Analysis of atmospheric ammonia and particulate ammonium by a sensitive fluorenscence method

Abstract

A sensitive fluorescence method for the analysis of atmospheric ammonia and particulate ammonium is described. The fluorescence of the ammonium-o-phthalaldehyde moiety is utilized in a flow injection system to effect a limit of detection of 204 ng m-3 (3σ) for atmospheric ammonia and 27 ng m3 (3σ) for particulate ammonium in 3-h air samples collected respectively on H3PO4-impregnated Whatman 41 and Teflon filters in a filter pack at 10 L min-1. The limit of detection for NH3may be reduced to 78 ng m-3 (3σ) by use of H3PO4-impregnated nylon filters. An intercomparison with the indophenol blue method is also described together with collection efficiencies on different impregnated filters. The analytical procedure is applicable also to ammonia collected by a denuder coated with phosphorous acid, with the detection limit of 450 ng m-3 (3σ) for a 3-h sample. A comparison of the filter-pack and denuder sampling methods indicated a small degree of evaporation of ammonium salt aerosol in the filter pack, leading to slight overestimation of ammonia concentrations. Ammonium aerosol concentrations measured by the two techniques were virtually identical since the superior inlet characteristics of the filter-pack sampler compensated for evaporative losses of ammonium salts. © 1988, American Chemical Society. All rights reserved.