Project No: 16304924

Title: Dry deposition and source apportionment of atmospheric particulate organic nitrogen (ON): towards both water-soluble and water-insoluble ON

Principal Investigator: Prof. Xu YU

Co-Investigator: Prof. Tzung-May FU, Prof. Jianzhen YU

Abstract:

Atmospheric nitrogen (N) deposition serves as a significant pathway of N nutrient input to terrestrial and aquatic ecosystems. Inorganic nitrogen (IN, mainly nitrate and ammonium) deposition has been widely measured and evaluated for its environmental effects. In comparison, organic nitrogen (ON) deposition has been less monitored, although it is also demonstrated to be bioavailable. In particular, the water insoluble fraction of ON was rarely measured due to the technical challenge in quantifying this fraction of N. Recently we have made a method breakthrough in creating an instrument that is highly sensitive in determining aerosol N, providing the opportunity to accurately quantify ON and water insoluble ON (WION) quantities and estimate the deposition of N from atmospheric particle-bound ON. In this project, we propose to investigate the size distribution of aerosol IN, water-soluble ON (WSON), and WION collected from different atmospheric environments including urban, suburban/rural, and forest sites to obtain a dry N deposition budget from aerosol IN, WSON, and WION. In addition, urea and amino acids, which tend to be significant aerosol ON components, will also be determined. Information on the size distribution of aerosol N is essential to evaluate its dry deposition since the deposition velocity of particles is highly dependent on particle size. Aerosol collection from different environments is important considering that the sources of aerosol N in different locations might vary significantly. Sizesegregated aerosol samples will be collected by a Micro-Orifice Uniform Deposition Impactor (MOUDI sampler) at one urban and one suburban/rural air quality research supersite in Hong Kong, and one forest site in Guangdong Province over a year. After this, lab analyses will be conducted to measure nitrogen (IN, WSON, and WION), carbon, major ions, urea, amino acids, and organic source markers in all collected size-segregated samples. The deposition fluxes of aerosol N will be estimated with the inferential technique (deposition flux equals to N concentration multiplied by deposition velocity), in which the deposition velocity is calculated by the GEOS-Chem chemical transport model (CTM). The estimated results will be validated by comparing with measurements of dry N deposition. The sources of aerosol WSON and WION will be apportioned using the positive matrix factorization (PMF) receptor model with the comprehensively measured source-indicative species. These efforts will shed light on the significance of atmospheric particulate ON deposition and uncover sources of ON, supplying high-quality observation data for holistically modelling N cycling and evaluating the environmental consequences.