Fine particulate pollution driven by nitrate in the moisture urban atmospheric environment in the Pearl River Delta region of south China.

To identify potential sources of fine particles (PM, with aerodynamic diameter (D) ≤ 2.5 μm) in urban Dongguan of south China, a comprehensive campaign was carried out in the whole 2019. Hourly PM and its dominant chemical components including organic carbon (OC), elemental carbon (EC), water-soluble inorganic ions (WSIIs) and thirteen elements were measured using online instruments. Gaseous pollutants including NH, HNO, NO, NO and O and meteorological parameters were also synchronously measured. PM was dominated by carbonaceous aerosols in summer and by WSIIs in the other seasons. PM and its dominant chemical components mostly peaked around noon (10:00-14:00 LST). Furthermore, high PM levels during the daytime were closely related with the increased NO levels. The high mass concentrations of NO in urban Dongguan during the daytime were likely related with regional transport of NO from suburban Dongguan, which was originated from the reaction between NO and O under the moisture condition during the nighttime. Seven major source factors for PM including secondary sulfate, ship emission, traffic emission, secondary nitrate, industrial processes, soil dust and coal combustion were identified by positive matrix factorization (PMF) analysis, which contributed 26 ± 14%, 16 ± 16%, 16 ± 10%, 14 ± 11%, 12 ± 11%, 8 ± 6% and 8 ± 6%, respectively, to annual PM mass concentration. Although secondary sulfate contributed much more than secondary nitrate to PM on annual basis, the latter exceeded the former source factor when daily PM mass concentration was higher than 60 μg m, indicating the critical role nitrate played in PM episode events.