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1.
The formation of secondary organic aerosol (SOA) results from the absorption of gas-phase organic oxidation products by airborne aerosol. Historically, modeling the formation of SOA has relied on relatively crude estimates of the capability of given parent hydrocarbons to form SOA. In more recent work, surrogate organic oxidation products have been separated into two groups, hydrophobic and hydrophilic, depending on whether the product is more likely to dissolve into an organic or an aqueous phase, respectively. The surrogates are then allowed to partition only via the dominant mechanism, governed by molecular properties of the surrogate molecules. The distinction between hydrophobic and hydrophilic is based on structural and physical characteristics of the compound. In general, secondary oxidation products, because of low vapor pressures and high polarities, express affinity for both the organic and aqueous aerosol phases. A fully coupled hydrophobic-hydrophilic organic gas-particle partitioning model is presented here. The model concurrently achieves mass conservation, equilibrium between the gas phase and the organic aerosol phase, equilibrium between the gas phase and the aqueous aerosol phase, and equilibrium between molecular and ionic forms of the partitioning species in the aqueous phase. Simulations have been performed using both a zero-dimensional model and the California Institute of Technology three-dimensional atmospheric chemical transport model. Simultaneous partitioning of species by both mechanisms typically leads to a shift in the distribution of products to the organic aerosol phase and an increase in the total amount of SOA predicted as compared to previous work in which partitioning is assumed to occur independently to organic and aqueous phases.  相似文献   

2.
The gas-particle partitioning of select semivolatile organic compounds (SOCs) was studied by injecting the SOCs into a 190 m3 Teflon film chamber containing a secondary organic aerosol (SOA) generated by volatilizing liquid -pinene into an ozone-concentrated atmosphere. The concentration of total suspended particulates (TSP) and gas and particle-phase SOCs was measured over the course of three experiments spanning a temperature range of 268–297 K and a relative humidity range of 55–100%. An equilibrium partition coefficient, Kp, was calculated for each sampling event. Empirical relationships were then developed to predict the partitioning of the SOCs on the SOA particle source as a function of temperature. Partitioning in this SOA system was compared to that of a SOA generated by the photochemical reaction of NOx with m-xylene. The results indicate that partitioning is similar between the two SOA systems. The effects of multiple particle sources on partitioning was also examined, revealing that a weighted average of predicted Kp values for individual sources can be used to predict partitioning in aerosol mixtures.  相似文献   

3.
Anthropogenic emissions alter biogenic secondary organic aerosol(SOA) formation from naturally emitted volatile organic compounds(BVOCs). We review the major laboratory and field findings with regard to effects of anthropogenic pollutants(NOx, anthropogenic aerosols, SO_2, NH_3) on biogenic SOA formation. NOx participate in BVOC oxidation through changing the radical chemistry and oxidation capacity, leading to a complex SOA composition and yield sensitivity towards NOx level for different or even specific hydrocarbon precursors. Anthropogenic aerosols act as an important intermedium for gas–particle partitioning and particle-phase reactions, processes of which are influenced by the particle phase state, acidity, water content and thus associated with biogenic SOA mass accumulation. SO_2 modifies biogenic SOA formation mainly through sulfuric acid formation and accompanies new particle formation and acid-catalyzed heterogeneous 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 the optical properties of SOA. The response of SOA formation behavior to these anthropogenic pollutants varies among different BVOCs precursors. Investigations on anthropogenic–biogenic interactions in some areas of China that are simultaneously influenced by anthropogenic and biogenic emissions are summarized. Based on this review, some recommendations are made for a more accurate assessment of controllable biogenic SOA formation and its contribution to the total SOA budget. This study also highlights the importance of controlling anthropogenic pollutant emissions with effective pollutant mitigation policies to reduce regional and global biogenic SOA formation.  相似文献   

4.
Global secondary organic aerosol formation (SOA) is currently assumed to be between 11.2 and 270 Tg/yr. This range of uncertainty is reflected in the gas-phase chemistry. In this study, we focus on the feedback of SOA formation on the concentrations of most important trace gases such as ozone, and compare it to the impact of monoterpene gas-phase chemistry with a newly developed reduced monoterpene mechanism (MMM) for either α- or β-pinene in the global chemistry transport model MATCH-MPIC. With this set-up an uncertainty range of 3.5–4.0% increase in annually averaged tropospheric ozone was found to be caused by the gas-phase chemistry of the investigated monoterpenes. Moreover, a strong feedback has been observed for NOx, HCHO, HNO3 and PAN. These observations are affected remarkably by different SOA formation approaches like partitioning or saturation vapour pressure limitation and by the structure of the monoterpene used, e.g. reducing the impact on tropospheric ozone to 1.2–1.9% by using the partitioning approach versus the simulation with gas-phase chemistry only. Therefore, a consideration of the individual processes associated with SOA formation seems to be necessary to reduce the uncertainty in SOA formation and to understand the impact of VOCs on atmospheric chemistry. An erratum to this article is available at .  相似文献   

5.
实验室模拟研究大气二次有机气溶胶的形成   总被引：1，自引：0，他引：1  
徐永福  贾龙 《大气科学》2018,42(4):767-785
二次有机气溶胶（SOA）是大气中重要的气溶胶组分,主要由挥发性有机物（VOCs）经化学转化形成,对天气、气候、大气环境和人体健康有重要影响,但至今其确切的化学成分和形成机制还十分不清楚。研究SOA的方法主要采用实验室单个物种或多物种的化学过程的模拟研究,野外实际大气的SOA化学成分、源汇和多尺度分析的观测研究,以及大气中SOA形成的数值模拟的回报和预报研究。实验室研究是对SOA形成过程中获取基础数据和推究SOA生成机制的最主要手段。在过去的几十年中,特别是近五年,SOA的研究取得了较大的进展,其中包括SOA前体物、SOA形成机制及影响因子的进一步理解。本文就这些方面展开了概要性的综述,重点强调了我国研究人员所做的研究工作。在采用实验室烟雾箱系统模拟研究SOA方面,首先简述了烟雾系统的发展以及表征,讨论了跟烟雾箱箱体相关的壁效应问题,重点综述了萜烯类、芳香烃类、小分子类等化学物种转化形成SOA的研究进展。在采用流动管和其他反应器类模拟研究SOA方面,重点讨论了挥发性有机物在颗粒物表面或在液相中所形成的SOA的主要化学成分及其可能的作用。  相似文献   

6.
Five aromatic hydrocarbons – benzene, toluene, ethylbenzene, p-xylene and 1,2,4-trimethylbenzene – were selected to investigate the laser desorption/ionization mass spectra of secondary organic aerosols (SOA) resulting from OH-initiated photooxidation of aromatic compounds. The experiments were conducted by irradiating aromatic hydrocarbon/CH3ONO/NO X mixtures in a home-made smog chamber. The aerosol time-of-flight mass spectrometer (ATOFMS) was used to measure the aerodynamic size and chemical composition of individual secondary organic aerosol particles in real-time. Experimental results showed that aerosol created by aromatics photooxidation is predominantly in the form of fine particles, which have diameters less than 2.5 μm (i.e. PM2.5), and different aromatic hydrocarbons SOA mass spectra have eight same positive laser desorption/ionization mass spectra peaks: m/z = 18, 29, 43, 44, 46, 57, 67, 77. These mass spectra peaks may come from the fragment ions of the SOA products: oxo-carboxylic acids, aldehydes and ketones, nitrogenated organic compounds, furanoid and aromatic compounds. The possible reaction mechanisms leading to these products were also discussed.  相似文献   

7.
A global 3-D Lagrangian chemistry-transport model STOCHEM is used to describe the tropospheric distributions of four components of the secondary atmospheric aerosol: nitrate, sulphate, ammonium and organic compounds. The model describes the detailed chemistry of the formation of the acid precursors from the oxidation of SO2, DMS, NOx, NH3 and terpenes and their uptake into the aerosol. Model results are compared in some detail with the available surface observations. Comparisons are made between the global budgets and burdens found in other modelling studies. The global distributions of the total mass of secondary aerosols have been estimated for the pre-industrial, present day and 2030 emissions and large changes have been estimated in the mass fractions of the different secondary aerosol components.  相似文献   

8.
(NH4)2SO4, CaCl2, Na2SiO3 and NaNO3 were selected as surrogates of inorganic seed aerosols of ambient atmosphere of Chinese urban areas, respectively, to study their effects on the formation of secondary organic aerosol (SOA) in the toluene/CH3ONO/NOx photooxidation system. The SMPS and aerosol laser time-of-flight mass spectrometer (ALTOFMS) was used to measure the aerodynamic size and chemical composition of individual SOA particles in real-time. Experimental results indicate that either the growth or products of SOA is affected by the presence of inorganic seed aerosol. Inorganic seed aerosols would promote growth rates of SOA formation at the start of the reaction and inhibits its formation rate with prolonging the reaction time. In the case of about 100 μg m?3 seed aerosol load, the addition of Na2SiO3 induced a same growth rate of SOA formation as NaNO3. The influence of four individual seed aerosols on the generation of SOA decreased in the order of CaCl2 > (NH4)2SO4 > NaNO3, Na2SiO3. The presence of Na2SiO3 or NaNO3 has no obvious effect on the growth rates of SOA formation, but it does increase the yield of organic acid and nitrogen-containing organic compounds, respectively. Besides the significantly effect on the growth rate of SOA formation, the presence of CaCl2 or (NH4)2SO4 can lead to the formation of high-molecular weight species which is found to be positively correlated with the hygroscopic behavior of seed aerosols. The CaCl2 shows the strongest hygroscopic behavior among the four individual seed aerosols, and the most significant promotion effect on the formation of the high-molecular weight species. It is proposed that the SOA generation enhancement and high-molecular weight products are achieved by particle-phase heterogeneous reactions induced and catalyzed by the acidity of CaCl2 and (NH4)2SO4 seed aerosols.  相似文献   

9.
To investigate the impacts of relative humidity(RH) on secondary organic aerosol(SOA) concentrations and chemical reactions, the carbonaceous aerosol components [i.e., organic carbon(OC) and element carbon(EC)] were quantified in daily PM2.5 samples collected at a background site in East China during summer 2015. Based on the method of EC-tracer, the concentration of secondary organic carbon(SOC) demonstrated an obvious negative relationship with RH higher than 60%. Moreover, the ratio of SOC/EC also exhibited obvious decreasing trends with increasing RH, indicating negative effects for chemical production of SOA under high RH conditions. Due to high RH,photochemistry was weakened, gaseous oxidant concentrations was lowered(e.g., significantly decreased O3 levels),and the production rates of SOA were relatively low. On the other hand, because of more water uptake under higher RH conditions, the aerosol droplet acidity was reduced and enhancement of SOA formation by acidity was accordingly absent. In addition, high RH also plays an important role in changing viscosity of pre-existing aerosol coatings,which can affect reactive uptake yield of SOA. Overall, the results from this study imply that SOA production may be more associated with photochemical processes, while aqueous-phase chemistry is not very important for some SOA formation in a moist ambient environment. In the ambient atmosphere, oxidant concentrations, reaction rates,airborne species, etc., are highly variable. How do these factors affect SOA yields under given ambient environment warrants further detailed investigations.  相似文献   

10.
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11.
Nitrogen-containing organic compounds (NOC) formed from secondary organic aerosols (SOA) age via reaction with reduced nitrogen species are a vital class of brown carbon compounds. NOC compounds from ammonia (NH3) gas-aging of benzene SOA were investigated in present study, and the experiments were performed by irradiating benzene/CH3ONO/NO/NH3 air mixtures in a home-made smog chamber. The particulate NOC products of aged benzene SOA in the presence of NH3 were measured by UV-Vis spectrophotometer, attenuated total reflectance-Fourier transform infrared (ATR-FTIR), and aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with Fuzzy C-Means (FCM) clustering algorithm, respectively. Experimental results demonstrated that NH3 has significant promotion effect on benzene SOA formation. Organic ammonium salts, such as ammonium glyoxylate, ammonium 6-oxo-2,4-hexadienoiclate, which are formed from NH3 reactions with gaseous organic acids were detected as the major particulate NOC products of NH3-aged benzene SOA. 1H–imidazole, 1H–imidazole-2-carbaldehyde and other imidazole products via the heterogeneous reactions between NH3 and dialdehydes of benzene SOA were successfully detected as important brown carbon constituents. The formation of imidazole products suggests that some ambient particles contained organonitrogen compounds may be come from this mechanism. The results of this study may provide valuable information for discussing NH3 deposition and SOA aging mechanisms.  相似文献   

12.
生物源与人为源有机气体氧化形成的二次有机气溶胶(SOA)对气候变化和人类健康具有重要影响。SOA的产生与其前体物研究已取得了一些进展,但由于有机气体之间存在复合相互作用以及SOA形成机制复杂,目前对不同有机气体混合体系中SOA的形成认知还比较匮乏。因此,深入了解有机气体多源、复杂的相互作用,摸清有机气体的大气氧化机制、SOA的形成及影响等对深入理解真实大气有机气体化学演变具有指导意义。本文旨在了解复合体系有机气体氧化生成SOA的相关研究进展。一方面总结了复合体系有机气体产生SOA质量浓度、产率、成分、挥发性、光学性质等的变化,侧重于实验室复合体系有机气体氧化对SOA形成的多重影响以及SOA组成元素、分子构成的变化特征,并总结了目前实验室基于模型对复合体系SOA生成的模拟研究和拟合情况;另一方面探究了环境因素,如相对湿度(RH)、温度(T)以及无机气体,如氮氧化物(NOx)、二氧化硫(SO2)、氨气(NH3)等对复合体系有机气体形成SOA的影响。  相似文献   

13.
Atmospheric particles contain a myriad of organiccompounds, including many multifunctional,water-soluble organic compounds. Many of thesecompounds are postulated to be secondary of origin. This work investigates the possible precursors ofseveral classes of multifunctional, water-solublesecondary organic compounds by analyzing the pathwaysleading to their formation, based on known gas-phasereactions. The analysis is termed `retrosynthetic'due to the backward direction of the analysis, fromproducts to precursors. Pathways for multi-functionalcompounds were generated combinatorially, consideringthe formation of one functional group at a time.Many multifunctional organic compounds with carboxylicacid, carbonyl, and hydroxy functional groups werefound to be first- or second-generation products ofcommon anthropogenic and biogenic volatile organiccompounds such as alkanes, alkenes, aromatics, andcyclic alkenes. The estimated yields of water-solubleorganic compounds from primary precursors ranged fromless than 1% to over 10%, based on stoichiometricconsiderations. The SOA formation index, whichcombines the concepts of yields and rates, was used tocompare the feasibility of the retrosyntheticpathways. Many of the candidate pathways involve theisomerization reaction of alkoxy radicals andoxygenated intermediate products such asmonocarboxylic acids and hydroxyaldehydes.  相似文献   

14.
A laboratory study was carried out to investigate the secondary organic aerosol products from photooxidation of the aromatic hydrocarbon toluene. The laboratory experiments consisted of irradiating toluene/propylene/NOx/air mixtures in a smog chamber operated inthe dynamic mode and collecting submicron secondary organic aerosol samples through a sampling train that consisted of an XAD denuder and a ZefluorTM filter. Oxidation products in the filter extracts were treated using O-(2,3,4,5,6,-pentafluorobenzyl)-hydroxylamine (PFBHA) to derivatize carbonyl groups followed by treatment with N,O-Bis(trimethylsilyl)-acetamide (BSTFA) to derivatize OH groups. The derivatized products were detected with a positive chemical ionization (CI) gas chromatography ion trap mass spectroscopy (GC-ITMS) system. The results of the GC-ITMS analyses were consistent with the previous studies that demonstrated the formation of multi-functional oxygenates. Denuder results showed that many of these same compounds were present in the gas, as well as, the particle phase. Moreover, evidence was found for a series of multifunctional acids produced as higher order oxidation products of the toluene/NOx system. Products having nearly the same mass spectrumwere also found in the ambient environment using identical analytical techniques. These products having multiple acid and alcoholic-OH moieties have substantially lower volatility than previously reported SOA products of the toluene photooxidation and might serve as an indicator for aromatic oxidation in the ambient atmosphere.  相似文献   

15.
A series of 60-year numerical experiments starting from 1851 was conducted using a global climate model coupled with an aerosol-cloud-radiation model to investigate the response of the Asian summer monsoon to variations in the secondary organic aerosol (SOA) flux induced by two different estimations of biogenic volatile organic compound (BVOC) emissions. One estimation was obtained from a pre-existing archive and the other was generated by a next-generation model (the Model of Emissions of Gases and Aerosols from Nature, MEGAN). The use of MEGAN resulted in an overall increase of the SOA production through a higher rate of gasto-particle conversion of BVOCs. Consequently, the atmospheric loading of organic carbon (OC) increased due to the contribution of SOA to OC aerosol. The increase of atmospheric OC aerosols was prominent in particular in the Indian subcontinent and Indochina Peninsula (IP) during the pre- and early-monsoon periods because the terrestrial biosphere is the major source of BVOC emissions and the atmospheric aerosol concentration diminishes rapidly with the arrival of monsoon rainfall. As the number of atmospheric OC particles increased, the number concentrations of cloud droplets increased, but their size decreased. These changes represent a combination of aerosol-cloud interactions that were favorable to rainfall suppression. However, the modeled precipitation was slightly enhanced in May over the oceans that surround the Indian subcontinent and IP. Further analysis revealed that a compensating updraft in the surrounding oceans was induced by the thermally-driven downdraft in the IP, which was a result of surface cooling associated with direct OC aerosol radiative forcing, and was able to surpass the aerosolcloud interactions. The co-existence of oceanic ascending motion with the maximum convective available potential energy was also found to be crucial for rainfall formation. Although the model produced statistically significant rainfall changes with locally organized patterns, the suggested pathways should be considered guardedly because in the simulation results, 1) the BVOC-induced aerosol direct effect was marginal; 2) cloud-aerosol interactions were modeldependent; and 3) Asian summer monsoons were biased to a nonnegligible extent.  相似文献   

16.
Organic aerosol constituents can influence the surface tension of nucleating cloud droplets and thereby modify the critical supersaturation necessary to activate aerosol particles. Model calculations, based on experiments carried out with different surrogates, led to contradictory conclusions on the effect of organic components on activation, indicating that the results depend very much on the surrogate selected. In order to reduce this uncertainty surface tension measurements were performed on real atmospheric aerosol components. Humic-like substances (HULIS) that accounted for 60% of the water-soluble organic carbon present in rural aerosol were isolated from 32 samples covering different seasons. The isolated organic matter present in a concentration of about 1 g L–1, decreased the surface tension of the aqueous solutions by 25–42% as compared to pure water. This effect was further enhanced when humic-like substances were mixed with ammonium sulphate. In order to support model calculations Szyskowski functions were fitted to the data to formulate the surface tension effect as a function of concentration.Finally, natural humic substances (fulvic and humic acids) were investigated under the same conditions. The experiments revealed that the surface tension decreasing effect of atmospheric humic-like substances differed from that of the studied terrestrial and aquatic humic substances: the latter substances decreased the surface tension of the aqueous solution to a lesser extent (7–23%) than atmospheric HULIS. This deviation can be explained with the different composition (e.g. the ratio of aromatic to aliphatic moieties) of the substances investigated.  相似文献   

17.
Fine particle of organic aerosol(OA), mostly arising from pollution, are abundant in Beijing. To achieve a better understanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer(HRTo F-AMS, Aerodyne Research Inc., USA) was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 ± 30 μg m-3, which was higher than in summer(13 ± 6.9 μg m-3). The elemental analysis 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, respectively. 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.  相似文献   

18.
To improve our understanding of aerosol formation and ageing in urban atmospheres, we have tested the ORISAM 0-D aerosol module (ORganic and Inorganic Spectral Aerosol Model). This module accounts for both types of primary carbonaceous particles (black carbon BC and primary organic carbon OCp) and also simulates the formation of secondary inorganic and organic particles (sulfates, nitrates, ammonium, water and secondary organic carbon particles OCsec) by attachment of gas precursors to pre-existing carbonaceous particles. Simulations were performed for surface aerosols over Greater Paris area during the ESQUIF summer 1998 and winter 2000 experiments. Results show that OCsec formation is highly dependent on temperature and insolation with more intense secondary formation in summer than in winter. Moreover in Summer, when atmospheric conditions shift from warm and humid to hot and dry, the model indicates a decreasing formation of secondary organic aerosols OCsec as shown by an increase of the OCp/(OCp+OCsec) ratio from 42 to 56%. These results satisfactorily compare with the few experimental available data for BC/(OCp+OCsec) ratios increasing from 24 to 37% against modelled values in the range 21–32%. ORISAM module sensitivity to initial size distributions, background concentrations and emissions of gases and primary carbonaceous particles was documented too. One main result is that the formation of secondary organic particles with ORISAM is very sensitive to the concentrations of gaseous precursors. At the present stage of ORISAM development, OCsec build up appears to be however less sensitive to particulate background concentrations.  相似文献   

19.
Organic aerosol formation resulting from the ozonolysis of α-pinene, myrcene and sabinene was investigated in a large aerosol chamber in the presence of aqueous seed aerosols. The chemical composition of the particles was monitored by an aerosol mass spectrometer (Aerodyne Research Inc.) as a function of time and the particle size. Smaller particles were found to contain more organics relative to sulfate than the larger ones. In contrast, the water to sulfate mass ratio was not dependent on the particle size. These experimental findings indicate the formation of organic layers on the particles. With the aid of an aerosol dynamic model we demonstrate that the observations are consistent with the formation of multilayered organic films having thicknesses of approximately 10 nm. The results also suggest that the films were formed through condensation of low-volatile oxidation products that did not take up water considerably. Even though dissolution of oxidation products into the particle aqueous phase cannot be conclusively ruled out, the most plausible interpretation of the results is that the monoterpene ozonolysis lead to the formation of organic coatings on aqueous aerosols. Such films are likely to form in regions with monoterpene emissions.  相似文献   

20.
Abstract This paper describes the effect of the presence of water-soluble organic compounds (WSOC) in aerosol particles on the aerosol critical supersaturation as defined by the Köhler theory and on cloud condensation nuclei (CCN) number concentration. Taking into account both the soluble mass increase and the surface tension depression due to WSOC, we calculated a substantial decrease of the aerosol critical supersaturation, which results in a large increase in CCN number concentration. CCN supersaturation spectra were computed for three different aerosol types: marine, rural and urban. The increase of CCN number concentration in the presence of WSOC (with respect to the case when only the inorganic aerosol compounds are considered) varies with aerosol type, with an increase up to 13% in the marine case, up to 97% in the rural case, and up to 110% in the urban case, for the supersaturation range typical of atmospheric conditions.  相似文献   

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