Ambient concentrations of atmospheric ammonia, nitrogen dioxide and nitric acid across a rural-urban-agricultural transect in southern Ontario, Canada

The spatial and temporal variation in ambient atmospheric concentrations of gaseous reactive nitrogen (Nr) species (ammonia [NH\$\_\3\\$], nitrogen dioxide [NO\$\_\2\\$] and nitric acid [HNO\$\_\3\\$]) were measured at four sites (spanning a transect in land use types: intensive agricultural, urbanagricultural transition, urban, and rural background) across southern Ontario, Canada. Atmospheric concentrations were measured with the Willems badge diffusive passive sampler for one year (April 2010March 2011) at two-week exposure periods (biweekly integrated concentration measurements); dry deposition was estimated using the inferential method. There was high spatial and temporal variability in the ambient concentrations and estimated dry deposition of NH\$\_\3\\$, NO\$\_\2\\$ and HNO\$\_\3\\$ across the four study sites. Annual average Nr concentrations were greatest at the urban site owing to high NO\$\_\2\\$ concentrations (>25