Spatial and temporal concentration of ambient atmospheric ammonia in southern Ontario, Canada

摘要

The spatial and temporal variability in ambient atmospheric ammonia (NH_3) concentration was evaluated across southern Ontario, Canada, during the period August 2007-December 2010 using the Willems badge diffusive passive sampler (under a two week measurement frequency). A network of 11 monitoring sites was established across a land use transect reflecting low to high agricultural activity based on agricultural statistics and reported emissions. Ambient two-week average NH_3 concentrations were lowest during the winter and highest during the spring consistent with seasonal agricultural activity; the largest range in observed NH_3 concentrations at an individual site was 0.4-15.8 μg m~(-3) (winter-spring; intensive agricultural site). Annual average ambient NH_3 concentrations ranged from 0.3 μg m~(-3) at low agricultural intensity (background) sites (n = 4) to 2.8 μg m~(-3) at intensive agricultural sites (n = 3); the largest range in biweekly NH_3 concentrations across the 11 monitoring sites (during one exposure period) was ～16 μg m~(-3) (spring season). Annual average concentrations ranged from 0.1 μg m~(-3) to 3.0 μg m~(-3) across sites; nonetheless, there was strong temporal coherence among all sites suggesting a common regional 'footprint' from agricultural emissions. Regional agricultural statistics correlated well with NH3 concentrations, cattle and pig numbers being the best predictors of annual average NH_3 concentrations across southern Ontario.