Fractal analysis of impact of PM on surface O sensitivity regime based on field observations.

Properties of PM that can change aerosol chemistry and photolysis rates have great impacts on O sensitivity regime, further affecting the production rate of surface O. However, responses of O sensitivity regime to changes in PM levels are difficult to be accurately determined, due to the complexity and nonlinearity of atmospheric chemistry. Here, based on long-term time series (2016-2020) of air quality variables in north and south Taiwan, fractal analysis along with Pearson correlation analysis are used to directly reveal the impacts of PM on O sensitivity regime in real atmosphere, by capturing the nonlinear dynamic relations among air pollutants. Great regional and seasonal difference in impacts of PM on O sensitivity regime may be ascribed to meteorological factors, PM components and levels of SO, NO, NO, etc. For north Taiwan, increased PM level can enhance the sensitivity of O formation to VOC in spring and summer, whereas the opposite effect can be observed in winter. But for south Taiwan, the influence of PM on O sensitivity regime is not statistically significant, excluding spring. Furthermore, feasibility and availability of fractal analysis is tested by simulations with Empirical Kinetics Modeling Approach (EKMA). The results demonstrate the capability of fractal analysis to identify the impacts of PM on O sensitivity regime in real atmosphere, which can provide suggestions for PM-O coordinated control strategies in regions suffering combined air pollution.