Analysis of an ozone episode in the Greater Bay Area based on low-cost sensor network.

Tropospheric ozone (O 3) is an important air pollutant with a significant impact on human health, agricultural crops, ecosystems, and global warming. In the Greater Bay Area (GBA), O 3 pollution concentration has shown an increasing trend in the last decade. It has become crucial to gain a deeper understanding of the factors contributing to this phenomenon. This study deployed a sensor network with high spatial-temporal resolution measurement of O 3 and its key precursors in mid-November 2022 during a severe O 3 episode. The spatial-temporal characteristics and contributions of local generation and regional transport were analyzed based on clustering methodology. The regional distribution and possible sources were also discussed in combination with the NAQPMS model and the HYSPLIT model. The results indicated that the O 3 episode was dominated by local generation while regional transport contributed to an average of 20 ppb in the GBA region, under the influence of sea-land winds and low-level anticyclones. Guangzhou showed the most severe O 3 pollution, with a maximum hourly concentration near 120 ppb, followed by Zhongshan, Dongguan, etc. The O 3 pollution of Hong Kong and Macau showed faster dispersion and less accumulation during the daytime. The O 3 concentrations of Huizhou and Jiangmen were the lowest, but the nighttime O 3 accumulation was close to 40 ppb during the episode. The study demonstrated ad-hoc deployment of high-density sensor networks is an effective tool to study the formation and transport of O 3 during episodic days with synoptic approaches by ad-hoc high-density sensor network measurement and combination of modeling tools. • A high O 3 episode was monitored by high-density ad-hoc sensor network in the Greater Bay Area (GBA) in November 2016. • The spatial-temporal characteristics and the contributions of local formation and regional transport were focused on the analysis. • This O 3 episode was mainly impacted by local generation, with only around 20 % coming from regional contribution. • High concentrations of O 3 precursors emissions and the favorable meteorological conditions were the main factors contributing to O 3 pollution in GBA. [ABSTRACT FROM AUTHOR]