Characteristics and sources of polycyclic aromatic hydrocarbons in dew in urban ecosystems in Northeast China

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in the atmospheres above major cities in Northeast China are relatively high. Dew is an effective way to settle and remove particulate and gaseous matter in the formation process. Notably, 16-PAH concentration dew analysis was conducted in four major cities (Harbin, Changchun, Shenyang and Dalian) from April to November 2023. In the study area, 2–3-ring PAHs dominated in dew in both the dissolved and particle phases, followed by 4-ring and 5–6-ring PAHs. Phe was the most common individual PAH in dew. Because PAHs in wet deposition are closely related to those in the atmosphere, the concentration of PAHs in dew was much lower than that in snow. The proportions of the gaseous-phase scavenging ratio (Wg) to the total scavenging ratio (Wt) in Harbin, Changchun, Shenyang and Dalian increased with increasing temperature, reaching 22.98%, 29.02%, 30.71% and 33.22%, respectively, which indicated that the ability of dew to remove PAHs in the particle phase was greater than that to remove PAHs in the gas phase. The concentration of dissolved-phase PAHs in dew was lower than that of particle-phase PAHs. The total PAH fluxes were 43.25, 33.35, 32.16, and 25.63 ng/m2·d in Harbin, Changchun, Shenyang and Dalian, respectively, decreasing from north to south. The dew amount was much smaller than the rainfall and snow amount (by two orders of magnitude), and the PAH flux in dew was much lower than that in rain and snow. Isomeric ratio assessment coupled with principal component analysis (PCA) indicated that the source of PAHs in dew was a combination of vehicle emissions and biomass and coal combustion. PAHs in dew mainly originated from local sources rather than from long-range atmospheric transport. This study revealed the effects of PAHs in dew on the air quality and the removal of PAHs by dew.