Search

• Characteristics, sources and health risks of PM 2.5 -bound elements were explored. • The accumulated cancer risk exceeded the threshold of 10−6. • Dust was the leading source, but traffic source was the main contributor of risks. • Serious health risks caused by trace elements existed in special events. To gain a comprehensive understanding of sources and health risks of trace elements in an area of China with high population densities and low PM 2.5 concentrations, 15 trace elements (Al, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Sn, Ba, Pb) in PM 2.5 were monitored from December 2020 to November 2021 in a representative city, Xiamen. The concentrations of trace elements in Xiamen displayed an obvious seasonal variation and were dominated by K, Fe, Al, Ca and Zn. Based on Positive Matrix Factorization analysis, source appointment revealed that the major sources of trace elements in Xiamen were traffic, dust, biomass and firework combustion, industrial manufacture and shipping emission. According to health risk assessment combined with the source appointment results, it indicated that the average noncarcinogenic risk was below the threshold and cancer risk of four hazardous metals (Cr, Ni, As, Pb) exceeded the threshold (10−6). Traffic-related source had almost half amount of contribution to the health risk induced by PM 2.5 -bound trace elements. During the dust transport period or Spring Festival period, the health risks exceeded an acceptable threshold even an order of magnitude higher, suggesting that the serious health risks still existed in low PM 2.5 environment at certain times. Health risk assessment reminded that the health risk reduction in PM 2.5 at southeastern China should prioritize traffic-related hazardous trace elements and highlighted the importance of controlling vehicles emissions in the future. [ABSTRACT FROM AUTHOR]

Surface ozone (O 3) has a significant impact on the air quality, and its concentrations have been increasing despite a distinct decrease in fine particulate matter (PM 2.5) since 2013 in China. However, the formation mechanisms of photochemical O 3 pollution in coastal regions are not fully understood. Therefore, an intensive field observation was conducted from July 8th to August 4th 2022 in Xiamen of Southeast China, combining with the observation-based model to reveal the formation and influencing factors of photochemical O 3 pollution affected by the Western Pacific Subtropical High (WPSH). Results indicate that O 3 pollution episodes were characterized by higher air temperature, lower relative humidity, lower wind speed, and higher concentrations of precursors (including volatile organic compounds (VOCs), NO x , and CO) compared with non-pollution episodes (p < 0.05). Stronger atmospheric oxidation capacity (AOC), OH reactivity, and RO x production rates during the O 3 pollution episodes led to the remarkable increases in O 3. Additionally, the photolysis of HCHO and other carbonyl compounds (48.6%), as well as O 3 photolysis (41.3%) contributed the largest to RO x radical production, promoting the rapid formation of O 3 during the pollution episodes. Reducing VOC concentrations not only decreased the net O 3 production rates and AOC, but also weakened RO x self-reactions (Self-Rxns). Notably, Self-Rxns were weakened when the reduction percentage of NO x was from 10% to 20%, but decreasing NO x concentrations intensified Self-Rxns in other reduction percentages of NO x. This study provides a better understanding of photochemical O 3 pollution mechanisms under the synoptic situation controlled by the WPSH, as well as the urgency of VOC reductions in the rapid development of coastal regions. • The field observation combing with model simulation were used to explore in situ O 3 photochemistry. • Elevated levels of precursors and enhanced atmospheric oxidation capacity accelerated O 3 formation. • VOC reductions decreased atmospheric oxidation capacity and weakened the RO x self-reactions. • HCHO greatly promoted RO x radical and O 3 formation. [ABSTRACT FROM AUTHOR]