Exploring PM2.5 pollution in a representative Northern Chinese county: Insights for air quality management

Counties have served as fundamental administrative units in China since the Qin Dynasty (221-206 BC), a tradition that continues today with hundreds of millions of residents living in county-level cities. Unlike higher- level cities such as municipalities and prefecture-level cities, counties differ significantly in size, development level, and development model, which can lead to distinct PM2.5 pollution patterns. This study focuses on Yishui County, a representative county in northern China, to explore its PM2.5 pollution characteristics and source contributions over a one-year period. Furthermore, the study compares Yishui's pollution profile with those of higher-level cities to provide insights into the relationship between development models and air quality. The annual average PM2.5 concentration in Yishui was 67.8 mu g/m3. Source apportionment using Discretized Normalized Positive Matrix Factorization (DN-PMF) identified six primary sources: dust (28.3%), secondary inorganic aerosols and residential coal combustion (SIA/RCC, 25.7%), vehicle emissions (24.6%), coal combustion (10.3%), industrial processes (9.1%), and biomass burning (2.0%). Dust was the dominant contributor, a notable divergence from patterns in higher-level cities. This disparity is likely attributed to Yishui's heavy reliance on real estate development as a primary economic driver, which significantly increases construction dust emissions. These results emphasize the impact of urbanization and economic structure on PM2.5 pollution, indicating that other counties in northern China undergoing similar development stages may face comparable air quality challenges.