The influence of aerosol particle composition on cloud droplet formation

A difference in partitioning between cloud droplets and interstitial air for two chemical species (elemental carbon and sulphur) with different expected behaviour in nucleation scavenging was observed in clouds at Mt. Kleiner Feldberg (825 m asl), near Frankfurt, Germany. The fraction of sulphur incorporated in cloud droplets was always higher than the fraction of elemental carbon. This difference in partitioning has also been observed in fog but under different pollution conditions in the Po Valley, Italy. Both these studies were based on bulk samples. In the present study at Kleiner Feldberg, impactor samples of the particles in the interstitial air and the cloud droplet residuals were taken and a single particle analysis was done on the samples. It was found that, for a given particle size, the majority of particles forming cloud droplets were soluble and that insoluble particles preferentially remained in the interstitial air.     

Photochemical activation of chlorine by iron-oxide aerosol

The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe₂O₃) aerosol particles (mainly hematite, specific surface ~150 m² g^?1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe₂O₃ at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L^?1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8?×?10²¹ atoms cm^?2 h^?1, respectively. In a further series of experiments, the pure Fe₂O₃ aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8?×?10²⁰ Cl atoms cm^?2 h^?1 (at ~4 ppb HCl) to 5?×?10²² Cl atoms cm^?2 h^?1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe₂O₃ experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl.     

Cloud condensation nuclei and cloud droplet measurements during ACE‐2

During the 2nd Aerosol Characterization Experiment (ACE‐2), relationships between stratocumulus cloud properties and aerosols were examined. Here, the relevant measurements including the cloud condensation nuclei (CCN) activation spectrum, updraft velocity, cloud microphysical and aerosol properties are presented. It is shown that calculations of droplet concentration based on updraft velocity and the CCN activation spectrum are consistent with direct observations. Also discussed is an apparent disparity among measurements of the CCN activation spectrum, the accumulation mode size distribution, and the composition of the submicrometric aerosol. The observed consistency between CCN, updraft and cloud droplets is a necessary refinement; however, extended analyses of the ACE‐2 data set are needed to guide improvements in model simulations of the interaction between aerosols and cloud microphysics. In particular, there is need for an examination of aerosol size spectra and chemical composition measurements with a view towards validating droplet activation schemes which relate the aerosol and cloud dynamical properties to cloud albedo.     

一次秋季冷锋降水过程气溶胶与云粒子分布的飞机观测

利用机载PMS（Particle Measuring Systems）测量系统,对2008年10月4—5日石家庄地区一次冷锋降水云系的3次气溶胶和云粒子探测资料进行了分析。结果表明,冷锋过境降水前后,气溶胶粒子分布差异较大。降水发生前,气溶胶粒子平均数浓度约为103cm-3,平均直径为0.95μm;气溶胶主要集中于3000m高度以下的对流层低层,云内气溶胶数浓度明显减少。降水发生后,气溶胶粒子平均数浓度约为102cm-3,比降水前约小1个量级,平均直径为1.28μm;气溶胶主要集中于1200m以下的近地面层,其数浓度随高度增加而降低。气溶胶粒子浓度在低层云区内水平变化较小,而在无云区和云下近地层水平起伏较大。云粒子平均浓度比气溶胶小1～2个量级。气溶胶粒子平均谱主要呈双峰型,而云粒子谱主要为单峰型。     

The influence of the organic aerosol component on CCN supersaturation spectra for different aerosol types

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.     

复合体系有机气体氧化生成二次有机气溶胶研究进展

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(NO_x)、二氧化硫(SO₂)、氨气(NH₃)等对复合体系有机气体形成SOA的影响。     

Emission of fine organic aerosol from traditional charcoal broiling in China

The indoor PM_2.5 aerosol samples for charcoal broiling source under Chinese traditional charbroiling and the ambient fine aerosols samples (PM_2.5) were collected in Beijing to investigate the characteristics of the charcoal broiling source and its impact on the fine organic aerosols in the atmosphere. The concentrations of 20 species of the trace organic compounds, including polycyclic aromatic hydrocarbons (PAHs), fatty acids, levoglucosan, and cholesterol in PM_2.5 were identified and quantified by GC/MS. The total PAHs and fatty acids emitted from charcoal broiling to PM_2.5 were 8.97 and 87,000 ng mg⁻¹ respectively. The concentrations of the light molecular weight (LMW) 3- and 4-ring PAHs were much higher than those of the high molecular weight (HMW) 5- and 6-ring PAHs. Fatty acids were the most abundant species in source profile, accounting for over 90% of all identified organic compounds. More polyunsaturated fatty acid (linoleic acids) than the saturated fatty acid (stearic acids) emitted in the cooking. Charcoal broiling is a minor source of PAHs compared to the source of biomass burning. Comparing the ratios of levoglucosan/fatty acid and levoglucosan/cholesterol in the charcoal broiling samples to the ambient samples, it is evident that meat cooking is an important source of fatty acids, but a less important source of cholesterol. Cooking, as one of the source of fine organic particles, plus other anthropogenic sources would be related to the formation of the severe haze occurred and spread over the urban atmosphere in most of the cities of China in the past several years.     

不同云滴数浓度参数化方案对硝酸盐气溶胶 第一间接效应影响的比较研究

在区域气候化学模式系统（RegCCMS）中,分别采用Hegg、Hansen、Ghan、Jones等4种云滴数浓度参数化方案,模拟研究了2003年10月硝酸盐气溶胶的浓度分布和第一间接气候效应,并对不同方案进行比较。结果表明,不同方案模拟的硝酸盐气溶胶分布大体上一致,主要集中在河南、山东、河北、四川等地,地面浓度最大值达18 μg/m3。Hegg、Hansen、Ghan、Jones等 4种云滴数浓度参数化方案计算得到的由硝酸盐气溶胶所造成的第一间接辐射强迫全国平均值分别为-148、-205、-161和-140 W/m2。4种方案模拟的硝酸盐气溶胶间接效应都表现为近地面气温下降,降水减少,其中Hansen方案的间接效应最强,Ghan、Hegg方案次之,Jones方案最弱。     

A physically‐based algorithm for estimating the relationship between aerosol mass and cloud droplet number

In this study, we present a relationship between total accumulation mode aerosol mass concentrations and cloud droplet number concentrations ( N _d). The fundamental aim with the present method is to arrive at a physically‐based conversion algorithm in which each step in the conversion is based on real physical processes that occur and can be observed in the atmosphere, and in which all of the fields involved can be observed or modeled. In the last conversion (the critical part in the algorithm), we use measurements of the size distributions of cloud droplet residual particles for different pollution conditions. This conversion assumes that the size of the residual particles can be described with a lognormal distribution function and uses the Hatch–Choate relationship to convert between residual volume and number. The relatively sparse data set with which we have developed the present algorithm results in a course classification of the aerosol mass field. Consequently, uncertainties need to be recognized when using the algorithm in its present form in model calculations. The algorithm has been used on data from 15 days and the agreement between calculated and observed N _d values is, with one exception, within a factor of 2 and for many of these cases also much better than a factor of 2. In addition to the results of the algorithm itself, we also present a least‐squares fit to the predicted N _d values. To improve the algorithm in the longer‐term requires more data of scavenging fractions, particle chemical composition and density, and residual particle size distributions as a function of aerosol mass loading and cloud type.     

Characterization of brown carbon constituents of benzene secondary organic aerosol aged with ammonia

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.     

不可溶性气溶胶对边界层暖云滴谱离散度影响的模拟研究

基于一维分档MISTRA边界层云模式,模拟研究了内部混有不可溶核的硫酸铵气溶胶对边界层暖云微物理特征的影响。结果表明：边界层内湍流动能通量是影响暖云发展的重要因素。云中液态水含量、过饱和度以及云滴谱离散度均随云中的高度增加而增大。云滴谱标准差是影响云滴谱离散度变化的主要因子。在暖云发展阶段,不可溶性核会增加云中过饱和度,进而导致云滴谱分别向大尺度和小尺度端拓宽,云滴谱标准差增大,云滴谱离散度随时间增加而增大的程度增强;在暖云减弱阶段,不可溶核会造成云中大尺度端云滴数浓度减少,云滴谱变窄,标准差变小,云滴谱离散度逐渐减小的特征减弱。     

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 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.     

Mass spectrometric study of aged benzene secondary organic aerosol in the presence of dry ammonium sulfate

Inorganic seed particles have relatively large surface area, and play an important role in the formation and aging of secondary organic aerosol (SOA). The effects of dry (NH₄)₂SO₄ which is the most commonly found in urban atmosphere on the aged benzene SOA were qualitatively studied utilizing aerosol laser time-of-flight mass spectrometer (ALTOFMS) coupled with Fuzzy C-Means (FCM) clustering algorithm in this study. Experimental results indicated that nitrophenol, oxocarboxylic acid, epoxide products are the predominant components in the aged benzene SOA in the presence of low concentration (about 10 μg m^?3) of dry (NH₄)₂SO₄. These aged products are the same as the previously obtained aged benzene SOA without (NH₄)₂SO₄ seed aerosol, indicating that low concentration of dry (NH₄)₂SO₄ acts just as the nucleation or condensation center of the SOA, and do not affect the chemical composition of SOA. However, 1 H-imidazole, 1 H-imidazole-2-carbaldehyde, hydrated 1 H-imidazole-2-carbaldehyde, 2,2′-biimidazole, hydrated N-glyoxal substituted 1 H-imidazole, N-glyoxal substituted hydrated 1 H-imidazole-2- carbaldehyde, hydrated mono glyoxal substituted hydrated 1 H-imidazole-2-carboxaldehyde, mono glyoxal substituted 2,2-biimidazole and hydrated glyoxal dimer substituted imidazole which are formed from ammonium ion reaction with glyoxal are the major particulate products in the aged benzene SOA in the presence of high concentration (about 100 μg m^?3) of dry (NH₄)₂SO₄. The retention of water on the dry (NH₄)₂SO₄ particles creates ammonium ion, which can promote the formation of high-molecular-weight (HMW) products through multiphase reactions such as hydration and polymerization of aldehydes form from OH-initiated oxidation of benzene.     

Laser desorption/ionization mass spectrometric study of secondary organic aerosol formed from the photooxidation of aromatics

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.     

德州市冬季大气挥发性有机物污染特征及其对臭氧和二次有机气溶胶生成的贡献

利用气相色谱-质谱仪/火焰离子检测器（Online-GC-MS/FID）对2017年冬季山东德州大气中99种挥发性有机物（VOCs）进行连续测量,研究了VOCs浓度和组分特征、日变化趋势、来源及其对臭氧（O₃）、二次有机气溶胶（SOA）生成的贡献.结果表明,德州大气VOCs平均体积分数为（47.74±33.11）×10^-9,烷烃占比最大,为40.66%.总VOCs及其组分表现出早晚体积分数高、中午体积分数低的日变化规律.德州大气中丙烷、丙烯、苯及甲苯和二氯甲烷分别受到液化石油气挥发、生物质燃烧、机动车排放和溶剂使用等人为源的影响.反向轨迹模型分析发现,北方内陆气团对德州VOCs体积分数具有一定贡献.烷烃、烯烃、芳香烃的臭氧生成潜势分别为（34.87±33.60）、（120.48±118.76）和（59.77±94.14）μg/m³,乙烯、丙烯、甲苯和间/对二甲苯的贡献较大.芳香烃氧化主导了SOA生成,其贡献率为93.7%,甲苯、间/对二甲苯、苯对SOA生成的贡献最大.为解决大气复合污染问题、实现臭氧和PM_2.5协同控制,德州应重点控制甲苯、间/对二甲苯等芳香烃的排放.