Analysis of the Spatial-Temporal Variation of the Surface Ozone Concentration and Its Associated Meteorological Factors in Changchun

Ozone (O-3) pollution has become one of the most challenging problems in China, and high O-3 concentrations have been a major air quality issue in Changchun. Based on continuous observation data of surface ozone concentrations from ten automatic air monitoring stations and meteorological data from the meteorological bureau in Changchun, the temporal and spatial variations of the O-3 concentration and its relationships with meteorological factors were analyzed by correlation analysis during the period of 2013-2017. The results showed the following: A single apex model of the annual mean O-3 concentrations of the daily maximum 8 h average (MDA8) was found from the data for 2013 to 2017 in Changchun, with the highest MDA8 O-3 concentrations in 2015 and a slight decline from then until 2017. The O-3 concentrations in the suburban areas and the south of Changchun were higher than those downtown and north of the city. The seasonal variation of O-3 concentrations was obvious, following the order summer > spring > autumn > winter, which was similar to the results of neighboring cities and provinces in Changchun. The days on which O-3 concentrations exceeded the standard were concentrated in summer and spring, and the total number of ozone excess days was 91 days; the maximum number of ozone excess days was in 2015. The O-3 concentration exceeded the standard in Changchun mainly in March-August, and its monthly mean value curve showed a bimodal type in which the highest values appeared in May and July, while the lowest values appeared in December. The diurnal pattern of ozone showed a single peak mode, and the peak value usually appeared at 14:00-16:00 while the minimum value appeared at 07:00-08:00. O-3 concentrations in Changchun and the six selected pollutants CO, NO, NO2, NOx, PM10, and PM2.5 were negatively correlated. Higher temperature is a necessary synoptic condition for ozone pollution in Changchun: when the temperature rose, O-3 concentrations increased significantly; further, O-3 concentrations were negatively correlated with relative humidity and atmospheric pressure and were positively correlated with temperature and solar radiation. The O-3 concentrations were highest when the wind scale approached 14-20 km/h and the wind direction was S. Combined with the research results in the surrounding areas of Changchun, it is indicated that there may be an ozone contribution from south of Changchun through long-range pollution transport and tropospheric subsidence.