Spatiotemporal characterization and regional contributions of O3 and NO2: An investigation of two years of monitoring data in Henan, China.

To investigate the characteristics of ground level ozone (O3) for Henan Province, the ambient air quality monitoring data of 2015 and 2016 were analyzed. The result showed that the 8 h-max-O3 concentrations displayed a distinct seasonality, where the maximum and minimum values, averaging 140.41, 54.19 μg/m3, occurred in summer and winter, respectively. There is a significant correlation between meteorological factors and O3 concentration. The Voronoi neighborhood averaging analysis indicated that O3, temperature, and ultraviolet radiation in Henan province were decreased from northwest to southeast, while relative humidity and precipitation displayed the opposite trend. Besides meteorological factors, the chemical processes play an essential role in ozone formation. Reactions of NO, NO2 and O3 form a closed system, and the partitioning point of the OX-component (O3 + NO2) was at 40 and 80 μg/m3 for nitrogen oxide (NOX) in winter and summer, respectively, with NO2 dominating at higher NOx pollution and O3 being the major component at lower levels. The relationship between oxidant (OX = O3+NO2) and NOx concentrations were evaluated to understand the regional and local contribution of OX. It showed that high regional contribution occurred in the spring, whereas the highest local contribution lead to the summer peak of O3 observed in Zhengzhou. This present study reveals important environment impacts from the photochemical process and the meteorological conditions in the region with better understanding on the O3 characterization.