Traffic is a major source of anthropogenic aerosol in urban atmosphere. In this study, aerosol particles were measured with a TEM-EDX system at the roadside of a main road in the northwestern part of Beijing, China, under clear and hazy conditions. Soot, organic, sulfur-rich (S-rich), mineral, and metal particles, as well as the mixtures, were frequently encountered in aerosols. Under hazy conditions, S-rich particles coated with organic matter (S-OM particles) accounted for most of the total particles (15% to 24%), followed by soot particles (18% to 21%), organic particles (17% to 21%), non-mixed S-rich particles (10% to 18%), and S-rich particles with soot-, mineral-, or metal-inclusions (here referred to as S-inclusion particles) (11% to 15%). Under clear conditions, non-mixed S-rich and organic particles were dominant components, while mineral and soot particles were secondary components, among which, ~14% of the total particles had a sulfate core or OM coating; inclusions of mixture particles were often mixed with sulfate cores. In the sulfate core–OM shell structure particles, the ratio of core diameter to the whole particle diameter was ~0.52 under hazy conditions and ~0.60 under clear conditions, indicating a substantial sulfate and organic formation on the particles. Soot particles accounted for 18% to 21% of the total particles. The relative growth of aged soot particles was higher under hazy conditions than under clear conditions. In sum, particles from traffic emissions on a main urban road aged with the formation of sulfate and organic matter.

The health effects of trace elements in PM_2.5 have been the subject of widespread public concern. In this study, the 18 trace elements in PM_2.5 samples collected at a national park were measured to analyze their concentrations, sources, and health risks. The results showed that the average concentration of 18 trace elements was 191.99 ng/m³ (0.89-1638.28). Higher concentrations of crustal elements are associated with northwestern air masses and southeastern air masses, while higher concentrations of anthropogenic elements are associated with southwestern air masses. The total non-carcinogenic risk of the harmful elements was below the acceptable threshold, for both adults (0.723) and children (0.448). The total carcinogenic risk of the hazardous elements was above the safe level for both adults and children, and the carcinogenic risk of the hazardous elements is As > Ni > Cr > Pb. Natural sources, vehicle emissions, coal combustion, biomass combustion, and industrial sources were identified by both the Absolute Principal Component Score-Multiple Linear Regression (APCS-MLR) model and the Positive matrix factorization (PMF) model. Both the APCS-MLR-HRA model and the PMF-HRA model indicated that vehicle emissions and industrial sources were the main contributors to non-carcinogenic risks, while industrial and coal combustion sources were the main contributors to carcinogenic risks. Mn was the main contributor to the non-carcinogenic risk, while As was the main contributor to the carcinogenic risk. Mn and As should be prioritized as control elements to address the higher non-carcinogenic and carcinogenic risks from vehicle emissions, industrial, and coal combustion sources.