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https://doi.org/10.5194/egusphere-2024-3471
https://doi.org/10.5194/egusphere-2024-3471
25 Nov 2024
 | 25 Nov 2024
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Rapid Increases of Ozone Concentrations over Tibetan Plateau Caused by Local and Non-Local Factors

Chenghao Xu, Jintai Lin, Hao Kong, Junli Jin, Lulu Chen, and Xiaobin Xu

Abstract. Changes in tropospheric ozone over the Tibetan Plateau (TP) profoundly affect the local ecosystems and human health. Yet previous studies on the TP ozone have focused on the background regions, with much less attention on the urban ozone. Here we quantify the ozone trends over the whole TP from 2015 to 2019 in the context of its long-term trends, with a focus on urban ozone. We use ozone measurements from 30 urban stations in 17 cities, the Waliguan baseline station, and four satellite products of tropospheric ozone. We further analyze the drivers of ozone trends through a combination of chemical transport model simulations, back-trajectory calculations, a bottom-up emission inventory, and a satellite-derived emission dataset of nitrogen oxides (NOx). We find a strong increase in deseasonalized urban ozone at the MEE stations from 2015 to 2019 (by 1.71 ppb yr-1). The urban ozone trend far exceeds the trend at Waliguan (by 0.26 ppb yr-1) and the TP average trend (by up to 0.08 ppb yr-1) derived from the four satellite products. Interannual variations in meteorology do not produce significant ozone trends over the TP. Non-local factors contribute positively to the urban ozone trends, due mainly to more frequent transport passing through the footprint layers (0–300 m above the ground) of non-local high-emission regions. Another important contributor to the urban ozone growth is the 26.5 % increase in local anthropogenic NOx emissions. Emission reductions in both the local and non-local source regions can help mitigate the rapid urban ozone growth over the plateau.

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Chenghao Xu, Jintai Lin, Hao Kong, Junli Jin, Lulu Chen, and Xiaobin Xu

Status: open (until 06 Jan 2025)

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Chenghao Xu, Jintai Lin, Hao Kong, Junli Jin, Lulu Chen, and Xiaobin Xu
Chenghao Xu, Jintai Lin, Hao Kong, Junli Jin, Lulu Chen, and Xiaobin Xu

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Short summary
We observed a strong increase in deseasonalized ozone at urban stations on the Tibetan Plateau from 2015 to 2019, far exceeding the trend at the baseline station Waliguan and the Tibet Plateau average trend of four tropospheric ozone products. By combining multiple datasets and modeling approaches, we identified the main contributing factors as more frequent transport passing through the lower layers of high-emission regions and the rapid increase in anthropogenic nitrogen oxide emissions.