Abstract
Ambient air is a core medium for monitoring of persistent organic pollutants (POPs) under the Stockholm Convention and is used in studies of global transports of POPs and their atmospheric sources and source regions. Still, data based on active air sampling remain scarce in many regions. The primary objectives of this study were to (i) monitor concentrations of selected POPs in air outside West Africa, and (ii) to evaluate potential atmospheric processes and source regions affecting measured concentrations. For this purpose, an active high-volume air sampler was installed on the Cape Verde Atmospheric Observatory at Cape Verde outside the coast of West Africa. Sampling commenced in May 2012 and 43 samples (24h sampling) were collected until June 2013. The samples were analyzed for selected polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), hexachlorobenzene (HCB) and chlordanes. The concentrations of these POPs at Cape Verde were generally low and comparable to remote sites in the Arctic for several compounds. Seasonal trends varied between compounds and concentrations exhibited strong temperature dependence for chlordanes. Our results indicate net volatilization from the Atlantic Ocean north of Cape Verde as sources of these POPs. Air mass back trajectories demonstrated that air masses measured at Cape Verde were generally transported from the Atlantic Ocean or the North African continent. Overall, the low concentrations in air at Cape Verde were likely explained by absence of major emissions in areas from which the air masses originated combined with depletion during long-range atmospheric transport due to enhanced degradation under tropical conditions (high temperatures and concentrations of hydroxyl radicals).
Highlights
Many persistent organic pollutants (POPs) have the potential for atmospheric long-range transport and are ubiquitous in the global environment (Pozo et al, 2006; Wania and Mackay, 1996)
Several regional monitoring networks have been established to assess the occurrence and trends of POPs in air in support of relevant regulatory programs and Conventions (Hillery et al, 1998; Hung et al, 2010; Kong et al, 2014; Tørseth et al, 2012). These early monitoring networks have been limited to active air sampling (AAS), but more recent advancements in passive air sampling have facilitated increased spatial coverage (Jaward et al, 2004a; Jaward et al, 2005; Shen et al, 2006) and even temporal trends (Schuster et al, 2011)
Long-term monitoring stations and/or networks targeting POPs in air based on AAS remain scarce and are mainly limited to industrialized regions in the northern hemisphere (Tørseth et al, 2012) and polar regions (Hung et al, 2010)
Summary
Many persistent organic pollutants (POPs) have the potential for atmospheric long-range transport and are ubiquitous in the global environment (Pozo et al, 2006; Wania and Mackay, 1996). Several regional monitoring networks have been established to assess the occurrence and trends of POPs in air in support of relevant regulatory programs and Conventions (Hillery et al, 1998; Hung et al, 2010; Kong et al, 2014; Tørseth et al, 2012). These early monitoring networks have been limited to active air sampling (AAS), but more recent advancements in passive air sampling have facilitated increased spatial coverage (Jaward et al, 2004a; Jaward et al, 2005; Shen et al, 2006) and even temporal trends (Schuster et al, 2011). There are examples of passive air sampling campaigns in tropical areas (Gioia et al, 2011; Klánová et al, 2009; Lammel et al, 2013)
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