Size fractionation and molecular composition of water-soluble inorganic and organic nitrogen in aerosols of a coastal environment

Abstract

This study reports the first high and low molecular weight measurements of dissolved organic nitrogen (DON) in size-fractionated atmospheric particles. The variations in concentration of nitrogen species corresponded to varying sources and weather conditions. The results indicate that continental, local, and marine origins are the key factors controlling the particle size distribution of inorganic and organic nitrogen species. For dissolved inorganic nitrogen and DON, relatively high concentrations and fine-mode particle (particle diameter <1 μm) enrichment were significantly affected by continental and locally derived sources, which were mainly attributable to anthropogenic activities. However, the coarse/fine ratios indicate that DON was derived from a coarse particle (particle diameter >1 μm) source that may be sea salt particles. To investigate the possible sources of DON, an ultrafiltration method was used to separate DON into high (HMW) and low (LMW) molecular weight categories. The results indicate that HMW-DON and LMW-DON contributed 57 ± 9% and 43 ± 9%, respectively, to the total DON concentration. Correlations and positive matrix factorization analysis of HMW-DON and LMW-DON levels with major and non-sea-salt ions indicated that HMW-DON and LMW-DON in coarse particles may be generated from continental soil dust and sea spray, respectively, whereas, in fine particles, DON may originate from aerosols derived from combustion processes. The annual fluxes of HMW-DON and LMW-DON were estimated to be 11.0 and 11.3 mmol m−2 yr−1, respectively. Consequently, the inputs of HMW-DON and LMW-DON appear to make equal contributions to DON in aerosols over the studied coastal area.