Recently, the team of Atmospheric Environment led by Professor CHEN Jinsheng in the Institute of Urban Environment, Chinese Academy of Sciences (IUE, CAS) had found the different impacts of artificial control and natural intervention on the formation mechanism of fine particles (PM_2.5) in atmosphere. Under the emission control of the major events and the typhoon weather, PM_2.5 had presented different chemical characteristics and formation mechanisms.

The 2016 G20 summit was held on 4-5 September 2016 in Hangzhou, the Yangtze River Delta (YRD) region of China. To improve air quality, control measures were adopted by the government in the YRD region. After the G20 summit, it was determined that typhoon Malarks had a significant influence on the YRD region, especially the coastal cities in the YRD region. Therefore, the strict control measures and typhoon occurred within a short period (September 2016) offer a valuable opportunity to study the difference in the formation mechanism of PM_2.5.

Our research was conducted in the coastal city Ningbo, which is adjacent to Hangzhou. Three distinct cases, i.e., a control case, a normal case, and a typhoon case, were investigated during the study period. The results showed that stable weather condition and the regional transport from inland regions could still result in high concentration of PM_2.5 even the strict emission control was implemented in the control case. The stagnant atmosphere with high relative humidity (RH) was beneficial for the transformation of SO2 to SO₄^2- and finally resulted in high proportion of SO₄^2- in the control case. The control and typhoon cases both resulted in extremely low NO₂, but the contribution of NO3- to PM_2.5 was decreased in the control case and increased in the typhoon case. The close correlation of the nitrate oxidation ratio (NOR) with Na⁺ and Mg²⁺ in the typhoon case was indicative of sea salt associated with the typhoon that provided a surface for the heterogeneous formation of NO3- .

The results mentioned above have been published at Atmospheric Environment, 224 (2020) 117312, and titled as ‘Impact of control measures and typhoon weather on characteristics and formation of PM2.5 during the 2016 G20 summit in China’. PhD student ZHANG Yanru is the first author. Professor CHEN Jinsheng and Associated Professor XU Lingling are the corresponding authors. This study was funded by the National Key Research and Development Program (2016YFC02005 & 2016YFE0112200), the National Natural Science Foundation of China (41575146), the Chinese Academy of Sciences Interdisciplinary Innovation Team Project, and the Natural Science Foundation of Fujian Province, China (2016J01201).

The different chemical characteristics of PM2.5 in the cases under emission control (Case 1), normal state (Case 2), and typhoon weather (Case 3).