[Characteristics, Ozone Formation Potential, and Source Apportionment of VOCs During the COVID-19 Epidemic in Xiong'an].

Many restrictive measures were implemented in China from January-February 2020 to control the rapid spread of COVID-19. Many studies reported that the COVID-19 lockdown impacted PM2.5, SO2, volatile organic compounds (VOCs), etc. VOCs play important roles in the production of ozone and PM2.5. Ambient VOCs in Xiong'an were measured from December 25, 2019 to January 24, 2020 (prior to epidemic prevention, P1) and from January 25, 2020 to February 24, 2020 (during epidemic prevention, P2) through a VOCs online instrument. In the study, VOCs characteristics and ozone generation potential (OFP) of ambient VOCs were analyzed, and source apportionment of VOCs were analyzed by using Positive Matrix Factorization (PMF). The results showed that φ(TVOCs) during epidemic prevention and control was 45.1×10-9, which was approximately half of that before epidemic prevention and control (90.5×10-9). The chemical composition of VOCs showed significant changes after epidemic prevention and control, the contribution rate of alkanes increased from 37.6% to 53.8%, and the contribution rate of aromatic hydrocarbons and halogenated hydrocarbons decreased from 13.3% and 12.0% to 7.5% and 7.8%, respectively. Aromatic hydrocarbons, halogenated hydrocarbons, and OVOCs decreased by more than 60%. Seven types of the top ten species were the same before and during the epidemic prevention and control, mainly low-carbon alkanes, olefins, aldehydes, and ketones. Dichloromethane, trichloromethane, and BTEXs decreased significantly. The OPP was 566 µg·m-3 and 231 µg·m-3 in P1 and P2, respectively. The OPP of VOCs decreased by more than 30%. The proportion of OFP contribution of aromatic hydrocarbons decreased significantly after the epidemic prevention and control, and the proportion of OFP contribution of alkanes and alkynes increased significantly. Positive matrix factorization (PMF) was then applied for VOCs sources apportionment. Six sources were identified, including background sources, oil-gas volatile sources, combustion sources, industrial sources, solvent use sources, and vehicle exhaust sources. The results showed that after the epidemic prevention and control, the contribution rate of solvent use sources to TVOCs decreased from 24% to 9%. The contribution rates of background sources, oil-gas volatile sources, and combustion sources increased from 13%, 34%, and 24% to 6%, 14%, and 13%, respectively. The relative contributions of vehicle exhaust sources before and after epidemic prevention and control were 21% and 18%, respectively. The observation points were affected by the emission of VOCs from paroxysmal industrial sources before the epidemic prevention and control. The emission was stopped after the epidemic prevention and control, and its contribution rate was reduced from 22% before the epidemic prevention and control to 1%. The concentrations of industrial sources, solvent sources, motor vehicle tail gas sources, and combustion sources decreased by 97%, 82%, 61%, and 15%, respectively, after the epidemic prevention and control. The concentration of background sources remained stable, and the concentration of oil and gas volatile sources increased by 7%. The control of production and traffic activities cannot reduce the emission of VOCs from oil and gas volatile sources, which is the focus of VOCs control in Xiong'an.

[Characteristics of Haze Pollution Episodes During Autumn and Winter in 2018 in Shijiazhuang].

The mass concentration and chemical composition of fine particles were continuously observed on-line from October 31 to December 3, 2018 at Hebei Key Laboratory of Haze Pollution Prevention and Control in Shijiazhuang. The characteristics of haze pollution in autumn and winter in Shijiazhuang were analyzed. The results showed that during the observation period, four haze pollution episodes occurred with PM2.5 as the primary pollutant, and the maximum daily concentration was 154, 228, 379, and 223 µg·m-3, respectively, reaching a heavy pollution level or above. The main components of PM2.5were water-soluble inorganic ions (WSⅡ) and carbon-containing aerosols, accounting for (60.7±15.6)% and (21.6±9.7)% of PM2.5 mass concentration, respectively. Compared with clean days, the mass concentration of WSⅡ and carbon aerosol during haze pollution increased by 4.4 times and 3.1 times, respectively, which was the main cause of haze pollution. NO3-, SO42-, and NH4+(SNA) were the main components of WSⅡ, accounting for (91.5±17.3)% of the total WSⅡ concentration, of which NO3- took up the highest proportion. The explosive growth of SNA during haze pollution was the main reason for the extremely high PM2.5concentration. Under non-high humidity conditions, the formation rates of unit mass substrates (NO3-, SO42-) were not significantly different, but the transformation of SO42- was significantly promoted after the liquid phase oxidation of SO2 was triggered under high humidity conditions. The atmosphere in Shijiazhuang is rich in NH3, and the molar ratio of n(NH4+) to n(NO3-+2×SO42-) in PM2.5 was greater than 1. The presence of a large amount of NH3 could promote the transformation of NO3- and SO42- and aggravate pollution. During the haze pollution period, the accumulation of primary pollutants from coal and motor vehicles was the main reason for the increase in carbon-containing aerosol. Compared with clean days, the formation of SOC was inhibited. Before the beginning of the warm season, the mobile form was the main pollution source of PM2.5, contributing 30.8% and 39.8% of PM2.5 mass concentration. With the increase of coal combustion emissions, the contribution of coal-fired sources gradually increased to 25.5%, becoming the primary pollution source.