AC1

Abstract

The gas emission rates of ammonia (NH3) and methane (CH4) from an artificial source covering a surface area of 254 m2 were determined by inverse dispersion modelling (IDM) from point and line-integrated concentration measurements with closed and open-path analyzers. Eight controlled release experiments were conducted with different release rates ranging from 3.8 ± 0.21 to 17.4 ± 0.4 mg s-1 and from 30.7 ± 1.4 to 142.8 ± 2.9 mg s-1 for NH3 and CH4, respectively. The distance between the source and concentration measurement positions ranged from 15 m to 60 m. Our study consisted of more than 200 fluxes averaged intervals of 10 min or 15 min. The different releases cover a range of different climate conditions: cold (< 5 °C), temperate (< 13 °C) and warm (< 18 °C). As the average of all releases with all instrument types, the CH4 recovery rate QbLS/Q was 0.95 ± 0.08 (n = 19). There was much more variation in the recovery of NH3, with an average of 0.66 ± 0.15 (n = 10) for all the releases with the line-integrated system. However, with an improved sampling line placed close to the source an average recovery rate of 0.82 ± 0.05 (n = 3) was obtained for NH3. Under comparable conditions, the recovery rate obtained with an open-path analyzer was 0.91 ± 0.07 (n = 3). The effects of measurement distance, physical properties of the sampling line, and deposition are discussed.