Abstract
To better evaluate the variations in concentration characteristics and source contributions of atmospheric volatile organic compounds (VOCs) during continuous haze days and non-haze days, hourly observations of atmospheric VOCs were conducted using a continuous on-line GC-FID (Airmo VOC GC-866) monitoring system during 1–15 March 2019, in urban areas of Beijing, China. The results showed that the total VOC concentrations during haze days and non-haze days were 59.13 ± 31.08 μg/m3 and 16.91 ± 7.19 μg/m3, respectively. However, the average O3 concentrations during the two haze days were lower than those of non-haze days due to the extremely low concentrations at night instead of the reported lower photochemical reaction in daytime. The ratio of OH radical concentration during haze and non-haze days indicating that the rate of photochemical reaction during haze days was higher than those of non-haze days from 13:00–19:00. The stable air conditions and the local diesel emission at night were the main reasons for the decreased O3 concentrations during haze days. Six major sources were identified by positive matrix factorization (PMF), namely, diesel exhaust, combustion, gasoline evaporation, solvent usage, gasoline exhaust, and the petrochemical industry, contributing 9.93%, 25.29%, 3.90%, 16.88%, 35.59% and 8.41%, respectively, during the whole observation period. The contributions of diesel exhaust and the petrochemical industry emissions decreased from 26.14% and 6.43% during non-haze days to 13.70% and 2.57%, respectively, during haze days. These reductions were mainly ascribed to the emergency measures that the government implemented during haze days. In contrast, the contributions of gasoline exhaust increased from 34.92% during non-haze days to 48.77% during haze days. The ratio of specific VOC species and PMF both showed that the contributions of gasoline exhaust emission increased during haze days. The backward trajectories, potential source contribution function (PSCF) and concentration weighted trajectory (CWT) showed that the air mass of VOCs during haze days was mainly affected by the short-distance transportation from the southwestern of Hebei province. However, the air mass of VOCs during non-haze days was mainly affected by the long-distance transportation from the northwest.
Highlights
IntroductionHaze pollution, which is characterized by a high concentration of PM2.5 (fine particulate matter with an aerodynamic diameter equal to or less than 2.5 μm), significantly affects atmospheric visibility [1,2], air quality, and global climate change [3], and is associated with increased respiratory symptoms and deaths [4,5]
Haze pollution, which is characterized by a high concentration of PM2.5, significantly affects atmospheric visibility [1,2], air quality, and global climate change [3], and is associated with increased respiratory symptoms and deaths [4,5]
During the whole observation period, the variation in volatile organic compounds (VOCs) was consistent with the variations in PM2.5, CO, and NOx, which indicated that the main sources for these pollutants were similar and their change was mainly influenced by the meteorological conditions
Summary
Haze pollution, which is characterized by a high concentration of PM2.5 (fine particulate matter with an aerodynamic diameter equal to or less than 2.5 μm), significantly affects atmospheric visibility [1,2], air quality, and global climate change [3], and is associated with increased respiratory symptoms and deaths [4,5]. Air Quality Standard [6]. The average annual concentration of PM2.5 of Beijing reached. The average annual concentration of Beijing decreased to 51 μg/m3 in 2018 [8] and the number of haze days noticeably declined due to the implementation of the “2 + 26” urban joint prevention and the various emission control measures, such as upgrading low-efficiency coal-fired industrial boilers and furnaces, tightening vehicle emission standards, controlling VOCs emission in the spraying industry and coal-fired power plants, and carrying out oil and gas recovery in gas stations. More effort must be made to meet the national annual standard of
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