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

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 (PM10), 2.5 (PM2.5), and 1 μm (PM1) were collected at an urban site in the core city of the Pearl River Delta region in summer 2013. The average PM10, PM2.5, and PM1 mass concentrations were 109 ± 28.4, 57.7 ± 15.0, and 50.9 ± 13.2 μg/m3, respectively. A PM‐driven haze bloom‐decay process was observed from 9 to 14 July and studied based on radiocarbon (14C) and stable nitrogen isotope (15N). The 14C results revealed that 87% of EC and 53% of OC in PM2.5 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 15N‐derived model showed that nonfossil sources contributed 5% of NH3 on 9 July, which increased to about 80% on 12 and 13 July. However, the 15N‐NO3− values were relatively stable, probably because of the large area of overlap in 15N‐NOx from biomass burning and traffic exhaust. To our knowledge, this work is the first study to report both daily 14C and 15N signals in China and identify nonfossil sources from rural/suburban areas as triggers of summer haze.

Fossil and Non-fossil Fuel Sources of Organic and Elemental Carbonaceous Aerosol in Beijing, Shanghai, and Guangzhou: Seasonal Carbon Source Variation

“…Table 3 lists the 14 C results from PM 2.5 in three cities during 2012-2014 published in previous studies. Compared with previous studies, the seasonal variations of carbon sources in the three cities were highly consistent with previous observations conducted in different seasons (Liu et al, 2014(Liu et al, , 2016Liu et al, 2017c;Liu et al, 2018). The carbon sources from OC and EC of high-PM 2.5 samples and low-PM 2.5 samples from each season were nearly consistent in this study (Fig.…”

“…Due to the limited data, these results might not reflect the true source variation over a 1-year period. For example, carbon source dynamics of carbonaceous aerosols during haze formation in Guangzhou indicated that there are significant differences in the carbon sources of high-PM 2.5 samples and low-PM 2.5 samples during spring and summer (Liu et al, 2016(Liu et al, , 2018. In addition, carbon sources of the high-PM 2.5 samples in Guangzhou winter also differ from each other (Liu et al, 2014).…”

“…Beijing, Shanghai, and Guangzhou are representative megacities located in different climatic regions (the Beijing-Tianjin-Hebei region, Yangtze River Delta region, and Pearl River Delta region, respectively) that suffer from severe air pollution due to rapid expansion of industry and transportation, sharply increasing the population and thus the demand for FFs (Ling et al, 2011;Feng et al, 2015;Zhang et al, 2015a;Ding et al, 2017;Wei et al, 2017). Although source apportionment of carbonaceous aerosols has been conducted in some cities (Liu et al, 2014;Elser et al, 2016;Liu et al, 2017c;Wei et al, 2017;Liu et al, 2018), the results are segmented and generally pertain to haze events during winter. In our previous research, several independent case studies were conducted in Guangzhou.…”

“…During spring (15 Mar-15 Apr 2013), FF sources majorly contributed to total carbonaceous aerosols (54 ± 5%) (Liu et al, 2016). During summer (25 Jun-15 Jul 2013), 87% of EC and 53% of OC in PM 2.5 were derived from FF sources on a typical summer day, but these values dropped significantly with invasion of NF-enriched air masses from rural and suburban areas (Liu et al, 2018). During autumn (15 Oct-15 Nov 2013), NF was the predominant source of total carbon (TC; average = 65 ± 7%) (Liu et al, 2017a).…”

The regional nature of nitrate-dominant haze pollution during autumn over the Pearl River Delta area

“…Furthermore, the accumulation of traffic emissions has frequently been reported as a primary cause of pollution events in urban areas of the PRD (Qin et al 2017). In contrast, biomass burning, which is extremely rare at most times of the year, nonetheless plays more important roles in particle concentrations and pollution events in the PRD in harvest season (Zhang et al 2010;Tao et al 2014;Wang et al 2016;Liu et al 2018;Zhou et al 2018). Influenced by multiple atmospheric conditions such as relative humidity and temperature, secondary processes, mainly generating sulfates, nitrates, and secondary organic aerosols, also substantially contribute to ambient aerosol concentrations (Hua et al 2015;.…”