Seasonal trends and potential sources of ambient air OCPs in urban and suburban areas in Dalian, China

A seasonal field campaign by passive sampling was conducted from February 2008 to February 2009, aiming to measure air concentrations of organochlorine pesticides (OCPs) in the urban and suburban areas in Dalian. At the urban site, similar annual average concentrations of alpha-endosulfan and alpha-HCH were found, both being approximately 4 times as high as those of p,p'-DDT and p,p'-DDE, while at the suburban site, the annual average concentration of alpha-endosulfan was 2.9 times as high as the average concentrations of alpha-HCH, p,p'-DDT and p,p'-DDE; concentrations of alpha-endosulfan, alpha-HCH and p,p'-DDE achieved annual peaks in summer. Back trajectory analysis revealed that the air concentration of alpha-endosulfan increased with the input of air masses from the land whereas decreasing air concentration of alpha-endosulfan at the urban site was associated with air masses from the sea. Pesticides used in local agriculture were identified to be major sources of alpha-endosulfan at both the urban and suburban sites, though long-range atmospheric transport from other sources might also contribute to atmospheric levels of this chemical over this coastal city. alpha-endosulfan, alpha-HCH, p,p'-DDT and p,p'-DDE in the air in Dalian might result from the atmospheric transport of the air masses from northeast area, Shandong peninsula and Korean peninsula. Emission due to "aged" DDT and HCH in contaminated local soils as well as atmospheric long-range transport were likely to be major sources of alpha-HCH, p,p'-DDT and p,p'-DDE at the suburban site. In addition, a fresh input of alpha-HCH and p,p'-DDT in the atmosphere could not be excluded in the urban area.