East Asia monsoon's influence on seasonal changes of beryllium-7 and typical POPs in near-surface atmospheric aerosols in mid-latitude city Qingdao, China

摘要

Near-surface atmospheric aerosols were collected at sampling frequency of 3 d per week for one year from August 2009 to July 2010 in Laoshan District, Qingdao, located in the mid-latitude coastal region of East Asia monsoon region. The samples were analyzed for cosmogenic nuclide beryllium-7 (~7Be), organochlorine pesticides (OCPs), and polychlorinated biphenyls (PCBs). The annual average ~7Be concentration was 6.83 ± 0.40 mBq m~(-3), with the variation range from 1.52 to 14.58 mBq m~(-3). The maximum and minimum levels were observed in September and May, respectively. Autumn and spring were the seasons with high ~7Be concentrations and summer was the lowest ~7Be season. Enhanced wet precipitation may have caused lower ~7Be observed in summer when southeasterlies were prevailing. Higher ~7Be concentrations in autumn 2009 were caused by the abnormal atmospheric circulation. Concentrations of HCHs, DDTs, and PCBs followed a trend of being lower in summer and higher in winter. Higher chlorinated PCB isomers were predominant in winter and lower chlorinated PCB isomers were predominant in summer. ΣOCPs generally showed positive correlations with ~7Be but were interrupted by the "spring leak maximum" episode for ~7Be in the atmosphere in April when the stratosphere-troposphere exchange was enhanced, and in December when abnormally high HCHs were observed. No significant correlation was found between ~7Be and PCBs except for PCB28. Seasonal oscillations in ~7Be and the ratios of POP/~7Be were observed.