Ozone production sensitivity trends analysis of Seoul using air quality monitoring stations measurements

Abstract

Many national and regional levels of efforts to control the abundance of ozone (O3) near the surface have been invested over the last few decades as understandings on tropospheric O3 deepens. However, the effectiveness of these efforts has been frequently questioned because the O3 concentration has not been reduced as anticipated, even though the precursors are under control. The main cause of difficulties in O3 control is to be in the limitations in characterizing O3 production sensitivity over the area of interest, which requires state-of-the-art researches in depth. Thus, not only the region with insufficient research resources, like Korea, but also for the season when these thorough research efforts lacked, likely struggles with the O3 issue. In this study, we introduce an efficient method to assess the O3 production sensitivity based on the measurements from the routine monitoring stations of air quality (O3, NO2, CO, SO2, PM10, and PM2.5) and synoptic weather parameters (temperature, precipitation, relative humidity and etc.). We investigate the ozone production rate, P(O3), via a proxy of time rated changes of ozone concentration as a function of NOx from 2001 to 2017, over Seoul, Korea. As a result, P(O3) of Seoul has been increasing, 33 % and 46 % for urban and roadside monitoring stations; urban sites generally have higher P(O3) and lower NO2 concentration than those in roadside sites; urban (roadside) stations have medians of 7.0 (3.6) ppb hr-1 for P(O3) and 36.1 (61.1) ppb for NO2. To evaluate the O3 production sensitivity, OPS, we introduce a new method using the day of week difference in P(O3) with respect to the NO2 concentration under the constant O3 loss condition. As a result, both urban and roadside sites show NOx-saturate characteristics since 2001. Further analysis including the reason of the increase in P(O3) as well as better validation for proxies needs to be carried out for making the best use of this research in guiding the air quality improvement policies.