PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) in urban Beijing during heating season: Hourly variations, sources, and health risks

Abstract

Understanding the dynamic variations, potential sources and corresponding health risks of polycyclic aromatic hydrocarbons (PAHs) is essential for developing emission reduction strategies to lower their concentrations and associated health risks. Measurements with 2-h resolution of 16 U.S. Environmental Protection Agency (EPA) priority-controlled PAHs in atmospheric PM_2.5 were carried out at the beginning and midterm of the heating season in urban Beijing during 2020. The measurements utilized an enhanced comprehensive two-dimensional gas chromatography mass spectrometry with aerosol thermal desorption technique. The daily average concentrations of PM_2.5-bound PAHs range from 27.3 to 34.8 ng/m³ in November at the beginning of the heating season, while elevated to 47.9–77.8 ng/m³ in December during the midterm of the heating season. The ratio of PAHs to PM_2.5 during the midterm of the heating season is four times higher than that at the beginning. This increase was due to the rise in concentrations of naphthalene (NaP), fluorene (FLR), and phenanthrene (PHE), along with the decrease in PM_2.5 concentrations in December. The overall diurnal variations exhibit high levels at night and early morning, contrasting with lower levels in the afternoon. However, compared to the beginning of the heating season, the diurnal variations of PAHs during the midterm show more pronounced enhancement and stronger fluctuations. Throughout the observation periods, coal and wood combustion from the local region surrounding Beijing are the primary emission sources of the 16 PAHs, indicating increased combustion emissions in winter due to higher heating demands. High time-resolution measurements captured transient high health risks by 16 PAHs, with the benzo(a)pyrene equivalent concentration (BaP_eq) temporarily exceeded 5 ng/m³, which may result in short-term acute or subacute health effects. This study provides novel understanding on the pollution of PAHs in atmospheric PM_2.5 during the heating season.