Monthly ammonia emissions from fertilizers in 12 Canadian Ecoregions

Emissions of ammonia (NH 3 ) from agriculture have been associated with transboundary atmospheric pollutant transport and potential human health problems. Specifically, NH 3 gas reacts in the atmosphere to form fine particles (PM 2.5 ) that are subject to long range transport and are considered to be associated with elevated risk of all-cause, lung-cancer and cardiopulmonary mortality. Agriculture is a major source of atmospheric NH 3 , and, of this, NH 3 from fertilizers is perhaps the most easily managed. Recent shifts in nitrogen (N) fertilizer materials and improved placement of urea and related fertilizers have resulted in marked changes in emissions. This paper describes a model developed to predict month-by-month emissions of fertilizer NH 3 , supported by surveys of farmers and fertilizer industry personnel that update information on fertilizer use. Compared with previous estimates by Environment Canada, the fraction of fertilizer N emitted as NH 3 is estimated to be 50% lower in the vast prairie regions (a very large reduction in total NH 3 ), and about 30% lower in eastern Canada. The estimate for 2006 is 1.0 × 10 8 kg NH 3 emitted directly from fertilizer application, 73% of this in the prairie region, and much of this in May. Overall, this indicates 6% of the applied fertilizer N is lost as NH 3 gas. Clearly, emission estimates are strongly dependent on up-to-date information about farm practices.