An aerosol is a suspension of fine solid or liquid particles in a gaseous phase.[i] Typically, aerosol are found in the air that we breathe. Aerosol can be made of many different substances, have very different chemical properties and are sometimes in a mixed state between liquid and solid. The terms particulate matter or particulates are sometimes used in place of aerosol. Examples of aerosol include dust, tobacco smoke, pollen, and soot.
Aerosol are ubiquitous in the atmosphere, and affect climate, human health, cloud formation, weather, visibility, corrosion, and the chemistry of the atmosphere. Smaller aerosol particles can cause several severe health effects, including premature death, aggravation of asthma, cardiovascular disease, and lung disease.[ii]
[ii] Air Quality in Ontario Report 2016, Ministry of the Environment, Conservation and Parks
Aerosol can either be directly emitted into the atmosphere (primary aerosol) or can form from the reaction and condensation of gaseous chemicals already existing in the atmosphere (secondary aerosol).[iii]
The major natural sources of aerosol are dust, volcanic activity and forest fires, which contribute to primary and/or secondary aerosol formation. Globally, about 10% of aerosol are anthropogenic in origin. Most of this 10% is in the northern hemisphere, particularly in north-American and European industrial and urban areas. In the Southern Hemisphere, agricultural activities in the Amazon and Central Africa release large amounts of aerosol.[iv] Anthropogenic sources of aerosol include energy production from fossil fuels, vehicle emissions, residential heating and slash-and-burn agriculture. Anthropogenic sources contribute to primary and secondary aerosol formation. For example: automobiles generate particles directly, and also emit organic compounds that contribute to the formation of secondary aerosol. [iii]
Once in the atmosphere, aerosol may be transported extensively or linger in a single area. The degree of transport depends on the weather conditions in the area. For example, aerosol may travel to Ontario from the United States to contribute more than 50% of Ontario’s particulate matter on heavily polluted days.[v]
[iii] Air Pollution Training Institute, U.S. Environmental Protection Agency
[v] Air Quality Ontario, Ministry of the Environment, Conservation and Parks
Aerosol composition varies hugely. Furthermore, particles composed of similar substances but with different ratios may have very different properties. Some of the aerosol that you may come into contact with in everyday life are soot, pollen, sea salt, fly ash (from coal combustion), mineral dust, and asbestos fibres.[vi]
The composition of aerosol is greatly influenced by associated formation processes. Aerosol which are directly emitted into the atmosphere are classified as primary aerosol, and their composition includes elemental carbon, and particles of geological origin (crustal matter). Secondary aerosol are synthesized from the combination and condensation of gaseous chemicals in the atmosphere, and mainly consist of volatile organic compounds, ammonium sulfate, and ammonium nitrate.[vii]
[vi] Grobety, B.; Giere, R.; Dietze, v.; Stille, P. Airborne Particles in the Urban environment, Elements 6(4); 229-234, 2010 [online]
[vii] Air Pollution Training Institute, U.S. Environmental Protection Agency
Aerosol cover a large range of sizes. Most aerosol range from 0.01 to 10 microns (µm) in aerodynamic diameter; the vast majority of atmospheric particulates are smaller than 1 micron in size.
Particulate matter (PM) is often classified into three categories: particles with diameter greater than 2.5 and less than 10 microns (PM10, coarse particles), particles with diameter greater than 0.1 to less than 2.5 microns (PM2.5, fine particles), and particles with diameter less than 0.1 microns (UFP, ultra-fine particles). This categorization has physiological significance – PM10 particulates can be respired, PM2.5 can be absorbed by the lungs upon respiration, and UFP can enter the blood stream and be absorbed by organs such as the brain.
Since agriculture generates significant amounts of anthropogenic aerosol, many anthropogenic aerosol are the same as the natural ones. Industrial aerosol may be entirely different; however, the huge range of industrial aerosol produced make generalizations difficult. For example: coal plants directly emit primary aerosol such as fly ash. Coal plants also produce chemicals such as volatile organic compounds (VOCs), sulfur dioxide (SO2), and nitrogen oxides (NOx) that react and condense in the atmosphere to form secondary aerosol.
Aerosol can influence the earth’s climate by reflecting radiation and affecting cloud formation. Aerosol may scatter electromagnetic radiation due to the wide range of particle sizes present. The sun’s incident radiation may be reflected back into space, or the earth’s secondary radiation may be reflected back towards the earth (as in the Greenhouse Effect).[viii]
Clouds play a vital role in the earth’s climate, and aerosol play a vital role in cloud formation. Normally, water condenses out of very humid air onto atmospheric aerosol to form aggregations of water droplets - clouds. Changing the concentration of atmospheric aerosol changes the number and size of the water droplets that make up the cloud. This changes the optical properties and lifetime of the cloud, which in turn changes the amount of radiation reflected by the cloud (the “indirect effect”).[viii] The details and consequences of these effects are not well documented. The effects of aerosol on climate are one of the major motivations for a deeper understanding of the role they play.
Particulate matter less than 2.5 micrometers in size (PM2.5) is a predominant cause of reduced visibility (haze). PM also contributes to acid deposition, causing damage to local ecosystems. PM may settle in bodies of water, resulting in an increased acidity of lakes and streams, and a modification of the nutrient balance of costal waters and river basins, causing large lakes to become unsuitable to support fish populations. Acid deposition contributes to corrosion, vegetation damage, and nutrient depletion in soil.
PM serves as a means of transport for pollutants such as heavy metals and pesticides. For example, persistent semi-volatile pollutants can evaporate into the atmosphere, bind to PM, and then be transported and deposited in a different geographical location.
Studies that look at large populations have made strong correlations between negative health impacts and PM2.5 mass concentration levels. Studies also base their findings on two types of exposure, either acute or chronic. Acute exposure to aerosol has been linked to respiratory and cardiopulmonary disease, an increase in hospital admissions and asthma symptoms or episodes. Chronic exposure is currently being linked to a decrease in life expectancy, weakening of the heart and cancer.
Although it is generally accepted that PM negatively impacts health, the physiological reasons as to why it does so, are still to be determined. Some studies that investigate the body’s physiological response to PM speculate it reduces oxygen transport to the body, reduces lung function, and acts as a carcinogenic and/or mutagen.
All people are susceptible to the negative effects of PM, with children and the elderly showing a higher sensitivity to aerosol concentration. Current research suggests that despite improvements in air quality over the last decade, exposure at the concentrations typically found in many parts of Canada is still causing adverse health effects.
The largest source of aerosol emissions in 2016 for Ontario was residential fuel combustion, which generated 56% of the total. Industrial activities and transportation also contribute significantly, generating 21% and 12% respectively.[ix]
Using electricity generated from coal-fired plants, driving a vehicle and burning wood in a stove or campfire are probably your biggest contributions to total aerosol emissions. Other common activities such as using a barbeque or gas-powered lawn mowers and edge cleaners can also contribute to the production of aerosol.
[ix] Air Quality in Ontario Report 2016, Ministry of the Environment, Conservation and Parks
Exposure to high concentrations of aerosol can occur in specific locations such as near some industrial plants, near or in heavy traffic, near a stove/BBQ while cooking, and/or being in the same room as a smoker. However, elevated concentrations of fine particulate matter can also be widespread and for example, cover much of Southern Ontario during periods of poor air quality. Individuals with existing health conditions are often advised to avoid locations with high particulate concentrations when possible, and stay inside when there is an air quality alert.
You can help reduce your aerosol emissions by doing some simple things that can make a big difference! Try using public transit when you can or riding a bike; also try a manual lawn mower. In order to significantly reduce smog and health problems, changes must be made on a larger scale. Tell your friends and make it an issue to your local government who regulates emission laws.
Ambient Air Quality Criteria (AAQC) are defined to determine which concentration of a contaminant in air is acceptable, based on protection against adverse effects on health or the environment. The Canada-wide Standard (CWS) for PM2.5 was implemented in 2010 as a reference to be reached by jurisdictions. Its value was 30µg/m3 for a 24-hour averaging time, based on the 98th percentile annual ambient measurement averaged for three consecutive years. This standard has been replaced in 2013 by the Canadian Ambient Air Quality Standards (CAAQS) which sets stricter targets. Its value for 2015 is 28µg/m3 for a 24-hour averaging time and is of 27µg/m3 for 2020. Jurisdictions are regularly required to report ambient air quality measurements against the CAAQS.
According to the Ontario Ministry of Environment’s 2016 Air Quality in Ontario Report, the CAAQS were not exceeded in 2016. The reported 24-hour PM2.5 CAAQS metric values ranged from 13µg/m3 for both Sudbury and Thunder Bay, to 25µg/m3 for Hamilton Downtown.
Currently, there is no similar standards for PM10 (coarse particles) or ultrafine particulate matter.
The amount of fine particulate matter (PM2.5) is, along ground-level ozone and nitrogen dioxide, one indicator used to determine the outdoor air quality via the Air Quality Health Index (AQHI). The AQHI is a tool developed by health and environmental professionals to communicate the health risk posed by air pollution. It is designed to help people make decisions to protect their health and the environment by limiting their exposure and reducing their personal contribution to air pollution. It is also used by the government to determine when to issue air quality alerts.
The AQHI uses a scale ranging from 1 to 10+ to indicate the level of health risk associated with the quality of the ambient air we breathe. The higher the number, the greater the health risk and the need to take precautions. The index describes the level of health risk associated with this number as ‘low’, ‘moderate’, ‘high’ or ‘very high’, and suggests steps to reduce exposure. It also forecasts local air quality and provides associated health advice. The AQHI does not measure the effects of air pollutants on human health.
Currently, there is no indication of how much PM2.5 one is exposed to indoors. Although, activities such as burning incense or candles, frying foods, cooking using natural gas stoves and ovens, and using wood burning stoves and furnaces are known to increase one’s exposure to PM.