Dry and Wet Depositions of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans in the Atmosphere in Taiwan

Abstract

The study has investigated the annual variation of the dry and wet depositions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) among different kinds of areas. A commercial suburban area, an industrial urban area, a coastal rural area and an agricultural rural area were chosen to measure the PCDD/F depositions in each season. The mean TEQ concentration, dry deposition flux and wet deposition in the industrial urban area all had the highest values, at 0.0958 pg I-TEQ/Nm3, 29.1 pg I-TEQ/m2-d and 47.8 pg/L, respectively. Additionally, the annual total deposition flux of PCDD/Fs in the commercial, industrial, coastal and agricultural areas was 168, 310, 135 and 115 ng/m2-year, respectively. The seasonal change of PCDD/Fs in air could be affected by heating and temperature inversion in winter or photodegradation and OH radical reaction in summer. The various homologue profiles of PCDD/Fs probably affect the distribution in environmental sinks, such as sediments or the living organisms in rivers or seas. Additionally, the results of statistical analysis indicated that PCDD I-TEQ dry deposition flux (ng I-TEQ/m2-month) was negatively correlated with the ambient temperature (r = –0.843) for the agricultural rural area, possibly due to vapor pressure (temperature-dependent) effect on the gas/particle PCDD/F partitioning. Furthermore, the PCDD/F concentration of wet deposition flux (ng I-TEQ/m2-month) was positively correlated with the monthly rainfall (r = 0.826–0.988) at the four sampling areas.