Revealing the nonlinear responses of PM2.5 and O3 to VOC and NOx emissions from various sources in Shandong, China.

Fine particulate matter (PM2.5) and ozone (O3) are the primary air pollutants that degrade air quality in China. Reducing precursor emissions reasonably, volatile organic compound (VOC) and nitrogen oxides (NOx), are the keys to achieving effective improvement of air quality. To better tackle this challenge, we revealed the nonlinear response of PM2.5 and O3 concentrations to precursor reduction from various sources in Shandong, China using the Weather Research and Forecasting-Comprehensive Air Quality Model Extensions (WRF-CAMx) models and Empirical Kinetics Modeling Approach (EKMA). VOC reductions from all sources presented a positive effect in reducing PM2.5 and O3 concentrations in four seasons, while both levels showed a trend of first increasing and then decreasing as the proportion of NOx reduction increased, except in summer. Focusing on VOC emissions reduction first is critical for reducing PM2.5 concentrations and the long-term improvement in PM2.5 requires strengthening the deep emission reduction of NOx. The reduction ratios of VOC and NOx emissions from all sources with 3:1 in spring and autumn, and 1:2 in summer were more conducive to reducing O3 concentrations. The reasonable emission reduction ratios of VOCs and NOx from industry, power, transportation, and residential sources were also evaluated. For example, the reduction ratios of VOC and NOx emissions with 2:1 from industry and residential, and 1:2 from power and transportation are beneficial for decreasing PM2.5 concentrations. This study offers valuable insights for formulating rational and effective PM2.5 and O3 control strategies.