资源环境科技发展态势分析平台

Atmospheric nitrogen is ubiquitous in the environment and hence plays an essential role in the nutrient balance over the whole ecosystem. However, its abundance and characteristics, particularly in the Himalayas, are not well understood. Therefore, to understand the abundance, sources, and seasonality of soluble nitrogenous species in the middle hills of the central Himalayas, aerosol samples were collected at Dhulikhel in Nepal from January to December 2018. The results of this study revealed that water-soluble inorganic nitrogen (WSIN) contributed the most to water-soluble total nitrogen with an abundance of ammonium nitrogen (NH₄⁺–N). Moreover, water-soluble organic nitrogen (WSON) contributed approximately 18% to aerosol total water-soluble nitrogen. The aerosol mass and WSIN species exhibited strong seasonality with considerably higher concentrations during dry periods and lower concentrations during the wet period. Furthermore, for dry periods, the HYSPLIT model revealed that nitrogen aerosols mainly originated from the Indo-Gangetic Plain region and were transported and deposited in the Himalayas through long-range atmospheric transport. The strong correlations of WSON with nssK⁺ (biomass burning) and nssCa²⁺ (crustal sources) and lack of a significant correlation with SO₄²⁻ indicated that primary sources are responsible for generating WSON rather than secondary processes in the Himalayas. The estimated dry deposition fluxes for NO₃⁻–N, NH₄⁺–N, and WSON were 1.56, 8.35, and 4.06 kg ha⁻¹ y⁻¹, respectively. This study also shows that increasing air contaminants and emissions over South Asia can enter the Himalayas and affect the human health and ecology of this fragile area.