A Study On The Seasonal Characteristics Of Dioxins In The Atmospheric Environment In

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzo-furans (PCDD/Fs) are one of hypertoxic persistent organic pollutants, which are not easy to degrade. Due to several happened PCDD/F containminations which had serious influence on health of people and environment, startling the world, governments and the public of nations highly focused on PCDD/F pollutions. Most of PCDD/Fs are diffused by atmosphere after entering into the environment from emission sources directly. Many important emission sources, like industries, transportations, centralized pollution treatments and a large number of living facilities, gather in the cities. Therefore, it is important to monitor of PCDD/F pollution levels and study of their pollution characteristics.Aiming to analyze temporal and spatial distributions of atmospheric PCDD/Fs, High Resolution Gas Chromatography/High Resolution Mass Spectrometer (HRGC/HRMS) isolope dilution was used to detect PCDD/F concentrations in ambient air samples, which were collected in six areas in Guangzhou during four different periods. Results showed, except industrial area, little differences were observed in concentrations and Toxic Equivalent Quantities (TEQs) of atmospheric PCDD/F at other areas, which ranged from 0.705 to 75.4 pg·m-3 and from 0.038 to 10.7 pg I-TEQ-m-3 in 2010-2011, respectively. Averaged atmospheric PCDD/F TEQs of background, residential, commercial and traffic sections were (356±165), (323±155), (370±94), (461±209) fg I-TEQ·m-3, respectively. By contrast, the averaged atmospheric PCDD/F TEQs in suburb and industrial sections were considerably high, which were (571±512) and (2.00×103±2.40×103) fg I-TEQ·m3, respectively. Spatial trend of atmospheric PCDD/F TEQs in Guangzhou presents that TEQs in urban (including residential, commercial and traffic sections) are less than those in suburban in general, while gradual decrease from the east to the west, and from the north to the south (except industrial area). It suggests that indurstrial area in the east and monsoon both have influence on spatial distribution of PCDD/F concentrations and TEQs.Little differences were observed on atmospheric PCDD/F concentrations in autumn, winter and spring ((16.2±6.01); (14.3±4.08); (14.3±12.7) pg-m-3), however, they are all higher than that in summer ((6.10±4.18) pg-m3). TEQs in spring are much higher than autumn, winter and summer ((0.415±0.212), (0.460±0.0967), (0.337±0.359) pg I-TEQ-m-3). As for seasonality of atmospheric PCDD/F concentrations at each site, except industrial area and suburb, concentrations at other sites are higher in rainy seasons (spring and summer) than those in dry seasons (autumn and winter). Moreover, TEQs in industrial area and suburb are considerably high in spring, while in other sites are relatively high in spring and winter, followed by autumn and summer. In summary, seasonality of atmospheric PCDD/F concentrations may be ascribed to influence of precipitation and monsoon in the rainy seasons, resulting in low PCDD/F concentrations. In the meanwhile, influence of dry and rainless weather in the dry seasons and northen air mass lead to relatively high PCDD/F concentrations. In particular, seasonality of atmospheric PCDD/F TEQs in industrial area may be impacted by pollution sources dominantly. In addition, higher atmospheric PCDD/F TEQs in spring in suburb may be derived from pollutants in indurstial area. They might be brought by prevailing sourtheast wind.As for congener profiles of 2378-PCDD/Fs at each monitoring area, results show that OCDD is dominant congener. Its fraction ranges from 20.8% to 69.6%. OCDF (3.1%-2.5%) and 2378-HpCDFs (5.1%-27.7%) follow by turn. In the meanwhile, the dominant congeners of PCDD/F homologues at each monitoring areas are TCDDs, TCDFs, PeCDFs, OCDD, HxCDFs and OCDF. Seasonality of congener profiles of 2,3,7,8-PCDD/Fs presents that high fractions of 2378-PeCDFs,2378-HxCDFs,2378-PeCDD, et al. occur in spring, high fractions of 2378-TCDD, OCDD occur in summer, however, main pollutants in autumn and winter are 2378-HpCDFs and OCDF. In addition, for PCDD/F homologues, main pollutants in spring are TCDFs and PeCDFs while TCDDs are dominant in summer and high-chlorinated dioxins and furans are dominant in autumn. However, main pollutants at each area are different.Based on correlation analysis between meteorological factors and atmospheric PCDD/F TEQs, Principle Component Analysis and the backward trajectory simulation of air flow, effects on seasonality of atmospheric PCDD/F TEQs were studied. Meteorological factors, like temperature, wind direction and precipitation have some influences on the seasonality of atmospheric PCDD/F TEQs. Result of PCA presents that most of plots gather in the rainy seasons and the dry seasons. Results of the backward trajectory simulation of air flow shows that the air flow in the the rainy seasons comes from eastern and southeastern sea, while that in the dry seasons comes mainly from northern and northwestern inland.