Evaluation of a diffusive sampling method for the determination of atmospheric ammonia

Abstract

A diffusive sampling method is presented for the determination of atmospheric levels of ammonia based on the collection of ammonia at the phosphoric acid coated bottom of small glass vials and subsequent flow injection analysis of the trapped ammonium. In order to avoid effects of varying wind velocities on the sampling rate, the tube-type samplers are covered with a hydrophobic microporous membrane. The experimentally obtained uptake rate of the diffusive samplers (i.e. 7.8 ml min−1) is in excellent agreement with the theory. The analytical characteristics of the method with respect to sensitivity, selectivity, dynamic range, precision and practicability are evaluated in detail. As the detectability of the proposed method is related to both the mass collected during exposure and the mass sensitivity of the detection step, the role of microanalytical procedures in general, and significance of meticulous control of contamination in particular are discussed. Under optimum conditions the gas-phase detection limit achievable (in terms of time independent exposure dose value) is about 2.3×103 μg m−3 s−1, which permits measurements at low μg m−3-levels with a time resolution of a few hours. Application of the method to indoor and outdoor measurements proved its suitability for routine purposes.