Characteristics of ozone pollution and the sensitivity to precursors during early summer in central plain, China.

In this study, we conducted an observation experiment from May 1 to June 30, 2018 in Zhengzhou, a major city in central China, where ground ozone (O3) pollution has become serious in recent years. The concentrations of O3 and its precursors, as well as H2O2 and meteorological data were obtained from the urban site (Yanchang, YC), suburban (Zhengzhou University, ZZU) and background sites (Ganglishuiku, GLSK). Result showed that the rates of O3 concentration exceeded Chinese National Air Quality Standard Grade II (93.3 ppbv) were 59.0%, 52.5%, and 55.7% at the above three sites with good consistency, respectively, indicating that O3 pollution is a regional problem in Zhengzhou. The daily peak O3 appeared at 15:00-16:00, which was opposite to VOCs, NOx, and CO and consistent with H2O2. The exhaustive statistical analysis of meteorological factors and chemical effects on O3 formation at YC was advanced. The high concentration of precursors, high temperature, low relative humidity, and moderately high wind speed together with the wind direction dominated by south and southeast wind contribute to urban O3 episodes in Zhengzhou. O3 formation analysis showed that reactive alkenes such as isoprene and cis-2-butene contributed most to O3 formation. The VOCs/NOx ratio and smog production model were used to determine O3-VOC-NOx sensitivity. The O3 formation in Zhengzhou during early summer was mainly under VOC-limited and transition regions alternately, which implies that the simultaneous emission reduction of alkenes and NOx is effective in reducing O3 pollution in Zhengzhou.