Stratospheric influence on surface ozone pollution in China.

Area of Science:

• Atmospheric Chemistry
• Environmental Science
• Air Quality Research

Background:

• Stratospheric intrusions to the surface (SITS) are a known cause of severe surface ozone (O3) pollution.
• Quantifying the national-scale, long-term impact of SITS on surface O3 has been challenging due to difficulties in measuring SITS frequency, duration, and intensity.

Purpose of the Study:

• To assess the national-scale impact of SITS events on surface ozone pollution in China from 2015 to 2022.
• To analyze the frequency, duration, and intensity of SITS events and their contribution to surface ozone levels.

Main Methods:

• Identification of 27,616 SITS events across China using dense surface measurements of O3 and carbon monoxide from 2015-2022.
• Analysis of SITS metrics (frequency, duration, intensity) and their correlation with surface O3 concentrations.

Main Results:

• SITS events are more frequent in high-elevation regions but more intense in plains.
• SITS enhances surface O3 by an average of 20 ppbv, contributing 30-45% to O3 during these events.
• SITS-induced O3 peaks in spring and autumn, with over 70% of warm-month SITS exacerbating pollution; a declining trend in SITS-induced O3 was observed from 2015-2022.

Conclusions:

• SITS significantly influences surface ozone levels across China, with distinct regional and seasonal patterns.
• Observed trends in SITS-induced ozone have implications for developing effective O3 mitigation strategies.
• Accurate measurement of SITS metrics is crucial for understanding and managing ozone pollution.