Aqueous-phase reactions of organic compounds are an important source of secondary organic aerosol(SOA)(Ervens 2011). Laboratory studies focused mostly on small aldehydes such as glyoxal(De Haan 2009;Tan 2009) as precu...
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Aqueous-phase reactions of organic compounds are an important source of secondary organic aerosol(SOA)(Ervens 2011). Laboratory studies focused mostly on small aldehydes such as glyoxal(De Haan 2009;Tan 2009) as precursors, and on pinene oxidation products(Lee 2011). We showed experimental results of aqueous-phase reactions of a semi-volatile and slightly water soluble methoxy-phenol from biomass burning, vanillin(C8H8O3). Reactions were performed in a vessel(Lee 2011) with UV(254 nm) irradiation under two conditions:(1) photochemical oxidation with H2O2 as an OH radical source;and(2) direct photolysis without H2O2 added. Solution of the resulted products, as well as the ammonium sulfate added(Lee 2011), was atomized continuously and dried before on-line analyses. An Aerodyne High-resolution Time-of-Flight Aerosol Mass Spectrometer(HR-To F-AMS) was used to measure the dried particle compositions, and a Hygroscopic Tandem Differential Mobility Analyzer(HTDMA) and a Cloud Condensation Nuclei counter(CCNc) were used to determine the particle growth factor and CCN activity respectively. Withou UV irradiation, most of vanillin evaporated to the gas phase during drying and gave negligible organic mass in particles(Figure 1, before time < 0 min). A large amount of SOA was formed and retained after reactions under both conditions, although products might be different under these two conditions according to HR-To F-AMS characterization(Figure 1). Off-line analyses by liquid chromatography-mass spectrometry(LC-MS) and gas chromatography-mass spectrometry(GC-MS) also confirmed that the product identities from these two conditions are different. Organic mass first increased rapidly and then decreased under condition(1), but kept increasing slowly under condition(2), as shown in Figure 1A and 1C, respectively. It was found that the degree of oxygenation of products from condition(1) first increased and then decreased, suggesting a competition between functionalization and fragme
The role of aqueous-phase chemistry in the formation of secondary organic aerosols(SOA) is still poorly constrained. Here we present observation results of the degree of oxygenation of organic aerosols(OA) based on hi...
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The role of aqueous-phase chemistry in the formation of secondary organic aerosols(SOA) is still poorly constrained. Here we present observation results of the degree of oxygenation of organic aerosols(OA) based on high-resolution time-of-flight aerosol mass spectrometer(HR-To F-AMS) measurements made at a coastal site in Hong Kong from late April to the end of May, 2011 for 37 days. Two foggy periods and one hazy period were chosen for detailed analysis to compare the changes in degree of oxygenation of OA due to different processes. The Extended Aerosol Inorganic Model(E-AIM) predicted fine particle liquid water content(LWC fp) was up to 85 μg/m3 during the foggy days. Particle concentration as measured by the HR-To F-AMS was up to 60 μg/m3 during the hazy days. The degree of oxygenation of OA, as indicated by several parameters including fraction of m/z 44 in organic mass spectra(f44), oxygen to carbon elemental ratio(O:C), and carbon oxidation state was evaluated against odd oxygen(O x) concentration, LWC fp, ionic strength(IS), and in-situ p H(p H is). Results suggested that for the hazy period, the high concentration of OA(on average 11 μg/m3) and the high degree of oxygenation were mainly due to gas-phase oxidation. During the foggy periods with low photochemical activities, the degree of oxygenation of OA was almost as high as that in the hazy days and significantly higher than that during non-fog/non-haze days. However, the evolution of OA behaved quite differently in these two foggy periods. The first foggy period in late April and early May had larger LWC fp and lower O x concentration and the OA had more semi-volatile oxygenated organic aerosols(SVOOA) as resolved by positive matrix factorization(PMF). The second foggy period in mid-May had higher O x concentration and lower LWC fp, and produced more low-volatility oxygenated organic aerosols(LVOOA). Examination into the particle-phase constituents suggests that partitioning may be the dominating process
珠江三角洲(PRD)近年来面临着越来越严重的大气污染问题,其中大气颗粒物污染问题尤为突出。为了解珠三角地区细颗粒物的长期变化趋势,本文收集2000-2010年文献中珠三角地区细颗粒物的相关数据,总结细颗粒物的质量浓度和化学组分长期变化特征,及其与污染源排放的关系。结果发现,2000-2010年珠三角地区细颗粒物质量浓度先上升后下降,2004-2005年浓度最高,达到85μg/m3,整体呈下降趋势,从2000年的49μg/m3下降到2010年的37μg/m3,11年的平均质量浓度为59.1μg/m3。细颗粒物中的含碳物质OC和EC变化趋势与PM2.5相同,先上升后下降,整体呈下降趋势,2004年含碳物质质量浓度达到最高值,分别为19.4和12.4μg/m3。主要是因2004年广州市灰霾天数达到131天,为近十年来灰霾天数最多年份,佛山市2004年能见度较其他年份也有所下降,2004年珠三角地区空气污染严重,污染物浓度较高(黄健,等,2008;陈欢欢,等,2010;陈慧娴,2011)。分析PM2.5与化学组分的相关性发现,PM2.5与OC、EC相关性最高,达到0.575和0.553。细颗粒物中的水溶性离子SO42-、NO3-和NH4+均呈上升趋势,分别从2000年的10.2、1.5和2.9μg/m3上升到2010年的12.2、6.4、5.3μg/m3,平均质量浓度分别为12.2、3.4、4.3μg/m3。由于城市化的发展,珠三角地区工业烟尘、粉尘的直接排放量虽大幅度减少,但是SO2和NOx等二次粒子的前体物排放量仍然很大,且O3浓度不断增加,大气氧化性增强,有利于无机二次颗粒物的生成(Wang et al.,2003;Zhang et al.,2004;Zheng et al.,2010),珠三角地区细颗粒物的无机二次污染日趋严重。珠三角地区细颗粒物中SO42-、NO3-、NH4+、OC和EC所占百分比分别为24%、6%、8%、21%和11%,共占细颗粒物百分达到70%,其中SO42-和OC贡献所占百分比最高。珠三角地区OC/EC比值主要介于2-5之间,表明珠三角地区二次有机碳的生成比较显著。通过对PRD不同功能区的细粒子颗粒物进行分析发现,道路和工业区细颗粒物质量浓度最高,可达到90μg/m3,城市和近郊约为60μg/m3,背景点浓度最低为38μg/m3。水溶性离子SO42-、NO3-和含碳物质均为工业区最高,城市和近郊次之。而NH4+为近郊浓度最高,工业区和道路反而较低,主要与近郊区的农业活动有关。通过分析水溶性离子与污染源的相关性发现,SO42-与电力消费量达到显著相关(α=0.05,R=0.626),火力发电燃煤产生的SO2通过化学反应产生SO42-对于细颗粒物中的SO42-有重要贡献。NO3-与机动车保有量(α=0.05,R=0.663)、电力消费(α=0.05,R=0.625)达到显著相关,机动车尾气和火电厂排放的NO x通过光化学反应生成的NO3-是大气中NO3-的重要来源(Zheng et al.,2009);NH4+与农业化肥施用量(R=0.699)达到显著相关,说明农业活动排放的NH3对于NH4+有重要影响(Zheng et al.,2012)。总体来说,珠三角地区细颗粒物二次污染问题突出,细粒子污染与珠三角地区不断增强的大气氧化性有关外,与工业、机动车尾气排放有很大关系,因此改善珠三角地区的细颗粒物污染问题,控制其前体物的排放是关键因素之一。
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