Decomposing Three Decades of Nitrogen Emissions in Canada

Abstract

AbstractReactive nitrogen (Nr) emissions arise from multiple economic sectors, each creating distinct Nr species and impacts on environmental quality. In Canada, the relative contribution of different Nr species to total Nr emissions varies considerably across provinces, yet these Nr species are often studied separately, making comparison difficult. Here, we synthesize data from national emission inventories, as well as agricultural and wastewater statistics, to estimate total and per capita Nr emissions trends across Canada's 10 provinces over three decades between 1990 and 2017. We classified emissions by 4 main species of Nr, 3 source sectors, and 13 subsectors. Nr emissions peaked around 2000 followed by reductions both nationally and across almost all provinces. Agriculture replaced fossil fuel combustion as the largest source of Nr emissions after 2008, coinciding with regulatory interventions that aimed to reduce NOx emissions from transportation, while NH3 from crop production increased in several provinces. Using an index decomposition analysis, we further assessed the socioeconomic drivers of Nr emissions changes, including the roles of emission intensity (Nr emissions per unit of economic output), affluence, population, and structural changes in the economy. Reduced emission intensity (an aggregate indicator of technology and policy changes) counteracted some of the effects of affluence and population as positive drivers of Nr emissions. Economic structural changes had both large negative and positive effects on Nr emissions. Our results underscore the importance of continued reductions in emissions intensity as well as shifting economies toward less Nr intensive sectors to further decouple affluence from Nr pollution.