Quantifying Pollution Events using Gas and Aerosol Observations via Flexible Receptor Framework over Urban Shanxi

Fine particular matter (PM) pollution still occurs frequently in China. Source apportionment of pollutants is a necessary prerequisite for proposing pollution prevention and control policies, and most studies have been conducted using receptor or air quality models. This work combined the composition of PM_2.5 and top-down gas pollutant emission (calculated by a Mass-Conserving inversion estimate framework based on daily TROPOMI NO₂ and CO columns and ground observation), and jointly analyzed the results using an Empirical Orthogonal Functions Principal Components Analysis (EOF) approach at 0.05°×0.05° over the Taiyuan Basin, an urban, economic, and industrial aera of Shanxi Province. This area presents an important study region wherein atmospheric pollution is relatively severe, with diverse pollutant sources and challenging topography. This method used is both flexible and demonstrates the details and correct days when the pollutant events happened. Various pollution sources have been detected, including dust and haze, emissions from industrial enterprises of different scales, and diverse combustion-related sources. In addition to standard source types, there are some more pronounced pollution events that can be found, such as during the Spring Festival of each year, there is a significant increase in CO/NO_x implying increased residential combustion sources. The same signal is even more obvious in rural areas during 2020 when the COVID-19 induced lockdowns occurred. At the same time in 2021, we demonstrate both further reduction of pollution from large enterprises and poorer control of small, scattered sources and residential combustion sources, including a further increase in CO/NO_x. The opposite result with a decrease in emission intensity and decrease CO/NO_x ratio in 2022 is observed, inferring a close relationship with strict control during the Winter Olympics. Diagnosis of pollution events by NO_x and CO Emissions calculated by Mass-Conserving Inversion method and compositions of PM_2.5 was successfully attempted, and it is hoped that it can form a basis for other rapidly changing regions found in topographically challenging regions throughout the Global South.