The impact of Climate Change on the Western Pacific Subtropical High and the related ozone pollution in Shanghai, China

Luyu Chang,Jianming Xu,Xuexi Tie,Wei Gao

doi:10.1038/s41598-019-53103-7

Abstract

Severe ozone (O3) episodes occur frequently in Shanghai during late-summers. We define geopotential height averaged over the key area region (122.5°E-135°E, 27.5°N -35°N) at 500 hPa as a WPSH_SHO3 index which has high positive correlation with surface O3 concentration in Shanghai. In addition, the index has a significant long-term increasing trend during the recent 60 years. Analysis shows the meteorological conditions under the strong WPSH_SHO3 climate background (compared to the weak background) have several important anomalies: (1) A strong WPSH center occurs over the key area region. (2) The cloud cover is less, resulting in high solar radiation and low humidity, enhancing the photochemical reactions of O3. (3) The near-surface southwesterly winds are more frequent, enhancing the transport of upwind pollutants and O3 precursors from polluted regions to Shanghai and producing higher O3 chemical productions. This study suggests that the global climate change could lead to a stronger WPSH in the key region, enhancing ozone pollution in Shanghai. A global chemical/transport model (MOZART-4) is applied to show that the O3 concentrations can be 30 ppbv higher under a strong WPSH_SHO3 condition than a weak condition, indicating the important effect of the global climate change on local air pollution in Shanghai.

Highlights

With rapid industrialization and urbanization in recent decades, China has been experienced persistent and serious air pollution problem, causing important impacts on human health and ecological environment[1,2,3,4,5]
This study suggests that the global climate change could lead to a stronger West Pacific Subtropical High (WPSH) in the key region, enhancing ozone pollution in Shanghai
Ozone is produced by a complicated chemical process, which initializes by the photochemical reactions of ozone precursors, such as nitrogen oxides (NOX) and volatile organic carbons (VOCS)[11,12,13]

Summary

Introduction

With rapid industrialization and urbanization in recent decades, China has been experienced persistent and serious air pollution problem, causing important impacts on human health and ecological environment (like crop damages)[1,2,3,4,5]. Tie et al (2009) suggest that radiation, wind speed and wind direction are the most important meteorological factors for causing the variability of surface ozone concentrations in Shanghai. These factors directly affect the photochemical reaction, regional transportation and diffusion process of ozone. Most of the previous studies examine the relationship between the WPSH and ozone on a daily scale He et al.[29] focus on an short-term ozone pollution event in Shanghai and finds that ozone mixing ratios in summertime at Chongming (a surface site in the northeast of Shanghai) are often higher during the days when the center of the WPSH locates to the southeast of that site, with a weak intensity.

Methods

Findings

Discussion

Conclusion