The warming Tibetan Plateau improves winter air quality in the Sichuan Basin, China

Shuyu Zhao,Xuexi Tie,Zebin Wang,Tian Feng

doi:10.5194/acp-20-14873-2020

Abstract

Abstract. Impacts of global climate change on the occurrence and development of air pollution have attracted more attention. This study investigates impacts of the warming Tibetan Plateau on air quality in the Sichuan Basin. Meteorological observations and ERA-Interim reanalysis data reveal that the plateau has been rapidly warming during the last 40 years (1979–2017), particularly in winter when the warming rate is approximately twice as much as the annual warming rate. Since 2013, the winter temperature over the plateau has even risen by 2 ∘C. Here we use the WRF-Chem model to lay emphasis on the impact of the 2 ∘C warming on air quality in the basin. The model results show that the 2 ∘C warming causes an enhanced easterly wind, an increase in the planetary boundary layer height (PBLH) and a decrease in the relative humidity (RH) in the basin. Enhanced easterly wind increases PM2.5 transport from the basin to the plateau. The elevated PBLH strengthens vertical diffusion of PM2.5, while the decreased RH significantly reduces secondary aerosol formation. Overall, PM2.5 concentration is reduced by 17.5 % (∼25.1 µg m−3), of which the reduction in primary and secondary aerosols is 5.4 and 19.7 µg m−3, respectively. These results reveal that the recent warming plateau has improved air quality in the basin, to a certain extent mitigating the air pollution therein. Nevertheless, the climate system is particularly complicated, and more studies are needed to demonstrate the impact of climate change on air quality in the downstream regions as the plateau is likely to continue warming. Highlights The Tibetan Plateau is rapidly warming, and the temperature has risen by 2 ∘C from 2013 to 2017. A warming plateau leads to an enhanced easterly wind, an increased PBLH and a decreased RH in the Sichuan Basin. The 2 ∘C warming significantly reduces PM2.5 concentration in the basin by 25.1 µg m−3, of which secondary aerosol is 19.7 µg m−3.

Highlights

The Tibetan Plateau is known as the third pole because of its high altitude and large area
To better simulate the atmospheric circulation over the plateau and its impact on air quality in the Sichuan Basin, we set the central location of the model domain at 32.2◦ N, 95.0◦ E over the plateau, and the simulation domain covers the Tibetan Plateau and the Sichuan Basin (Fig. 1)
The index of agreement (IOA) of air temperature and relative humidity (RH) are 0.85 and 0.79, respectively (Fig. S4a and b in the Supplement), suggesting that the model captures the diurnal cycle of temperature and the variability of RH well

Summary

Introduction

The Tibetan Plateau is known as the third pole because of its high altitude and large area. Xu et al (2017) suggest that the climate warming anomaly in the lower and middle troposphere over the continent around the Yangtze River Delta has led to more haze days in winter during recent decades Another opinion suggests that climate change in the past 2 decades has been favorable for air pollution dispersion in northern China via enhancing mid-latitude cold surges in winter (Zhao et al, 2018). The foggy weather, southwest vortex and low-level shear line over the basin are closely associated with the plateau (Zhu et al, 2000) These changes in weather conditions induced by the plateau undoubtedly affect the development and dispersion of air pollution in the basin, because the huge terrain can trigger a thermodynamic forcing, which is of great importance for weather conditions in the surrounding regions (Bei et al, 2016; 2017; Zhao et al, 2015). We calculate the effect of the relationship on air quality in the basin

Observations

Model configuration and experiments

The warming Tibetan Plateau in the last 4 decades

Model validation

Conclusions