No abstract

Based on PM_2.5 chemical database from literature and our observations, chemical species and reconstructed speciation of PM_2.5 in several representative Chinese megacities and across China were compared to draw insights into the characteristics of PM_2.5 speciation. PM_2.5 mass and speciation varied substantially over geographical regions in China. Near six-fold variations in average PM_2.5 concentrations (34.0–193.4 μg m⁻³) across China were found with high PM_2.5 levels (>100 μg m⁻³) appearing along northern region and in western urban areas. At both urban and rural sites in eastern region, sum of sulfate, nitrate, and ammonia (SNA) typically constituted 40–57% of PM_2.5 mass, indicative of the regional characteristics of fine particulate pollution and more intensive "complex atmospheric pollution" compared to western region. Particulate organic matter (POM) had constant and significant contribution to PM_2.5 mass. POM plus SNA accounted for 62–90% of PM_2.5 mass at most of the sites. PM_2.5 speciation in China was also characterized by high content of mineral dust. In four representative megacities (i.e. Beijing, Chongqing, Shanghai, and Guangzhou) with substantially higher levels of all the species except that NO₃⁻, NH₄⁺, and EC in PM_2.5 than those in Los Angeles, distinct differences in nitrate and sulfate levels and their mass ratio [NO₃⁻]/[SO₄²⁻] imply that mobile source is likely more important than stationary (coal combustion) source in Guangzhou whereas in Chongqing the situation is contrary. The observed intra-city variations in PM_2.5 mass and speciation indicate that local emissions and regional transportation both contributed significantly to high fine particles levels in Beijing, while local contribution likely played a predominant role in Chongqing. During the ten-year period from 1999 through 2008 in urban Beijing, both SNA and [NO₃⁻]/[SO₄²⁻] exhibited steadily increasing trends, implying that the characteristic of "complex atmospheric pollution" and the contribution from mobile sources were both being enhanced

Fine particulate matter (PM 2.5 ) is a significant health issue in Chinese megacities. However, little information is available regarding the PM 2.5 -bound toxic organics, especially their sources, atmospheric transformations, and health implications. In this study, we assessed the levels of polycyclic aromatic hydrocarbons (PAHs) and their nitrated, hydroxylated, and oxygenated derivatives (i.e., NPAHs, OHPAHs, and OPAHs, respectively) in PM 2.5 collected in Beijing over a 1 year period. The median concentration of 23 PAHs, 15 NPAHs, 16 OHPAHs, and 7 OPAHs in PM 2.5 was 53.8, 1.14, 1.40, and 3.62 ng m À3 , respectively. Much higher concentrations and mass percentages for all species were observed in the heating season, indicating a higher toxicity of PM 2.5 during this period of time. Positive matrix factorization was applied to apportion the sources of PAHs and their derivatives. It was found that traffic emissions in the nonheating season, and coal combustion and biomass burning in the heating season, were the major primary sources of PAHs and their derivatives. Secondary formation, however, contributed significantly to the derivatives of PAHs (especially NPAHs and OPAHs) in the nonheating season, suggesting significant impacts of atmospheric transformation on the toxicity of PM 2.5 .