资源环境科技发展态势分析平台

The North China Plain (NCP) is the most heavily polluted region in China and the explosive growth (EG) events of PM_2.5 frequently occur in winter in this region. A campaign from 17 Nov. 2018 to 1 Mar 2019 was conducted at a rural site in NCP. EG events of PM_2.5 were defined as the dynamic increase in PM_2.5 concentration by 100 μg/m³ within half day. The intensity of EG events were then graded by the time cost, i.e. 3, 6 and 9 h. EG events with a total number of 120 were identified during the study. Mean growth rates and corresponding standard deviations of PM_2.5 of 3 h-, 6 h- and 9 h-EG events were 43.4 ± 6.9, 19.3 ± 1.8 and 12.5 ± 0.5 μg/m³/h, respectively. All of them except one 3 h-EG event occurred with windspeed lower than 2 m/s. Based on the evolution of hourly chemical composition of PM_2.5, the EG events were investigated on their formation mechanism. The average mass fraction ratios of SNA (sulphate, SO₄²⁻; nitrate, NO₃⁻; ammonium, NH₄⁺) in PM_2.5 were 26.3%/18.7%, 32.6%/18.0% and 33.6%/26.9% in 3 h-, 6 h- and 9 h-EG events in the daytime/nighttime, respectively. About two thirds of EG events occurred in the nighttime with a significant increase in the concentrations of organic matter (OM) and chloride (Cl⁻), which is attributable to nocturnal primary emissions such as coal combustion. In addition, CO-scaled growth rate was calculated as chemical growth rate, the results indicate that OM was the dominant components in EG events.