Ambient ozone pollution at a coal chemical industry city in the border of Loess Plateau and Mu Us Desert: characteristics, sensitivity analysis and control strategies.

In this study, ambient ozone (O) pollution characteristics and sensitivity analysis were carried out in Yulin, a city in the central area of the Loess Plateau during 2017 to 2019 summer. O concentrations increased for 2017 to 2019. Correlation and statistics analysis indicated high temperature (T > 25 °C, low relative humidity (RH < 60%), and low wind speed (WS < 3 m/s) were favorable for O formation and accumulation, and the O pollution days (MDA8 O > 160 µg/m) were predominantly observed when the wind was traveling from the easterly and southerly. O concentration in urban area of Yulin was higher than that in background. The pollution air masses from Fenwei Plain increase the level and duration of O pollution. In order to clarify the formation mechanism and source of O, online measurements of volatile organic compounds (VOCs) were conducted from 7 July to 10 August in 2019. The average of VOCs concentration was 26 ± 12 ppbv, and large amounts of alkenes followed by aromatics, characteristic pollutants of the coal chemical industry, were detected in the ambient air. To further measure the sensitivity, the observation-based model (OBM) simulation was conducted. Empirical Kinetic Modeling Approach (EKMA) plot and relative incremental reactivity (RIR) value indicated Yulin located on VOCs-limited regime. That implied a slight decrease of NO may increase O concentration. When the emission reduction ratio of anthropogenic VOCs/NO higher than 1:1, the O will decrease. O control strategies analysis shows that the O targets of 5% and 10% O concentration reductions are achievable through precursor control, but more effort is needed to reach the 30% and 40% reduction control targets.