Canada's National Environmental Indicator Series 2003

Sulphur dioxide emissions for eastern Canada (million tonnes)

Headline Indicators | Technical supplements | Data (in HTML)

Meter Calculation

Trend in total emissions from 1991 to 2000.

Indicator content	Supporting indicators
• Context • Indicators • Actions • Linkages • Challenges • Home	• Nitrogen oxide emissions in Canada • Trends in lake sulphate levels • Trends in lake acidity • Wet sulphate deposition • Wet nitrate deposition

Context

Acid rain is caused by pollutants such as sulphur dioxide and nitrogen oxides, which are emitted into the atmosphere primarily as a result of human activity. These pollutants are then chemically converted to sulphuric and nitric acids. Dilute forms of these acids fall to the Earth as rain, hail, drizzle, freezing rain, or snow (wet deposition) or are deposited as acid gas or particles (dry deposition). Eastern Canada receives the most acid deposition, posing a particular problem because of the generally poor ability of soils in this region to neutralize the acid. Acid deposition has many adverse effects on ecosystems. It can slow tree growth and kill trees by acidifying the soil from which the roots get their nutrients. It can also acidify sensitive lakes, rivers, and streams and cause metals to leach from surrounding soils into the water system. These conditions may impair aquatic ecosystems and alter species composition. As well, acid deposition deteriorates some building materials and poses a risk to some historic structures. Human exposure to particulate matter, including sulphate and acidic aerosols, may result in respiratory disorders.

Indicators

By 2000, Canada's sulphur dioxide emissions were 45% lower than the 1980 level and 20% below the national target set for 2000 onward. Similarly, eastern Canadian emissions of sulphur dioxide were approximately 30% below the cap for this part of the country. Canadian nitrogen oxide emissions, however, have increased slightly since the early 1980s and have remained at approximately 2 million tonnes since 1991. The area in eastern Canada annually receiving 20 kilograms or more of wet sulphate per hectare shrank considerably between the two periods 1980-1983 and 1996-2000. At the same time, the pattern of wet nitrate deposition changed very little. Of 152 lakes monitored for the effects of acid rain in Ontario (mostly in the Sudbury region), Quebec, and the Atlantic Region since the early 1980s, 41% have showed some improvement in acidity levels, 50% have showed no change, and 9% have become worse. Lake sulphate levels, which have shown considerably more improvement than acidity levels, respond to reductions in sulphur dioxide emissions. However, a time lag of many years is required before this translates into widespread regional improvements in lake acidity or alkalinity.

Nitrogen oxide emissions in Canada (million tonnes)

Technical supplements | Data (in HTML)

Trends in lake sulphate levels 1981-1997 (percentage of number of lakes studied)

Technical supplements | Data (in HTML)

Trends in lake acidity 1981-1997 (percentage of number of lakes studied)

Technical supplements | Data (in HTML)

Top

Actions

The Canadian Acid Rain Program, involving the governments of Canada and the seven eastern provinces, was established in 1985 with the goal of reducing sulphur dioxide emissions to 40% below 1980 levels by 1994. It was hoped that this action would reduce the deposition of sulphates in eastern Canada to below the 20 kilograms per hectare per year critical load for protecting moderately sensitive ecosystems. Due to improved understanding of the effects of acid rain, the critical load levels have since been re-evaluated and lowered, depending on the sensitivity of the area. Further action against acid rain depended on the cooperation of the United States, the source of about half the acid rain in eastern Canada. In 1991, Canada and the United States entered into the Canada-U.S. Air Quality Agreement to further reduce sulphur dioxide and nitrogen oxide emissions. Canada agreed to a permanent national limit of 3.2 million tonnes per year for sulphur dioxide emissions and a 10% reduction in projected nitrogen oxide emissions, both by 2000. In October 1998, federal, provincial, and territorial energy and environment ministers signed the Canadawide Acid Rain Strategy for Post 2000, aimed at creating new sulphur dioxide emission reduction targets for some provinces. Under the strategy, Ontario, Quebec, New Brunswick and Nova Scotia have committed to additional sulphur dioxide emission cuts of 50% beyond established caps. Several provinces are developing emission reduction targets for nitrogen oxides; at present, however, only Ontario has set an emission target.

Linkages

Acid rain is linked to energy consumption, particularly the combustion of fossil fuels. Transportation is a leading consumer of fossil fuels and a significant source of nitrogen oxide emissions, so improvements in fuel efficiency and composition and alternative fuel use can be expected to contribute to reductions in acid rain. Because nitrogen oxide emissions contribute to ground-level ozone, a key ingredient in smog, a reduction in these emissions would help to improve air quality. Acid rain affects aquatic and forest ecosystems, impairing ecosystem health and productivity and reducing biodiversity. Particulate sulphate in smog poses a risk to human health.

Wet sulphate deposition four-year mean (kilograms/hectare per year)

Technical supplements

Wet nitrate deposition four-year mean (kilograms/hectare per year)

Technical supplements

Challenges

The effects of acid rain on fish, wildlife, and plants are not well known. Lake sensitivity is proving greater than initially thought, and an estimated 800 000 square kilometres, extending from central Ontario through southern Quebec and across much of Atlantic Canada, will continue to receive sulphate deposition that impairs ecosystems, even after current Canadian and U.S. control programs are fully implemented. Scientists estimate that a further 75% reduction in sulphur dioxide emissions beyond current commitments is needed in targeted regions. Although sulphur dioxide has been well studied, nitrogen oxide deposition is still not well understood, highlighting the need for more monitoring and a review of critical loadings. If nitrate deposition continues at present levels, its contribution to acidification could eventually erode the benefits gained from the reductions in sulphur dioxide emissions. Acid deposition, lake temperature, and increased ultraviolet radiation exposure caused by stratospheric ozone depletion interact in complex ways to affect aquatic life, emphasizing the importance of taking action on multiple issues simultaneously.

Websites of interest

Environmental Signals: National Indicator Series 2003 Home

Introduction

Highlights

Meter description

Ecological life-support systems

Human health and well-being

Natural resources sustainability

Human activities

Conclusions

Technical supplements

PDF (2867kb)

View in print format

View in print format	Previous Top Next Indicator Home
	\| What's New \| About Us \| Your Environment \| Information/Publications \| Weather \| Home \|
	Français \| Contact Us \| Help \| Search \| Canada Site \|
	The Green Lane^TM, Environment Canada's World Wide Web site
	Last updated: 2005-04-11	Important Notices and Disclaimers