The Georgia Basin-Puget Sound Airshed Characterization Report 2014: chapter 2

2. Fundamental Concepts of Air Quality

Bruce Thomson and Rebecca Saari (Environment Canada)

Air quality is primarily defined by the quantity of pollutants present in the atmosphere. Poor visibility, offensive odours and visible plumes also influence the perceived air quality; these issues are also, though not solely, related to pollutant concentrations.

The atmosphere is primarily composed of nitrogen, oxygen and water vapour. However, many other compounds can be present in trace amounts; those which are harmful to human health or the environment are termed pollutants.

Air quality standards and objectives are pollutant concentration thresholds based on levels of concern for human health and the environment. They can be used by governments and the public to identify the need for action. Ambient concentrations of pollutants are routinely measured and compared to air quality goals, standards and objectives.

Ambient air quality is determined by two dominant factors: emissions and atmospheric processes. Emissions are the release of chemicals into the atmosphere. Atmospheric processes are the mechanisms that transport, transform, disperse and deposit the emissions after they are released. The combination of contaminant emissions and atmospheric processes determines the ambient air pollutant concentrations and, thus, the air quality.

2.1 Air Pollutants

There are many chemical species that can be classified as air pollutants. However, some of these are short-lived or present in very small amounts. This study focuses on those pollutant species with important contributions to poor air quality in the Georgia Basin/Puget Sound airshed.

Poor regional air quality occurs when pollutant concentrations are elevated. Depending on the pollutants present and other environmental factors, poor air quality can negatively impact human health, property, visibility, wildlife, vegetation, and other human activities and natural cycles. 

A prolonged period of poor air quality results in a smog episode. Originally coined in 1905 by Des Voeux, the term “smog” is defined as natural fog contaminated by industrial pollutants, a mixture of smoke and fog. Today, the term is commonly applied to any incidence of air pollution regardless of the presence of fog; however, some visible pollutant manifestation, such as haze, is almost always implied.

Smog is the phenomenon that first drew international attention to the importance of air quality. Historical smog episodes resulting in fatalities in the United Kingdom and the United States sparked the adoption of the first clean air acts in the 1950s and 1960s.

Following the adoption of the Clean Air Acts in the United States and Canada (later replaced by the Canadian Environmental Protection Act 1999), the most common components of smog have been the focus of monitoring and regulatory efforts in both countries. In Canada, this group of air pollutants is referred to as the “criteria air contaminants” (CAC), while the United States uses the term “criteria air pollutants.” The list of criteria pollutants includes oxides of sulphur (SO_x), oxides of nitrogen (NO_x), ozone (O₃), carbon monoxide (CO) and fine particulate matter (PM). The United States includes lead in this list, while Canada includes volatile organic compounds (VOCs) and ammonia (NH₃) (United States Environmental Protection Agency, 2010; Environment Canada, 2010). Particulate matter, itself a pollutant, can also be composed of toxic heavy metals, such as arsenic and lead, or toxic organic compounds.

Criteria air contaminants are known to cause both environmental and health impacts. Bates and Vedal (2002) describe in detail health-related impacts of airborne pollutants including CACs. One of the more important aspects of this discussion centres on the very low concentrations of air pollutants that can cause serious effects on sensitive members of the population, such as asthmatics and those suffering from chronic obstructive pulmonary disease. The authors also contend that current air quality standards and objectives do not protect human health; other research shows that current standards and objectives do not protect ecosystem health.

Canada includes VOCs and ammonia in their list of CACs and related contaminants. Both are widespread contaminants that contribute to regional smog and haze, as precursors to secondary pollutants. Volatile organic compounds (VOCs) are a group of chemicals that react with other airborne pollutants to form O₃, PM and other compounds. VOCs also include airborne persistent organic pollutants (POPs), which are of particular concern because of their ability to bioaccumulate in living organisms. Similarly, ammonia (NH₃) is a precursor to secondary PM and is toxic.

Greenhouse gases (GHG) like carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and ozone (O₃) affect the global climate. Other criteria air contaminants, including sulphur dioxide and particulate matter, have variable impacts that can be important but may be short-lived compared to the impacts of the long-lived greenhouse gases (IPCC, 2007). Air quality and climate change are known to interact, and the significance of climate change for air quality in the airshed is discussed in Chapter 13 of this report.

2.2 Air Quality Standards

Air contaminant concentrations are compared to standards, objectives and guidelines as a basis for assessing air quality, comparing air quality between airsheds, and identifying the need for control measures.

There are national, provincial, and regional ambient air quality standards for the criteria air contaminants mentioned above. The standards that apply to the airshed for ozone and particulate matter in Canada and the U.S. are given in Table 2.1.

Notes:

^* Achievement based on the 3-year average of the annual 4^th-highest daily maximum 8-hour ozone concentrations.
¹ Health Canada 2006
² The CWS (CCME, 2000) will be replaced by the more stringent CAAQS (CCME, 2012); the 2020 standards will be reviewed in 2015.
³ BC MHLS 2010
⁴ Metro Vancouver 2005
⁵ FVRD 2010
⁶ U.S. EPA 2010
⁷ WHO 2005

Notes:

* Achievement based on the annual 98^th percentile of daily 24-hour average concentrations, averaged over 3 consecutive years.
** Achievement based on annual average concentrations, averaged over 3 consecutive years
*** Voluntary planning objective.
**** An objective never to be exceeded.
¹ BC MHLS 2010
² Metro Vancouver 2005 and Metro Vancouver 2008
³ U.S. EPA 2010
⁴ WHO 2005
⁵ The CWS (CCME, 2000) will be replaced by the more stringent CAAQS (CCME, 2012); the 2020 standards will be reviewed in 2015.
⁶ Puget Sound Clean Air Agency 2006

There are no ambient air quality standards or objectives for visibility, although visibility loss is an important issue in the Georgia Basin/Puget Sound area. In the Puget Sound, mitigation of visibility impairment is regulated by the U.S. Regional Haze Rule (U.S. EPA, 1999a). This rule is intended to improve visibility in Class 1 areas, aiming to eliminate human-caused visibility impairment in these areas by 2064 (U.S. EPA, 1999b) (WA DOE, 2003). The rule requires improving Class 1 area visibility on the haziest days (the worst 20%) and ensuring no degradation on the clearest days (the best 20%) (Oregon DEQ, 2010). Canada lacks a regulatory imperative to manage visibility, although efforts toward the development of management strategies exist in the Georgia Basin. Metro Vancouver enshrined visibility improvement as one of its three air management goals (Metro Vancouver, 2005). Regional, provincial and federal agencies have formed the British Columbia Visibility Coordinating Committee to develop a framework for visibility management, using the Lower Fraser Valley as a pilot project (Clearair.bc, 2013). A visibility goal for the province of British Columbia may result from these efforts, which are described in detail in Chapter 9, “Visibility”.

2.3 Air Pollutant Emissions

Air pollution enters the atmosphere when it is emitted by a source. Emissions of air pollutants can come from anthropogenic and natural sources. Anthropogenic sources are often easily identified. Natural emissions are harder to quantify but can contribute significantly to the total emissions in the airshed.

Total air emissions are inventoried on a regular basis to understand air pollutant sources and how emissions are changing over time. Details of the recent emission inventories in the airshed are presented in Chapter 5, “Emissions”.

2.3.1 Anthropogenic Sources

Anthropogenic emissions tend to be highest in densely populated areas, such as metropolitan Vancouver, Seattle, Tacoma and Victoria.

Anthropogenic emissions to the atmosphere include:

• Industrial pollution from the burning of fossil fuels or wood waste for power; the burning of municipal, hospital, and hazardous waste; the use of solvents and coatings in manufacturing processes; the primary and secondary smelting of aluminum and steel; petroleum refining; pulp and paper manufacturing; lumber and veneer production; the transportation of products, etc.;
• Pollution related to lifestyle choices such as transportation; home heating, use of woodstoves, the outdoor burning of waste and the use of pesticides; and
• Agricultural and silvicultural emissions, including ammonia from animal waste, smoke from prescribed burning of fields and forests, windblown dust from exposed soils due to tilling and the use of pesticides.

Anthropogenic emissions may also exhibit seasonal, hebdomadal and diurnal patterns. For example, particulate emissions from woodstoves dominate during the winter, while agricultural burning is most significant in the summer and fall. Emissions from mobile sources show morning and evening peaks corresponding to rush hour periods.

2.3.2 Natural or Biogenic Sources

Emissions from natural sources such as vegetation, wetlands, oceans, volcanoes, wind-blown dust and wildfires contribute to air pollutants and influence air quality.

The largest source of natural emissions in the airshed is vegetation, particularly trees. Both deciduous and coniferous trees produce gaseous chemicals. The quantity of these emissions depends on the time of year and local weather conditions. In the spring, under sunny skies and warm temperatures, trees produce tonnes of gaseous emissions per day (Moran and Makar, 2001). Other important sources of natural emissions are marine areas and bogs.

Some major natural sources and their emissions include:

• Vegetation, wildfires and wetlands, which account for the largest contribution from natural sources and produce volatile organic compounds (VOC);
• In addition to VOCs, wildfires and biomass burning produce large quantities of fine particulate matter, oxides of nitrogen and organic chemicals; and
• Salt water bodies and volcanoes, which emit inorganic compounds, like sulphur and sodium, and which can contribute to the formation of secondary pollutants, such as ozone and fine particulate matter.

Some natural processes show seasonal variability related to growth patterns; others, like wildfires, are highly variable both temporally and spatially.  Rare occurrences such as the eruptions of Mount St. Helens during the 1980s, can contribute significant amounts of SO₂ and other pollutants. These emissions from natural sources are presented in more detail in Chapter 5 “Emissions”.

2.4 Atmospheric Fate and Transport of Air Pollutants

After a chemical becomes airborne, atmospheric processes begin to determine its fate. Some pollutants remain unchanged and are swept out of the atmosphere by air currents or precipitation, often polluting receiving environments such as water or soil. Other chemicals may be altered by physical processes or chemical reactions that produce a new secondary compound. This is the case when NO_x and VOCs react in the presence of sunlight to form O₃.

The factors that determine the fate of air pollutants are numerous. Weather affects the chemical and physical transformation and transport of pollutants through changes in temperature, radiation, atmospheric stability, dynamics, moisture, precipitation, and other variables. This study focuses on those meteorological conditions that are important to the fate of air pollutants. Other meteorological factors unique to the area are mentioned, but only as they relate to air quality.

2.5 Chapter Summary

Air quality is a measure of the condition of air and is primarily defined by the quantity of pollutants present in the atmosphere. Pollutants that are short-lived or present in very small amounts are some of the most important contributors to poor air quality in the Georgia Basin/Puget Sound region. The most common components of smog are currently monitored in both the U.S. and Canada. In Canada, this group of air pollutants is referred to as the “criteria air contaminants” (CACs), while the United States uses the term “criteria air pollutants.” Measured air contaminant concentrations are compared to national, provincial and regional standards, objectives and guidelines as a basis for assessing air quality, comparing air quality between airsheds, and identifying the need for control measures.

Air pollution enters the atmosphere when it is emitted by a source which can be natural or anthropogenic. Anthropogenic emissions tend to be highest in densely populated areas such as metropolitan Vancouver, Seattle, Tacoma and Victoria. Sources of anthropogenic emissions include industrial pollution, pollution related to lifestyle choices and agricultural emissions. The largest source of natural emissions in the airshed is vegetation. Other sources include wetlands, oceans, volcanoes, wind-blown dust and wildfires.

Once a pollutant becomes airborne, atmospheric processes play a major role in terms of transport and transformation. While some pollutants may remain unchanged and are transported out of the atmosphere, others may be altered via physical processes or chemical reactions to produce new secondary compounds.

2.6 References

Bates, D.V., and S. Vedal, 2002. Chapter 4: Adverse Health Effects. In: A Citizen’s Guide to Air Pollution - Second Edition. David Suzuki Foundation, Vancouver, BC. ISBN 0-9689731-2-4, 391 pp.

BC MHLS (British Columbia Ministry of Healthy Living and Sport), 2010. Air Quality Objectives and Standards for British Columbia and Canada.  (Accessed: February 25, 2010)

Clearair.bc. 2013.

CCME (Canadian Council of Ministers of the Environment), 2000. Canada-Wide Standards for Particulate Matter and Ozone. Canadian Council of Ministers of the Environment. June, 2000. (Accessed: April 19, 2010)

CCME (Canadian Council of Ministers of the Environment), 2012. Canadian Ambient Air Quality Standards (CAAQS) for Fine Particulate Matter (PM_2.5) and Ozone. October, 2012. (Accessed: December 19, 2012)

Environment Canada, 2010. Criteria Air Contaminants and Related Pollutants. (Accessed: April 19, 2010)

FVRD (Fraser Valley Regional District), 2010. Presentation on the Draft Air Quality Management Plan at the Lower Fraser Valley Air Quality Coordinating Committee Meeting by Bob Smith, April 15, 2010 in Vancouver, BC.

Health Canada, 2006. Regulations Related To Health And Air Quality. (Accessed: April 19, 2010)

IPCC(Intergovernmental Panel on Climate Change), 2007. IPCC Fourth Assessment Report: Climate Change 2007. (Accessed: April 19, 2010)

Metro Vancouver, 2005. Air Quality Management Plan (2005). (Accessed: February 25, 2010)

Metro Vancouver, 2008. Air Quality Management Plan Progress Report - October 2008. (Accessed: February 25, 2010)

Moran, M.D. and Makar, P.A, 2001. Chapter 3: The nature of the sources of emissions. In: Precursor contributions to ambient fine particulate matter in Canada. Environment Canada, Meteorological Service of Canada, Atmospheric and Climate Sciences Directorate, 327 pp.

Oregon DEQ (Oregon Department of Environmental Quality), 2010. Regional Haze. (Accessed: July 21, 2010).

Puget Sound Clean Air Agency, 2006. 2005 Air Quality Data Summary. (Accessed: February 25, 2010)

U.S. EPA (Environmental Protection Agency), 1999a. Federal Register, 40 CFR Part 51, Regional Haze Regulations, Final Rule, July 1, 1999. 

U.S. EPA (Environmental Protection Agency), 1999b. Fact Sheet on Final Regional Haze Regulations for Protection of Visibility in National Parks and Wilderness Areas.

U.S. EPA (Environmental Protection Agency), 2010. National Ambient Air Quality Standards (NAAQS). (Accessed: February 25, 2010)

WA DOE (Washington State Department of Ecology), 2003. 2000 - 2002 Air Quality Trends Report. April 2003 report for the WA DOE Air Quality Program.

WHO (World Health Organization), 2005. WHO Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide - Global update 2005 - Summary of risk assessment. (Accessed: April 22, 2010)