Abstract
ABSTRACTMonitoring atmospheric deposition fluxes (dry and wet deposition) is of great importance in tracing the environmental fate and behavior of PCDD/Fs. To further understand the characteristics of both dry and wet PCDD/F deposition in Northern China, two cities, namely Harbin and Shijiazhuang were investigated. During 2014, in Harbin, the monthly dry deposition fluxes of total-PCDD/Fs-WHO2005-TEQ ranged between 308 and 1290 pg WHO2005-TEQ m–2 month–1, with an annual flux of 8240 pg WHO2005-TEQ m–2 year–1; however, in Shijiazhuang, the dry deposition fluxes ranged from 699 to 2230 pg WHO2005-TEQ m–2 month–1, with an annual 15400 pg WHO2005-TEQ m–2 year–1. Monthly dry deposition velocities of particle phase total-PCDD/Fs-WHO2005-TEQ are similar, ranging between 0.42 and 0.94 cm s–1 (average 0.59 cm s–1) and between 0.42 and 0.92 cm s–1 (average 0.6 cm s–1) in Harbin and Shijiazhuang, respectively. Due to the low level of rainfall in Northern China, the monthly wet deposition fluxes were in the range of 3–79.9 (369 pg WHO2005-TEQ m–2 year–1) and 0–140 pg WHO2005-TEQ m–2 month–1 (622 pg WHO2005-TEQ m–2 year–1) in Harbin and Shijiazhuang, respectively. In addition, the average scavenging ratios of total-PCDD/Fs-WHO2005-TEQ were 31900 and 30700 in Harbin and Shijiazhuang, respectively. Combined with dry and wet deposition, the annual total (dry + wet) deposition flux in Shijiazhuang (16100 pg WHO2005-TEQ m–2 year–1) is 1.9 times of magnitude higher than that in Harbin (8610 pg WHO2005-TEQ m–2 year–1). The results indicated that the dry deposition flux was the major mechanism for removal of PCDD/Fs from the atmosphere in Northern China. By examining both the PM2.5 level and total-PCDD/Fs-WHO2005-TEQ deposition in Northern China, and comparing the values with those found in other places, it is clear that there is an urgent need to control the particulate emissions in this area.
Highlights
Increased vehicular traffic and other combustion processes have resulted in a significant increase in ambient particulate matter (PM) over the past two decades
Fd,T: the total PCDD/F deposition flux contributed by the summation of both gas- and particle-phase fluxes; Fd,g: the PCDD/F deposition flux contributed by the gas phase; Fd,p: the PCDD/F deposition flux contributed by the particle phase; CT: the measured concentration of total PCDD/Fs in the ambient air; Vd,T: the dry deposition velocity of total PCDD/Fs; Cg: the calculated concentration of PCDD/Fs in the gas phase; Vd,g: the dry deposition velocity of the gas-phase PCDD/Fs; Cp: the calculated concentration of PCDD/Fs in the particle phase; Vd,p: the dry deposition velocity of the particle-phase PCDD/Fs
The monthly concentrations of totalPCDD/Fs-WHO2005-TEQ in the ambient air are derived from the particulate matter (PM2.5, PM10, TSP)
Summary
Increased vehicular traffic and other combustion processes have resulted in a significant increase in ambient particulate matter (PM) over the past two decades. Fine particulate matter (dp ≤ 2.5 μm, PM2.5) has aroused widespread public concern, since it has been found to contain toxic compounds like PCDD/Fs, contribute to poor air quality, and have adverse effects on human health and global climate change (Laden et al, 2000; Chow et al, 2015). There are 210 possible congeners of PCDD/Fs (75 PCDDs and 135 PCDFs), and of these 17 with chlorine atoms attached to the 2, 3, 7 and 8 positions have been shown to be more toxic, with highly adverse effects on human health. The major distribution pathway of PCDD/Fs is through air (Lohmann and Jones, 1998; Kao et al, 2006; Lee et al, 2009), and they can remain in the environment for a long time and transport long distances (Lee et al, 2003; Zhang et al, 2009), resulting in the widespread distribution of
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