Atmospheric aerosols collected from each season in urban Beijing have been studied using time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). The chemical composition of atmospheric aerosol particles during various atmospheric pollution levels was analyzed and distinguished by principal component analysis (PCA). The differences and sources of the components of the aerosol particles were explored. The results showed that the fine particulate matter from heavily polluted days mainly consists of inorganic salts and organic compounds, such as hydrocarbons, nitrogen‐ or sulfur‐containing hydrocarbons, and their oxides. Samples collected from clean days in the four seasons were also analyzed. Only the samples collected in spring showed a significant difference from the other three seasons. We concluded that the main source of pollution in the Beijing urban area was fossil fuel combustion from motor vehicles.

ABSTRACT:We chose a traffic intersection that were heavily polluted in Haidian District of Beijing as the representative monitoring point to collect of atmospheric particulate samples within four seasons, respectively, and analysis of the PM 2.5 and PAHs levels and their contribution to haze in Beijing atmosphere. The results showed that the concentration of PM 2.5 and seasonal characteristics of PAHs follow this order: winter> autumn> spring> summer in Haidian District of Beijing, and the composition of PAHs are mainly four and five membered ring derivatives. In addition, by using the ratio calculation method, it was concluded that the combustion contributes the most for PAHs in PM 2.5 contamination in Beijing. RESEARCH METHODS, SAMPLING AREA AND TIMEAtmospheric aerosol sample collection was performed by collecting PM 2.5 particulate matter samples using Thermo2025i instrument (the United States). The key points are Chegong zhuang Road and Baishi Bridge South, on behalf of the typical traffic pollution areas in urban. Sampling time was selected from designated days in spring, summer, autumn and winter in 2014, and Spring Festival's Eve of 2015. PM 2.5 LEVELS IN DIFFERENT SEASONS IN A TRAFFIC INTERSECTION IN BEIJINGThe aim of this study was to analyze the seasonal variation of PM 2.5 pollution in Beijing from January to December in 2014 and January to March in 2015.The seasonal concentrations of PM 2.5 were 78.3 μg / m³, 68.3 μg / m³, 89.6 μg / m³ and 98.7 μg / m³ in Spring, Summer, Autumn, and Winter respectively. It can be seen that the seasonal characteristics were as follows: winter> autumn> spring> summer. The level of PM 2.5 in spring was lower in Haidian District, because the strong wind in spring of Beijing could greatly dilute the concentration of PM 2.5 . In summer, there was lots of rainy days in Beijing, which also plays negative roles for the level of PM 2.5 . VARIATION OF PAHS IN DIFFERENT SEASONS IN A TRAFFIC INTERSECTION IN BEIJINGThe US Environmental Protection Agency published 16 kinds of priority PAHs, the study of these 16 kinds of PAHs as a research object was performed at an important traffic junction in Haidian district of Beijing, was selected as a monitoring point, the content of PM 2.5 and PAHs are shown in and Figure 1, respectively. The results of monitoring and analyzing showed that there were some differences in the compositional characteristics of PAHs in different seasons. Overall, 4 and 5 membered rings are the main components of PAHs, accounting for about 80% of the total PAHs. the BaP content was the highest during the winter heating period, with an average concentration of 5.13 ng/m 3 ; the concentrations of PAHs in air PM 2.5 were obviously different in different seasons, partly due to the semi-volatility of the 4 membered-ring PAHs and the low volatility of the 6 membered-ring PAHs.338

Phthalates contaminants in PM 2.5 were analysed qualitatively and quantitatively. A total of 15 phthalates were detected. Some of them are documented by the U.S. Environmental Protection Agency priority pollutants list, which were identified as environmental hormones. The higher content of phthalates in summer is mainly caused by the higher temperature. On the other hand, coal combustion has less influence on it.