This study investigated the seasonal variation and chemical characteristics of atmospheric PM_2.5 at an urban site in Hanoi City of Vietnam in summer (July 2020) and winter (January 2021) periods. The study results showed that the average value of daily PM_2.5 concentrations observed for the winter period was about 3 times higher than the counterpart for the summer period. The concentrations of major species in atmospheric PM_2.5 (SO₄²⁻, NH₄⁺, K⁺, OC and EC) measured during the winter period were also significantly higher than those during the summer period. The contribution of secondary sources to the measured OC (the largest contributor to PM_2.5) was larger than that of primary sources during the winter period, compared to those in the summer period. The correlation analysis among anions and cations in PM_2.5 suggested that different sources and atmospheric processes could influence the seasonal variations of PM_2.5 species. The unfavorable meteorological conditions (lower wind speed and lower boundary layer height) in the winter period were identified as one of the key factors contributing to the high PM_2.5 pollution in this period. With the predominance of north and northeast winds during the winter period, the long-range transport of air pollutants which emitted from the highly industrialized areas and the intensive fire regions in the southern part of China and Southeast Asia region were likely other important sources for the highly elevated concentrations of PM_2.5 and its chemical species in the study area.

This study investigated the airborne concentration of PM₁₀ and 20 trace elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Na, Pb, Ti, V, Zn) in residential, industry, traffic road, coal mining, thermal power plant area of Bac Giang province. The average PM₁₀ concentration was highest at coal site, followed by traffic 1 sites, industrial sites and traffic 2 sites, the residential sites, and lowest at the power plant site located in mountain area. While Al, Ca, Fe, K, Mg, Na were the most abundant elements in all sampling sites, accounting for 73–96% of total obtained elements, the concentration of As, Cd, Cr, Cu, Mn, Ni, Pb, V, and Zn occupied from 2.9 to 23.2%. Noticeably, the concentrations of Cd were from 7 to 65 times higher than the concentration limit for Cd (0.1 ng/m³) according the World Health Organization (WHO). Although, the Hazard Index (HI values) of all metals were found to be within the safe level for both children and adults, the Carcinogenic Risk (CR) of Cr and As in all sites were closed to the acceptable levels for children, implying a potential carcinogenic risks of these metals.

PM₁₀ levels, concentrations of trace metals, source apportionment, and potential health risks exposed to PM₁₀-bound metals via inhalation pathway were investigated at industrial, traffic and residential sites in Bac Giang, Vietnam. The average PM₁₀ concentration exhibited the highest value at the industrial sites, followed by the traffic sites, and the residential sites. The PM₁₀ mass was 1.38 to 3.39 times higher than the National Air Quality Standard (QCVN 05:2013/BTNMT) (150 µg/m³ for 24 h). The concentrations of non-crustal trace elements (As, Cd, Cr, Ni, Pb, V, and Zn) at industrial sites were at a higher level than at the traffic and residential sites. Enrichment Factors analysis and principal component analysis (PCA) were performed for source apportionment of PM₁₀ in Bac Giang. Four potential emission sources including traffic-related emissions, industry, use of pesticides, and coal combustion were identified. The results of pollution load index and health risk assessments showed higher contamination levels and higher non-carcinogenic and carcinogenic risks posed to children and adults in the vicinity of the industrial sites than the traffic and residential sites. The HQ value for Cr greater than 1 at industrial sites expressed the adverse health effects among humans should be a concern. Further, the health risk of adults exposed to toxic elements via inhalation contact was more pronounced than the children at all sampling sites.