Chemical characteristics, sources, and formation mechanisms of PM2.5 before, during, and after the Spring Festival in a plateau city of Southwest China

To study chemical characteristics, sources and formation mechanisms of PM2.5 during the Spring Festival (SF), 39 elements, 9 water–soluble ions (WSIs) and 8 fractions of carbonaceous species in PM2.5 and PM10 at two sites in Kunming were investigated. The results indicated that the average mass concentration of PM2.5 and PM10 were 61.03 ± 25.11 and 80.48 ± 30.08 μg/m3 in the urban area, and 18.96 ± 4.66 and 56.76 ± 21.69 μg/m3 in the suburban area, respectively. Concentrations of PM2.5 peaked significantly on the Chinese New Year (NYE) and the Lantern Festival (LF) in the urban area. Compared to the previous day of NYE, Ba and Sr concentrations increased by 22.1 and 39.2 times in urban areas, and by 6.5 and 8.3 times in suburban areas. The sum of sulfate, nitrate, and ammonium (SNA) accounted for 82.03% and 60.38% of WSIs in urban and suburban areas, respectively. The most abundant carbonaceous species in urban and suburban areas were OC3 and EC1. According to the Positive Matrix Factorization (PMF) calculation, secondary formation (41.76%) was the predominant sources of PM2.5, and the contribution of fireworks to PM2.5 was 9.06%. The formation of secondary organic carbon (SOC) occurred through heterogeneous reactions. SNA was derived from heterogeneous reaction and photochemical reaction. [Display omitted] •Ba, Sr and K concentrations were significantly elevated during the spring festival.•Fireworks burning have more notable influences on air quality in mountainous cities.•The emission of fireworks is accompanied by a transitory increase in ozone concentrations.