Canadians are becoming increasingly aware of and concerned about the future health of the environment, and in particular the quality of the air. Although some hazardous contaminants in the air, such as lead, have declined in recent years, others remain and continue to become more problematic. Canada is a large industrialized country, responsible for the release of a variety of pollutants into the air. In addition to this, certain areas of Canada are located downwind of industrialized areas of the U.S., with resultant higher levels of pollution. Despite this, Canadians enjoy good air quality when compared to many other countries.
However, evidence gathered over the last ten years has increased concerns about the health effects of air pollutants. As a result governments and the public have increasingly focussed on this area.
Air is a mixture of gases that surrounds the earth and makes up our atmosphere. Pure air consists of 21% oxygen and 78% nitrogen by volume, plus traces of other substance and gases both natural and anthropogen (man-made). The air that we breathe may actually contain thousands of chemical and biological substances. Many of these are pollutants such as: ground-level ozone (O3), total suspended particulate (TSP), fine particulate matter less than 2.5 microns in diameter (PM2.5) or particles less than 10 microns in diameter (PM10), sulphur dioxide (SO2), carbon monoxide (CO), nitrogen oxides (NOx), volatile organic compounds (VOCs), sulphate (SO4), and nitrates (NO3).
The most commonly measured outdoor air pollutants in Canada include ground-level ozone, particulate matter, carbon monoxide, sulphur dioxide and nitrogen oxides. These substances are the principal ingredients or precursors of smog, and some also contribute to acid rain.
Additional air pollutants of concern include toxic metals (lead, mercury, cadmium, manganese, etc.), and compounds such as benzene, formaldehyde, polychlorinated biphenyl's (PCBs), dioxins, and other persistent organic compounds.
Outdoor air contaminants come from both natural and human sources. Natural sources include smoke from forest fires, wind-blown dust from soil and volcanoes, bacteria, fungi and chemicals released by plants and animals. However, air pollution is primarily associated with everyday human activities. Pollutants are released by motor vehicles, industrial processes (pulp and paper mills, ore smelters, petroleum refineries, power generating stations and incinerators), and the burning of fossil fuels such as gas, oil, coal and wood.
Air pollutants can be carried thousands of miles across borders and oceans or from one urban area to another. This phenomenon is common around the world and is referred to as "long-range atmospheric transport" or "transboundary pollution".
Ozone is a naturally occurring gas in the lower atmosphere that increases in concentration when volatile organic compounds (VOCs) and nitrogen oxides (NOx) react in the presence of sunlight and stagnant air. High levels of ground-level ozone often occur during hot summer days in or downwind of heavily populated areas, where sources emit the necessary VOCs and NOx to produce ozone.
Ground-level ozone, a primary component of smog, differs markedly from the protective blanket of ozone high above the earth (also known as the 'ozone layer' or 'stratospheric' ozone), which acts to shield the Earth's surface from intense ultraviolet radiation produced by the sun.
Ground-level ozone has been linked with a broad spectrum of human health effects. Because of its reactivity, ozone can injure biological tissues and cells. Exposure to ground-level ozone for even short periods at relatively low concentrations has been found to significantly reduce lung function in healthy people during periods of exercise. This decrease in lung function is generally accompanied by other symptoms including tightness of the chest, pain and difficulty breathing, coughing and wheezing. The data on health effects of ozone have been examined in human epidemiological studies and exposure to ozone has been associated with mortality, hospital admissions, emergency department visits, and other adverse health effects.
Nitrogen oxides include a number of gases that are composed of oxygen and nitrogen. In the presence of sunlight these substances can transform into acidic air pollutants such as nitrate particles. The combustion of fuel for transportation, home, and industrial use accounts for approximately 94% of the emissions of nitrogen oxides produced by human activities in Canada. The nitrogen oxides family of gases can be transported long distances in our atmosphere. Nitrogen oxides play a key role in the formation of smog (ground-level ozone). At elevated levels, NOx can impair lung function, irritate the respiratory system and, at very high levels, make breathing difficult, especially for people who already suffer form asthma or bronchitis.
Volatile organic compounds are a group of carbon-containing compounds that tend to evaporate quickly at ordinary temperatures. VOCs are present in our atmosphere at very low levels. Generally, VOCs are found in higher concentrations indoors than outdoors. VOCs can react with nitrogen oxides to form ground-level ozone. Thousands of natural and synthetic chemicals are VOCs, including benzene which is a natural component of crude oil and petroleum products. Some VOCs are carcinogenic, such as formaldehyde and benzene, and some are irritants as a group of precursors to ozone.
SO2 is a naturally occurring substance that becomes problematic at higher concentrations. Like nitrogen oxides, sulphur dioxide is produced primarily by industrial processes and fuel combustion. SO2 can be chemically transformed in the atmosphere in the presence of other chemicals and sunlight to form acidic pollutants such as sulfuric acid and sulphates. SO2 is a common air pollutant found in outdoor environments. SO2 can cause breathing problems in people with asthma, but at relatively high levels of exposure. There is some evidence that exposure to elevated SO2 levels may increase hospital admissions and premature deaths.
The principal human source of CO is from fuel combustion, primarily vehicles. CO concentrations are much higher in urban areas due to the number of human sources, although this gas is also released by natural sources such as volcanoes and forest fires. It is an odourless gas which when inhaled, reduces our body's ability to use oxygen. Health effects associated with relatively low-level, short-term exposure to CO include decreased athletic performance and aggravated cardiac symptoms. At the levels typically found in large cities, CO may increase hospital admissions for cardiac diseases, and there is also evidence of an association with premature deaths.
For more information regarding relevant issues, see the Meteorological Service of Canada (Environment Canada)
Airborne particles are known as 'particulate matter (PM)'or simply 'particles'. These particles are very small solids and/or liquids that are produced by a variety of natural and man-made sources. Airborne particles vary widely in their chemical composition and size.
The size of particles may range from 0.005 µm to 100 µ m in diameter. The suspended portion (total suspended particulates or TSP i.e. found floating in air) is generally less than 40 µm. PM10 are particles that are 10 µm or less in diameter. PM10 are split into two portions; coarse particles (PM2.5-10) and fine particles (PM2.5). PM2.5 are particles of 2.5 µm or less in diameter. The finer particles pose the greatest threat to human health because they can travel deepest into the lungs. Particles are also an important component of smog. Short-term exposure to airborne particles at the levels typically found in urban areas in North America is associated with a variety of adverse effects. Particulates can irritate the eyes, nose and throat and cause coughing, breathing difficulties, reduced lung function and an increased use of asthma medication. Exposure to particulates is also associated with an increase in the number of emergency department visits, an increase in hospitalizations of people with cardiac and respiratory disease and in premature mortality.
A variety of other contaminants can be found in our air such as hydrogen sulphide (H2S), total reduced sulphur (TRS) compounds, toxic metals (cadmium, chromium, nickel, manganese), formaldehyde, polychlorinated biphenyls (PCBs), dioxins, and other persistent organic pollutants (POPs). Each is released by human sources and associated with direct effects on human health.
The term smog was first used to describe the combination of smoke and fog in the atmosphere. In recent years it has become the term given to the chemical soup that is often visible as a yellow-brown haze that hangs over many cities on calm summer days. Smog is a mixture of airborne chemicals which originate from or are produced by motor vehicle and industrial pollution.
A major component of smog is ground-level ozone (O3), which is formed when two main pollutants, nitrogen oxides (NOx) and volatile organic compounds (VOCs) react in sunlight and stagnant air. Airborne particles such as fine particles or sulphates are also an important component of smog. Because smog formation depends on heat and sunlight, smog generally peaks in late afternoon and early evening. Smog is most obvious in large cities, although suburban and rural communities are not spared. The Windsor-Quebec corridor, the Atlantic provinces and the Lower Fraser Valley in British Columbia have the most smog episodes in Canada.
Breathing in smog has adverse and varied consequences for human health with the cardio-respiratory system being the main target of concern. Wherever its location and whether visible or not, smog is hazardous to human health.
For more information on smog issues, consult the Clean Air website from Environment Canada
You can also find more information on this topic at the following sites:
Air pollution from the burning of fossil fuels is the major cause of acid rain. Acid rain is the popular name for precipitation acidified by atmosphere pollutants. Acid rain is caused by pollutants such as nitrogen oxides (NOx) and sulphur dioxide (SO2), which in the atmosphere are converted chemically to nitric acid and sulphuric acid. Diluted forms of these two acids fall to earth as rain, or snow.
More than 90% of the NOx and SO2 emissions occuring in North America are due to human activities. Acidic pollutants may be transported over great distances by winds and weather systems. It is estimated that more than 50% of the acid rain falling in Southern Ontario and the Atlantic region come from U.S. sources.
Acid rain can affect lakes, forests, materials such as buildings and cars and human health. The health concerns related to acid rain are derived primarily from the precursors SO2 and NOx. In the air SO2 can react with water and other chemicals to form very fine particles. NOx is a precursor of ozone and particles.
For more information on this topic:
Human activities are affecting the Earth's atmosphere in ways we have never experienced before. The emissions of greenhouse gases into the atmosphere have increased at a rapid rate during the past few decades and the large scale combustion of fossil fuels is currently one of the biggest contributing factors affecting this kind of change. The principal greenhouse gases are:
These gases have the ability to absorb infrared radiation from the sun and to trap this energy. The trapping of this heat is known as the greenhouse effect, which results in a global warming of the atmosphere with various impacts on Earth. Each of these greenhouse gases has unique sources and characteristics. Carbon dioxide is the most common greenhouse gas and is responsible for about half of the atmospheric heat retained by greenhouse gases. The effects of global climate change include more frequent heat waves, unstable weather systems, violent and more frequent weather events (storms, hurricanes, floods), threats to food and water supplies, change in vector-borne disease distributions, among other things. The implications for human health are enormous.
Consult the Climate Change for more information on the health effects of climate change
For more information on this topic :