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The influence of gas-to-particle conversion on measurements of ammonia exchange over forest

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Author: Oss, R. van · Duyzer, J. · Wyers, P.
Type:article
Date:1998
Publisher: Elsevier Sci Ltd
Place: Exeter, United Kingdom
Institution: TNO Milieu, Energie en Procesinnovatie
Source:Sutton, M.A.Lee, D.S.Dollard, G.J.Fowler, D., Proceedings of the 1995 International Conference on Atmospheric Ammonia: Emissions, Deposition and Environmental Impacts, 2 October 1995 through 4 October 1995, Culham, UK, Conference code: 48535, 3, 32, 465-471
series:
Atmospheric Environment
Identifier: 234367
doi: DOI:10.1016/S1352-2310(97)00280-X
Keywords: Perception · Ammonium nitrate · Apparent emission · Chemistry modelling · Flux reversal · Nitric acid · Ammonia · Atmospheric aerosols · Atmospheric chemistry · Atmospheric composition · Evaporation · Mathematical models · Nitric acid · Particulate emissions · Plants (botany) · Ammonium nitrate · Air pollution

Abstract

Measurements of vertical gradients of ammonium nitrate aerosol and NH3 are used together with HNO3 concentrations to study the influence of gas-to-particle conversion (gtpc) on surface exchange processes above a forest. A numerical model of surface exchange, in which a description of gtpc was incorporated, is used to interpret the measurements. The model suggests that evaporation of particulate NH4NO3 during the day can lead to situations where upward fluxes of NH3 and HNO3 are observed above the forest, while both gases are deposited at the surface. At the same time, this mechanism provides an explanation for the observed aerosol deposition fluxes, which we found to be larger than theoretically possible. Further support for our hypothesis was found in the analysis of a larger data set which showed that in many cases sub-equilibrium concentrations of NH3 and HNO3 (which may lead to evaporation of NH4NO3 aerosol) coincide with apparent emission fluxes of NH3.