The spatiotemporal variation and key factors of SO₂ in 336 cities across China

Sulfur dioxide (SO₂) pollution has become a severe concern in China, which is closely linked to human health. Here, the officially released data of SO₂ in the 336 prefecture-level cities in 2015 across the whole China were firstly collected to understand the spatiotemporal variation of the SO₂ concentration. At a national scale, the SO₂ concentration was highest in winter, followed by one in spring and autumn, and the lowest one in summer. The spatial econometric models, the geographical weight regression (GWR) model, and the generalized additive model (GAM) were then applied to examine the interaction of socioeconomic factors (e.g., gross domestic production (GDP)) and the meteorological indicators (e.g., precipitation) on the SO₂ level in the 336 cities over China. The results suggested that the SO₂ concentration was negatively associated with GDP, precipitation, wind speed (WS), and relative humidity (RH), while it showed the positive relationship with gross industrial production (GIP), population, and temperature. GDP in the Jiangsu and Zhejiang provinces presented the negative correlations with the SO₂ concentration, suggesting the adaptation of industrial structure has occurred in the developed region. The positive effect of GIP on the SO₂ concentration increased from West China to North China because many energy-intensive industries were concentrated on North China. The GAM analysis suggested that the combined effects of the adverse meteorological condition (e.g., RH = 50–60%) and the higher GIP contributed to severe SO₂ pollution. Therefore, the SO₂ emission from the heavy industries especially in NCP should be reduced and many energy-intensive plants in the region should be moved to some cities with favorable diffusion condition.