Investigation of the Ultraviolet Photolysis Method for the Determination of Organic Nitrogen in Aerosol Samples

Abstract

The research objective was to adapt the ultraviolet (UV)-photolysis method to determine dissolved organic nitrogen (DON) in aqueous extracts of aerosol samples. DON was assumed to be the difference in total concentration of inorganic nitrogen forms before and after sample irradiation. Using a 2 2 factorial design the authors found that the optimal conversion of urea, amino acids (alanine, aspartic acid, glycine, and serine), and methylamine for a reactor temperature of 44°C occurred at pH 2.0 with a 24-hr irradiance period at concentrations Ͻ33 M of organic nitrogen. Different decomposition mechanisms were evident: the photolysis of amino acids and methylamine released mainly ammonium (NH 4 ϩ ), but urea released a near equimolar ratio of NH 4 ϩ and nitrate (NO 3 Ϫ ). The method was applied to measure DON in the extracts of aerosol samples from Tampa, FL, over a 32-day sampling period. Average dissolved inorganic (DIN) and DON concentrations in the particulate matter fraction PM 10 were 78.1 Ϯ 29.2 nmol-Nm Ϫ3 and 8.3 Ϯ 4.9 nmol-Nm Ϫ3 , respectively. The ratio between DON and total dissolved nitrogen ([TDN] ϭ DIN ϩ DON) was 10.1 Ϯ 5.7%, and the majority of the DON (79.1 Ϯ 18.2%) was found in the fine particulate matter (PM 2.5 ) fraction. The average concentrations of DIN and DON in the PM 2.5 fraction were 54.4 Ϯ 25.6 nmol-Nm Ϫ3 and 6.5 Ϯ 4.4 nmol-Nm Ϫ3 , respectively.

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

“…Differences in the molecular weight of ON compounds in the environment may reflect variations in sources [ Wedyan and Preston , 2008]. A wide range of ON compounds have been found in the atmosphere, including amino acids [ Wedyan and Preston , 2008; Coury and Dillner , 2009], urea [ Mace et al , 2003; Simoneit et al , 2004; Calderon et al , 2006], aza‐arenes [ Chen and Preston , 2004; Svabensky et al , 2009], nitrogenated soot [ Azambre et al , 2006], humic substances [ Samburova et al , 2005a, 2005b], and many more. Atmospheric aerosols contain up to 50% organic components by weight, and high molecular weight (HMW) materials contribute up to 30% of the total organic aerosol mass [ Samburova et al , 2005a].…”