraerosolmassconcentrationcorrespondstohigheraerosolwatercontent,leadingtofastersulfateproductionandmoreseverehazepollution.INTRODUCTIONPersistenthazeshroudingBeijingandtheNorthChinaPlain(NCP)dur-ingcoldwinterperiodsthreatensthehealthof~400millionpeoplelivinginaregionof~300,000km2.CharacteristicfeaturesofthewinterhazeinnorthernChinaincludestagnantmeteorologicalconditionswithlowmixingheights,highrelativehumidity(RH),largeemissionsofprimaryairpollutants,andfastproductionofsecondaryinorganicaerosols,espe-ciallysulfate(seesectionM1)(1–5).Analyzingsurface-basedobserva-tionsatasiteinBeijingduringJanuary2013(seesectionM2)andusingconcentrationratiosofsulfatetosulfurdioxide([SO42−]/[SO2])asaproxyforthesulfateproductionrate(5),wefindthatsulfatepro-ductionincreasesasPM2.5(particulatematterwithadiameteroflessthan2.5mm)levelsincrease(Fig.1A).Ratiosaresixtimeshigherduringthemostpollutedperiods(PM2.5>300mgm−3)thanduringcleantomoderatelypollutedconditions(ratiosof0.1whenPM2.5<50mgm−3).Traditionalairqualitymodels,however,failtocapturethiskeyfeatureofNCPwinterhazeeventsevenafteraccountingforaerosol-radiation-meteorologyfeedback(seesectionsM2andM3)(6–8).Thechemicalmechanismsusedinthesemodelsusuallycomprisegas-phaseoxidationofsulfurdioxidebyOHradicalsandaqueous-phasereactionpathwaysincloudwater,involvingH2O2andO3,resultinginsulfateproductionratesthatscalewiththeintensityofsolarultraviolet(UV)radiation(9,10).DuringNCPhazedays,UVradiationissignificantlyreducedbecauseoftheaerosoldimmingeffect,resultinginadecreaseofmostoxidantconcentrations(5).Figure1BshowsthatthemiddayO3valuesdropfrom~22partsperbillion(ppb)undercleanconditionsto~1ppbduringthehazeperiod(andalsolosetheirtypicaldiurnalvariation,fig.S1).Thereducedoxidantlevelsandincreasedsulfateproductionsuggesttheexistenceofamissingsulfateproductionpathway.Evenafterconsid-eringthegasphaseandcloud/fogchemistry,thereisstillalargegapbetweenmodeledandobservedsulfate(Fig.1C).AddinganapparentheterogeneousprocesswithsulfateproductionratesthatscalewithaerosolsurfaceareaandRHcangreatlyimprovemodelpredictions(seesectionsM3toM5)(7),butthechemicalmechanismofthemissingsulfateproductionpathwayhasnotyetbeenidentified.RESULTSANDDISCUSSIONWefindthatreactivenitrogenchemistryinaerosolwatercanexplainthemissingsourceofsulfateinNCPwinterhaze.Aerosolwaterisakeycomponentofatmosphericaerosols,whichservesasamediumthatenablesaqueous-phasereactions(11–13).Theaerosolwatercon-tent(AWC)inBeijing,calculatedusingmeasurementsofRHandaerosolcompositionandtheISORROPIA-IIthermodynamicequilib-riummodel(seesectionM6)(14–16),iswellcorrelatedwiththemissingsulfatecontent,thedifferencebetweenmeasuredandmodeledsulfate(D[SO42−])(Fig.1C)(seesectionsM2toM4),suggestingitsinvolvementinthesulfateproduction.Notethatbecauseofthesalt-inducedfreezingpointdepression(17),aerosolwaterwillnotfreezeforawintertemperatureof~271KinBeijing.Takingtheimpactofmasstransferandionstrengthintoaccount,wemakeaconservativeestimationofsulfateproductionratefordif-ferentreactionsintheaerosolwaterunderrelevantatmospherictracespeciesconcentrationconditions(seesectionsM4andM7toM9)andfindNO2tobethemostimportantoxidantinBeijingduringhazeperiods(Fig.2B).Inthepresenceofaerosolwater,gas-phaseNO2canpartitionintothecondensedphase,reactwithSO2dissolvedintheaqueousphase,andproducesulfateaswellasnitrite(R1)(18).2NO2ðaqÞþHSO3ÀðaqÞþH2OðaqÞ→3HþðaqÞþ2NO2ÀðaqÞþSO42ÀðaqÞðR1ÞUnderheavyhazeconditions(PM2.5≥300mgm−3),thesulfatepro-ductionratesoftheNO2reactionpathway(R1)are~1to7mgm−3h−1,muchhigherthanthereactionratesinvolvingotherimportantaqueousoxidantssuchasO3andH2O2.AccordingtoZhengetal.(7),anad-ditionalsulfateproductionof~3mgm−3h−1isneededtoexplainthe1MultiphaseChemistryDepartment,MaxPlanckInstituteforChemistry,Mainz55128,Germany.2StateKeyJointLaboratoryofEnvironmentSimulationandPollutionControl,SchoolofEnvironment,TsinghuaUniversity,Beijing100084,China.3CollegeofEngi-neering,UniversityofIowa,IowaCity,IA52242,USA.4CenterforGlobalandRegionalEnvironmentalResearch,UniversityofIowa,IowaCity,IA52242,USA.5CenterforEarthSystemScience,TsinghuaUniversity,Beijing100084,China.6InstituteforEnvironmentalandClimateResearch,JinanUniversity,Guangzhou511443,China.Theseauthorscontributedequallytothiswork.†Correspondingauthor.Email:yafang.cheng@mpic.de(Y.C.);hekb@tsinghua.edu.cn(K.H.);u.poschl@mpic.de(U.P.);h.su@mpic.de(H.S.)SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20161of11observationsintheseverewinterhazeperiodsofBeijing(seesectionM9),whichfallsrightintotherangeofproductionratesfromthechem-icalreactionmechanismweproposed(R1).AsillustratedinFig.2,sul-fateproductioninaerosolwaterunderhazeconditionsdiffersfromthatinclouddroplets,wherethemajoroxidationpathwaysarereactionswithH2O2andO3,andNO2playsonlyaminorrole(12,19).Thus,traditionalairqualitymodelsusuallyincludeonlytheH2O2andO3re-actionpathwaysofsulfateproductionintheaqueousphase,whereastheNO2reactionpathwayisneglected(7,20).TheAWCistypicallythreetofiveordersofmagnitudelowerthanthewatercontentofcloudorfog(21).Onthisbasis,howcantheNO2reactionpathwaybecomeimportantinsuchtinyamountsofwater?TheincreasedimportanceisduetotherelativelyhighaerosolpHandelevatedNO2concentrationsinBeijingandtheNCPduringhazeperiods.AsshowninFig.2,aqueousoxidationratesofS(IV)byNO2andO3arestronglypH-dependent.HighpHincreasesthesol-ubilityandtheeffectiveHenry’slawconstantofSO2,pullingmoreSO2intotheaerosolwaterandthusincreasingthereactionrate.WhenpHincreasesbyoneunit,thereactionratesincreasebyoneandtwoordersofmagnitudeforNO2andO3,respectively.TheH2O2reactiondoesnotshowastrongdependencebecausehighpHreducesitsreac-tionratecoefficient,whichoffsetstheeffectofincreasedsolubility.ComparedwithNorthAmericaandEurope,aerosolsintheNCParemoreneutralized(22),asshownbyahighercation-to-anionratio(Fig.1D).ThisneutralizedfeatureisalsowelldocumentedandisthereasonthatacidrainrarelyoccursinnorthernChina(seesectionM10)(22).UsingtheISORROPIA-IIthermodynamicequilibriummodel(seesectionM6)(14–16)andinsituaerosolbulkcompositionmeasurements,weobtainaveragepHvaluesof5.4to6.2foraerosolwaterunderNCPhazeconditions(seesectionsM6andM9).Similarcalculationsbasedonsize-segregatedaerosolcompositionmeasure-mentsevenshowahighereffectivepHandsulfateproductionrates(fig.S2).ElevatedNO2isanotherkeyfactorthatleadstofastsulfateforma-tion.SubstantialamountsofNO2comefromdirectemissionofNOx(=NO+NO2).AlthoughtheNO2-to-NOxratioswerereducedbe-causeofweakphotochemistryduringthehazeevent,thestagnantweathertrappedmoreNO2nearthesurface,resultinginelevatedNO2concentrationsthatwere,onaverage,threetimeshigherthanthoseundercleanconditions(~66ppb,Fig.1B).TheseperiodsofhighestNO2levelsoccurredwhentheconcentrationsofotherphoto-chemicaloxidantsthatcanproducesulfate(H2O2,O3,andOH)werelow(Fig.1Bandfig.S1).ChangesinpHandprecursorconcentrationstogetherleadtothetransitionfromanH2O2-dominatedregimeofaqueoussulfateproductioninclouddropletstoanNO2-dominatedregimeofaqueoussulfateproductioninhaze(Fig.2).EarlierstudieshadalreadysuggestedthattheNO2reactionpathwaymaycontributetosulfateformationinfogsunderpollutedconditions(23,24),but806040200NO2(ppb)0–5050–100100–300>300PM2.5(µgm–3)35302520151050MiddayO3(ppb)O3NO21.41.21.00.80.60.40.20.0[SO42–]/[SO2]0–5050–100100–300>300PM2.5(µgm–3)300250200150100500SO42–(obs.-model,µgm–3)12008004000Aerosoldropletsolution(µgm–3)4002000AWC(µgm–3)EuropeEastAsiaNorthAmerica2.42.01.61.20.80.40.0Anions(µmolm–3)2.42.01.61.20.80.40.0Cations(µmolm–3)ABCDFig.1.CharacteristicfeaturesofamajorhazeeventinBeijing,China(January2013).(A)Sulfate/sulfurdioxideratio([SO42−]/[SO2])and(B)middayozone(O3)concentrations(10:00to15:00localtime)andnitrogendioxide(NO2)concentrationsatdifferentfine-particle(PM2.5)concentrationlevels.(C)Correlationoftheunexplainedsulfateconcentration(DSO42−=observation−model)(seesectionsM2andM3)withaerosoldropletsolutionandAWC(color-coded).(D)Anion-to-cationratioinPM2.5asobservedinBeijing(solidsymbols)andinotherstudiesinnorthernChina(opensymbols)(tableS1)comparedtothecharacteristicratiosreportedforaircraftmeasurementsintheArcticofoutflowfromEastAsia,Europe,andNorthAmerica(solidred,blue,andgreenlines;here,onlyNH4+,NO3−,andSO42−wereconsidered)(87).SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20162of11duringtheBeijinghazeeventofJanuary2013,fogwasnotobservedandsulfateproductionbyNO2occurredinaerosolwaterinstead.SulfateproductionratesfromtheNO2reactionpathway(R1)calculatedonthebasisofmeasurementdata(hourlyconcentrationsofNO2,SO2,PM2.5,andRH;sectionsM2andM4)showapositivedependenceonthePM2.5concentration,varyingfrom0.01mgm−3h−1underrelativelycleanconditionstonearly10mgm−3h−1inthemostpollutedperiods(pinkcirclesinFig.3).ThesereactionratescanaccountforthesystematicunderpredictionofmodelsandexplainthelargemissingsourceofsulfateintheBeijinghaze(blackdiamondsinFig.3).Undercleanconditions,theOHreaction(greencrossesinFig.3)dom-inatestheoxidationpathwaysofSO2.Asparticleconcentrationsincreaseandmoresulfateisproduced,thephotochemistryslowsdown,leadingtolessOH,andsulfateproductionviathispathwaydecreases.Fromthisaspect,theOHreactionhasanegativefeedback,whichisself-bufferedagainstheavypollution.AsPM2.5concentrationsandRHincreasesimul-taneously[aspecialfeatureofhazeeventsinNCP(5)],theOHreactionbecomesweaker,whereastheaqueous-phasereactionofNO2startstoplayamoreimportantrole.FortheJanuary2013conditionsatPM2.5~100to200mgm−3,theaqueous-phasereactionbecomesthedominantoxidationpathway(Fig.3).IncontrasttotheOHreaction,theNO2re-actionshowsapositivefeedbackmechanism,wherehigherparticlemat-terlevelsleadtomoreaerosolwater,whichacceleratessulfateproductionandfurtherincreasestheaerosolconcentration.ThispositivefeedbackintensifiesthePM2.5levelsduringhazeperiods,resultinginaseriesofrecord-breakingpollutionevents.TheNO2reactionwithSO2inaerosolwaterproducesnotonlysul-fatebutalsonitrite(R1),whichmayundergosubsequentoxidationordisproportionationreactionsformingnitrate.Thisisconsistentwiththehighnitrateconcentrationsobservedduringthehazeevent,whichareofsimilarmagnitudetothesulfateconcentrations(upto~160mgm−3)(5)andhavealsonotyetbeenexplainedbyairqualitymodels(7).Depend-ingonthepHvalueofthehazedroplets,nitritecanalsoformnitrousacid(HONO)andundergoreversiblepartitioningwiththegasphase(25,26).Moreover,thereleaseofHONOremovesH+,whichmayhelptosustainthedropletacidityandefficientsulfateproduction(27,28).Forthesamehazeperiods,recordhighaerosolnitriteconcentrationsofupto~12mgm−3wereobservedinShandong,northernChina,withnitriteconcentrationswellcorrelatedwithNOxathighRH(>50%)(25).Thenitrite-to-HONOmolarratioof~3inShandongisahundredtimeshigherthantheratioobservedduringapollutioneventinNanjing,YangtzeRiverDeltaofChina,whereonlytraceamountsofnitriteweredetectedintheaerosolphase(upto~0.4mgm−3),andtheaerosolwatertherewasmoreacidic(pH~4)(24,25).ThisfurtherconfirmsthemoreneutralizedfeatureofaerosolparticlecompositionandhazeinnorthernChina.OurstudyunfoldsanewandmorecomprehensiveconceptualmodelofsulfateformationinNCPhazeevents,includingnotonlythetraditionalOH,H2O2,andO3reactionpathwaysinatmosphericgasphaseandcloudchemistrybutalsotheNO2reactionpathwayinaerosolwater(Fig.4).TheNO2pathwaymaynotbelimitedtowinterhazebecauseitmayalsobeimportantatnightandduringfogeventsinpollutedregionswithhighboundarylayerconcentrationsofPM2.5andNO2andelevatedRH(23,24).TheimportanceofmultiphasechemistryholdsforawiderangeofaerosolpH.Whenaerosolsbecomemoreacid-ic,thesulfateproductioncanbemaintainedatahighratethroughTMIreactions(Fig.2B).TheimportantroleofaerosolpHinthemultiphasereactionpathwayhighlightstheneedtobetterunderstandthesourcesofammoniaandalkalineaerosolcomponentsfromnaturalandanthropo-genicemissions(soildust,seawater,agriculture,energy,industrial,and8765432pH10–710–610–510–410–310–210–1100101102103BeijinghazeH2O2O3TMINO28765432pH10–510–410–310–210–1100101102103104105d[SO42–]/dt(µgm–3h–1)ClouddropletsABFig.2.Aqueous-phasesulfateproductionbysulfurdioxideoxidationundercharacteristicconditions.Sulfateproductionratesfor(A)clouddropletsand(B)BeijinghazeplottedagainstpHvalue.Lightblue–andgray-shadedareasindicatecharacteristicpHrangesforcloudwaterundercleantomoderatelypollutedconditionsandaerosolwaterduringseverehazeepisodesinBeijing,respectively.Thecoloredlinesrepresentsulfateproductionratescalculatedfordifferentaqueous-phasereactionpathwayswithoxidants:hydrogenperoxide(H2O2),ozone(O3),transitionmetalions(TMIs),andnitro-gendioxide(NO2).Characteristicreactantconcentrationsandmodelcalculationsforcloudsandhazearetakenfromtheliteratureandobservations,andspecifiedinMaterialsandMethods(seesectionsM7toM9)(12,21).10–310–210–1100101d[SO42–]/dt(µgm–3h–1)8006004002000PM2.5(µgm–3)NO2reactionOHreactionMissingsourceFig.3.ImportanceoftheNO2reactionpathwayforsulfateproductionintheBeijinghaze(January2013).Sulfateproductionratescalculatedfortheaqueous-phaseNO2reactionpathway(pH5.8)andthegas-phaseOHreactionpathwaycomparedtothemissingsourceofsulfate.Crossesandcirclesrepresenthourlyproductionratescalculatedonthebasisofmeasurementdata,andthediamondsrepresenttheaveragemissingsource(arithmeticmean±SD)(seesectionsM3toM5)(7).Thepink-shadedareashowsthemaximumandminimumsulfateproduc-tionratesbytheNO2reactionpathwayboundedbytheaerosolwaterpHrangingfrom5.4to6.2duringhazeperiods.SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20163of11traffic).Furthermore,reactivenitrogenchemistryinaerosolwatermightalsoplayaroleinnitrateandsecondaryorganicaerosolproduc-tionduringhazedayswhenphotochemistryisreduced.OurresultsrevealthecomplexnatureofhazepollutioneventsinChina,whereNOxisnotonlyaprecursorfornitratebutalsoanim-portantoxidantforsulfateformation.Thus,reductionsofNOxemis-sionsareexpectedtoreducenitrate,sulfate,andPM2.5muchmorethananticipatedbytraditionalairqualitymodels.AlargedecreaseinPM2.5hasalreadybeenobservedinrelationtotrafficandenergycontrolmeasuresduringtheBeijingOlympicGamesin2008andoth-ereventsintheNCP.Heavyhazeconditionswithhighpollutantcon-centrationlevelsandlargelyneutralizedaerosolwaterarekeyfeaturesofatmosphericchemistryintheNCP.Thesefeatureswillneedtobeconsideredinfutureairqualityandpollutantemissioncontrolstrate-giesinnorthernChina,andperhapsalsoinotherregions.MATERIALSANDMETHODSM1.TheJanuary2013hazeinBeijingTheseverehazeepisodeinJanuary2013isoneoftheworstatmosphericpollutioneventseverrecordedinChina(2,9).InBeijing,thedailyfine-particle(PM2.5)concentrationreachedupto400mgm−3,exceedingtheWorldHealthOrganizationguidelinevalueby16times.TheweakEastAsianwintermonsoon,whichresultedinweakenedsurfacewindsandtheanomaloussoutherlywinds,wasresponsibleforthehazeevents(4).Thesoutherlywindstransportedmorewatervaporfromtheseatoeast-ernChina.Theanomaloushigh-pressuresystemat500hPasuppressedconvection.Thus,theairinJanuarywasmorestagnant,trappingmoreairpollutantsandwatervapornearthesurface.ThehighPM2.5concen-trationreducedthesolarradiationandatmosphericphotochemistry,resultingindecreasesintheconcentrationofphotochemicalproductssuchasOHandO3(fig.S1).AmajorfeatureofPM2.5pollutionduringthishazeeventwasthelargecontributionfromsecondaryspecies,includinginorganic(mainlysulfate,nitrate,andammonium)andorganicspecies(2,5).However,contributionfromsecondaryinorganicspecies(suchassulfateandni-trate)showedanincreasingtrendwithincreasingpollutionlevels,whereascontributionfromorganicsdecreased(5).Thefastproductionofsulfate,however,cannotbereproducedbymodelsimulations,whichhaveimplementedaerosol-meteorology-radiationfeedbackandastate-of-the-artchemicalmechanism(6,7),thatis,thegas-phaseoxidationbyOH(29,30)andaqueous-phaseoxidationincloudsbyH2O2andO3(12,21).StabilizedCriegeeintermediates(sCIs)werealsosuggestedasanoxidantofSO2butcontributeminorH2SO4productioncomparedwiththeconventionalOHreactioninthemidday(31–33).FurtheranalysishasshownthatthemodelsimulationcanbeimprovedbyintroducinganapparentheterogeneousprocesswithareactionratecoefficientscaledwithRH(seesectionM3)(7).M2.SamplinglocationandexperimentalmethodsWeperformedaerosolmeasurementsfrom1to31January2013ontheroofoftheEnvironmentalScienceBuilding(40°00′17″N,116°19′34″E,~10mabovetheground)onthecampusofTsinghuaUniversity,anurbanbackgroundsiteinBeijing.TableS2summarizestheaerosol-relatedparametersandexperimentalmethods.ConcentrationsofPM2.5andPM10weremeasuredbyanonlinePM-712monitor(KimotoElectricCo.Ltd.)equippedwithaU.S.EnvironmentalProtectionAgen-cyPM10inletandaPM2.5virtualimpactor(34).SO42−andotherionsinPM2.5weremeasuredbyanonlineACSA-08monitor(KimotoElectricCo.Ltd.)andthefilter-basedanalysis.ThePM2.5filtersampleswerecollectedfrom12to24Januarybymedian-volumesamplers(Laoying)onprebakedQuartzfilters(2500QAT-UP;PallCorporation)withaflowrateof100litersmin−1(35).ThefiltersampleswereanalyzedbytheDionexionchromatograph(DX-600forcationsandICS-2000foranions)(DionexCorporation)fortheconcentrationofwater-solubleinorganicions,includingNa+,K+,Ca2+,Mg2+,NH4+,SO42−,NO3−,andCl−.Organiccarbon(OC)andelementarycarbonconcentrationsinPM2.5weremeasuredbyaSunsetModel4semicontinuouscarbonanalyzer(Beaverton)withaNationalInstituteforOccupationalSafetyandHealth–typetemperatureprotocol(36).Afactorof1.6wasadoptedtoconvertthemassofOCintothemassoforganics(37,38).GaseousairpollutantsSO2,NO2,andO3weremeasuredbytheAtmosphericEnvironmentMonitoringNetwork(39).ThemeteorologydataweremeasuredbytheMilos520WeatherStation(VAISALAInc.).Morede-tailscanbefoundintheworkofZhengetal.(5).M3.WRF-CMAQmodelsimulationTheWeatherResearchandForecasting—CommunityMultiscaleAirQuality(WRF-CMAQ)modelsystemwasusedtodeterminethemissingsourceofsulfatethroughcomparisonwithobservationaldata.WRFisanew-generationmesoscalenumericalweatherpredictionsystemdesignedtoserveawiderangeofmeteorologicalapplications(www.wrf-model.org/),andCMAQisathree-dimensionalEulerianatmosphericchemistryandtransportmodelingsystemthatsimulatesmultipollutants(www.cmascenter.org/cmaq/).ThereleasesofWRFv3.5.1andCMAQv5.0.1wereusedinthisstudy.CloudchemistryPhotochemistryHazechemistrySO2+NO2SO42−SO2+OHSO42−SO2+H2O2/O3SO42–SO2NOXNH3DustFig.4.ConceptualmodelofsulfateformationinhazeeventsinNCP.ThetraditionalOH,H2O2,andO3reactionpathwaysinatmosphericgasphaseandcloudchemistryareincludedhere,aswellastheNO2reactionpathwayinaerosolwaterwithelevatedpHandNO2concentrationsproposedinthisstudy.SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20164of11ThemodelsimulationwasconfiguredthesameasintheworkofZhengetal.(7),asdetailedintableS3.Tobettercharacterizethestagnantmeteorologicalconditions,weappliedobservationalnudg-ingfortemperature(T)andRH[abovetheplanetaryboundarylayer(PBL)],andwind(withinandabovethePBL).ThesurfaceroughnessiscorrectedaccordingtoMassandOvens(40)byincreasingthefrictionvelocityby1.5timesinthePBLscheme,whichsignificantlyreducedthehighbiasesinwindandRHsimu-lations.Ingeneral,thesimulatedT,RH,andwindatthegroundsurfaceagreewithobservations(7).Forthegas-phasereactions,weusedtheCB05mechanismwithactivechlorinechemistryandtheupdatedtoluenemechanismofWhittenetal.(41).Fortheaqueous-phasereactionsinclouds,weusedtheupdatedmecha-nismoftheRADMmodel(20,42).Reactionsrelevantforthesul-fateformationwerediscussedindetailinsectionM4.Here,theWRF-CMAQmodelingresultswereusedinthefollowinganalysis:(i)themodeledsulfateconcentration[SO42−]wasusedtocalculateD[SO42−],thedifferencebetweenobservedandmodeled[SO42−],and(ii)themodeledOHandH2O2concentrationswereusedintheestimationofsulfateformationfromthegas-phasereactionofOHwithSO2andtheaqueous-phasereactionofH2O2withHSO3−.M4.ProductionofsulfateinWRF-CMAQmodelAccordingtocurrentunderstanding,secondarysulfateisproducedthroughtheoxidationofSO2.IntheWRF-CMAQmodel,oxidationoccursbothinthegasphaseandinthecloud/fogdroplets.Inthegasphase,themajorpathwayistheOH-initiatedreaction(12,43)OHþSO2þM→HO2þSulfateðM1Þinwhichthesecond-orderkineticconstantcanbeexpressedaskTðÞ¼k0ðTÞ½M1þk0ðTÞ½Mk∞ðTÞ8<:9=;0:6ZandZ¼1þlog10k0ðTÞ½Mk∞ðTÞ2()−1ðM2Þwhere[M]istheconcentrationofN2andO2,andk0(T)andk∞(T)rep-resentthelow-andhigh-pressurelimitingrateconstants,respectively.Theirtemperaturedependencecanbeexpressedask0TðÞ¼k3000T300Ànandk∞TðÞ¼k300∞T300ÀmðM3Þwherek0300=3.3×10−31cm6molecule−2s−1andn=4.3,andk∞300=1.6×10−12cm3molecule−1s−1andm=0.Incloud/fogdroplets,thefollowingaqueousreactionshavebeenin-cludedintheWRF-CMAQmodel(7).Theexpressionoftheirreactionrate,aswellastheratecoefficients,issummarizedintableS4.HSO3ÀþH2O2→SO42ÀþHþþH2OðM4ÞSO2þO3þH2O→SO42Àþ2HþþO2ðM5ÞHSO3ÀþO3→SO42ÀþHþþO2ðM6ÞSO32ÀþO3→SO42ÀþO2ðM7ÞSO2þH2Oþ0:5O2þFeðIIIÞ=MnðIIÞ→SO42Àþ2HþðM8ÞHSO3ÀþCH3OOH→SO42ÀþHþþCH3OHðM9ÞHSO3ÀþCH3COOOH→SO42ÀþHþþCH3COOHðM10ÞM5.ApparentheterogeneousuptakeofSO2onaerosolsurfacesToimprovethemodelsimulationforthewinterhazeeventsinBeijingandtheNCP,Zhengetal.(7)suggestedtheuseofanapparentheter-ogeneousuptakecoefficient(g)ofSO2onaerosolsurfacesasafunctionofRH(Eq.M11).gisdefinedastheratioofthenumberofcollisionsthatresultinthereactionSO2(g)+Aerosol→SO42−tothetheoreticaltotalnumberofcollisions.TheoverallratesofSO2uptakeandsulfateproductionareasfastasifthewholeaerosolsurfaceiscoveredbydust(44).Althoughtheexactmechanismsupportingthisfastproductionrateisstillunknown(7),thisapparentheterogeneoussourceofsulfatecanaccountfortheunderpredictionofmodeledsulfate,withsignificantreductionofnormalizedmodelbiasfrom−54.2to6.3%.g¼glow;0%≤RH≤50%glowþðghighÀglowÞ=ð1–0:5ÞÂðRHÀ50%Þ;50%<RH≤100%ðM11Þwhereglow=2×10−5andghigh=5×10−5.Withg,asulfateproductionrateRH,gcanbedeterminedbyEq.M12:RH;g¼d½SO42Àdt¼RpDgþ4gnÀ1SaerosolSO2½ðM12ÞwhereRpistheradiusofaerosolparticles,Dgisthegas-phasemoleculardiffusioncoefficientofSO2,nisthemeanspeedofgaseousSO2mole-cules,andSaerosolisthesurfaceareaconcentrationofaerosolparticles.M6.ISORROPIA-IImodelcalculationTheISORROPIA-IImodel(15)wasusedtocalculatetheAWCandpH.TheISORROPIA-IIisathermodynamicequilibriummodelthatpredictsthephysicalstateandcompositionofatmosphericinorganicaerosols.Itcanbeusedintwomodes:thereversemodeandthefor-wardmode.Thereversemodecalculatedthethermodynamicequilib-riumbasedonaerosol-phaseconcentrations,whereastheforwardmodereliedonbothaerosol-phaseandgas-phaseconcentrations(16).ItsabilityinpredictingAWCandpHhasbeendemonstratedbyGuoetal.(45)andXuetal.(16).ToevaluatetheaerosolpHandAWC,weperformedbothreverse-modeandforward-modemodelsimulationsandusedtheiraveragesforfurtheranalyses.ThegaseousNH3wasnotmeasuredinourJan-uarycampaign,butlong-termmeasurement(46)showsacompactcorrelationbetweenNH3andNOxconcentrationsinthewintersea-sonofBeijing.Accordingly,weestimatedtheNH3concentrationfromtheobservedNOxconcentrationwithanempiricalequationderivedfromMengetal.(46),thatis,NH3(ppb)=0.34×NOx(ppb)+0.63.SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20165of11ThecontributionoforganiccompoundstoAWC,Worg(themassconcentrationofaerosolwaterassociatedwithorganics),wasesti-matedbythesameapproachofGuoetal.(45)Worg¼OMrorg⋅rw⋅korgð100%=RHÀ1ÞðM13ÞwhereOMisthemassconcentrationoforganicmatter,rwisthedensityofwater(rw=1.0×103kgm−3),rorgisthedensityoforganics(rorg=1.4×103kgm−3)(45),andkorgisthehygroscopicityparameter(47)oforganicaerosolcompositions.Weadoptedakorgof0.06basedonpre-viouscloudcondensationnucleimeasurementsinBeijing(48).M7.KineticsofmasstransportFormultiphasereactions,theoverallreactionratedependsnotonlyontherateofchemicalreactionsbutalsoonthemasstransportindifferentmediumandacrosstheinterface.Toaccountfortheeffectsofmasstransport,weadoptedtheformulationofastandardresistancemodel(12)1RH;aq¼1Raqþ1Jaq;limðM14ÞwhereRH,aqisthesulfateproductionrate,Raqistheaqueous-phasereac-tionrate,andJaq,limisthelimitingmasstransferrate.FortheoxidationofS(IV)byagivenoxidantOxi(12)Raq¼ðk0½SO2⋅H2Oþk1½HSO3Àþk2½SO32ÀÞ½OxiðM15Þwhere[SO2·H2O],[HSO3−],[SO32−],and[Oxi]aretherespectiveaqueous-phaseconcentrations,andk0,k1,andk2arethecorrespondingsecond-orderreactionratecoefficientsasdetailedintableS4.Theaqueous[Oxi]isassumedtobeinequilibriumwithitsgas-phaseconcentrationandcanbedeterminedbyHenry’slaw(12)½X¼p∞ðXÞ⋅HðXÞðM16Þwherep∞(X)(atm)isthepartialpressureofspeciesXinthebulkgasphaseandH(Matm−1)istheeffectiveHenry’sconstant(tableS5).ThelimitingmasstransferrateJaq(Ms−1)iscalculatedbyEqs.M17andM18(12)Jaq;lim¼minfJaqðSO2Þ;JaqðOxiÞgðM17ÞJaqðXÞ¼kMTðXÞ⋅p∞ðXÞ⋅HðXÞðM18ÞwhereXreferstoSO2ortheoxidantOxisuchasO3,H2O2,andNO2.ThemasstransferratecoefficientkMT(s−1)canbecalculatedby(12)kMTXðÞ¼Rp23Dgþ4Rp3anÀ1ðM19ÞwhereRpistheaerosolradius,andRp23Dgand4Rp3anarethecontinuumregimeresistanceandthefree-molecular(orkinetic)regimeresistance,respectively.Dgisthegas-phasemoleculardiffusioncoefficient,andnisthemeanmolecularspeedofX.aisthemassaccommodationco-efficientofXonthedropletsurface,whichaccountsforimperfectstickingofimpingingmoleculestothesurface,andweadoptedliter-aturevaluesof0.11,0.23,2.0×10−3(12),and2.0×10−4(49)forSO2,H2O2,O3,andNO2,respectively.Aqueous-phasemasstransfercanbeignoredforthesizerangeconsideredhere(Dp≤2.5mm)(12).AnequivalentRpof0.15and15mmwasassumedforaerosolsandclouddroplets,respectively.M8.Influencesofionicstrengthonaqueoussulfate-producingreactionsAerosolliquidwaterconstitutesanaqueouselectrolytethatcanbeex-tremelyconcentratedwithhighionicstrength(I)upto100M(50).Thishighlyconcentratedchemicalenvironmentwillaffecttheinclina-tionofaspeciestoparticipateintheaqueous-phasechemicalreac-tions,reflectedbyanapparentreactionrateconstant(k)differentfromthatinanidealsolution(21).TheinfluenceofIonkiscomplicatedandisnotyetfullyunder-stood.Accordingtocurrentunderstanding,Iaffectskthroughitsintegratedeffectsontheactivitycoefficient(a)ofreactantsandproductsformostreactions(51).Forexample,forareactionwherereactantsAandBformanactivatedcomplex(AB),whichthenquicklydecomposesintoafinalproductP(A+B→(AB)→P),thek-Idependencecanbedescribedas(51)logkkI¼0¼logaAþlogaBÀlogaðABÞðM20ÞwherekI=0referstothekineticconstantatIof0M.TheoriesusedtopredictaiatgivenIvariedwiththerangesofIandthespeciesnature,thatis,beinganionoraneutralspecies,assummarizedintableS6.Majoraqueoussulfate-producingreactionsconsideredhereincludeS(IV)oxidationbyH2O2,O3,TMI+O2,andNO2(Fig.2).Amongthesereactions,theinfluenceofIhasbeenstudiedexperimentally,withIrang-ingupto~5MforH2O2andslightlyhigherthan1MforO3andTMI+O2.Theobservedk-Irelationshipsofthesereactionsagreewiththeore-ticalpredictionssummarizedintableS7(52–56).Asshowninfig.S3,withincreasingionicstrength,therateconstantforH2O2decreasesfirstwhenIisbelow~1MandbeginstoincreaseonceIgoesabove~1M(52,57).ForO3,therateconstantispositivelyrelatedtoI.ForTMI+O2[here,onlyFe(III)andMn(II)areconsideredaseffectivecatalyzingTMIs(58,59)],therateconstantdecreasessignificantlywithincreasingI,evenwithoutconsideringthesulfateinhabitationeffect(referringtotheeffectthattheformationofthesulfate-TMIcomplexwouldreducecatalyticallyactiveTMIconcentrations)(55,60).Currently,however,nok-IrelationshipwasreportedforNO2,whereassomeplausibleestimationcanbemadeonthebasisoftheprin-cipleoftheoriesdiscussedabove.TwokindsofmechanismshavebeensuggestedfortheNO2-S(IV)reactions.Oneistheoxygen-atomtransferreaction(61)2NO2þSO2À3↔ðO2NÀSO3ÀNO2Þ2ÀðM21aÞðO2NÀSO3ÀNO2Þ2ÀþOHÀ↔HOÀSO3ÀðNO2Þ23ÀðM21bÞSCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20166of11HOÀSO3ÀðNO2Þ23ÀþOHÀ→2NO2ÀþSO2À4þH2OðM21cÞinwhichthefirstreaction(Eq.M21a)istherate-controllingstep.Theothermechanismisanelectrontransferreaction(62–64)NO2þSO2À3→NO2ÀþSO3•ÀðM22Þfollowedbythesulfurauto-oxidationprocesses(12).Thefirstreaction(Eq.M22)istherate-controllingstepbecausefollow-upreactionswithradicalsareveryfast.Forbothmechanisms,therate-controllingstepoftheNO2-S(IV)reactionisareactionofanionwithaneutralmolecule.AccordingtoHerrmann(51),thek-IrelationforthistypeofreactionshouldfollowlogkkI¼0¼bIðM23Þwherebisthekineticsaltingcoefficient.AccordingtoKameokaandPigford(65),bisexpectedtobepositive.Givenapositiveb,in-creasingIwillleadtoanincreaseink,asshownbythereddashedcurveinfig.S3(wetakeanarbitraryvalueof0.5M−1forb,whichisnotdeterminedfromexperimentsandisusedonlyforthepurposeofillustration).DuringthesevereBeijinghazes(whenPM2.5ishigherthan300mgm−3),ionicstrengthinaerosolliquidwaterrangedfrom13to43M,aspredictedbytheISORROPIA-IImodel(seesectionM6)(15).Directextrapolationoftheobserved/predictedk-Irelationship(fig.S3)intosuchhighrangesofionicstrengthmaynotbeappropriate.Thus,therateconstantsaretakenasfordilutedsolution,althoughbasedoncurrentobservationsandtheories(tableS7andfig.S3),thistreatmentwillleadtoconservativeestimationsoftherealsulfatepro-ductionratesoftheNO2,O3,andH2O2pathwaysinFig.2butanoverestimationoftheTMI+O2pathway.M9.DatausedinFig.2Detaileddescriptionsonhowtoderivethesulfateproductionratefordifferentaqueous-phaseoxidationpathwaysofSO2(thatis,byH2O2,O3,TMI+O2,andNO2)inFig.2canbefoundinthestudyofSeinfeldandPandis(12).Theaqueous-phasereactionsinvolvedarelistedasRe-actionsR1andM4toM8.TherateexpressionsandratecoefficientsandtheconstantsthatweusedforcalculatingtheapparentHenry’sconstantaresummarizedintablesS4andS5,respectively.InFig.2,the“clouddroplets”scenarioistakenfromtheworkofSeinfeldandPandis(12)andHerrmannetal.(21):[SO2(g)]=5ppb,[NO2(g)]=1ppb,[H2O2(g)]=1ppb,[O3(g)]=50ppb,[Fe(III)]=0.3mM,[Mn(II)]=0.03mM,liquidwatercontent=0.1gm−3,andclouddropletradiusRp=15mm.Inthisscenario,thetemperatureTistakentobethesameasthatusedinthe“Beijinghaze”scenariodescribedbelow.The“Beijinghaze”scenariowastakenaccordingtothemeasure-mentdataduringthemostpollutedhazeperiods(PM2.5>300mgm−3).Theaveragevalueswereusedinourcalculation:[SO2(g)]=40ppb,[NO2(g)]=66ppb,[H2O2(g)]=0.01ppb,[O3(g)]=1ppb,AWC=300mgm−3,aerosoldropletradiusRp=0.15mm,andT=271K.Theconcentrationsof[Fe(III)]and[Mn(II)]arepH-dependent(fig.S4).ThepHdependenceismostlyduetotheprecipitationequilibriumofFe(OH)3andMn(OH)2FeðIIIÞ½¼Ksp;FeðOHÞ3½OHÀ3and½MnðIIÞsat¼Ksp;MnðOHÞ2½OHÀ2ðM24ÞwhereKsp;FeðOHÞ3andKsp;MnðOHÞ2aretheprecipitationconstantsofFe(OH)3andMn(OH)2,respectively(66).WhenallFe(OH)3andMn(OH)2aredissolved,furtherdecreaseofpHwillnotincrease[Fe(III)]and[Mn(II)],resultinginaplateauatlowpH(fig.S4).ThetotalsolubleFeandMnareestimatedtobe18and42ngm−3,respectively,basedondataintheliteratureandobservationsinBeijing(2,59,66–70).TheseverehazeeventsobservedinBeijingarearegionalphenom-enon(5).BecauseBeijingislocatedinthenorthwesternedgeofthepollutedarea,theairpollutionincitiessouthofBeijingisevenmoresevere.NO2concentrationsinBeijingarecomparabletothesoutherncities,whereasSO2concentrationsinthelatteraretypicallytwotofourtimeshigherthanthoseinBeijing(fig.S5).Thus,thesulfatepro-ductionratefromtheNO2pathwaythatwepredictedwiththeBeijingdatainFig.2isaconservativeestimationforthecontributionofthispathwaytothesulfateformationinthewholeNCP.ConsideringthatregionaltransportfromcitiessouthofBeijinghascontributedtotheseverehazeepisodeinJanuary2013(5,71)andjudgingfromtheairpollutiontrendshowninfig.S5,thepollutedairparcelscouldtypicallyhavebeenprocessedunderseverehazeconditionsinBeijingandincitiessouthofitformorethan3daysbeforethepeakpollutionhourinBeijing.Becausecloudamountswerelow(7,72,73)duringtheJanuary2013winterhazeperiods,weassumedthataerosolsspent100%oftheirlifetimeundernoncloudconditions(RH<100%)(21).Undertheseconditions,toproducetheobservedsulfateconcentration(~200mgm−3),therequiredaverageheterogeneousproductionratecanbedeterminedtobe~3mgm−3h−1.Thisestimationalsofallsintotherangesof1to7mgm−3h−1thatwepredictedfortheNO2pathwayinFig.2.M10.AerosolacidityinnorthernChinaTheneutralizedfeatureofaerosolsinEastAsia(includingBeijingandtheNCP)hasbeenwelldocumentedintheliterature,withhighcation-to-anionratios(45,74–86).AircraftmeasurementsintheArcticfurthersupportthisconclusion,showingthattheaerosolsintheArcticcharac-terizedascomingfromtheoutflowofEastAsiaweremostlyneutralized,whereastheaerosolstransportedfromNorthAmericatotheArcticwerehighlyacidic(linesinFig.1D)(87).ThelowaerosolacidityinEastAsiacanbeattributedtoitshighNH3andmineraldustemissions.Forexample,in2008,theemissionratiosofNH3to2×SO2(molarratioofNH3emissiondividedbytwicetheSO2emission)are0.37,0.86,and1.04forNorthAmerica,Europe,andEastAsia,respectively(87).NorthernChinaisexpectedtohaveahigheratmosphericneutralizingcapacitythanotherpartsofEastAsiabecauseofthehighNH3emissioninthisregion.Bothsatellitedata(88,89)andemissioninventories(90)showthatnorthernChinaisoneofthemostNH3-richareasinEastAsiabecauseofitsintenseagricultureactivities.TheNCP(thatis,thecitiesofBeijingandTianjinandtheprovincesofHebei,Henan,andShandong)accountsfor30to40%ofthetotalNH3emissionsinChina(90)whilecon-tributing~20%oftheemissionsforSO2andNOx(91).SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20167of11Thehighmassfractionofmineraldust(10to20%)isadistinctcharacteristicofPM2.5intheNCP(2,70,92,93).Theinfluenceofmin-eralaerosolsisalsohigherfornorthernChinathanforsouthernChina(94–98).Majorsourcesofmineralaerosolsincludeurbanfugitivedust(resuspendedroaddust,constructiondust,etc.)andthelong-rangetransportedAsiandust(99–101).Themineraldustsareobservedtobeinternallymixedwithsulfate,nitrate,andammonia,suggestingtheirparticipationinatmosphericprocessing(102–105).Withoutmineralcomponents(Ca2+,Mg2+,K+,andNa+),aerosolpHinnorthernChinamaydropbelow5.6,showinganacidicnature(37).Inaddition,despitethehighemissionofacidicgases(SO2andNOx),rainwaterinnorthernChinahasaveragepHvalueshigherthan5.6(fig.S6),suggestinganalkalinetendencyincontrasttootherareas(forexample,theUnitedStates)(12,22).ApHof5.6isoftentakenasthe“natural”acidityofrainwater(waterinequilibriumwithCO2),whichhasbeenconsideredasthedemarcationlineofacidicprecipi-tation(12).ThehighpHvaluesinrainwaterofnorthernChinaarecausedbyalkalineaerosolparticles(12),whichhavealargebufferingcapacitytooffsettheeffectsofanthropogenicacidity.M11.ContributionfromsCIsandNO3radicalsWehavealsoinvestigatedthereactionsofS(IV)withNO3radicalsandsCIs,bothofwhichshowminorcontributions(0.03and0.69%)comparedtoourproposedmechanismS(IV)+NO2(aq).OxidationbyNO3radicals.AnaverageNO3radicalconcentrationof~2.5×10−3partspertrillionwasdeterminedbyourmodelingresultsfortheseverepollutionperiods.TakinganeffectiveHenry’sconstantof0.6Matm−1forNO3andare-actionrateconstantof1.4×109M−1s−1(106),wedeterminedasulfateproductionrateof5.1×10−4mgm−3h−1fortheNO3reaction.Thisrateisonly0.03%comparedtotheproposedmechanismS(IV)+NO2(aq)atpH5.8(Fig.2)andisthusnegligible.OxidationbysCI.AccordingtoMauldinetal.(31),wecalculatedRsCI,thesulfatefor-mationratefromthesCImechanism,byRsCI¼ksCIþSO2½sCI½SO2ðM25Þwhere[sCI]and[SO2]aretheconcentrationsofsCIandSO2,respectively,andthereactionratecoefficientksCIþSO2is6×10−13cm3molecule−1s−1.TheconcentrationofsCIcanbedeterminedbythefollowingequation(31)½sCI¼YsCIkO3þalkene½O3½alkenetsCIðM26ÞwhereYsCIistheyieldofsCI~0.5,kO3þalkeneisthecorrespondingratecoefficientforthereactionofO3withindividualalkenes,andtsCIisthelifetimeofthesCI,whichis0.2s(31).Aftertakingatypicalalkeneprofileforthehazeperiod(107),wedeterminedanRsCIof~0.69%oftheproposedS(IV)+NO2(aq)mechanism.SUPPLEMENTARYMATERIALSSupplementarymaterialforthisarticleisavailableathttp://advances.sciencemag.org/cgi/content/full/2/12/e1601530/DC1fig.S1.WeakenedphotochemistrybyaerosoldimmingeffectsduringJanuary2013inBeijing.fig.S2.ImportanceoftheNO2reactionpathwayforsulfateproductionintheBeijinghaze(January2013).fig.S3.Influenceofionicstrength(I)onrateofaqueoussulfate-producingreactions.fig.S4.EstimationofFe3+andMn2+concentrationsasafunctionofaerosolwaterpHduringBeijinghazes.fig.S5.RegionalpollutionacrosstheNCPduringJanuary2013.fig.S6.AnnualprecipitationpHofChinain2013.fig.S7.ThesameasFig.2butwithalowerlimitofreactionrateconstantsreportedbyLeeandSchwartz(18).tableS1.PreviouslyreportedconcentrationsofcationsandanionsinPM2.5duringwinterforcitiesinNCPusedinFig.1D.tableS2.Summaryoffieldobservationandmethodsinthisstudy.tableS3.Domain,configurations,andmajordynamicandphysicaloptionsusedinWRFv3.5.1.tableS4.Rateexpressionandratecoefficientsofrelevantaqueous-phasereactions.tableS5.ConstantsforcalculatingtheapparentHenry’sconstant(H).tableS6.Summaryofsuggestedactivitycoefficient(a)–ionicstrength(I)dependence.tableS7.Influenceofionicstrength(I)onrateofaqueoussulfate-producingreactions.References(108–128)REFERENCESANDNOTES1.P.Brimblecombe,TheBigSmoke(Methuen,1987).2.R.-J.Huang,Y.Zhang,C.Bozzetti,K.-F.Ho,J.-J.Cao,Y.Han,K.R.Daellenbach,J.G.Slowik,S.M.Platt,F.Canonaco,P.Zotter,R.Wolf,S.M.Pieber,E.A.Bruns,M.Crippa,G.Ciarelli,A.Piazzalunga,M.Schwikowski,G.Abbaszade,J.Schnelle-Kreis,R.Zimmermann,Z.An,S.Szidat,U.Baltensperger,I.ElHaddad,A.S.H.Prévôt,HighsecondaryaerosolcontributiontoparticulatepollutionduringhazeeventsinChina.Nature514,218–222(2014).3.S.Guo,M.Hu,M.L.Zamora,J.Peng,D.Shang,J.Zheng,Z.Du,Z.Wu,M.Shao,L.Zeng,M.J.Molina,R.Zhang,ElucidatingsevereurbanhazeformationinChina.Proc.Natl.Acad.Sci.U.S.A.111,17373–17378(2014).4.R.Zhang,Q.Li,R.Zhang,MeteorologicalconditionsforthepersistentseverefogandhazeeventovereasternChinainJanuary2013.Sci.ChinaEarthSci.57,26–35(2014).5.G.J.Zheng,F.K.Duan,H.Su,Y.L.Ma,Y.Cheng,B.Zheng,Q.Zhang,T.Huang,T.Kimoto,D.Chang,U.Pöschl,Y.F.Cheng,K.B.He,ExploringtheseverewinterhazeinBeijing:Theimpactofsynopticweather,regionaltransportandheterogeneousreactions.Atmos.Chem.Phys.15,2969–2983(2015).6.J.Wang,J.Wang,S.Wang,J.Jiang,A.Ding,M.Zheng,B.Zhao,D.C.Wong,W.Zhou,G.Zheng,L.Wang,J.E.Pleim,J.Hao,Impactofaerosol–meteorologyinteractionsonfineparticlepollutionduringChina’sseverehazeepisodeinJanuary2013.Environ.Res.Lett.9,094002(2014).7.B.Zheng,Q.Zhang,Y.Zhang,K.B.He,K.Wang,G.J.Zheng,F.K.Duan,Y.L.Ma,T.Kimoto,Heterogeneouschemistry:AmechanismmissingincurrentmodelstoexplainsecondaryinorganicaerosolformationduringtheJanuary2013hazeepisodeinNorthChina.Atmos.Chem.Phys.14,16731–16776(2014).8.R.Zhang,G.Wang,S.Guo,M.L.Zamora,Q.Ying,Y.Lin,W.Wang,M.Hu,Y.Wang,Formationofurbanfineparticulatematter.Chem.Rev.115,3803–3855(2015).9.D.H.Ehhalt,F.Rohrer,DependenceoftheOHconcentrationonsolarUV.J.Geophys.Res.105,3565–3571(2000).10.F.Rohrer,H.Berresheim,Strongcorrelationbetweenlevelsoftropospherichydroxylradicalsandsolarultravioletradiation.Nature442,184–187(2006).11.C.Pilinis,J.H.Seinfeld,D.Grosjean,Watercontentofatmosphericaerosols.Atmos.Environ.23,1601–1606(1989).12.J.H.Seinfeld,S.N.Pandis,AtmosphericChemistryandPhysics,fromAirPollutiontoClimateChange(Wiley,2006).13.B.Ervens,B.J.Turpin,R.J.Weber,Secondaryorganicaerosolformationinclouddropletsandaqueousparticles(aqSOA):Areviewoflaboratory,fieldandmodelstudies.Atmos.Chem.Phys.11,11069–11102(2011).14.A.Nenes,S.N.Pandis,C.Pilinis,Continueddevelopmentandtestingofanewthermodynamicaerosolmoduleforurbanandregionalairqualitymodels.Atmos.Environ.33,1553–1560(1999).15.C.Fountoukis,A.Nenes,ISORROPIAII:AcomputationallyefficientthermodynamicequilibriummodelforK+-Ca2+-Mg2+-NH4+-Na+-SO42−-NO3−-Cl−-H2Oaerosols.Atmos.Chem.Phys.7,4639–4659(2007).16.L.Xu,H.Guo,C.M.Boyd,M.Klein,A.Bougiatioti,K.M.Cerully,J.R.Hite,G.Isaacman-VanWertz,N.M.Kreisberg,C.Knote,K.Olson,A.Koss,A.H.Goldstein,S.V.Hering,J.deGouw,K.Baumann,S.-H.Lee,A.Nenes,R.J.Weber,N.LeeNg,EffectsofanthropogenicemissionsonaerosolformationfromisopreneandmonoterpenesinthesoutheasternUnitedStates.Proc.Natl.Acad.Sci.U.S.A.112,37–42(2015).17.T.Koop,B.Luo,A.Tsias,T.Peter,Wateractivityasthedeterminantforhomogeneousicenucleationinaqueoussolutions.Nature406,611–614(2000).18.Y.N.Lee,S.E.Schwartz,PrecipitationScavenging,DryDepositionandResuspension(Elsevier,1983),pp.453–470.SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20168of1119.X.Huang,Y.Song,C.Zhao,M.Li,T.Zhu,Q.Zhang,X.Zhang,PathwaysofsulfateenhancementbynaturalandanthropogenicmineralaerosolsinChina.J.Geophys.Res.119,14165–14179(2014).20.C.J.Walcek,G.R.Taylor,Atheoreticalmethodforcomputingverticaldistributionsofacidityandsulfateproductionwithincumulusclouds.J.Atmos.Sci.43,339–355(1986).21.H.Herrmann,T.Schaefer,A.Tilgner,S.A.Styler,C.Weller,M.Teich,T.Otto,A.Che,Troposphericaqueous-phasechemistry:Kinetics,mechanisms,anditscouplingtoachanginggasphase.Chem.Rev.115,4259–4334(2015).22.J.Cao,X.Tie,W.F.Dabberdt,T.Jie,Z.Zhao,Z.An,Z.Shen,OnthepotentialhighaciddepositioninnortheasternChina.J.Geophys.Res.118,4834–4846(2013).23.S.N.Pandis,J.H.Seinfeld,Mathematicalmodelingofaciddepositionduetoradiationfog.J.Geophys.Res.94,12911–12923(1989).24.Y.Xie,A.Ding,W.Nie,H.Mao,X.Qi,X.Huang,Z.Xu,V.-M.Kerminen,T.Petäjä,X.Chi,A.Virkula,M.Boy,L.Xue,J.Guo,J.Sun,X.Yang,M.Kulmala,C.Fu,Enhancedsulfateformationbynitrogendioxide:Implicationsfromin-situobservationsattheSORPESStation.J.Geophys.Res.120,12679–12694(2015).25.L.Wang,L.Wen,C.Xu,J.Chen,X.Wang,L.Yang,W.Wang,X.Yang,X.Sui,L.Yao,Q.Zhang,HONOanditspotentialsourceparticulatenitriteatanurbansiteinNorthChinaduringthecoldseason.Sci.TotalEnviron.538,93–101(2015).26.H.Su,Y.Cheng,R.Oswald,T.Behrendt,I.Trebs,F.X.Meixner,M.O.Andreae,P.Cheng,Y.Zhang,U.Pöschl,SoilnitriteasasourceofatmosphericHONOandOHradicals.Science333,1616–1618(2011).27.A.Laskin,D.J.Gaspar,W.Wang,S.W.Hunt,J.P.Cowin,S.D.Colson,B.J.Finlayson-Pitts,Reactionsatinterfacesasasourceofsulfateformationinsea-saltparticles.Science301,340–344(2003).28.B.Alexander,R.J.Park,D.J.Jacob,Q.B.Li,R.M.Yantosca,J.Savarino,C.C.W.Lee,M.H.Thiemens,Sulfateformationinsea-saltaerosols:Constraintsfromoxygenisotopes.J.Geophys.Res.110,D10307(2005).29.W.R.Stockwell,J.G.Calvert,ThemechanismoftheHO-SO2reaction.Atmos.Environ.17,2231–2235(1983).30.M.A.Blitz,K.J.Hughes,M.J.Pilling,Determinationofthehigh-pressurelimitingratecoefficientandtheenthalpyofreactionforOH+SO2.J.Phys.Chem.A107,1971–1978(2003).31.R.L.MauldinIII,T.Berndt,M.Sipilä,P.Paasonen,T.Petäjä,S.Kim,T.Kurtén,F.Stratmann,V.-M.Kerminen,M.Kulmala,Anewatmosphericallyrelevantoxidantofsulphurdioxide.Nature488,193–196(2012).32.S.Kim,A.Guenther,B.Lefer,J.Flynn,R.Griffin,A.P.Rutter,L.Gong,B.K.Cevik,PotentialroleofstabilizedCriegeeradicalsinsulfuricacidproductioninahighbiogenicVOCenvironment.Environ.Sci.Technol.49,3383–3391(2015).33.M.Boy,D.Mogensen,S.Smolander,L.Zhou,T.Nieminen,P.Paasonen,C.Plass-Dülmer,M.Sipilä,T.Petäjä,L.Mauldin,H.Berresheim,M.Kulmala,OxidationofSO2bystabilizedCriegeeintermediate(sCI)radicalsasacrucialsourceforatmosphericsulfuricacidconcentrations.Atmos.Chem.Phys.13,3865–3879(2013).34.N.Kaneyasu,S.Yamamoto,K.Sato,A.Takami,M.Hayashi,K.Hara,K.Kawamoto,T.Okuda,S.Hatakeyama,Impactoflong-rangetransportofaerosolsonthePM2.5compositionatamajormetropolitanareainthenorthernKyushuareaofJapan.Atmos.Environ.97,416–425(2014).35.Q.Zhang,F.Duan,K.He,Y.Ma,H.Li,T.Kimoto,A.Zheng,OrganicnitrogeninPM2.5inBeijing.Front.Environ.Sci.Eng.9,1004–1014(2015).36.G.J.Zheng,Y.Cheng,K.B.He,F.K.Duan,Y.L.Ma,AnewlyidentifiedcalculationdiscrepancyoftheSunsetsemi-continuouscarbonanalyzer.Atmos.Meas.Tech.7,1969–1977(2014).37.J.K.Zhang,Y.Sun,Z.R.Liu,D.S.Ji,B.Hu,Q.Liu,Y.S.Wang,CharacterizationofsubmicronaerosolsduringamonthofseriouspollutioninBeijing,2013.Atmos.Chem.Phys.14,2887–2903(2014).38.L.Xing,T.Fu,J.J.Cao,S.C.Lee,G.H.Wang,K.F.Ho,M.Cheng,C.You,T.J.Wang,SeasonalandspatialvariabilityoftheOM/OCmassratiosandhighregionalcorrelationbetweenoxalicacidandzincinChineseurbanorganicaerosols.Atmos.Chem.Phys.13,4307–4318(2013).39.G.Tang,Y.Wang,X.Li,D.Ji,S.Hsu,X.Gao,Spatial-temporalvariationsinsurfaceozoneinNorthernChinaasobservedduring2009–2010andpossibleimplicationsforfutureairqualitycontrolstrategies.Atmos.Chem.Phys.12,2757–2776(2012).40.C.Mass,D.Ovens,WRFmodelphysics:Progress,problems,andperhapssomesolutions,the11thWRFUsers’Workshop,21–25June,NCARCenterGreenCampus,http://www2.mmm.ucar.edu/wrf/users/workshops/WS2010/presentations/session4/4-1_WRFworkshop2010Final.pdf(2010)[accessedDecember2015].41.G.Z.Whitten,G.Heo,Y.Kimura,E.McDonald-Buller,D.T.Allen,W.P.L.Carter,G.Yarwood,AnewcondensedtoluenemechanismforCarbonBond:CB05-TU.Atmos.Environ.44,5346–5355(2010).42.J.S.Chang,R.A.Brost,I.S.A.Isaksen,S.Madronich,P.Middleton,W.R.Stockwell,C.J.Walcek,Athree-dimensionalEulerianaciddepositionmodel:Physicalconceptsandformulation.J.Geophys.Res.92,14681–14700(1987).43.NASA/JetPropulsionLaboratory,ChemicalKineticsandPhotochemicalDataforUseinAtmosphericStudies(NASA/JetPropulsionLaboratory,2010).44.Y.Zhang,G.R.Carmichael,TheroleofmineralaerosolintroposphericchemistryinEastAsia—Amodelstudy.J.Appl.Meteorol.38,354–366(1999).45.H.Guo,L.Xu,A.Bougiatioti,K.Cerully,S.Capps,J.Hite,A.Carlton,S.Lee,M.Bergin,N.Ng,A.Nenes,R.Weber,Fine-particlewaterandpHinthesoutheasternUnitedStates.Atmos.Chem.Phys.15,5211–5228(2015).46.Z.Y.Meng,W.L.Lin,X.M.Jiang,P.Yan,Y.Wang,Y.M.Zhang,X.F.Jia,X.L.Yu,CharacteristicsofatmosphericammoniaoverBeijing,China.Atmos.Chem.Phys.11,6139–6151(2011).47.M.D.Petters,S.M.Kreidenweis,Asingleparameterrepresentationofhygroscopicgrowthandcloudcondensationnucleusactivity.Atmos.Chem.Phys.7,1961–1971(2007).48.S.S.Gunthe,D.Rose,H.Su,R.M.Garland,P.Achtert,A.Nowak,A.Wiedensohler,M.Kuwata,N.Takegawa,Y.Kondo,M.Hu,M.Shao,T.Zhu,M.O.Andreae,U.Pöschl,Cloudcondensationnuclei(CCN)fromfreshandagedairpollutioninthemegacityregionofBeijing.Atmos.Chem.Phys.11,11023–11039(2011).49.D.J.Jacob,Heterogeneouschemistryandtroposphericozone.Atmos.Environ.34,2131–2159(2000).50.Y.Cheng,H.Su,T.Koop,E.Mikhailov,U.Pöschl,Sizedependenceofphasetransitionsinaerosolnanoparticles.Nat.Commun.6,5923(2015).51.H.Herrmann,Kineticsofaqueousphasereactionsrelevantforatmosphericchemistry.Chem.Rev.103,4691–4716(2003).52.F.Maaß,H.Elias,K.J.Wannowius,Kineticsoftheoxidationofhydrogensulfitebyhydrogenperoxideinaqueoussolution:Ionicstrengtheffectsandtemperaturedependence.Atmos.Environ.33,4413–4419(1999).53.H.G.Maahs,KineticsandmechanismoftheoxidationofS(IV)byozoneinaqueoussolutionwithparticularreferencetoSO2conversioninnonurbantroposphericclouds.J.Geophys.Res.88,10721–10732(1983).54.J.Lagrange,C.Pallares,P.Lagrange,Electrolyteeffectsonaqueousatmosphericoxidationofsulphurdioxidebyozone.J.Geophys.Res.99,14595–14600(1994).55.L.R.Martin,M.W.Hill,Theironcatalyzedoxidationofsulfur:Reconciliationoftheliteraturerates.Atmos.Environ.21,1487–1490(1987).56.L.R.Martin,M.W.Hill,A.F.Tai,T.W.Good,Theironcatalyzedoxidationofsulfur(IV)inaqueoussolution:DifferingeffectsoforganicsathighandlowpH.J.Geophys.Res.96,3085–3097(1991).57.H.M.Ali,M.Iedema,X.-Y.Yu,J.P.Cowin,IonicstrengthdependenceoftheoxidationofSO2byH2O2insodiumchlorideparticles.Atmos.Environ.89,731–738(2014).58.A.HussJr.,P.K.Lim,C.A.Eckert,Oxidationofaqueoussulfurdioxide.1.Homogeneousmanganese(II)andiron(II)catalysisatlowpH.J.Phys.Chem.86,4224–4228(1982).59.B.Alexander,R.J.Park,D.J.Jacob,S.Gong,Transitionmetal-catalyzedoxidationofatmosphericsulfur:Globalimplicationsforthesulfurbudget.J.Geophys.Res.114,D02309(2009).60.L.R.Martin,T.W.Good,Catalyzedoxidationofsulfurdioxideinsolution:Theiron-manganesesynergism.Atmos.Environ.25,2395–2399(1991).61.C.L.Clifton,N.Altstein,R.E.Huie,Rateconstantforthereactionofnitrogendioxidewithsulfur(IV)overthepHrange5.3-13.Environ.Sci.Technol.22,586–589(1988).62.T.Nash,Theeffectofnitrogendioxideandofsometransitionmetalsontheoxidationofdilutebisulphitesolutions.Atmos.Environ.13,1149–1154(1979).63.R.E.Huie,ThereactionkineticsofNO2.Toxicology89,193–216(1994).64.G.Spindler,J.Hesper,E.Brüggemann,R.Dubois,T.Müller,H.Herrmann,Wetannulardenudermeasurementsofnitrousacid:LaboratorystudyoftheartefactreactionofNO2withS(IV)inaqueoussolutionandcomparisonwithfieldmeasurements.Atmos.Environ.37,2643–2662(2003).65.Y.Kameoka,R.L.Pigford,Absorptionofnitrogendioxideintowater,sulfuricacid,sodiumhydroxide,andalkalinesodiumsulfiteaqueoussolutions.Ind.Eng.Chem.Fundam.16,163–169(1977).66.T.E.Graedel,C.J.Weschler,Chemistrywithinaqueousatmosphericaerosolsandraindrops.Rev.Geophys.19,505–539(1981).67.N.Meskhidze,W.L.Chameides,A.Nenes,G.Chen,Ironmobilizationinmineraldust:CananthropogenicSO2emissionsaffectoceanproductivity?Geophys.Res.Lett.30,2085(2003).68.F.Solmon,P.Y.Chuang,N.Meskhidze,Y.Chen,AcidicprocessingofmineraldustironbyanthropogeniccompoundsoverthenorthPacificOcean.J.Geophys.Res.114,D02305(2009).69.S.-C.Hsu,G.T.F.Wong,G.-C.Gong,F.-K.Shiah,Y.-T.Huang,S.-J.Kao,F.Tsai,S.-C.C.Lung,F.-J.Lin,I.-I.Lin,C.-C.Hung,C.-M.Tseng,Sources,solubility,anddrydepositionofaerosoltraceelementsovertheEastChinaSea.Mar.Chem.120,116–127(2010).70.S.Tian,Y.Pan,Z.Liu,T.Wen,Y.Wang,Size-resolvedaerosolchemicalanalysisofextremehazepollutioneventsduringearly2013inurbanBeijing,China.J.Hazard.Mater.279,452–460(2014).71.Z.Wang,J.Li,Z.Wang,W.Yang,X.Tang,B.Ge,P.Yan,L.Zhu,X.Chen,H.Chen,W.Wand,J.Li,B.Liu,X.Wang,W.Wand,Y.Zhao,N.Lu,D.Su,ModelingstudyofregionalseverehazesSCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December20169of11overmid-easternChinainJanuary2013anditsimplicationsonpollutionpreventionandcontrol.Sci.ChinaEarthSci.57,3–13(2014).72.B.Zhang,Y.Wang,J.Hao,Simulatingaerosol–radiation–cloudfeedbacksonmeteorologyandairqualityovereasternChinaunderseverehazeconditionsinwinter.Atmos.Chem.Phys.15,2387–2404(2015).73.Y.Wang,Q.Zhang,J.Jiang,W.Zhou,B.Wang,K.He,F.Duan,Q.Zhang,S.Philip,Y.Xie,EnhancedsulfateformationduringChina’sseverewinterhazeepisodeinJanuary2013missingfromcurrentmodels.J.Geophys.Res.119,10425–10440(2014).74.P.K.Quinn,D.J.Coffman,T.S.Bates,T.L.Miller,J.E.Johnson,K.Voss,E.J.Welton,C.Neusüss,DominantaerosolchemicalcomponentsandtheircontributiontoextinctionduringtheAerosols99cruiseacrosstheAtlantic.J.Geophys.Res.106,20783–20809(2001).75.R.J.Park,D.J.Jacob,B.D.Field,R.M.Yantosca,M.Chin,Naturalandtransboundarypollutioninfluencesonsulfate-nitrate-ammoniumaerosolsintheUnitedStates:Implicationsforpolicy.J.Geophys.Res.109,D15204(2004).76.S.-H.Chu,PM2.5episodesasobservedinthespeciationtrendsnetwork.Atmos.Environ.38,5237–5246(2004).77.T.K.V.Nguyen,M.D.Petters,S.R.Suda,H.Guo,R.J.Weber,A.M.G.Carlton,TrendsinparticlephaseliquidwaterduringtheSouthernOxidantandAerosolStudy.Atmos.Chem.Phys.14,10911–10930(2014).78.D.Voutsa,C.Samara,E.Manoli,D.Lazarou,P.Tzoumaka,IoniccompositionofPM2.5aturbansitesofnorthernGreece:Secondaryinorganicaerosolformation.Environ.Sci.Pollut.Res.21,4995–5006(2014).79.U.Makkonen,A.Virkkula,J.Mäntykenttä,H.Hakola,P.Keronen,V.Vakkari,P.P.Aalto,Semi-continuousgasandinorganicaerosolmeasurementsataFinnishurbansite:Comparisonswithfilters,nitrogeninaerosolandgasphases,andaerosolacidity.Atmos.Chem.Phys.12,5617–5631(2012).80.V.-M.Kerminen,R.Hillamo,K.Teinilä,T.Pakkanen,I.Allegrini,R.Sparapani,Ionbalancesofsize-resolvedtroposphericaerosolsamples:Implicationsfortheacidityandatmosphericprocessingofaerosols.Atmos.Environ.35,5255–5265(2001).81.M.Sillanpää,R.Hillamo,S.Saarikoski,A.Frey,A.Pennanen,U.Makkonen,Z.Spolnik,R.VanGrieken,M.Braniš,B.Brunekreef,M.-C.Chalbot,T.Kuhlbusch,J.Sunyer,V.-M.Kerminen,M.Kulmala,R.O.Salonen,ChemicalcompositionandmassclosureofparticulatematteratsixurbansitesinEurope.Atmos.Environ.40,212–223(2006).82.A.Ianniello,F.Spataro,G.Esposito,I.Allegrini,M.Hu,T.Zhu,ChemicalcharacteristicsofinorganicammoniumsaltsinPM2.5intheatmosphereofBeijing(China).Atmos.Chem.Phys.11,10803–10822(2011).83.L.-x.Yang,D.-c.Wang,S.-h.Cheng,Z.Wang,Y.Zhou,X.-h.Zhou,W.-x.Wang,InfluenceofmeteorologicalconditionsandparticulatematteronvisualrangeimpairmentinJinan,China.Sci.TotalEnviron.383,164–173(2007).84.S.Long,J.Zeng,Y.Li,L.Bao,L.Cao,K.Liu,L.Xu,J.Lin,W.Liu,G.Wang,J.Yao,C.Ma,Y.Zhao,Characteristicsofsecondaryinorganicaerosolandsulfatespeciesinsize-fractionatedaerosolparticlesinShanghai.J.Environ.Sci.26,1040–1051(2014).85.S.N.Behera,M.Sharma,Investigatingthepotentialroleofammoniainionchemistryoffineparticulatematterformationforanurbanenvironment.Sci.TotalEnviron.408,3569–3575(2010).86.E.Stone,J.Schauer,T.A.Quraishi,A.Mahmood,ChemicalcharacterizationandsourceapportionmentoffineandcoarseparticulatematterinLahore,Pakistan.Atmos.Environ.44,1062–1070(2010).87.J.A.Fisher,D.J.Jacob,Q.Wang,R.Bahreini,C.C.Carouge,M.J.Cubison,J.E.Dibb,T.Diehl,J.L.Jimenez,E.M.Leibensperger,Z.Lu,M.B.J.Meinders,H.O.T.Pye,P.K.Quinn,S.Sharma,D.G.Streets,A.vanDonkelaar,R.M.Yantosca,Sources,distribution,andacidityofsulfate–ammoniumaerosolintheArcticinwinter–spring.Atmos.Environ.45,7301–7318(2011).88.L.Clarisse,C.Clerbaux,F.Dentener,D.Hurtmans,P.-F.Coheur,Globalammoniadistributionderivedfrominfraredsatelliteobservations.Nat.Geosci.2,479–483(2009).89.A.Boynard,C.Clerbaux,L.Clarisse,S.Safieddine,M.Pommier,M.VanDamme,S.Bauduin,C.Oudot,J.Hadji-Lazaro,D.Hurtmans,P.-F.Coheur,FirstsimultaneousspacemeasurementsofatmosphericpollutantsintheboundarylayerfromIASI:AcasestudyintheNorthChinaPlain.Geophys.Res.Lett.41,645–651(2014).90.X.Huang,Y.Song,M.Li,J.Li,Q.Huo,X.Cai,T.Zhu,M.Hu,H.Zhang,Ahigh-resolutionammoniaemissioninventoryinChina.GlobalBiogeochem.Cycles26,GB1030(2012).91.Q.Zhang,D.Streets,G.Carmichael,K.B.He,H.Huo,A.Kannari,Z.Klimont,I.S.Park,S.Reddy,J.S.Fu,D.Chen,L.Duan,Y.Lei,L.T.Wang,Z.L.Yao,Asianemissionsin2006fortheNASAINTEX-Bmission.Atmos.Chem.Phys.9,5131–5153(2009).92.F.Yang,J.Tan,Q.Zhao,Z.Du,K.He,Y.Ma,F.Duan,G.Chen,Q.Zhao,CharacteristicsofPM2.5speciationinrepresentativemegacitiesandacrossChina.Atmos.Chem.Phys.11,5207–5219(2011).93.J.-j.Cao,Q.-y.Wang,J.C.Chow,J.G.Watson,X.-x.Tie,Z.-x.Shen,P.Wang,Z.-s.An,ImpactsofaerosolcompositionsonvisibilityimpairmentinXi’an,China.Atmos.Environ.59,559–566(2012).94.T.Okuda,J.Kato,J.Mori,M.Tenmoku,Y.Suda,S.Tanaka,K.He,Y.Ma,F.Yang,X.Yu,F.Duan,Y.Lei,DailyconcentrationsoftracemetalsinaerosolsinBeijing,China,determinedbyusinginductivelycoupledplasmamassspectrometryequippedwithlaserablationanalysis,andsourceidentificationofaerosols.Sci.TotalEnviron.330,145–158(2004).95.J.Duan,J.Tan,S.Wang,J.Hao,F.Chai,Sizedistributionsandsourcesofelementsinparticulatematteratcurbside,urbanandruralsitesinBeijing.J.Environ.Sci.24,87–94(2012).96.G.Zhang,X.Bi,L.Y.Chan,X.Wang,G.Sheng,J.Fu,Size-segregatedchemicalcharacteristicsofaerosolduringhazeinanurbanareaofthePearlRiverDeltaregion,China.UrbanClim.4,74–84(2013).97.Y.L.Sun,Z.F.Wang,P.Q.Fu,T.Yang,Q.Jiang,H.B.Dong,J.Li,J.J.Jia,Aerosolcomposition,sourcesandprocessesduringwintertimeinBeijing,China.Atmos.Chem.Phys.13,4577–4592(2013).98.Y.Wang,G.Zhuang,X.Zhang,K.Huang,C.Xu,A.Tang,J.Chen,Z.An,Theionchemistry,seasonalcycle,andsourcesofPM2.5andTSPaerosolinShanghai.Atmos.Environ.40,2935–2952(2006).99.J.-J.Cao,Z.-X.Shen,J.C.Chow,J.G.Watson,S.-C.Lee,X.-X.Tie,K.-F.Ho,G.-H.Wang,Y.-M.Han,WinterandsummerPM2.5chemicalcompositionsinfourteenChinesecities.J.AirWasteManag.Assoc.62,1214–1226(2012).100.H.Wang,S.-C.Tan,Y.Wang,C.Jiang,G.-y.Shi,M.-X.Zhang,H.-Z.Che,AmultisourceobservationstudyofthesevereprolongedregionalhazeepisodeovereasternChinainJanuary2013.Atmos.Environ.89,807–815(2014).101.X.Y.Zhang,Y.Q.Wang,T.Niu,X.C.Zhang,S.L.Gong,Y.M.Zhang,J.Y.Sun,J.Brandt,AtmosphericaerosolcompositionsinChina:Spatial/temporalvariability,chemicalsignature,regionalhazedistributionandcomparisonswithglobalaerosols.Atmos.Chem.Phys.12,779–799(2012).102.Y.Hu,J.Lin,S.Zhang,L.Kong,H.Fu,J.Chen,Identificationofthetypicalmetalparticlesamonghaze,fog,andclearepisodesintheBeijingatmosphere.Sci.TotalEnviron.511,369–380(2015).103.H.Hwang,C.-U.Ro,Directobservationofnitrateandsulfateformationsfrommineraldustandsea-saltsusinglow-ZparticleelectronprobeX-raymicroanalysis.Atmos.Environ.40,3869–3880(2006).104.L.Li,M.Li,Z.Huang,W.Gao,H.Nian,Z.Fu,J.Gao,F.Chai,Z.Zhou,AmbientparticlecharacterizationbysingleparticleaerosolmassspectrometryinanurbanareaofBeijing.Atmos.Environ.94,323–331(2014).105.Q.Yuan,W.Li,S.Zhou,L.Yang,J.Chi,X.Sui,W.Wang,Integratedevaluationofaerosolsduringhaze-fogepisodesatoneregionalbackgroundsiteinNorthChinaPlain.Atmos.Res.156,102–110(2015).106.Y.Rudich,R.K.Talukdar,A.R.Ravishankara,MultiphasechemistryofNO3intheremotetroposphere.J.Geophys.Res.103,16133–16143(1998).107.S.Guo,J.Tan,J.Duan,Y.Ma,F.Yang,K.He,J.Hao,Characteristicsofatmosphericnon-methanehydrocarbonsduringhazeepisodeinBeijing,China.Environ.Monit.Assess.184,7235–7246(2012).108.R.Zhang,J.Jing,J.Tao,S.-C.Hsu,G.Wang,J.Cao,C.S.L.Lee,L.Zhu,Z.Chen,Y.Zhao,Z.Shen,ChemicalcharacterizationandsourceapportionmentofPM2.5inBeijing:Seasonalperspective.Atmos.Chem.Phys.13,7053–7074(2013).109.K.He,Q.Zhao,Y.Ma,F.Duan,F.Yang,Z.Shi,G.Chen,SpatialandseasonalvariabilityofPM2.5acidityattwoChinesemegacities:Insightsintotheformationofsecondaryinorganicaerosols.Atmos.Chem.Phys.12,1377–1395(2012).110.Y.Sun,G.Zhuang,Y.Wang,L.Han,J.Guo,M.Dan,W.Zhang,Z.Wang,Z.Hao,Theair-borneparticulatepollutioninBeijing—Concentration,composition,distributionandsources.Atmos.Environ.38,5991–6004(2004).111.X.Gao,L.Yang,S.Cheng,R.Gao,Y.Zhou,L.Xue,Y.Shou,J.Wang,X.Wang,W.Nie,P.Xu,W.Wang,Semi-continuousmeasurementofwater-solubleionsinPM2.5inJinan,China:Temporalvariationsandsourceapportionments.Atmos.Environ.45,6048–6056(2011).112.M.-D.Chou,M.J.Suarez,C.-H.Ho,M.M.-H.Yan,K.-T.Lee,Parameterizationsforcloudoverlappingandshortwavesingle-scatteringpropertiesforuseingeneralcirculationandcloudensemblemodels.J.Climate11,202–214(1998).113.E.J.Mlawer,S.J.Taubman,P.D.Brown,M.J.Iacono,S.A.Clough,Radiativetransferforinhomogeneousatmospheres:RRTM,avalidatedcorrelated-kmodelforthelongwave.J.Geophys.Res.102,16663–16682(1997).114.A.Xiu,J.E.Pleim,Developmentofalandsurfacemodel.PartI:Applicationinamesoscalemeteorologicalmodel.J.Appl.Meteorol.40,192–209(2001).115.J.E.Pleim,Acombinedlocalandnonlocalclosuremodelfortheatmosphericboundarylayer.PartI:Modeldescriptionandtesting.J.Appl.Meteorol.Clim.46,1383–1395(2007).116.J.S.Kain,TheKain–Fritschconvectiveparameterization:Anupdate.J.Appl.Meteorol.43,170–181(2004).117.S.-Y.Hong,J.-O.J.Lim,TheWRFsingle-moment6-classmicrophysicsscheme(WSM6).J.KoreanMeteor.Soc.42,129–151(2006).118.T.Ibusuki,K.Takeuchi,Sulfurdioxideoxidationbyoxygencatalyzedbymixturesofmanganese(II)andiron(III)inaqueoussolutionsatenvironmentalreactionconditions.Atmos.Environ.21,1555–1560(1987).SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December201610of11119.P.Debye,E.Hückel,Theinterionicattractiontheoryofdeviationsfromidealbehaviorinsolution.Z.Phys.24,185(1923).120.P.Debye,W.McAuley,Theelectricfieldoftheionsandtheneutralsalteffect.PhysikZ26,22(1925).121.C.W.Davies,T.Shedlovsky,Ionassociation.J.Electrochem.Soc.111,85C–86C(1964).122.H.C.Helgeson,T.H.Brown,A.Nigrini,T.A.Jones,Calculationofmasstransferingeochemicalprocessesinvolvingaqueoussolutions.Geochim.Cosmochim.Acta34,569–592(1970).123.K.S.Pitzer,Electrolytetheory—ImprovementssinceDebyeandHueckel.Acc.Chem.Res.10,371–377(1977).124.K.S.Pitzer,ActivityCoefficientsinElectrolyteSolutions(CRCPress,1991).125.F.J.Millero,J.B.Hershey,G.Johnson,J.-Z.Zhang,ThesolubilityofSO2andthedissociationofH2SO3inNaClsolutions.J.Atmos.Chem.8,377–389(1989).126.C.Bretti,F.Crea,C.Foti,S.Sammartano,Solubilityandactivitycoefficientsofacidicandbasicnonelectrolytesinaqueoussaltsolutions.2.Solubilityandactivitycoefficientsofsuberic,azelaic,andsebacicacidsinNaCl(aq),(CH3)4NCl(aq),and(C2H5)4NI(aq)atdifferentionicstrengthsandatt=25°C.J.Chem.Eng.Data51,1660–1667(2006).127.C.Bretti,F.Crea,C.DeStefano,S.Sammartano,G.Vianelli,SomethermodynamicpropertiesofDL-tyrosineandDL-tryptophan.Effectoftheionicmedium,ionicstrengthandtemperatureonthesolubilityandacid–baseproperties.FluidPhaseEquilib.314,185–197(2012).128.A.J.Rusumdar,“Treatmentofnon-idealityinthemultiphasemodelSPACCIMandinvestigationofitsinfluenceontroposphericaqueousphasechemistry,”thesis,BrandenburgUniversityofTechnology,Cottbus,Germany(2013).AcknowledgmentsFunding:ThisstudywassupportedbytheMaxPlanckSociety(MPG),theNationalNaturalScienceFoundationofChina(21107061,21190054)andtheEUprojectBACCHUS(603445)andPEGASOS(265148).Y.C.thankstheMPGMinervaprogram.G.Z.thanksChineseScholarshipCouncilforfinancialsupportofherstudyattheMaxPlanckInstituteforChemistry.Authorcontributions:K.H.,Y.C.,andG.Z.proposedtheinitialidea.Y.C.andH.S.designedandledthestudy.G.Z.,Y.C.,andH.S.conductedthedataanalyses.C.W.,Q.M.,andB.Z.performedthemodelsimulation.Q.Z.andK.H.providedthefieldobservationandsupportedthemodelanalyses.Z.W.andM.G.supportedthemodelanalyses.Y.C.,H.S.,G.Z.,andU.P.interpretedthedata.Y.C.,H.S.,U.P.,G.Z.,andG.C.wrotethemanuscript,withinputsfromallcoauthors.Competinginterests:Theauthorsdeclarethattheyhavenocompetinginterests.Dataandmaterialsavailability:Alldataneededtoevaluatetheconclusionsinthepaperarepresentinthepaperand/ortheSupplementaryMaterials.Additionaldatarelatedtothispapermayberequestedfromtheauthors.Originalsubmission17December2015Transferredsubmission7July2016Accepted30November2016Published21December201610.1126/sciadv.1601530Citation:Y.Cheng,G.Zheng,C.Wei,Q.Mu,B.Zheng,Z.Wang,M.Gao,Q.Zhang,K.He,G.Carmichael,U.Pöschl,H.Su,ReactivenitrogenchemistryinaerosolwaterasasourceofsulfateduringhazeeventsinChina.Sci.Adv.2,e1601530(2016).SCIENCEADVANCESRESEARCHARTICLEChengetal.Sci.Adv.2016;2:e160153021December201611of11

1、当您付费下载文档后，您只拥有了使用权限，并不意味着购买了版权，文档只能用于自身使用，不得用于其他商业用途（如 [转卖]进行直接盈利或[编辑后售卖]进行间接盈利）。
2、本站所有内容均由合作方或网友上传，本站不对文档的完整性、权威性及其观点立场正确性做任何保证或承诺！文档内容仅供研究参考，付费前请自行鉴别。
3、如文档内容存在违规，或者侵犯商业秘密、侵犯著作权等，请点击“违规举报”。

碎片内容

碳中和的最新文档