The contribution of industrial emissions to ozone pollution: identified using ozone formation path tracing approach.

Wintertime meteorological conditions are usually unfavorable for ozone (O) formation due to weak solar irradiation and low temperature. Here, we observed a prominent wintertime O pollution event in Shijiazhuang (SJZ) during the Chinese New Year (CNY) in 2021. Meteorological results found that the sudden change in the air pressure field, leading to the wind changing from northwest before CNY to southwest during CNY, promotes the accumulation of air pollutants from southwest neighbor areas of SJZ and greatly inhibits the diffusion and dilution of local pollutants. The photochemical regime of O formation is limited by volatile organic compounds (VOCs), suggesting that VOCs play an important role in O formation. With the developed O formation path tracing (OFPT) approach for O source apportionment, it has been found that highly reactive species, such as ethene, propene, toluene, and xylene, are key contributors to O production, resulting in the mean O production rate (P) during CNY being 3.7 times higher than that before and after CNY. Industrial combustion has been identified as the largest source of the P (2.6 ± 2.2 ppbv h), with the biggest increment (4.8 times) during CNY compared to the periods before and after CNY. Strict control measures in the industry should be implemented for O pollution control in SJZ. Our results also demonstrate that the OFPT approach, which accounts for the dynamic variations of atmospheric composition and meteorological conditions, is effective for O source apportionment and can also well capture the O production capacity of different sources compared with the maximum incremental reactivity (MIR) method.