Abstract:

The formation, transformation, transportation, and deposition of inorganic and organic nitrogen within fine particles is critical in the nitrogen cycle. To understand the concentrations, compositions, and seasonal variations of the nitrogen-containing components within submicron particles (PM$_{1}$) in Shanghai, PM$_{1}$ samples were collected in Shanghai during 2017—2018 using a high-volume sampler. The concentrations of water-soluble ions and water-soluble organic nitrogen (WSON) were measured using ion chromatography and UV/Vis photometry. The annual average concentrations of NH$_{4}^{+}$-N, NO$_{3}^{-}$-N, and WSON within PM$_{1}$ in Shanghai were 1.79, 0.97, and 0.41 μg/m³ respectively. NH$_{4}^{+}$-N showed the highest contribution (56 %) to the water-soluble total nitrogen (WSTN), followed by NO$_{3}^{-}$-N (31 %), while the annual contribution of WSON to WSTN was 13 %. The concentrations of the nitrogen-containing components within PM$_{1}$ in Shanghai were highest in winter and lowest in summer. However, the contributions of NH$_{4}^{+}$-N, NO$_{3}^{-}$-N, and WSON to WSTN differed. The contribution of NH$_{4}^{+}$-N to WSTN showed a small seasonal variation, and a distinct trend of higher in winter (38 %) and lower in summer (18 %) was observed for the contribution of NO$_{3}^{-}$-N, while the contribution of WSON to WSTN was the highest in summer (22 %) and lowest in winter (8 %). Positive matrix factorisation (PMF) showed that secondary formation and the burning of biomass contributed 48 % of the WSON within PM$_{1}$ in Shanghai, with coal combustion contributing 11 %, secondary formation from biogenic volatile organic compounds 20 %, and emissions from kitchens and vehicles 21 %. The sources of WSON varied significantly according to season.

Key words: submicron particles, nitrogen-containing components, seasonal variation, source distribution