Polycyclic aromatic hydrocarbons in PM2.5 from an e-waste source site and a receptor site in Southern China: Atmospheric transport and process implications

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are potential contaminants released from informal electronic waste (e-waste) recycling. PAHs in PM2.5 collected at a rural e-waste (source) site and a background (receptor) site in Southern China were measured. Seasonal variations and regional transport of PAHs were investigated, and their sources and atmospheric processes were implied. The median concentrations of ∑18PAHs at the e-waste site (13.7 ng/m3) were one order of magnitude higher than those at the background site (median = 1.54 ng/m3), indicating the informal e-waste dismantling was a significant source. The seasonal variations of PAH concentrations at the two sites were similar, exhibiting noticeably unimodal distributions in winter, predominantly associated with the strengthened e-waste dismantling activities. Three molecular diagnostic ratios (MDRs) can be collectively used as potential markers of field informal e-waste burning sources. The dispersion model revealed that regional atmospheric transport from this e-waste site was a source of PAHs in the background air. Some MDRs significantly changed at the background site compared to the source site but could not be explained by the lifetime and/or gas-particle partition of the isomers. The differences complied with recent theories about the multiphase reactivity and evaporation of PAHs on aerosols. It was proposed that in warm and humid climates, the losses of PAHs from PM2.5 were dominated by their phase separation or diffusion, which was n-octanol/water partition coefficient (KOW) dependent. This hypothesis was further supported by data in the literature.