Nitrogen speciation and isotopic composition of aerosols collected at Himalayan forest (3326 m a.s.l.): Seasonality, sources and implications

Nitrogenous aerosols are ubiquitous in natural environment and thus play a vital role in the nutrient balance as well as Earth’s climate system. However, their abundance, sources, and deposition process are poorly understood, particularly in the fragile and eco-sensitive Himalayan and Tibetan Plateau (HTP) region. In this work, we report measurement of different forms of nitrogen and isotopic composition in aerosol samples collected from a forest site in the HTP (i.e. Southeast Tibet). Our results revealed that both, organic and inorganic nitrogen contribute almost equally with high abundance of ammonium nitrogen (NH4+-N) and water-insoluble organic nitrogen (WION) contributing ~40% each to aerosol total nitrogen (TN). A clear seasonality with concentrations of nitrogen species ~2 times higher in winter than in summer, however, no significant diurnal variation was found for any species. Nitrogen isotopic composition (δ15N) showed a similar seasonality to concentrations, with higher values in winter and lo...