Size, composition, and mixing state of individual aerosol particles in a South China coastal city

Aerosol samples were collected in summer in Macao,a coastal city of the Pearl River Delta Region in China.Morphology,size,elemental composition,and mixing state of individual aerosol particles were determined by scanning electron microscopy coupled energy dispersive X-ray(SEM/EDX) and transmission electron microscopy(TEM).Based on the morphologies of 5711 aerosol particles,they consist of soot(32%),mineral(17%),secondary(22%),and unknown fine particles(29%).The sizes of these particles were mostly distributed between 0.1 and 0.4 μm.Compositions of 202 mineral particles were obtained by SEM/EDX.Mineral particles were mainly classified into three types:Si-rich,Ca-rich,and Na-rich.The compositions of typical mineral particles can indicate their sources in sampling location.For example,mineral particles,collected along the main street,were associated with trace amounts of heavy metals,such as Zn,Ti,Mn,Ba,Pb,and As.TEM observations indicate that most Na-rich particles were aged sea salt particles(e.g.,Na2SO4 and NaNO3) which formed through heterogeneous chemical reactions between sea salt and acidic gases.Additionally,aging time of soot was short in Macao due to high humidity,high temperature,and high levels of sunlight in Macao.Most of soot and fine mineral dust particles were internally mixed with secondary particles.     

Photochemistry of chrysene adsorbedon several types of particle

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采暖期开始前后北京大气颗粒物中化学元素特征及来源

为比较研究采暖期与非采暖期大气颗粒物的特征,2006年11月,在北京城区采用Andersen分级撞击式采样器进行了大气气溶胶分级采样,并利用ICP-MS对其中22种化学元素浓度进行了分析.结果表明,采暖期As、Se、Mo、Cd浓度较采暖前上升2倍以上,Zn、Pb、Tl、K、Se、As、Cu、Cd、Ag在细粒径段的分布出现大幅度的增长,Zn、Na出现向细粒径段移动的趋势.因子分析表明,在采暖期燃烧源的贡献增强,地壳源的贡献减弱.     

秸秆焚烧期的碳黑气溶胶观测及研究

2007年5～6月在合肥市郊3个站点连续实时监测碳黑气溶胶,研究其在秸秆焚烧期的变化特征和来源.正常时期碳黑气溶胶平均质量浓度约为4.85　μg/m³,而秸秆焚烧期其平均浓度约为 8.38　μg/m³,这说明秸秆焚烧是碳黑气溶胶的重要来源.同步监测的PM₁₀与BC一致性较好,相关系数为0.74,一般情况下BC约占PM₁₀的4.7%,而秸秆焚烧期BC/PM₁₀的统计平均值较高,约为7.9%.比对2004年秸秆焚烧期BC浓度数据,证实了合肥市在实行农作物秸秆禁烧后,碳黑气溶胶的污染情况有较大好转.     

滨海新区局部大气颗粒物中多环芳烃污染特征研究

在滨海新区局部区域汉沽和大港采集了TSP和PM10样品,分析了不同颗粒物中多环芳烃的不同期别污染和分布特征,结果表明,多环芳烃的污染水平存在明显的季节性特征,采暖期多环芳烃和可吸入颗粒物中苯并[a]芘浓度均远远高于非采暖期。多环芳烃在不同期别也有不同的分布特征,非采暖期均是高环类多环芳烃占主导地位,比例超过60%;而在采暖期则是中环类多环芳烃占主导。     

萃取－同步荧光光谱法测定大气飘尘中苯并（a）芘

提出用浓Ｈ２ＳＯ４从大气飘尘样品的环己烧提取液中一次萃取后，用同步荧光光谱测定苯并（ａ）芘的方法。选用△λ为２０ｎｍ时可获最佳效果，用浓硫酸萃取的时间仅１ｍｉｎ，苯并（ａ）芘在浓硫酸相中１ｈ内稳定，样品加标的回收率为８５％，其它多环芳烃化合物在５３０—６００ｎｍ的测定波长范围不干扰苯并（ａ）芘的测定。用乙酰化滤纸层析－荧光分光光度的统一方法作为对比对实际样品进行了测定，结果与后者的偏差在±１５％以内，分析周期可缩短２４ｈ。     

Seasonal variation and source apportionment of organic and inorganic compounds in PM2.5 and PM10 particulates in Beijing, China

The distribution and source of the solvent-extractable organic and inorganic components in PM 2.5(aerodynamics equivalent diameter below 2.5 microns),and PM 10(aerodynamics equivalent diameter below 10 microns) fractions of airborne particles were studied weekly from September 2006 to August 2007 in Beijing.The extracted organic and inorganic compounds identified in both particle size ranges consisted of n-alkanes,PAHs(polycyclic aromatic hydrocarbons),fatty acids and water soluble ions.The potential emission sources of these organic compounds were reconciled by combining the values of n-alkane carbon preference index(CPI),%waxC n,selected diagnostic ratios of PAHs and principal component analysis in both size ranges.The mean cumulative concentrations of n-alkanes reached 1128.65ng/m3 in Beijing,74% of which(i.e.,831.7ng/m3) was in the PM 2.5 fraction,PAHs reached 136.45ng/m3(113.44ng/m3 or 83% in PM 2.5),and fatty acids reached 436.99ng/m3(324.41ng/m3 or 74% in PM 2.5),which resulted in overall enrichment in the fine particles.The average concentrations of SO42-,NO3-,and NH4+ were 21.3±15.2,6.1±1.8,12.5±6.1μg/m3 in PM 2.5,and 25.8±15.5,8.9±2.6,16.9±9.5μg/m3 in PM 10,respectively.These three secondary ions primarily existed as ammonium sulfate((NH4)2SO4),ammonium bisulfate(NH4HSO4) and ammonium nitrate(NH4NO3).The characteristic ratios of PAHs revealed that the primary sources of PAHs were coal combustion,followed by gasoline combustion.The ratios of stearic/palmitic acid indicated the major contribution of vehicle emissions to fatty acids in airborne particles.The major alkane sources were biogenic sources and fossil fuel combustion.The major sources of PAHs were vehicular emission and coal combustion.     

Lead Levels in the Airborne Dust Particulates of an Urban City of Central India

The dust fall-out rate, distribution pattern andconcentration of lead in the particulate fall-outmatters in urban Raipur city covering an area of 160 km² during one hydrological year i.e. November1996–June 1997, has been described. The entire cityhas been divided into 6 zones comprising ofindustrial, commercial, residential and heavy trafficareas. A monthly collection and analysis of dustfall-out rate between 3.0(±0.1) and91.3(±1.2) metric tonnes km^-2 month^-1 wereobserved at all 6 sampling sites. The total annualflux of lead in the fall-out of the city at differentzones is in the range 0.0065–0.4304 kg km^-2yr^-1. The results show that dust fall-out and thelead levels both are at higher magnitudes in winterand autumn. These large levels of air pollutants havealso been correlated with some meteorological parameters like relative humidity and temperature, and strong positive correlations have been observed.     

Flame propagation behaviors of nano- and micro-scale PMMA dust explosions

Flame propagation behaviors of nano- and micro-polymethyl methacrylate (PMMA) dust explosions were experimentally studied in the open-space dust explosion apparatus. High-speed photography with normal and microscopic lenses were used to record the particle combustion behaviors and flame microstructures. Simple physical models were developed to explore the flame propagation mechanisms. High-speed photographs showed two distinct flame propagation behaviors of nano- and micro-PMMA dust explosions. For nano-particles, flame was characterized by a regular spherical shape and spatially continuous combustion structure combined with a number of luminous spot flames. The flame propagation mechanism was similar to that of a premixed gas flame coupled with solid surface combustion of the agglomerates. In comparison, for micro-particles, flame was characterized by clusters of flames and the irregular flame front, which was inferred to be composed of the diffusion flame accompanying the local premixed flame. It was indicated that smaller particles maintained the leading part of the propagating flame and governed the combustion process of PMMA dust clouds. Increasing the mass densities from 105 g/m³ to 217 g/m³ for 100 nm PMMA particles, and from 72 g/m³ to 170 g/m³ for 30 μm PMMA particles, the flame luminous intensity, scale and the average propagation velocity were enhanced. Besides, the flame front became more irregular for 30 μm PMMA dust clouds.     

腐殖酸絮凝体形成过程中初期搅拌条件对其形态结构的影响

以腐殖酸为研究对象,采用硫酸铝为混凝剂进行混凝杯罐实验,借助PDA在线监测系统、图像解析法及粒子图像测速技术分析评价絮凝体的构造特征,着重探讨了混凝过程中初期快速搅拌条件对絮凝体形态结构的影响.结果表明,快速搅拌条件对腐殖酸絮凝体的形成过程及形态结构有着显著影响.最佳快速搅拌条件为:搅拌历时l min,搅拌强度300 r·min-,此时形成的絮凝体结构密实,抗剪切能力强,整体性能最优,絮凝体分形维数、强度及平均粒径分别为1.8842、0.164 N·m-2、0.43 mm.腐殖酸絮凝体的形成包括不溶性微粒的产生及初期颗粒的形成与结合等过程,其中,不溶性微粒的形成及初期颗粒的致密化过程是决定最终絮凝体形态构造的重要环节,而快速搅拌条件影响着混凝剂扩散混合效果和初期颗粒的形成速率与致密化程度,这也是初期快速搅拌条件对于腐殖酸混凝过程有显著影响的一个重要因素.