Evidence of Rural and Suburban Sources of Urban Haze Formation in China: A Case Study From the Pearl River Delta Region

Abstract

Abstract Although particulate matter (PM)‐driven haze is a common phenomenon in many Chinese cities, studies on the sources of its key components, such as organic carbon (OC) and elemental carbon (EC), are poorly constrained. In this study, PM with aerodynamic diameters less than 10 (PM 10 ), 2.5 (PM 2.5 ), and 1 μm (PM 1 ) were collected at an urban site in the core city of the Pearl River Delta region in summer 2013. The average PM 10 , PM 2.5 , and PM 1 mass concentrations were 109 ± 28.4, 57.7 ± 15.0, and 50.9 ± 13.2 μg/m 3 , respectively. A PM‐driven haze bloom‐decay process was observed from 9 to 14 July and studied based on radiocarbon ( 14 C) and stable nitrogen isotope ( 15 N). The 14 C results revealed that 87% of EC and 53% of OC in PM 2.5 were derived from fossil sources on a typical summer day (9 July), while these values fell to 79% and 40% on 12 July and 76% and 29% on 13 July, respectively, due to the invasion of nonfossil‐enriched air masses from rural/suburban areas. In addition, a 15 N‐derived model showed that nonfossil sources contributed 5% of NH 3 on 9 July, which increased to about 80% on 12 and 13 July. However, the 15 N‐NO 3 − values were relatively stable, probably because of the large area of overlap in 15 N‐NO x from biomass burning and traffic exhaust. To our knowledge, this work is the first study to report both daily 14 C and 15 N signals in China and identify nonfossil sources from rural/suburban areas as triggers of summer haze.