Decomposing Three Decades of Nitrogen Emissions in Canada

• Published in: Earth's future 2022-09, Vol.10 (9), p.n/a
• Main Authors: McCourt, S., MacDonald, G. K.
• Format: Article
• Language: English
• Subjects: Affluence; Agricultural wastes; Agriculture; Air pollution; Ammonia; Climate change; Crop production; decomposition analysis; Decomposition reactions; Economic sectors; Economics; Emission inventories; Emissions; Emissions control; Environmental impact; Environmental quality; Fossil fuels; Fuel combustion; leaching; Nitrogen; Nitrogen emissions; Nitrogen oxides emissions; nitrous oxide; Species; Statistical analysis; Wastewater
• ISSN: 2328-4277; 2328-4277
• DOI: 10.1029/2022EF002774

Reactive 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. Plain Language Summary Human activity releases different forms of reactive nitrogen (any form other than inert nitrogen gas) to the environment in several ways, including fertilizer use and burning fossil fuels. Excess reactive nitrogen contributes to air and water pollution as well as climate change. We therefore examined long‐term emission trends of multiple types and sources of reactive nitrogen across Canadian provinces between 1990 and 2017. We investigated what factors were driving changes in emissions, such as population and economic growth, by using an “index decomposition analysis.” Our results show that, while most reactive nitrogen emissions in the 1990s came from burning fossil fuels, agriculture became the dominant source of