Temporal dynamics of SO and NO pollution and contributions of driving forces in urban areas in China.

SO and NO pollution have significantly reduced the air quality in China in past decades. Haze and acid rain have negatively affected the health of animals, plants, and human beings. Documented studies have shown that air pollution is influenced by multiple socioeconomic driving forces. However, the relative contributions of these driving forces are not well understood. In this study, using the structural equation model (SEM), we quantified the contributing effects of various forces driving air pollution in 2015 in prefecture-level cities of China. Our results showed that there has been significant control of SO pollution in the past 20 years. The annual average SO concentration has dropped from 83 μg/m in 1996 to 21 μg/m in 2015, while the annual average NO concentration has increased from 47 μg/m in 1996 to 58 μg/m in 2015. We evaluated data on the annual average concentrations of SO, which in some cities may mask the differences of SO concentrations between different months. Hence, SO pollution should continue to be controlled in accordance with existing policies and regulations. However, we suggest that NO should become the new focus of air pollution prevention and treatment. The SEM results showed that industrial scale, city size, and residents' activities have a significant impact on NO pollution. Among these, industrial scale had the highest contribution. The findings from our study can provide a theoretical basis for the formulation of NO pollution control policy in China.