PM2.5-bound synchronous polycyclic aromatic hydrocarbons and heavy metals in in a typical cold city in northern China: Differences in heating and non-heating periods

Heating process in cold cities leads to elevated levels of PM_2.5-bound polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), which are health concerns for their carcinogenic and mutagenic characteristics. In this study, the variations and potential health risks attributable to PM_2.5-bound synchronous PAHs and HMs were assessed in non-heating and heating periods in 2023 in Harbin, a typical cold city in northern China. Results showed that PAHs and HMs concentrations during the heating period (19.77 ng/m³ and 55.79 ng/m³) were higher than the non-heating period (2.11 ng/m³ and 34.67 ng/m³). During the heating period, PAHs primarily originated from pyrogenic activities (70.82 %), while traffic-related sources were dominant in the non-heating period (74.40 %). HMs were predominantly contributed by road dust and diesel emissions. The results of the health risk assessment show that direct inhalation of heavy metals and PAHs in PM_2.5 through the respiratory tract poses a certain carcinogenic risk to both adults and children, while the non-carcinogenic health risks are relatively low. Specifically, elements such as Sb, Cd, As, Pb, and Mn exhibit significant carcinogenic risks, while the health risks of other substances are at a lower level. The concentration of pollutants is significantly higher during the heating season than in the non-heating season, and the exposure effects among different populations are in the order of adults > adolescents > children. Additionally, in each age group, the lifetime excess cancer risk values are mostly distributed within the range of 10^-6 to 10^-4, gradually approaching the international safety threshold (1 × 10^-6). This result indicates that the heavy metals and PAHs contained in PM_2.5 in the atmosphere of Harbin have potential carcinogenic risks. This study reveals the key characteristics of health risks related to PAHs and HMs in cold regions, providing a scientific basis for effectively conducting air quality supervision and ensuring public health.