Why do aerosols matter?
Where do aerosols come from?
What are aerosols made of?
How big is an aerosol particle?
Are anthropogenic aerosols and natural aerosols different?
What impact do aerosols have on the earth’s climate?
What are the environmental impacts of aerosols?
Are aerosols hazardous to my health?
How do I contribute to aerosol emissions?
What can I do to reduce my exposure to and production of aerosol emissions?
Are there any standards we can use to evaluate aerosol exposure?
What action does Ontario take to enforce aerosol emission requirements?
How much PM2.5 am I exposed to?
What is an aerosol?
An aerosol is a suspension of fine solid or liquid particles in a gaseous phase.[i]Typically, aerosols are found in the air that we breathe. Aerosols 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 aerosols. Examples of aerosols include dust, tobacco smoke, pollen, and soot.
Aerosols are ubiquitous in the atmosphere, and affect climate, human health, cloud formation, weather, visibility, corrosion, and the chemistry of the atmosphere.[ii]Smaller aerosol particles can cause several severe health effects, including premature death, aggravation of asthma, cardiovascular disease, and lung disease.[iii]
Aerosols can either be directly emitted into the atmosphere (primary aerosols) or can form from the reaction and condensation of gaseous chemicals already existing in the atmosphere (secondary aerosols).[iv]
The major natural sources of aerosols are dust, volcanic activity and forest fires, which contribute to primary and/or secondary aerosol formation. Globally, about 10% of aerosols are anthropogenic in origin. Most of this 10% is in the northern hemisphere, particularly in the area of industry, overgrazed grasslands and slash-and-burn agriculture.[v]Anthropogenic sources of aerosols include energy production from fossil fuels, vehicle emissions, and residential heating. 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 aerosols. [vi]
Once in the atmosphere, aerosols may be transported extensively or linger in a single area. The degree of transport depends on the weather conditions in the area. For example, aerosols may travel to Ontario from the United States to contribute more than 50% of Ontario’s particulate matter on heavily polluted days.[vii]
Aerosol composition varies hugely. Furthermore, particles composed of similar substances but with different ratios may have very different properties. Some of the aerosols 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.[viii]
The composition of aerosols is greatly influenced by associated formation processes. Aerosols which are directly emitted into the atmosphere are classified as primary aerosols, and their composition includes elemental carbon, and particles of geological origin (crustal matter). Secondary aerosols 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.4
Aerosols cover a large range of sizes. Most aerosols 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 aerosols, many anthropogenic aerosols are the same as the natural ones. Industrial aerosols may be entirely different; however, the huge range of industrial aerosols produced make generalizations difficult. For example: coal plants directly emit primary aerosols 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 aerosols.
Aerosols can influence the earth’s climate by reflecting radiation and affecting cloud formation. Aerosols 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).[ix]
Clouds play a vital role in the earth’s climate, and aerosols play a vital role in cloud formation. Normally, water condenses out of very humid air onto atmospheric aerosols to form aggregations of water droplets - clouds. Changing the concentration of atmospheric aerosols 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”).[x]The details and consequences of these effects are not well documented. The effects of aerosols 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 aerosols 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 contributor to aerosol emissions in 2002 for Ontario was industry, which overall generated 46% of the total. However, residential activities and transportation also contribute significantly, generating 29% and 18% respectively.[xi]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 aerosols.
Exposure to high concentrations of aerosols 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.
Effective in 2010, the Canada-wide Standard (CWS) for PM2.5 is 30µg/m3 for a 24-hour averaging time. This value is based on the 98th percentile annual ambient measurement averaged for three consecutive years. The CWS must be met by jurisdictions in 2010, with reporting required in 2011. The progress of jurisdictions towards reaching the CWS for PM2.5 began in 2006. According to the Ontario Ministry of Environment’s 2005 Air Quality in Ontario Report, southwestern Ontario exceeds the CWS for PM2.5 more often than eastern and northern Ontario. Currently, there is no standard for PM10 or ultrafine particulate matter.
The Ministry of Environment’s Sector Compliance Branch seeks to enforce pollutant emission regulations. The Sector Compliance Branch performs province-wide sweeps of industrial sectors in Ontario to determine specific facilities that exceed legal emission values. Emission standards are based on point of impingement guidelines, which set a limit for the concentration of a pollutant that traverses beyond the facility’s property. The point of impingement standard for PM2.5 is 100 µg/m3 (averaged 30-minute measurements). Note there is no point of impingement standard for PM10.
The Sector Compliance Branch aims to educate members of industries who exceed emission standards, and assists with the development of abatement plans. In severe cases of non-compliance, tickets are issued, and investigations may lead to prosecution.
As of August 23, 2002, PM2.5 was added to Ontario’s Air Quality Index (AQI), which uses a scale ranging from 0 to 100 to categorize the quality of the ambient air we breathe. For example: an AQI below 32 indicates ambient air is of relatively good quality, while an AQI ranging from 32-49 indicates the possibility of adverse effects in sensitive people, particularly children, the elderly, and those with existing respiratory conditions.
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.
[i]Random House Unabridged Dictionary, © Random House, Inc. 2006.
[ii]Nucleation of Atm Aerosols
[iii]Air Quality in Ontario 2005