Analysis of passive-sampler monitored atmospheric ammonia at 74 sites across southern Ontario, Canada

Author:

Yao X. H.,Zhang L.ORCID

Abstract

Abstract. Weekly/biweekly concentrations of atmospheric NH3 were collected using passive samplers at 74 sites across southern Ontario, Canada during the period from June 2006 to March 2007 with tens of sites running as early as March 2006. The annual average of NH3 (AAN) at all the sites across southwestern Ontario was over 1 µg m–3, a value that was recently proposed as the new critical level for protecting vegetation. High ANN values (3.6–6.1 µg m–3) were observed at eight sites located inside the intensive livestock production zones. The AAN values at the sites across southeastern Ontario were generally less than 1 µg m–3 and the values were less than 0.4 µg m–3 at non-agricultural sites. Regional transport from the southwest region to the southeast region was identified to be the main contributor to the observed NH3 at the southeastern non-agricultural sites. However, different transport mechanisms were proposed in different seasons. The transport of NH3 produced through bi-directional air-surface exchange along air mass trajectories was believed to be the main mechanism in the hot seasons while the transport of NH4NO3 produced at source locations followed by its evaporation at receptor sites was thought to be dominant in the cold seasons. A sharp increase in NH3 concentration was surprisingly observed at 20 out of the 74 sites during the coldest two weeks when ambient temperature was lower than −7 °C, and cannot be explained by known sources or with existing knowledge. Recently developed NH3 emission inventory for southern Ontario was also evaluated with the measurement data and emissions within two small zones were identified to be potentially underestimated.

Publisher

Copernicus GmbH

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