Near-source particulate emissions and plume dynamics from agricultural field operations

Particulate matter emissions generated by agricultural field preparation and harvesting operations were measured remotely via aerosol lidar and sampled simultaneously with a variety of aerosol point samplers in order to quantify dust plume space and time dynamics and particulate mass and number concentrations. Data for two cotton operations (disking, harvesting) in a flood-irrigated field in New Mexico are presented. Dust plume dynamics varied with boundary layer meteorological conditions, especially atmospheric stability, with plume maximum height significantly lower under stable conditions. Plume tracking indicated little change in plume area with height under unstable conditions and plume movement depended on wind speed and direction. Particle mass distributions indicate approximately 50% of the measured PM₁₀ mass was PM_2.5, significantly higher than previously reported values, possibly due to the near-source nature of the samples collected here. Variability in plume movement matched the variability in short-term wind fluctuations and this variability helps explain why models that utilize long-term averages perform poorly when trying to capture plume dynamics for nonsteady sources such as tractor operations.     

Size-resolved aerosol chemical concentrations at rural and urban sites in Central California, USA

Aerosol size distributions were measured with Micro Orifice Uniform Deposit Impactor (MOUDI) cascade impactors at the rural Angiola and urban Fresno Supersites in California's San Joaquin Valley during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS) winter campaign from December 15, 2000 to February 3, 2001. PM_2.5 filter samples were collected concurrently at both sites with Sequential Filter Samplers (SFS). MOUDI nitrate (NO₃⁻) concentrations reached 66 μg/m³ on January 6, 2001 during the 1000–1600 PST (GMT-8) period. Pair-wise comparisons between PM_2.5 MOUDI and SFS concentrations revealed high correlations at the Angiola site (r > 0.93) but more variability (r < 0.85) at the Fresno site for NO₃⁻, sulfate (SO₄⁼), and ammonium (NH₄⁺). Correlations were higher at Fresno (r > 0.87) than at Angiola (r < 0.7) for organic carbon (OC), elemental carbon (EC), and total carbon (TC). NO₃⁻ and SO₄⁼ size distributions in Fresno were multi-modal and wider than the uni-modal distributions observed at Angiola. Geometric mean diameters (GMD) were smaller for OC and EC than for NO₃⁻ and SO₄⁼ at both sites. OC and EC were more concentrated on the lowest MOUDI stage (0.056 µm) at Angiola than at Fresno. The NO₃⁻ GMD increased from 0.97 to 1.02 µm as the NO₃⁻ concentration at Angiola increased from 43 to 66 µg m^− 3 during a PM_2.5 episode from January 4–7, 2001. There was a direct relationship between GMD and NO₃⁻ and SO₄⁼ concentrations at Angiola but no such relationships for OC or EC. This demonstrates that secondary aerosol formation increases both concentration and particle size for the rural California environment.     

Extreme Particulate Levels at a Western Pacific Coastal City: The Influence of Meteorological Factors and the Contribution of Long-Range Transport

The 4-year data sets (1998–2001) of PM₁₀ and other gaseous pollutants at four rural and urban monitoring sites provided by Environmental Protection Department of Hong Kong have been analyzed for days of extremely high and low PM₁₀ levels. The annual means of PM₁₀ concentrations are between 37 and 57 μg/m³. The level of high PM₁₀ concentration is defined from the comparison of local and international standards. Episode days are mainly controlled by different meteorological conditions: the continental outflow, the land-sea breeze/weak synoptic forcings and the approaching tropical cyclones. Integrated approaches have been used to distinguish between the predominantly “territory wide” and “long-range transport” (LRT) episode days. Case studies of these types of episodes are presented and the number of episode days per year for each type has been estimated. It is found that the LRT contributions are significant and account for ∼66% of the PM₁₀ episode days. Very high correlations between CO and PM₁₀ concentrations, and between SO₂ and PM₁₀ concentrations, can be found during the “territory wide” episode days which implies the important contributions of fossil fuel combustion to the PM₁₀ episodes. The number of “low level” PM₁₀ days per year has decreased by a factor near 3 from 1998 to 2001. Precipitation scavenging is the major process causing low levels of PM₁₀, irrespective of the associated weather systems. The regional annual background level is ∼9 μg/m³. With the exception of seasalt components, the average elemental concentrations of major inorganic species are similar for all of the sites during LRT events and constitute representative compositions of PM₁₀ during such events.     

Influence of traffic emissions on the composition of atmospheric particles of different sizes – Part 1: concentrations and elemental characterization

Epidemiological studies initially considered the impact of total solid particles on human health, but according to the acquired knowledge about the worse effect of smaller particles, those studies turned to consider the impact of PM₁₀. However, for the last decade PM_2.5 began to be more important, once as they are smaller they can penetrate deeper in the lungs, being possible their trapping in alveoli and worse effects on human health. Therefore, more information on PM_2.5 should be provided namely concerning the levels and elemental composition. Considering the relevance of traffic on the emission of particles of small sizes, this work included the detailed characterization of PM₁₀ and PM_2.5, sampled at two sites directly influenced by traffic, as well as at two reference sites, aiming a further evaluation of the influence of PM₁₀ and PM_2.5 on public health. The specific objectives were to study the influence of traffic emission on PM₁₀ and PM_2.5 characteristics, considering concentration, size distribution and elemental composition. PM₁₀ and PM_2.5 samples were collected using low-volume samplers; the element analyses were performed by particle induced X-ray emission (PIXE). At the sites influenced by traffic emissions PM₁₀ and PM_2.5 concentrations were 7–9 and 6–7 times higher than at the background sites. The presence of 17 elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn and Pb) was determined in both PM fractions; particle metal contents were 3–44 and 3–27 times higher for PM₁₀ and PM_2.5, respectively, than at the backgrounds sites. The elements originated mostly from anthropogenic activities (S, K, V, Mn, Ni, Zn and Pb) were predominantly present in PM_2.5, while the elements mostly originated from crust (Mg, Al, Si and Ca) predominantly occurred in PM_2.5–10. The results also showed that in coastal areas sea salt spray is an important source of particles, influencing PM concentration and distributions (PM₁₀ increased by 46%, PM_2.5/PM₁₀ decreased by 26%), as well as PM compositions (Cl in PM₁₀ was 11 times higher).     

Characteristics of organic and elemental carbon in PM2.5 samples in Shanghai, China

Shanghai is the largest industrial and commercial city in China, and its air quality has been deteriorating for several decades. However, there are scarce researches on the level and seasonal variation of fine particle (PM_2.5) as well as the carbonaceous fractions when compared with other cities in China and around the world. In the present paper, abundance and seasonal characteristics of PM_2.5, organic carbon (OC) and elemental carbon (EC) were studied at urban and suburban sites in Shanghai during four season-representative months in 2005–2006 year. PM_2.5 samples were collected with high-vol samplers and analyzed for OC and EC using thermal-optical transmittance (TOT) protocol. Results showed that the annual average PM_2.5 concentrations were 90.3–95.5 μg/m³ at both sites, while OC and EC were 14.7–17.4 μg/m³ and 2.8–3.0 μg/m³, respectively, with the OC/EC ratios of 5.0–5.6. The carbonaceous levels ranked by the order of Beijing > Guangzhou > Shanghai > Hong Kong. The carbonaceous aerosol accounted for  30% of the PM_2.5 mass. On seasonal average, the highest OC and EC levels occurred during fall, and they were higher than the values in summer by a factor of 2. Strong correlations (r = 0.79–0.93) between OC and EC were found in the four seasons. Average level of secondary organic carbon (SOC) was 5.7–7.2 μg/m³, accounting for  30% of the total OC. Strong seasonal variation was observed for SOC with the highest value during fall, which was about two times the annual average.     

武汉市冬季灰霾期PM2.5中水溶性无机离子的特征

2018年1月,利用颗粒物采样器采集武汉市大气PM_2.5样品并进行水溶性无机离子（F^-、Cl^-、NO₃^-、SO₄^2-、Na⁺、NH₄⁺、K⁺、Mg²⁺、Ca²⁺）的分析.结果表明,NO₃^-、SO₄^2-、NH₄⁺是PM_2.5中最主要的3种水溶性无机离子,除Mg²⁺与Ca²⁺外,PM_2.5与WSⅡs （水溶性无机离子）之间的相关性显著,且移动源贡献占主导地位.阴阳离子平衡表明武汉市冬季灰霾期PM_2.5呈中性或弱酸性.通过混合单粒子拉格朗日综合轨迹模式模拟并采用分层聚类得出了4种主要的后向气流轨迹及相应的PM_2.5和水溶性离子浓度,结果表明区域传输对此次灰霾期影响较大.     

Influence of traffic emissions on the composition of atmospheric particles of different sizes—Part 2: SEM–EDS characterization

In urban areas traffic is the major contributor to atmospheric particulate matter and exposure to these particles currently represents a serious risk to human health. The attention has been recently focused more on the particles of smaller sizes (PM_2.5) which penetrate deeper in respiratory system causing severe health effects. Therefore, more information on PM_2.5 should be provided, namely concerning morphological and chemical characterization. Aiming further evaluation of the impact of traffic emissions on public health, this work evaluated the influence of traffic on the chemical and morphological characteristics of PM₁₀ and PM_2.5, collected at one site influenced by traffic emissions and at one reference site. Chemical and morphological characteristics of 1,000 individual particles were determined by scanning electron microscopy combined with energy dispersive spectrometer (SEM–EDS). Cluster analysis (CA) was used to identify different types of particles that occurred in PM, aiming the identification of the respective emission sources. Traffic PM_2.5 were dominated by particles composed of Fe oxides and alloys (67%) which were related to traffic emissions (this percentage was 3.7 times higher than at the background site); in PM_2.5–10 the abundance of Fe oxides and alloys were 20% and 0% for the traffic and background sites, respectively. Background PM_2.5 were mainly constituted by aluminum silicates (63%) related to natural sources (this percentage was 2.5 times higher than at the traffic site); the abundances of aluminum silicates in PM_2.5–10 were 74% and 73% for traffic and background sites, respectively. It was concluded that traffic emissions were mainly present in PM_2.5 (the percentage of particles associated to these emissions was 3.4 times higher than in PM_2.5–10), while coarse particles were dominated by material of natural origin (the percentage of particles associated was 1.2 and 3.0 times higher than in PM_2.5 for traffic and background sites, respectively). Previous results obtained by proton induced X-ray emission (PIXE) were consistent with SEM–EDS analysis that showed to be very useful to complement elemental analysis of different PM_2.5 and PM_2.5–10.     

Long-term measurements of atmospheric PM<Subscript>2.5</Subscript> and its chemical composition in rural Korea

Long-term measurements of ambient particulate matter less than 2.5 μm in diameter (PM_2.5) and its chemical compositions were performed at a rural site in Korea from December 2005 to August 2009. The average PM_2.5 concentration was 31 μg m⁻³ for the whole sampling period, and showed a slightly downward annual trend. The major components of PM_2.5 were organic carbon, SO₄²⁻, NO₃⁻, and NH₄⁺, which accounted for 55 % of total PM_2.5 mass on average. For the top 10 % of PM_2.5 samples, anionic constituents and trace elements clearly increased while carbonaceous constituents and NH₄⁺ remained relatively constant. Both Asian dust and fog events clearly increased PM_2.5 concentrations, but affected its chemical composition differently. While trace elements significantly increased during Asian dust events, NO₃⁻, NH₄⁺ and Cl were dramatically enhanced during fog events due to the formation of saturated or supersaturated salt solution. The back-trajectory based model, PSCF (Potential Source Contribution Function) identified the major industrial areas in Eastern China as the possible source areas for the high PM_2.5 concentrations at the sampling site. Using factor analysis, soil, combustion processes, non-metal manufacture, and secondary PM_2.5 sources accounted for 77 % of the total explained variance.     

Chemical characterization and multivariate analysis of atmospheric PM<Subscript>2.5</Subscript> particles

The new European Council Directive (PE-CONS 3696/07) frames the inhalable (PM₁₀) and fine particles (PM_2.5) on priority to chemically characterize these fractions in order to understand their possible relation with health effects. Considering this, PM_2.5 was collected during four different seasons to evaluate the relative abundance of bulk elements (Cl, S, Si, Al, Br, Cu, Fe, Ti, Ca, K, Pb, Zn, Ni, Mn, Cr and V) and water soluble ions (F⁻, Cl⁻, NO₂ ⁻, NO₃ ⁻, SO₄ ²⁻, Na⁺, NH₄ ⁺, Ca²⁺ and Mg²⁺) over Menen, a Belgian city near the French border. The air quality over Menen is influenced by industrialized regions on both sides of the border. The most abundant ionic species were NO₃ ⁻, SO₄ ²⁻ and NH₄ ⁺, and they showed distinct seasonal variation. The elevated levels of NO₃ ⁻ during spring and summer were found to be related to the larger availability of the NO_x precursor. The various elemental species analyzed were distinguished into crustal and anthropogenic source categories. The dominating elements were S and Cl in the PM_2.5 particles. The anthropogenic fraction (e.g. Zn, Pb, and Cu) shows a more scattered abundance. Furthermore, the ions and elemental data were also processed using principal component analysis and cluster analysis to identify their sources and chemistry. These approach identifies anthropogenic (traffic and industrial) emissions as a major source for fine particles. The variations in the natural/anthropogenic fractions of PM_2.5 were also found to be a function of meteorological conditions as well as of long-range transport of air masses from the industrialized regions of the continent. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于国际大气化学—气候模式比较计划模式数据评估未来气候变化对中国东部气溶胶浓度的影响

气候变化引起的地面气溶胶浓度变化与区域空气质量密切相关。本文利用“国际大气化学—气候模式比较计划”（Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP）中4个模式的试验数据分析了RCP8.5情景下2000~2100年气候变化对中国气溶胶浓度的影响。结果显示,在人为气溶胶排放固定在2000年、仅考虑气候变化的影响时,2000~2100年气候变化导致中国北部地区（31°N~45°N, 105°E~122°E）硫酸盐、有机碳和黑碳气溶胶分别增加28%、21%和9%,硝酸盐气溶胶在中国东部地区减少30%。气候变化对细颗粒物（PM_2.5）浓度的影响有显著的季节变化特征,冬季PM_2.5浓度在中国东部减少15%,这主要是由硝酸盐气溶胶在冬季的显著减少造成的;夏季PM_2.5浓度在中国北部地区增加16%,而长江以南地区减少为9%,这可能与模式模拟的未来东亚夏季风环流的增强有关。     

Source identification of PM2.5 particles measured in Gwangju, Korea

The UNMIX and Chemical Mass Balance (CMB) receptor models were used to investigate sources of PM_2.5 aerosols measured between March 2001 and February 2002 in Gwangju, Korea. Measurements of PM_2.5 particles were used for the analysis of carbonaceous species (organic (OC) and elemental carbon (EC)) using the thermal manganese dioxide oxidation (TMO) method, the investigation of seven ionic species using ion chromatography (IC), and the analysis of twenty-four metal species using Inductively Coupled Plasma (ICP)-Atomic Emission Spectrometry (AES)/ICP-Mass Spectrometry (MS). According to annual average PM_2.5 source apportionment results obtained from CMB calculations, diesel vehicle exhaust was the major contributor, accounting for 33.4% of the measured PM_2.5 mass (21.5 μg m^− 3), followed by secondary sulfate (14.6%), meat cooking (11.7%), secondary organic carbon (8.9%), secondary nitrate (7.6%), urban dust (5.5%), Asian dust (4.4%), biomass burning (2.8%), sea salt (2.7%), residual oil combustion (2.6%), gasoline vehicle exhaust (1.9%), automobile lead (0.5%), and components of unknown sources (3.4%). Seven PM_2.5 sources including diesel vehicles (29.6%), secondary sulfate (17.4%), biomass burning (14.7%), secondary nitrate (12.6%), gasoline vehicles (12.4%), secondary organic carbon (5.8%) and Asian dust (1.9%) were identified from the UNMIX analysis. The annual average source apportionment results from the two models are compared and the reasons for differences are qualitatively discussed for better understanding of PM_2.5 sources.Additionally, the impact of air mass pathways on the PM_2.5 mass was evaluated using air mass trajectories calculated with the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward trajectory model. Source contributions to PM_2.5 collected during the four air mass patterns and two event periods were calculated with the CMB model and analyzed. Results of source apportionment revealed that the contribution of diesel traffic exhaust (47.0%) in stagnant conditions (S) was much higher than the average contribution of diesel vehicle exhaust (33.4%) during the sampling period. During Asian dust (AD) periods when the air mass passed over the Korean peninsula, Asian dust and secondary organic carbon accounted for 25.2 and 23.0% of the PM_2.5 mass, respectively, whereas Asian dust contributed only 10.8% to the PM_2.5 mass during the AD event when the air mass passed over the Yellow Sea. The contribution of biomass burning to the PM_2.5 mass during the biomass burning (BB) event equaled 63.8%.     

A study to discriminate local,urban and regional source contributions to the particulate matter concentrations in the city of Dresden,Germany

The fractions of local traffic (LT), urban background (UBG) and regional background (RBG) of the particle pollution at a traffic-influenced kerbside in Dresden, Germany, were determined by measurements of size-segregated mass concentration, chemical composition and particle size distributions in a network of five measurement stations partly existing and partly set up for this study. Besides the kerbside station, one urban background site and three rural sites were included in the study. Using data from these different sites, the LT, UBG, and RBG contributions were calculated, following the approach of Lenschow et al. (2001). At the kerbside site, 19% of the total number concentration (Dp_St = 10–600 nm) could be attributed to the RBG, 15% to the UBG, and 66% to the LT immediately nearby. Particle mass concentrations up to Dp_aer = 420 nm RBG amounts to 68%, UBG to 21%, and LT only to 11%. Highest mass concentrations were observed at all stations in autumn and winter during easterly inflow directions. The local traffic fraction of PM₁₀ mass at the kerbside station was found to be 30% for westerly inflow, but only 7% for southeasterly inflow due to the dominating transport fraction from up to 80% of the particle mass at this inflow direction. Size-resolved investigation showed the main fractions in both the particle size ranges of Dp_aer = 0.42 to 1.2 and 0.14 to 0.42 μm at all stations. The main components sulphate, ammonium and total carbon showed higher concentrations at south-eastern/eastern inflow in autumn at all stations, while nitrate at the kerbside and urban background site was higher during westerly inflow in winter. The chemical composition at the regional background site at westerly inflow (12% nitrate, 8% sulphate, 11% total carbon) was significantly different from that at easterly inflow (3% nitrate, 15% sulphate, 22% total carbon). The prevailing part of the ionic mass was always found in the fine particle range of Dp_aer = 0.14 to 1.2 μm at all stations. For all inflow directions highest total carbon concentrations were observed at the kerbside station, especially in the ultra-fine size range of Dp_aer = 0.05 to 0.14 μm with up to 30% of the whole carbon. PAH concentrations were always higher at south-eastern/eastern inflow especially during wintertime. Trace metal components and silicon were found mainly in the coarse mode fraction at the kerbside resulting from abrasion or resuspension.     

Source identification of PM2.5 in an arid Northwest U.S. City by positive matrix factorization

Spokane, WA is prone to frequent particulate pollution episodes due to dust storms, biomass burning, and periods of stagnant meteorological conditions. Spokane is the location of a long-term study examining the association between health effects and chemical or physical constituents of particulate pollution. Positive matrix factorization (PMF) was used to deduce the sources of PM_2.5 (particulate matter ≤2.5 μm in aerodynamic diameter) at a residential site in Spokane from 1995 through 1997. A total of 16 elements in 945 daily PM_2.5 samples were measured. The PMF results indicated that seven sources independently contribute to the observed PM_2.5 mass: vegetative burning (44%), sulfate aerosol (19%), motor vehicle (11%), nitrate aerosol (9%), airborne soil (9%), chlorine-rich source (6%) and metal processing (3%). Conditional probability functions were computed using surface wind data and the PMF deduced mass contributions from each source and were used to identify local point sources. Concurrently measured carbon monoxide and nitrogen oxides were correlated with the PM_2.5 from both motor vehicles and vegetative burning.     

Geochemistry of regional background aerosols in the Western Mediterranean

The chemical composition of regional background aerosols, and the time variability and sources in the Western Mediterranean are interpreted in this study. To this end 2002–2007 PM speciation data from an European Supersite for Atmospheric Aerosol Research (Montseny, MSY, located 40 km NNE of Barcelona in NE Spain) were evaluated, with these data being considered representative of regional background aerosols in the Western Mediterranean Basin. The mean PM₁₀, PM_2.5 and PM₁ levels at MSY during 2002–2007 were 16, 14 and 11 µg/m³, respectively. After compiling data on regional background PM speciation from Europe to compare our data, it is evidenced that the Western Mediterranean aerosol is characterised by higher concentrations of crustal material but lower levels of OM + EC and ammonium nitrate than at central European sites. Relatively high PM_2.5 concentrations due to the transport of anthropogenic aerosols (mostly carbonaceous and sulphate) from populated coastal areas were recorded, especially during winter anticyclonic episodes and summer midday PM highs (the latter associated with the transport of the breeze and the expansion of the mixing layer). Source apportionment analyses indicated that the major contributors to PM_2.5 and PM₁₀ were secondary sulphate, secondary nitrate and crustal material, whereas the higher load of the anthropogenic component in PM_2.5 reflects the influence of regional (traffic and industrial) emissions. Levels of mineral, sulphate, sea spray and carbonaceous aerosols were higher in summer, whereas nitrate levels and Cl/Na were higher in winter. A considerably high OC/EC ratio (14 in summer, 10 in winter) was detected, which could be due to a combination of high biogenic emissions of secondary organic aerosol, SOA precursors, ozone levels and insolation, and intensive recirculation of aged air masses. Compared with more locally derived crustal geological dusts, African dust intrusions introduce relatively quartz-poor but clay mineral-rich silicate PM, with more kaolinitic clays from central North Africa in summer, and more smectitic clays from NW Africa in spring.     

不同降水强度对PM2.5的清除作用及影响因素

云和降水过程是大气污染物的重要清除途径,但由于降水过程和大气污染颗粒物本身的复杂性,目前降水过程对大气污染物的清除机制及影响因素有待深入研究。该文利用2014年3月—2016年7月在北京地区连续观测的PM_2.5和降水数据,研究了不同降水强度对PM_2.5的清除率,以及雨滴谱、风速和降水持续时间对PM_2.5清除率的影响。研究表明:降水强度越大,对PM_2.5清除效率越高。小雨、中雨和大雨对PM_2.5清除率平均值分别为5.1%,38.5%和50.6%。小雨不但对PM_2.5的清除率最低,而且对PM_2.5的清除效果也存在很大差异,约50%的小雨个例中PM_2.5质量浓度出现减小情况,而另外50%的小雨个例中,PM_2.5质量浓度出现增加情况。在持续时间长或地面风速增大的情况下,小雨也表现出较高的清除率。在中雨和大雨情况下,PM_2.5质量浓度均出现明显减小情况。但降水持续时间和风速对中雨和大雨的清除率影响较小,这是由于中雨和大雨一般在较短时间内即可清除大部分PM_2.5,因此,对降水的持续时间和风速大小不敏感。     

Size distributions of ambient air particles and enrichment factor analyses of metallic elements at Taichung Harbor near the Taiwan Strait

This work attempts to characterize metallic elements associated with atmospheric particulate matter on a dry deposition plate, a TE-PUF high-volume air sampler and a universal air sampler. Dry deposition fluxes of particulates and concentrations of total suspended particulate, fine (PM_2.5) and coarse (PM_2.5–10) particulate matters were collected at Taichung harbor sampling sites from August 2004 to January 2005. Chemical analyses of metallic elements were made using a flame atomic absorption spectrophotometer coupled with hollow cathode lamps. Concentrations of metal elements in the forms of coarse particles and fine particles as well as the coarse/fine particulate ratios were presented. Statistical methods such as correlation analysis, principal component analysis and enrichment factor analysis were performed to compare the chemical components and identify possible emission sources at the sampling sites. Metallic elements of Cu, Zn, Pb, Cr, Ni and Mg had higher EF_crust ratios in winter and spring than in summer and autumn. Diurnal and nocturnal variations of metallic element concentrations in fine and coarse particles were also discussed.     

Microscopic morphology and size distribution of particles in PM<Subscript>2.5</Subscript> of Guangzhou City

Samples of airborne PM_2.5 particles in Guangzhou urban area were collected during the autumn of 2006 and the spring of 2007. The morphologies and elemental compositions of individual particles were determined by Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometer (SEM-EDX). The obtained images were further analyzed for size distribution by an image analysis system. Based on the morphology, particles in PM_2.5 were classified into four groups: soot aggregates, minerals, fly ash and others. The amount of soot aggregates and minerals were higher than that of fly ashes. The distributions of particles by number and size in two seasons were bimodal with 90% less than 1.0 μm in diameter. The primary peak from the autumn samples was in the size range of 0.4 ~ 0.5 μm, and 0.3 ~ 0.4 μm for the spring samples. More soot aggregates (36.1%) and minerals (61.5%) were found than fly ash (2.4%) in autumn, but soot aggregates (89.9%) was the dominant particle type in spring. The size distribution of particles according to the volume was generally opposite to that according to the number. Particles less than 1.0 μm were as high as 89.5% in number but contributed only 18.9% in volume, indicating that fine particles contributed relatively little in volume although existing in large numbers.     

Reconstructed light extinction coefficients using chemical compositions of PM<Subscript>2.5</Subscript> in winter in Urban Guangzhou,China

The objective of this study was to reconstruct light extinction coefficients (b ext ) according to chemical composition components of particulate matter up to 2.5 μm in size (PM 2.5 ). PM 2.5 samples were collected at the monitoring station of the South China of Institute of Environmental Science (SCIES, Guangzhou, China) during January 2010, and the online absorbing and scattering coefficients were obtained using an aethalometer and a nephelometer. The measured values of light absorption coefficient by particle (b ap ) and light scattering coefficient by particle (b sp ) significantly correlated (R 2 > 0.95) with values of b ap and b sp that were reconstructed using the Interagency Monitoring of Protected Visual Environments (IMPROVE) formula when RH was <70%. The measured b ext had a good correlation (R 2 > 0.83) with the calculated b ext under ambient RH conditions. The result of source apportionment of b ext showed that ammonium sulfate [(NH 4 ) 2 SO 4 ] was the largest contributor (35.0%) to b ext , followed by ammonium nitrate (NH 4 NO 3 , 22.9%), organic matter (16.1%), elemental carbon (11.8%), sea salt (4.7%), and nitrogen dioxide (NO 2 , 9.6%). To improve visibility in Guangzhou, the effective control of secondary particles like sulfates, nitrates, and ammonia should be given more attention in urban environmental management.     

武汉市源成分谱特征研究

通过采集武汉市土壤风沙尘、建筑水泥尘、城市扬尘、餐饮源、生物质燃烧源、工业煤烟尘和电厂煤烟尘等7类源样品,并分析其碳组分、水溶性离子组分和无机元素组分,建立PM₁₀和PM_2.5源成分谱.研究表明,地壳元素Si、Ca、Al以及Fe等是土壤风沙尘的主要特征组分,其中Si是含量最高的成分,也是土壤风沙尘的标识组分.无组织建筑水泥尘中Si和Ca元素含量较高,将Ca元素作为无组织建筑水泥尘区别其他源类的重要元素,而有组织建筑水泥尘中OC、SO₄^2-含量比无组织建筑水泥尘高.城市扬尘中Ca的含量相对较高,表明城市扬尘受到建筑水泥尘影响较多.生物质燃烧源成分谱中OC的含量远高于成分谱中其他组分,另外Cl^-和K的平均含量也较高,K一般为生物质源的特征元素.     

春季中国东部气溶胶化学组成及其分布的模拟研究

本文利用区域空气质量模式RAQMS（Regional Air Quality Model System）,对2009年春季中国东部气溶胶主要化学成分及其分布进行了模拟研究。与泰山站观测资料的对比结果显示,模式能比较合理地反映气溶胶浓度的逐日变化特征。整体上,模式对无机盐气溶胶的模拟好,分别高估和低估黑碳和有机碳气溶胶浓度,其原因与排放源、二次有机气溶胶化学机制和模式分辨率的不确定性有关。模拟结果显示,春季气溶胶浓度高值主要集中于华北、四川东部、长江中下游等地区。受东南亚生物质燃烧和大气输送的影响,中国的云南和广西等地区有机碳浓度高于中国其他地区。中国西北部沙尘浓度较高,而且向东输送并影响到中国东部和南方部分地区。中国东部的华北、四川东部、长江中下游等地PM_2.5（空气动力学直径在2.5微米以下的颗粒物）污染严重,4月平均PM_2.5浓度超过了我国日平均PM_2.5浓度限值。中国东部泰山站的观测和模拟结果都显示近地面硝酸盐浓度超过硫酸盐,中国北部对流层中硝酸盐的柱含量也大于硫酸盐,而在中国南部则相反,这一方面与春季中国云量 南多北少的分布特征以及云内液相化学反应有关,另一方面也与南北温差对气溶胶形成的影响有关。就整个中国东部而言,虽然硫酸盐的柱含量（46 Gg）仍大于硝酸盐（42 Gg）,但比较接近,反映出我国氮氧化物排放迅速增加的趋势。春季中国地区对流层中PM₁₀（空气动力学直径在10微米以下的颗粒物）及其化学成分柱含量分别为:990.8 Gg（PM₁₀）,52.6 Gg（硫酸盐）,48.2 Gg（硝酸盐）,32.1 Gg（铵盐）,22.9 Gg（黑碳）和74.1 Gg（有机碳）,有机碳（OC）中一次有机碳（POC）和二次有机碳（SOC）分别占60%和40%,中国东部PM₁₀中人为气溶胶和沙尘分别占30%和70%,反映了春季沙尘对我国大气气溶胶的重要贡献。