Analysis for sources of atmospheric α- and γ-HCH in gas and particle-associated phase in Dalian, China by multiple regression

Atmospheric concentrations of α- and γ-hexachlorocyclohexanes were measured once a week in Dalian throughout 2008, using a high-volume air sampler, to estimate diurnal, monthly and seasonal variations. Multiple regression analysis was used to estimate the impact of selected meteorological conditions on atmospheric concentrations of hexachlorocyclohexanes and to identify the potential source regions. Overall, α- and γ-hexachlorocyclohexanes were mainly associated with the gas phase, with an annual mean gas-phase concentration of 36 ± 30 and 10 ± 9.8 pg m−3 respectively. On the other hand, mean particle (PM10) associated concentrations throughout the year were 1.9 ± 2.4 and 0.46 ± 0.43 pg m−3 respectively. Gas-phase concentration of α- and γ-hexachlorocyclohexanes peaked in the autumn season whereas highest concentrations in the particle phase were measured in spring. Ratio of α-/γ-isomer ranged from 3.7 to 7.4 in the gas phase which was close to the ratio in technical hexachlorocyclohexanes (5-7). In the particle-associated phase this ratio ranged from 1.2 to 3.8, with the exception of daytime samples in spring (up to 16) and summer seasons (up to 14) and this exception could be due to the isomerization from γ- to α- in ambient air, at least partly resulted from the impact of sunlight. Regression analysis showed that, at the sampling site, concentrations of α- and γ-hexachlorocyclohexanes in the gas phase were both elevated with increasing temperature and wind speed, whereas in the particle-associated phase their concentrations tended to remain stable.