Contrast in Secondary Organic Aerosols between the Present Day and the Preindustrial Period:The Importance of Nontraditional Sources and the Changed Atmospheric Oxidation Capability

Quantifying differences in secondary organic aerosols(SOAs)between the preindustrial period and the present day is crucial to assess climate forcing and environmental effects resulting from anthropogenic activities.The lack of vegetation information for the preindustrial period and the uncertainties in describing SOA formation are two leading factors preventing simulation of SOA.This study calculated the online emissions of biogenic volatile organic compounds(VOCs)in the Aerosol and Atmospheric Chemistry Model of the Institute of Atmospheric Physics(IAP-AACM)by coupling the Model of Emissions of Gases and Aerosols from Nature(MEGAN),where the input vegetation parameters were simulated by the IAP Dynamic Global Vegetation Model(IAP-DGVM).The volatility basis set(VBS)approach was adopted to simulate SOA formation from the nontraditional pathways,i.e.,the oxidation of intermediate VOCs and aging of primary organic aerosol.Although biogenic SOAs(BSOAs)were dominant in SOAs globally in the preindustrial period,the contribution of nontraditional anthropogenic SOAs(ASOAs)to the total SOAs was up to 35.7%.In the present day,the contribution of ASOAs was 2.8 times larger than that in the preindustrial period.The contribution of nontraditional sources of SOAs to SOA was as high as 53.1%.The influence of increased anthropogenic emissions in the present day on BSOA concentrations was greater than that of increased biogenic emission changes.The response of BSOA concentrations to anthropogenic emission changes in the present day was more sensitive than that in the preindustrial period.The nontraditional sources and the atmospheric oxidation capability greatly affect the global SOA change.

Effects of seed aerosols on the growth of secondary organic aerosols from the photooxidation of toluene

Hydroxyl radical （.OH）-initiated photooxidation reaction of toluene was carried out in a self-made smog chamber. Four individual seed aerosols such as ammonium sulfate, ammonium nitrate, sodium silicate and calcium chloride, were introduced into the chamber to assess their influence on the growth of secondary organic aerosols （SOA）. It was found that the low concentration of seed aerosols might lead to high concentration of SOA particles. Seed aerosols would promote rates of SOA formation at the start of the reaction and inhibit its formation rate with prolonging the reaction time. In the case of ca. 9000 pt/cm^3 seed aerosol load, the addition of sodium silicate induced a same effect on the SOA formation as ammonium nitrate. The influence of the four individual seed aerosols on the generation of SOA decreased in the order of calcium chloride〉sodium silicate and ammonium nitrate〉ammonium sulfate.

Characterization of Organic Aerosols in Beijing Using an Aerodyne High-Resolution Aerosol Mass Spectrometer

Fine particle of organic aerosol （OA）, mostly arising from pollution, are abundant in Beijing. To achieve a better un- derstanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer （HR- ToF-AMS, Aerodyne Research Inc., USA） was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 4-30 μg m-3, which was higher than in summer （13 4-6.9 μg m-3）. The elemental anal- ysis found that OA was more aged in summer （oxygen-to-carbon （O/C） ratios were 0.41 and 0.32 for summer and autumn, respectively）. Positive matrix factorization （PMF） analysis identified three and five components in summer and autumn, re- spectively. In summer, an oxygenated OA （OOA）, a cooking-emission-related OA （COA）, and a hydrocarbon-like OA （HOA） were indentified. Meanwhile, the OOA was separated into LV-OOA （low-volatility OOA） and SV-OOA （semi-volatile OOA）; and in autumn, a nitrogen-containing OA （NOA） was also found. The SOA （secondary OA） was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components, especially the POA （primary OA）, in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.

Molecular compositions and sources of organic aerosols at a rural site on the Guanzhong Plain,Northwest China:The importance of biomass burning

The concentration of PM_(2.5)has considerably reduced in recent years,but remains relatively high in China.In particular,the increasing contribution of organic compounds to PM_(2.5)generates popular pressure for further reductions,resulting in an urgent need to study organic aerosol(OA).To investigate the molecular composition and source contribution of OA in the rural area of the Guanzhong Plain,Northwest China,PM_(2.5)samples were collected during 3–23 August 2016 and 5–20 January 2017 and studied for more than 100 organic tracer compounds.The mean concentration of total measured organic compounds is 662±296 ng/m^(3)in summer and 3258±1925 ng/m^(3)in winter.Levoglucosan is the most abundant single compound found throughout the sampling period,which is a crucial tracer for biomass burning emissions,preliminary suggesting that biomass burning is an essential source of OA.In summer,organic compounds such as lipid compounds,sugar compounds,and polycyclic aromatic hydrocarbons(PAHs),more come from higher plants,wood burning,vehicle exhausts,plastic waste,and other direct emission sources.Oxygenated PAHs(OPAHs),nitrophenols,and phthalic acids more come from the atmosphere through the oxidation reaction of aromatic precursors,especially photochemical oxidation.However,in winter,most of the increases in concentrations of organic compounds are attributed to biomass burning.The analysis of a haze event(14–19 January 2017)during the winter sampling period shows that the increases in the concentration of organic compounds are unaccompanied by strong secondary formation under lower relative humidity(49.1%±13.5%).The main reason for the growth of OA in this haze event is the accumulation of primary OA(POA).The source apportionment by the positive matrix factorization(PMF)model shows that biomass burning(37.1%)is the primary source of OA in the rural regions of the Guanzhong Plain,especially in winter(40.6%).The contribution of secondary formation decreases from 26.0%in summer to 16.9%in winter,and the contribution of fossil fuel emissions is comparable across both seasons.

Seasonal variation and size distribution of biogenic secondary organic aerosols at urban and continental background sites of China

Size-resolved biogenic secondary organic aerosols （BSOA） derived from isoprene and monoterpene photooxidation in Qinghai Lake, Tibetan Plateau （a continental background site） and five cities of China were measured using gas chromatography/mass spectrometry （GC/MS）. Concentrations of the determined BSOA are higher in the cities than in the background and are also higher in summer than in winter. Moreover, strong positive correlations （R^2 = 0.44-0.90） between BSOA and sulfate were found at the six sites, suggesting that anthropogenic pollution （i.e., sulfate） could enhance SOA formation, because sulfate provides a surface favorable for acid-catalyzed formation of BSOA. Size distribution measurements showed that most of the determined SOA tracers are enriched in the fine mode （〈3.3 μm） except for cis-pinic and cis-pinonic acids, both presented a comparable mass in the fine and coarse （〉3.3 μm） modes, respectively. Mass ratio of oxidation products derived from isoprene to those from monoterpene in the five urban regions during summer are much less than those in Qinghai Lake region. In addition, in the five urban regions relative abundances of monoterpene oxidation products to SOA are much higher than those of isoprene. Such phenomena suggest that BSOA derived from monoterpenes are more abundant than those from isoprene in Chinese urban areas.

PM_(2.5)characterization of primary and secondary organic aerosols in two urban-industrial areas in the East Mediterranean

Primary and secondary organic aerosols in PM_(2.5)were investigated over a one-year campaign at Zouk Mikael and Fiaa,Lebanon.The n-alkanes concentrations were quite similar at both sites(26-29 ng/m^(3))and mainly explained by anthropogenic emissions rather than natural ones.The concentrations of total Polycyclic Aromatic Hydrocarbons(PAHs)were nearly three times higher at Zouk Mikael(2.56 ng/m^(3))compared to Fiaa(0.95 ng/m^(3)),especially for indeno[1,2,3-c,d]pyrene linked to the presence of the power plant.A characteristic indeno[1,2,3-c,d]pyrene/(indeno[1,2,3-c,d]pyrene+benzo[g,h,i]perylene)ratio in the range0.8-1.0 was determined for heavy fuel oil combustion from the power plant.Fatty acids and hopanes were also investigated and were assigned to cooking activities and vehicular emissions respectively.Phthalates were identified for the first time in Lebanon with high concentrations at Zouk and Fiaa(106.88 and 97.68 ng/m^(3) respectively).Moreover,the biogenic secondary aerosols revealed higher concentrations in summer.The total terpene concentration varied between 131 ng/m^(3) at Zouk Mikael in winter to 469 ng/m3 at Fiaa in summer.Additionnally,the concentrations of the dicarboxylic acids especially for adipic and phthalic acids were more influenced by anthropogenic sources.The analysis of molecular markers and diagnostic ratios indicated that the sites were strongly affected by anthropogenic sources such as waste open burning,diesel private generators,cooking activities,road transport,power plant,and industrial emissions.Moreover,results showed different pattern during winter and summer seasons.Whereas,higher concentrations of biogenic markers were clearly encountered during the summer period.

SIMULATION OF SPATIO-TEMPORAL DISTRIBUTION CHARACTERISTICS AND RADIATIVE FORCING OF ORGANIC CARBON AEROSOLS IN CHINA

The International Centre for Theoretical Physics(ICTP,Italy) Regional Climate Model version 3.0(RegCM3) is used to simulate spatio-temporal distribution characteristics and radiative forcing(RF) of organic carbon(OC) aerosols in and around China.The preliminary simulation results show that OC aerosols are mostly concentrated in the area to the south of Yellow River and east of Tibetan Plateau.There is a decreasing trend of column burden of OC aerosols from south to north in China.The maximum value of column burden of OC aerosols is above 3 mg/m2 and located in the central and southern China,southeastern Tibet,and southwestern China's Yunnan,Guizhou,Sichuan provinces.The simulation on the seasonal variation shows that the maximum value of column burden of OC aerosols appears in winter and the secondary value is in spring and the minimum in summer.The RF of OC aerosols which varies seasonally is negative at the top of the atmosphere(TOA) and surface.The spatio-temporal characteristics of the RF of OC aerosols are basically consistent with that of IPCC,implying the high accuracy of the parameterization scheme for OC aerosols in RegCM3.

Seasonal characteristics and provenance of organic aerosols in the urban atmosphere of Liaocheng in the North China Plain:Significant effect of biomass burning

To better understand the seasonal characteristics of urban organic aerosol(OA)in the North China Plain(NCP),PM2.5 samples in the urban atmosphere of Liaocheng were collected and analyzed.The molecular distribution of the organic markers in the urban atmosphere of Liaocheng reveals that n-alkanes(39.3%)was the most abundant species all year round,followed by saccharides(28.2%),phthalic acids(Ph,20.8%),biogenic secondary organic aerosol(BSOA)tracers(9.4%),and polycyclic aromatic hydrocarbon(PAHs,2.3%).PM2.5,organic carbon(OC),elemental carbon(EC),and primary organic markers exhibit the highest concentrations in winter,due largely to the increased biomass burning and coal combustion for house heating in local and surrounding regions.However,the concentration and relative abundance of BSOA are significantly higher in summer than other seasons,induced by the more favorable meteoro-logical conditions that would promote the emissions of biogenic volatile organic compounds(BVOCs)and the secondary production of BSOA.The ratios of OC/EC and 3-methyl-1,2,3-butanetricarboxylic acid to cis-pinic acid plus cis-pinonic acid(MBTCA/(PA+PNA)are higher in the warm seasons than those in the cold seasons,indicating that the oxidation of OA is sensitive to air temperature.Compared to 2017,the concentration level of PAHs during wintertime decreased by 40.8%,confirming that the stringent regulation of coal burning is effective.The highest concentration of high molecular weight(HMW)n-alkanes and three anhydrosugars in winter,and the close correlation of levoglucosan with HMW n-al-kanes suggests that the impact of biomass burning was more significant in winter.The same seasonal characteristic of the ratios of high-/low-NO_(x) products with NO_(x) and the strong correlation of high-/low-NO_(x) products with levoglucosan indicate that the formation of isoprene SOA(SOA1)tracers was signif-icantly influenced by anthropogenic emissions.The molecular compositions,the distributions of fire spots,backward trajectories of air masses,and correlation analysis suggest that air pollution events in spring were primarily resulted from biomass burning and secondary oxidation,while pollution events in winter were largely driven by the increased combustion sources,and promoted aqueous secondary formation.Our results suggest that the reduction of biomass and coal combustion should be taken into account to improve the urban air quality in the NCP.

A Smog Chamber Facility for Qualitative and Quantitative Study on Atmospheric Chemistry and Secondary Organic Aerosol

In order to investigate the atmospheric oxidation processes and the formation of secondary organic aerosol （SOA）, an indoor environmental reaction smog chamber are constructed and characterized. The system consists of the collapsible ～830 L FEP Teflon film main reactor, in which the atmospheric chemical reactions take place and the formation of SOA occurs under the simulated atmospheric conditions, and the diverse on-line gas- and particle-phase instrumentation, such as the proton transfer reaction mass spectrometer, the synchrotron radiation photoionization mass spectrometer, the aerosol laser time-of-flight mass spectrometer, and other traditional commercial instruments. The initial characterization experiments are described, concerning the temperature and ultraviolet light intensity, the reactivity of the pure air, the wall loss rates of gaseous compounds and particulate matter. And the initial evaluation experiments for SOA yields from the ozonolysis of α-pinene and for mass spectra of the products resulting from the photooxidation of OH initiated isoprene are also presented, which indicate the applicability of this facility on the studies of gas-phase chemical mechanisms as well as the formation of SOA expected in the atmosphere.

Characterization of Organic Aerosol at a Rural Site in the North China Plain Region:Sources,Volatility and Organonitrates

The North China Plain(NCP)is a region that experiences serious aerosol pollution.A number of studies have focused on aerosol pollution in urban areas in the NCP region;however,research on characterizing aerosols in rural NCP areas is comparatively limited.In this study,we deployed a TD-HR-AMS(thermodenuder high-resolution aerosol mass spectrometer)system at a rural site in the NCP region in summer 2013 to characterize the chemical compositions and volatility of submicron aerosols(PM_(1)).The average PM_(1)mass concentration was 51.2±48.0μg m^(−3) and organic aerosol(OA)contributed most(35.4%)to PM_(1).Positive matrix factorization(PMF)analysis of OA measurements identified four OA factors,including hydrocarbon-like OA(HOA,accounting for 18.4%),biomass burning OA(BBOA,29.4%),lessoxidized oxygenated OA(LO-OOA,30.8%)and more-oxidized oxygenated OA(MO-OOA,21.4%).The volatility sequence of the OA factors was HOA>BBOA>LO-OOA>MO-OOA,consistent with their oxygen-to-carbon(O:C)ratios.Additionally,the mean concentration of organonitrates(ON)was 1.48−3.39μg m−3,contributing 8.1%-19%of OA based on cross validation of two estimation methods with the high-resolution time-of-flight aerosol mass spectrometer(HRToF-AMS)measurement.Correlation analysis shows that ON were more correlated with BBOA and black carbon emitted from biomass burning but poorly correlated with LO-OOA.Also,volatility analysis for ON further confirmed that particulate ON formation might be closely associated with primary emissions in rural NCP areas.

Chemical composition and size distribution of secondary organic aerosol formed from the photooxidation of isoprene

Photooxidation of isoprene leads to the formation of secondary organic aerosol （SOA）. In this study, the chemical composition of SOA formed from OH-initiated photooxidation of isoprene has been investigated with gas chromatography/mass spectrometry （GC/MS） and a home-made aerosol time-of-fiight mass spectrometer. Sampling particles generated in a home-made smog chamber. The size distribution of SOA particles was detected by a TSI 3321 aerodynamic particle size spectrometer in real time. Results showed that SOA created by isoprene photooxidation was predominantly in the form of fine particles, which have diameters less than 2.5 μm. The obtained mass spectra of individual particles show that products of the OH-initiated oxidation of isoprene contain methyl vinyl ketone, methacrolein, formaldehyde, and some other hydroxycarbonyls. The possible reaction mechanisms leading to these products were also discussed.

Seasonal Variations of Terrestrial OC Sources in Aerosols over the East China Sea: The Influence of Long-Range Air Mass Transport

Aerosols represent an important source of terrestrial organic carbon(OC)from the East Asian continent to the China marginal seas,thus their provenance and transport play important roles in the global carbon cycle.Fifty samples of total suspended particle were collected seasonally from the nearshore Huaniao Island(HNI)in East China Sea(ECS)from April 2018 to January 2019;and they were analyzed for total organic carbon(TOC)content and stable carbon isotope(δ^(13)C),as well as terrestrial bio-markers including n-alkanes(C_(20)-C_(33)),n-alkanols(C_(20)-C32)and n-fatty acids(n-FAs,C_(20)-C30),to distinguish the seasonal variabili-ties of terrestrial OC sources and reveal the influence of the long-range air mass transport on these sources.The TOC-δ^(13)C values(range from−27.3‰to−24.3‰)and molecular distributions of terrestrial biomarkers both suggested that terrestrial OC contribu-tions to aerosols had significant seasonal variations.The source indices of terrestrial biomarkers(e.g.,Fossil%=82.8%for n-alkanes)revealed that the fossil fuel OC contributions,including coal burning and vehicular emission,were higher in winter,mainly because of the long-range air mass transport from the north of the East Asian continent.The terrestrial plant OC contributions were higher in summer(e.g.,Wax%=32.4%for n-alkanes),likely due to local vegetation sources from HNI and East Asian continental air masses.Cluster analysis of air mass backward-trajectories clearly showed that transport pathway plays an important role in determining the organic constituents of aerosols in China marginal seas.A comparison of these terrestrial OC contributions from different air mass origins suggested that fossil fuel OC showed less variations among various air mass origins from northern China in winter,while terrestrial plant OC sources from northern and southern China in summer contributed more than that from the air masses transported through the ECS.These results provided a basis for future quantification of terrestrial OC from different origins in marine aerosols,by combining biomarker index and carbon isotopes.

Size distribution of the secondary organic aerosol particles from the photooxidation of toluene

In a smog chamber, the photooxidation of toluene was initiated by hydroxyl radical （OH.） under different experimental conditions. The size distribution of secondary organic aerosol（SOA） particles from the above reaction was measured using aerodynamic particle sizer spectrometer. It was found from our experimental results that the number of SOA particles increased with increasing the concentration of toluene. As the reaction time prolonged, the sum of SOA particles was also increased. After a reaction time of 130 min, the concentration of secondary organic aerosol particles would be kept constant at 2300 particles/cm^3. Increasing illumination power of blacklamps could significantly induce a higher concentration of secondary organic aerosol particle. The density of SOA particles would also be increased with increasing concentration of CH30NO, however, it would be decreased as soon as the concentration of CH30NO was larger than 225.2 ppm. Nitrogen oxide with initial concentration higher than 30. 1 ppm was also found to have little effect on the formation of secondary organic aerosol.

Effect of illumination intensity and light application time on secondary organic aerosol formation from the photooxidation of α-pinene

Secondary organic aerosol （SOA） formation from hydroxyl radical （OH.） initiated photooxidation of α-pinene was investigated in a home-made smog chamber. The size distribution of SOA particles was measured using aerodynamic particle sizer spectrometer. The effects of illumination intensity and light application time on SOA formation for α-pinene were evaluated. Experimental results show that the concentration of SOA particles increased significantly with an increasing of illumination intensity, and the light application time, the concentration, and the size of SOA particles were also increased. In addition, the factors influencing the formation of SOA were discussed. In addition, this article compared the effect of α-pinene with that of toluene, and discussed the contribution of α-pinene to SOA formation.

Anthropogenic Effects on Biogenic Secondary Organic Aerosol Formation

Anthropogenic emissions alter biogenic secondary organic aerosol(SOA)formation from naturally emitted volatileorganic compounds(BVOCs).We review the major laboratory and field findings with regard to effects of anthropogenicpollutants(NO_(x),anthropogenic aerosols,SO_(2),NH_(3))on biogenic SOA formation.NO_(x) participate in BVOC oxidationthrough changing the radical chemistry and oxidation capacity,leading to a complex SOA composition and yield sensitivitytowards NO_(x) level for different or even specific hydrocarbon precursors.Anthropogenic aerosols act as an importantintermedium for gas-particle partitioning and particle-phase reactions,processes of which are influenced by the particlephase state,acidity,water content and thus associated with biogenic SOA mass accumulation.SO_(2)modifies biogenic SOAformation mainly through sulfuric acid formation and accompanies new particle formation and acid-catalyzedheterogeneous reactions.Some new SO_(2)-involved mechanisms for organosulfate formation have also been proposed.NH_(3)/amines,as the most prevalent base species in the atmosphere,influence biogenic SOA composition and modify theoptical properties of SOA.The response of SOA formation behavior to these anthropogenic pollutants varies amongdifferent BVOCs precursors.Investigations on anthropogenic-biogenic interactions in some areas of China that aresimultaneously influenced by anthropogenic and biogenic emissions are summarized.Based on this review,somerecommendations are made for a more accurate assessment of controllable biogenic SOA formation and its contribution tothe total SOA budget.This study also highlights the importance of controlling anthropogenic pollutant emissions witheffective pollutant mitigation policies to reduce regional and global biogenic SOA formation.

Vertical Profiles of Volatile Organic Compounds in Suburban Shanghai

As Volatile Organic Compounds(VOCs)are one of the precursors of ozone,their distribution and variable concentrations are highly related to local ozone pollution control.In this study,we obtained vertical profiles of VOCs in Shanghai’s Jinshan district on 8 September and 9 September in 2016 to investigate their distribution and impact on local atmospheric oxidation in the near surface layer.Vertical samples were collected from heights between 50 m and 400 m by summa canisters using an unmanned aerial vehicle(UAV).Concentrations of VOCs(VOCs refers to the 52 species measured in this study)varied minimally below 200 m,and decreased by 21.2%from 100 m to 400 m.The concentrations of VOCs above 200 m decreased significantly in comparison to those below 200 m.The proportions of alkanes and aromatics increased from 55.2%and 30.5%to 57.3%and 33.0%,respectively.Additionally,the proportion of alkenes decreased from 13.2%to 8.4%.Toluene and m/p-xylene were the key species in the formation of SOA and ozone.Principal component analysis(PCA)revealed that the VOCs measured in this study mainly originated from industrial emissions.

Second organic aerosol formation from the ozonolysis of α-pinene in the presence of dry submicron ammonium sulfate aerosol

An indoor chamber facility is described for investigation of atmospheric aerosol chemistry. Two sets of α-pinene ozonolysis experiments were conducted in the presence of dry ammonium sulfate seed particle: ozone limited experiments and α-pinene limited experiments. The concentration of gas phase and particle phase species was monitored continuously by on-line instruments and recorded automatically by data sampling system. The evolution of size distribution was measured by a scanning mobility particle sizer ...

Effect of coal mine organic aerosol on the methane/air lower explosive limit

Organic aerosol is formed in coal mines due to heat release and evaporation of organics from coal during the longwall operation.This frictional heating occurs when a metallic cutting bit strikes a rock.Thus formed organic aerosol can contribute significantly to the explosivity of methane/air atmosphere in coal mines.In this paper,the flammable limits for the methane-air mixtures with organic aerosol are determined.For this purpose,organic aerosol is synthesizes from the coal-tar pitch in a laboratory evaporation-nucleation flow chamber.Aerosol particles synthesized under laboratory conditions are aggregates consisting of small primary particles with the fractal-like dimension Df=2.0±0.1,which is close to Df=2.1±0.1 of coal mine aerosol.It is shown that the flammability of organic aerosol/methane mixture in air is in good agreement with the Le Chatelier additive principle.The lower ignition limit for the pure organic aerosol in air is 44 g/m^3.

Photo-oxidation of Isoprene with Organic Seed： Estimates of Aerosol Size Distributions Evolution and Formation Rates

Indoor smog chamber experiments have been conducted to investigate the dynamics of sec- ondary organic aerosol （SOA） formation from OH-initiated photo-oxidation of isoprene in the presence of organic seed aerosol. The dependence of the size distributions of SOA on both the level of pre-existing particles generated in situ from the photo-oxidation of trace hydrocarbons of indoor atmosphere and the concentration of precursor, has been investi- gated. It was shown that in the presence of high-level seed aerosol and low-level isoprene （typical urban atmospheric conditions）, particle growth due to condensation of secondary organic products on pre-existing particles dominated; while in the presence of low-level seed aerosol and comparatively high-level isoprene （typical atmospheric conditions in rural re-gion）, bimodal structures appeared in the size distributions of SOA, which corresponded to new particle formation resulting from homogeneous nucleation and particle growth due to condensation of secondary organic products on the per-existing particles respectively. The effects of concentrations of organic seed particles on SOA were also investigated. The particle size distributions evolutions as well as the corresponding formation rates of new particles in different conditions were also estimated.

Model analysis of secondary organic aerosol over China with a regional air quality modeling system(RAMS-CMAQ)

The regional air quality modeling system RAMS-CMAQ was updated to incorporate secondary organic aerosol （SOA） production from isoprene and sesquiterpene and to account for the SOA production rate dependence on NOx and SOA aging. The system was then used to simulate spatiotemporal distributions of SOA concentration and its major constituents over China in winter. Modeled monthly mean SOA concentrations were high in central and eastern China and low in western regions. The highest SOA appeared in regions from Beijing-Tianjin-Hebei （BTH） to the middle reaches of the Yangtze River and areas from Sichuan Basin to the southwest border of China, where SOA contributions were less than 10% of the organic aerosol （OA）. The lowest concentration was in the Qinghai-Tibet Plateau, accounting for 20%-30% of OA. It is notable that contributions from anthropogenic precursors to SOA were significant in winter, especially the wide areas of central and eastern China with contributions generally varying from 50% to 80% of the total SOA. Beijing was used as an example location representative of the heavily polluted BTH area for analysis of major components of SOA. Though the modeled concentration of SOA was still underestimated compared to the observations, it still showed that xylene and toluene were the two greatest contributors to anthropogenic SOA, which was in agreement with the observations. SOA produced from monoterpene was the greatest contributor to biogenic SOA due to the high mass yield of monoterpene, followed by isoprene. More than 57% of SOAs were aged, which may increase the extinction effect of SOA.