- 期刊
- OpenAccess
Variations of Chemical Composition and Source Apportionment of PM_(2.5) during Winter Haze Episodes in Beijing
摘要
PM_(2.5) samples were collected in Beijing between February 24 and March 12 of 2014, and analyzed to examine chemical compositions and origins of the PM_(2.5) at pollution levels of clean (PM_(2.5) ＜ 75 μg m^(-3)), light-medium (75-150 μg m^(-3)), heavy (150-250 μg m^(-3)) and severe (＞ 250 μg m^(-3)). The mean PM_(2.5) concentration was 137.7 ± 124.8 μg m^(-3) during the observation period, accounting for 66% of PM_(10). As all aerosol species concentrations increased with the pollution level, the contributions of secondary inorganic aerosols (SIA) to PM_(2.5) continuously increased while the contributions of OC and EC decreased, indicating a substantial contribution from secondary formation to the elevation of PM_(2.5) pollution. The acidity of PM_(2.5), the ratio of anion microequivalent concentration to cation, increased from 0.96 to 1.08 as pollution levels increased. Using a PMF model, secondary inorganic aerosols, industrial emissions, soil dust, traffic emissions, and coal combustion and biomass burning were identified as contributors to the PM_(2.5), and on average accounted 46%, 20%, 10%, 6% and 18% of the PM_(2.5), respectively, in the observation period. Industrial emissions were the dominant PM_(2.5) source during the clean period (60%). Except for traffic emission, sources of PM_(2.5) at the light-medium level were consistent, accounting for 17%-29%. Secondary inorganic aerosols were the largest origin of PM_(2.5) at heavy and severe pollution levels, accounting for 40% and 78%, respectively. In addition, the 48 h transport distances of air masses decreased from 2000 km (clean) to 300 km (severe level) and the proportion of air masses from south pollution areas in the total air masses at each pollution level increased from 0% to 97%, indicating that the stability of near surface air and the northerly transport of pollutants from the south at local and regional scales played a the key role in the PM_(2.5) elevation.
延伸閱讀
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