Evolution of summer surface ozone pollution patterns in China during 2015-2020

Surface ozone is one of the most severe air pollutants in China and is influenced by meteorological processes on multiple scales. By identifying the two dominant patterns of ozone pollution through Empirical Orthogonal Functions method, we show here that the widespread pollution processes in China may be closely related to highpressure anomaly in North China and low-pressure anomaly in the western Pacific, respectively. The positive time period of the first pattern (PC1P) extracts the distribution characteristics of the most severe periods of ozone pollution in summer time. It is physically linked to the high-pressure anomaly in North China centered on the Huanghuai Region, which eventually induced the high-temperature anomaly and low-humidity anomaly that enhanced the photochemical reactions to elevate the ozone levels. The spatial and temporal evolution of ozone pollution during this meteorological process shows a uniform pollution characteristic in the northern region and a higher increase in ozone concentration in the Huanghuai Region. The positive time period of the second pattern (PC2P) is associated with the variation of the low-pressure anomaly in the western Pacific. It indicates uniformly high ozone pollution in the south, especially in the Yangtze River Delta, the middle reaches of the Yangtze River (MYR) and the Pearl River Delta. Our results highlight that summer ozone pollution in eastern China is closely related to weather patterns. In addition, it is noteworthy that in the positive time period, the annual growth trends of Huanghuai Region in the first pattern (PC1P) and MYR in the second pattern (PC2P) are significantly higher than the growth trends of the megacity clusters, which requires the attention of relevant policy-making authorities.

Automated summary

By using the Empirical Orthogonal Functions method, this study identifies two dominant patterns of ozone pollution in China. It reveals a close relationship between widespread pollution processes in China and high-pressure and low-pressure anomalies in North China and the western Pacific, respectively. The first pattern is associated with a high-pressure anomaly in North China, leading to high-temperature and low-humidity anomalies that enhance photochemical reactions and elevate ozone levels. The second pattern is related to the low-pressure anomaly in the western Pacific, resulting in uniformly high ozone pollution in the south, especially in the Yangtze River Delta, the middle reaches of the Yangtze River, and the Pearl River Delta.