| Atmospheric aerosols are ubiquitous in the Earth’s atmosphere. Carbonaceous aerosols, one of the major components of atmospheric aerosols, have received increasing attention in recent years owing to their impacts on global radiation balance, climate change, public health and visibility degradation. In order to better understand the sources, transport processes, formation mechanisms and mixing states of atmospheric aerosols and carbonaceous aerosols, we conducted several intensive field campaigns in urban (Beijing, Ji’nan and Hong Kong), suburban (Tung Chung in Hong Kong) and mountainous (Mt. Heng) sites in China.Atmospheric carbonaceous aerosols measurements were carried out in Beijing, Ji’nan and Hong Kong. We obtained the concentration levels and seasonal variations of carbonaceous aerosols in Ji’nan and Hong Kong sites. In order to investigate the effects of massive short-term emission control measures adopted around2008on the air quality in Beijing, we conducted intensive field studies in three consecutive Augusts from2007,2008and2009. The three-year comparison of data indicated that the emission control measures improved the air quality during the2008Beijing Olympic Games as well as leaving long-term impact on the air quality in Beijing. Through comparing the characteristics of carbonaceous aerosols in northern and southern China, we found that the concentrations of carbonaceous aerosols and OC/EC ratios were higher in northern China than those in southern China, especially in winter, which were possibly due to the coal combustions.To understand the sources and formation processes of atmospheric carbonaceous aerosols in rural and mountainous areas of the southern China, an intensive measurement campaign was conducted at the summit of Mt. Heng during the spring of2009. The mean concentrations of OC, EC and PM2.5were3.01,0.54,40.7μg m-3, respectively. The estimated average SOC concentration was1.85μg m-3(1.52μg m-3for non-biomass burning period), accounting for more than half of the OC mass at Mt. Heng. We observed a good correlation between droplet-mode sulfate and SOC, indicating the occurrence of in-cloud SOA formation at Mt. Heng. The positive relationship between aerosol acidity and SOC suggests the enhancement of SOC by acid-catalyzed heterogeneous reactions. During the observation period, the air masses were mostly from the PRD and the eastern coast regions, demonstrating the impact of the long-range transport of pollutants from these developed regions to the rural areas in southern China. High concentrarions of carbonaceous aerosols and potasium were observed at the early stage of the observation, which were found to be related with the biomass burning events in Southeast Asia.To study the production and aging of organic aerosols in a subtropical environment, we measured hourly resolved organic carbon (OC) and element carbon (EC) in PM2.5at a receptor site (Tung Chung, TC) in Hong Kong from August2011to May2012. We found that the SOC and odd oxygen (Ox) were highly correlated during the summer and autumn seasons, suggesting that photochemical processing contributed to the formation of organic aerosols. Therefore, we quantitatively studied the photochemical aging of organic aerosol during the smog episodes in summer and autumn. The results showed that the PRD cities and Hong Kong were the source regions and that aerosol particles became more aged as they were advected toward the receptor TC site. The SOC production rates were estimated to be in the range of1.31-1.82μg m-3ppmv-1h-1in autumn and3.86μg m"3ppmv-1h-1in summer, with the summer rate in the upper end of the range observed in the U.S. and Mexico City. The reduced rates in the autumn episodes may be due to decreased level of photochemistry. The results of this study can help improve modeling the formation of organic aerosols in polluted sub-tropical environments.To evaluate the wintertime regional brown haze in northern China, trace gases and aerosols were measured at an urban site in Ji’nan from9-20November,2009. Transmission electron microscope (TEM) was applied to analyze the individual particle aerosols. We found that over90%of particles contained ammoniated sulfate (AS) in foggy, clear and haze days. Based on their mixing states, aerosol particles were further grouped into eight classes:AS-soot, AS-OM, AS-fly ash, AS-CaSO4, AS-soot/OM/fly ash, AS, AS-mineral, and others. Based on the estimations from TEM analysis, relative number fractions of both AS-soot (20%) and AS-soot/OM/fly ash (20%) from hazy days exceeded those from clear days (13%and12%), implying that coagulation is an important mixing mechanism in polluted air. Comparisons of TEM images of individual particles collected in foggy, clear and haze days, we found that many ambient AS particles from foggy and hazy days retained considerable water on their surfaces.We investigated the microscopic characteristics of individual particle aerosols collected in one photochemical pollution episode in Hong Kong. The results revealed large contrasts of aerosol physico-chemical properties on clean and smoggy days, with thick organic coatings internally mixed with inorganic sulfate for all particle sizes in the aged plumes from the PRD region.Trace metals in PM2.5were measured at one industrial site and one urban site in Ji’nan during September,2010. Individual particle aerosols and PM2.5samples were collected concurrently at both sites. The results show that mass concentrations of PM2.5(130μg m-3) and trace metals (4.03μgm-3) at the industrial site were1.3times and1.7times higher than those at the urban site, respectively, indicating that industrial activities nearby the city can emit trace metals into the surrounding atmosphere. Correlation coefficient analysis and principal component analysis revealed that Cu, Fe, Mn, Pb, and Zn were originated from vehicular traffic and industrial emissions at both sites; As, Cr, and part of Pb from coal-fired power plant; Ba and Ti from natural soil. Based on the TEM analysis, we found that most of the trace metals were internally mixed with secondary sulfate/organic particles. These internally mixed trace metals in the urban air may have different toxic abilities compared with externally mixed trace metals. |
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