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Nitrous Oxide and Oxides of Nitrogen Nitrous oxide (N20) is one of several forms of oxides of nitrogen (NOx) which results from combustion of fossil fuels. Table 9 indicates N2O emissions for Canada. Those from anthropogenic sources are small compared to natural releases. Most NOx are in the form of nitric oxide (NO), with about 1% of NOx emittcd from stationary sources as N 0 NO contributes to ground-level smog which can have negative impacts on human health. As indicated earlier, natural gas contains no nitrogen so does not by itself produce N2O, but during combustion nitrogen from air is converted into NOx. While the figures shown for natural gas in Table 9 -6 would change slightly as a result of the CGA'S updated Figures for I 990, the table is sufficiently accurate to illustrate that N2O from the entire natural gas cycle in Canada is under 2% of total Canadian N20 anthropogenic emissions. Global N20, in turn, is 5% of anthropogenic greenhouse gas emissions, on a carbon dioxide equivalent basis.NOx emissions from the full natural gas cycle, including end use, totalled 330 kilotonnes in 1990 (Table 4). Environment Canada's 1990 Emissions Inventory indicated that total NOx production in 1990 was 2062 Kt (Canadian Emissions Inventory of Criteria Air Contaminants (1990), EPS 5/AP/7E February 1996). In the Environment Canada report, vehicles (43%) and electricity generation from coal and oil (12%) are the largest sector components of NOx emissions.
Conclusions The production, processing, transmission, distribution and use of natural gas causes emissions of greenhouse gases — carbon dioxide, methane, and nitrous oxide — as well as oxides of nitrogen which contribute to formation of smog. However, the volume of emissions from natural gas is small, particularly in relation to the benefits from the efficient use of natural gas.The principal greenhouse gas emitted from the natural gas cyde is carbon dioxide. Two-thirds of this gas results from end use combustion at the burner tip. The total quantity of carbon dioxide from natural gas in Canada (industry and end use combined) in 1995 was 148,343 kilotonnes. This is about 30% of all carbon dioxide emissions from anthropogenie Canadian sources and 0.7% of the total global emissions of carbon dioxide (Table 1). It is consistent with recognition that natural gas provides 31% of Canada’s primary energy. As determined from the most recent studies, the 1995 emissions of carbon dioxide from natural gas are about 12% lower than earlier estimates from Natural Resources Canada and Environment Canada publications. Emissions of methane from the natural gas cycle are of worldwide concern because methane is considered to have a much greater global warming potential than carbon dioxide. Natural gas, 95% methane in Canada, can be considered a major source of this greenhouse gas. Total methane emissions from the natural gas cycle in Canada for 1995 were determined to be 1143 kilotonnes, almost all of which was from natural gas industry operations. The 1990 emissions of methane from natural gas operations in Canada were estimated by Environment Canada (Table 6) to be less than the methane emissions from animals and animal waste, and about two-thirds of the methane released from landfills.Table 6 1990 Methane Emissions (selected items)
Total All Sources
Methane Emissions and Opportunities for Control, Sept. 90, 88 to 90 data.
estimated. (d) Total shown is consensus estimate from EPA to ± 100 Kr.Table 7 Methane Emissions as % of Marketable Natural Gas Production
Figures from Radian study MMscm/yr is million standard cubic metres per year; scm is standard cubic metres. [)espite its higher global warming potential, 1995 Canadian natural gas methane emissions amounted to 13.8% of all greenhouse gas emissions from natural gas, on a carbon dioxide equivalent basis (Table 5). This is because the volume of methane emissions is considerably less than the volume of carbon dioxide resulting primarily from natural gas combustion. The CGA study indicated |
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