Long-term variation of the levels, compositions and sources of size-resolved particulate matter in a megacity in China

摘要

To investigate the long-term trends and variations of the levels, compositions, size distribution and sources of particulate matter (PM), long-term monitoring campaigns of PM_(10) and PM_(2.5) were performed in a megacity in China (Chengdu) during the period from 2009 to 2011. The average concentration of PM_(10) was 172.01 ± 89.80 μg/m~3 and that of PM_(2.5) was 103.15 ± 59.83 μg/m~3, with an average PM_(2.5)/PM_(10) of 0.60. Enrichments of the important species indicated that the fractions of crustal elements were higher in PM_(10) than those in PM_(2.5), while the abundance of organic carbon (OC) and secondary ions was enriched in the fine PM. Quantitative source apportionments of both PM_(10) and PM_(2.5) were performed by PMF. PM_(10) and PM_(2.5) in Chengdu were influenced by similar source categories, and their percentage contributions were in the same order: crustal dust was the highest contributor, followed by vehicular exhaust, secondary sulfate, secondary nitrate and cement dust. Crustal dust and cement dust contributed a higher percentage to PM_(10) than to PM_(2.5), while vehicular exhaust and secondary particles provided higher percentage contributions to PM_(2.5). In addition, PMF-HCA was performed to investigate the characteristics of the sources of the clustered samples, identifying three periods: crustal dust dominant-period, secondary sulfate dominant-period and comprehensive source influenced-period. Planting, reduction of precursors, and banning high-emission vehicles should be implemented to control crustal dust, secondary particles and vehicular exhaust in Chengdu. Furthermore, the size-resolved and the period-resolved control would be more effective.