Characteristics of O3 Pollution and Key Precursors in Chengdu During Spring

To study the characteristics of O3 pollution and identify the key precursors for O3 formation in Chengdu in spring, O3 concentrations in April between 2016 and 2018 were analyzed, and on-line measurements of O3 and the precursors(VOCs and NOx) were also studied at an urban site. The results showed that the O3 pollution level in April increased year by year, and diurnal variations showed a unimodal distribution. When the ambient temperature was more than 20℃, the wind speed was between 1 and 1.5 m·s-1, and the relative humidity was less than 65%, the probability of O3 pollution occurring in April was more than 80%. In April 2018, the average concentrations of NOx and VOCs during O3 pollution days were 2.3-times and 2-times higher than non-pollution days. Furthermore, an OBM method was used to calculate the RIR values of different ozone precursors. This showed that the RIR values of anthropogenic VOCs, CO, biogenic VOCs, and NOx for ozone were 2.4, 0.87, 0.06, and -2.6, respectively, indicating that O3 formation in Chengdu was generally VOC-limited. The RIR values of the VOC species showed that m/p-xylene, ethylene, trans-2-butane, propylene, o-xylene, toluene, acetone, isoprene, isopentane, and n-butane were the key active VOC species of ozone formation.