Differences in VOCs characteristics, source analysis and health risk evaluation of O₃clean and polluted days in summer in an industrial city in the Fenwei Plain

From June to August 2023, a 50-day online monitoring of VOCs was conducted in an industrial city in the Fenwei Plain. Combined with the air pollutant data (O3, NOx, PM2.5, PM10) and meteorological data (temperature, humidity, wind direction, wind speed) of the local state-controlled stations, the current situation of summer air quality in the study area was analyzed, and the differences in VOCs composition and photochemical reactivity between O3 clean days and pollution days were explored. The PMF model was used to analyze the source of VOCs, and the health risks of toxic VOCs were evaluated. The results showed that the concentrations of NOx, PM2.5 and PM10 reached the standard during the monitoring period, and the hourly concentration of O3 was higher than the national secondary standard (200 μg·m−3) for 14 days. These 14 days were defined as O3 pollution days, and O3 was more susceptible to wind speed, temperature and precursors. Ethane, acetaldehyde and ethylene were the top three species in volume fraction. Except for OVOCs, the other VOCs had the lowest concentration at noon, and OVOCs had a high value at noon. The OFP (95.8 × 10−9) and LOH (5.10 s−1) on the pollution day were higher than those on the clean day (81.8 × 10−9, 4.22 s−1), indicating that the photochemical reaction activity of the precursors on the O3 pollution day was stronger and the conversion rate was higher. The photochemical sensitivity analysis showed that the summer O3 generation in the study area was controlled by VOCs. The PMF model determined that the contribution of pollution sources in summer was gasoline vehicle emission source (33.9%) > coking industry emission source (32.8%) > solvent use emission source (16.1%) > plant emission source (12.0%) > diesel vehicle emission source (3.5%) > chemical industry emission source (1.7%). The health risk assessment of 44 toxic VOCs showed that acrolein (HQ = 1.61) was the only species that exceeded the acceptable risk standard, indicating that it had a non-carcinogenic risk, and benzene, acetaldehyde and some halogenated hydrocarbons (Risk > 10−6) had a possible carcinogenic risk.