International Air Quality Advisory Board

SPECIAL REPORT ON
TRANSBOUNDARY AIR QUALITY ISSUES

November 1998

1. SEAMLESS BORDER

1.1 One Atmosphere

A wide range of pollutants is released into the atmosphere throughout North America on a daily basis. In the past few decades, both Canada and the United States have made a significant effort to characterize emissions and quantify the relative amounts of pollutants emitted by natural and anthropogenic sources. Anthropogenic emissions change continuously with time, particularly in their chemical composition and their amounts. The pollutants emitted into the atmosphere are transported by wind from source to receptors. In the course of their travel, these pollutants can react in the atmosphere to create other pollutants. Some, such as sulfur dioxide (SO2), have short average residence times in the atmosphere and may react quickly; others, such as chlorofluorocarbons (CFCs) and persistent organic pollutants (POPs), may exist for years and be transported long distances.

Since the mid 1970's, the study of air pollution issues and the establishment of controls have been based on either one or a small family of pollutants. For example, the primary pollutant considered under the acid rain issue was SO2, and controls were put in place to control only SO2. It has recently been shown, however, that nitrogen emissions continue to contribute to acid rain and should be addressed. This emphasizes the need to look at the total picture. The atmosphere can be seen as the one common element; that is, there is only one atmosphere, and most of the pollutants of concern are transported in that atmosphere and/or undergo chemical transformations there.

Figure 1-1 is one depiction of the myriad of processes occurring in the atmosphere. Some contaminants are to a great extent manmade; others, such as mercury can be released by human activity ('manmade') or directly from deposits in the earth's crust ('natural'). Considering mercury further, some portion is released from both sources into the atmosphere where it can be subjected to transport (in some instances over long distances) as well as, in some cases, transformation into derivative compounds. Some contaminants are contained within particles and participate in the processes affecting them. Clouds can capture (scavenge) some portion of these pollutants, with the resulting deposition back to earth in the form of rainfall. Others continually return via dry deposition.

Figure 1-1 Atmospheric Processes
Schroeder, W.H. and Lane, D.A. The fate of toxic airborne pollutants. Environmental Science and Technology 22(3), 240-246. 1988.

After either form of deposition, pollutants may return to the atmosphere from the site of their deposition (which may be some distance from the original source) in gaseous form (volatilization) or in the resuspension of particles. This cycle of deposition and re-entry to the atmosphere (the grasshopper effect) can be repeated. The effect of these various mechanisms can be transport of the pollutant hundreds or even thousands of kilometers prior to its sustained return to earth.

Identifying and understanding these processes will give a better understanding of what occurs to all the pollutants found in the atmosphere. This in turn should prompt efforts to address issues more comprehensively and effectively. Rather than addressing issues such as acid rain, smog, fine particulate matter, or toxics singularly, which can lead to additional unforeseen difficulties and negative outcomes, issues should be addressed simultaneously and consistently in a holistic fashion -- the same way the atmosphere integrates what is released into it.

1.2 Regional Airshed Management

A variety of regional air quality management frameworks for managing air pollution is being considered in the United States and Canada. Some are designed to deal with a single issue, such as ground-level ozone (O3) or acid rain, or even a single pollutant, such as SO2. Others are evolving as regional multi-pollutant, multi-issue management regimes, which may become the frameworks used for managing air quality in the future. In addition, both countries are trying to determine how to better coordinate and apply these evolving regional frameworks in, and perhaps across, border regions.

It is important to distinguish between emission source regions and receptor regions, where effects occur. Because air pollutants are transported in the atmosphere, their adverse effects can occur not only within the emission source regions but also in other regions downwind of the primary contributing sources. For some air issues, such as persistent toxic substances (PTSs), the primary source regions and the primary receptor regions of concern may not be at all coincident; they may, in fact, be quite distant from each other. The pollutants can be controlled, however, only where they are emitted. Therefore, it may be more effective to address these issues by emission source region instead of by the more traditional "airshed" management approach.

The following examples will give a better understanding of the evolving air management frameworks.

1.3 Single Issue Management Regimes

1.3.1 Management of Ground-Level Ozone

Figure 1-2 shows the five geographic regimes in place or being considered for managing ground-level ozone in Eastern North America:

  • the Ozone Transport Region (OTR), an ozone management region formally designated under the U.S. Clean Air Act (CAA) and covering 13 states in the northeastern United States;
  • the Ozone Transport Assessment Group (OTAG) region, covering 37 states in the eastern half of the United States, in which ozone control options are being considered for the region as a whole and for sub-regions within the OTAG domain;
  • the Regional Ozone Study Area (ROSA), a region including eight states and an area in southern Ontario jointly designated by the United States and Canada as a logical and scientifically defensible geographic domain for managing ozone in a transboundary context; and
  • the Regional Smog Management Plan (RSMP) areas in southern Ontario, southern Quebec, and the southern Atlantic areas of central and eastern Canada. (There is a fourth RSMP in the Lower Fraser Valley of British Columbia.)

Many of these geographic regimes are described in further detail in subsequent sections of this report.

Figure 1-2
Source Regions (Emission Management Areas for Smog)
Prepared by IJC staff with input from Environment Canada and U.S. EPA

1.3.2 Management of Acidifying Emissions

Figure 1-3 shows the Sulfur Oxides Management Area (SOMA) formally designated by Canada in the Second Sulfur Protocol under the United Nations Economic Commission for Europe (UNECE) Convention on Long-Range Transboundary Air Pollution (LRTAP).

Figure 1-3
Source Regions (Emission Management Areas for Acid Rain)
Prepared by IJC Staff with input from Environment Canada and U.S. EPA

Whereas the management regime for the first phase of Canada's acid rain program of 1985 encompassed the entire territory of the seven easternmost provinces, the second phase now under development is focusing on the SOMA, which is the primary Canadian source region contributing to the residual acidification problem. Acidification is expected to continue in Eastern Canada into the year 2010, even after full implementation of the Canadian Phase 1 control program and the Acid Rain Program under Title IV of the U.S. Clean Air Act.

Prior to the Canadian signing of the UNECE Second Sulfur Protocol, the SOMA was also recognized by the United States as the only area of Canada contributing to acidification in the United States. Hence it is a logical source region for managing SO2 emissions, both from the domestic and transboundary perspectives. It is also being considered in Canada as an appropriate geographic domain for managing both NOX emissions, which contribute to acidification and ozone formation, and ammonia emissions, which contribute to ambient air particulate loadings.

As illustrated by the outer boundary in Figure 1-3, the SOMA region might, if fully extended to the transboundary context for addressing acid rain and particulates, be combined with the SO2 source region in the United States, which modeling has shown to be the primary U.S. source region contributing to the acid deposition region of concern in Eastern Canada.

1.4 Multi-pollutant, Multi-effect Management Regimes

1.4.1 U.S. Joint Implementation Program for Ozone, Particulates, and Regional Haze

Through the CAA Advisory Committee, the United States is developing an integrated regional approach for implementing the proposed new ambient air quality standards for fine particulate matter (PM2.5) and ozone and for addressing regional haze. The implementation plan would delineate Areas of Violation (AOVs), which are areas with degraded air quality, and Areas of Influence (AOIs), which are emission source regions that contribute most to contamination in the AOVs. Regionally Integrated Plans (RIPs) would be developed to manage emissions within the AOIs, and Regional Air Management Partnerships (RAMPs) would be established to develop the RIPs.

The designation of AOVs and AOIs is based on recognizing that an AOI where controls are needed may have quite a different geographic extent than an AOV, depending on distribution of emission sources, pollutant transport distances, and meteorology. The AOI could, for example, be either a larger region encompassing a smaller AOV domain or a completely separate area upwind of an AOV.

1.4.2 Canadian Regional Smog Management Plans

At present, four multi-pollutant, multi-effect RSMPs are being developed in Canada. These plans will initially address ozone and particulates, but may also provide the framework for addressing other air pollutants such as persistent toxic substances. The four RSMPs cover the following geographic areas:

  • the Lower Fraser Valley of B.C.;
  • Southern Ontario;
  • Southern Quebec; and
  • the Southern Atlantic Region (southern parts of Nova Scotia and New Brunswick).

These RSMPs will be augmented by national measures contained in a National Smog Management Plan (NSMP). RSMPs to address regional hot spots, along with a base national program that provides benefits throughout Canada, comprise the framework envisaged for integrated air management in Canada in the future. Additional RSMPs may be developed as required. The current RSMPs may also be expanded to address other issues, such as deterioration in visibility caused by particulates. Particulate contamination is much more widespread than that of ozone, with ambient particulate concentrations just as high in western Canadian cities (Calgary) as they are in cities such as Toronto that are within the current RSMP domains.

Observations

Jurisdictions on both sides of the border are moving toward a more integrated approach to air issues management. Although some single air issue management schemes are still being considered (e.g. OTAG), both countries appear to be moving toward comprehensive multi-pollutant air management programs for selected emission source regions as a way of managing air quality in the future. Although currently focusing on ozone and particulates, such programs could be expanded to include all air pollutants of concern being emitted from a given region, including air toxics and greenhouse gases.

Even with a regionally focused air management program, however, the need remains for a complementary national program to develop and implement those emission reduction measures that are best handled at the national level, particularly those dealing with vehicles, fuels, and consumer products. Both the United States and Canada have such national programs. Ideally, an overall air management framework would combine the national program and those regional programs designed to further reduce emissions in key source regions.

An air management framework with a strong regional focus and a comprehensive multi-pollutant approach offers many advantages over single-pollutant, single-issue programs:

  • improved efficiency for both governments and industry;
  • more effective selection of emission control measures that address a range of pollutants (e.g. measures to control greenhouse gases could control other air pollutants);
  • a single comprehensive package of measures for industry, allowing them to better plan for the future; and
  • some assurance of environmental integrity by providing regional based controls.

1.5 Pollutants

1.5.1 Sulfur dioxide (SO2)

Historically, emissions of SO2 from uncontrolled coal burning, together with smoke from domestic, industrial and other sources, constituted the earliest recognized air pollutants. In both Canada and the United States between 1980 and 1997, mandated controls on stationary sources have led to substantial reductions in the annual tonnage of SO2 emissions; further reductions are expected over the next decade. A key to these reductions has been the control of emissions from large smelters and coal-fired electrical generating plants.

From 1980 to 1994, SO2 emissions in the United States and Canada are estimated to have declined by 6.0 million tonnes (6.6 million tons), or 23%. Over the same period, the seven eastern provinces of Canada lowered emissions from 3.4 million to 1.5 million tonnes (3.8 million to 1.7 million tons), a reduction of more than 55%.

Since sulfates are a major component of acid rain, SO2 emission reductions were an essential part of the strategy in both countries to reduce the formation of acid species. Controls on the sulfur content of diesel fuel in both countries has also led to a further reduction in SO2 emissions.

Sulfur dioxide can contribute to adverse effects in both natural vegetation and humans. Natural vegetation is sensitive to SO2 and to the aerosol (sulfuric acid) to which it is a precursor. The effects on vegetation have been quantified. In addition, it has been known for over a decade that asthmatic subjects are sensitive to SO2. Protective standards have generally been based on this effect. While the role of SO2 and sulfates in causing long-term human health effects is less well established, it is now generally agreed that aerosol sulfates, an important component in PM2.5 pollution, cannot be ignored in this regard. Monitoring networks for SO2 are generally satisfactory, and the resources deployed to record changes in acid deposition have provided adequate information to allow long-term trends to be documented.

1.5.2 Nitrogen oxides (NOX)

This report includes a special discussion of oxides of nitrogen (see Section 2). Oxides of nitrogen include NO (nitric oxide), which is emitted as a consequence of combustion processes such as those associated with vehicles and electrical power generation. Nitric oxide is rapidly oxidized to nitrogen dioxide (NO2), which is a relatively stable compound. Ambient NO2 in North America is used as a general indicator of the density of automobile and truck traffic, since in terms of total tonnage, this sector generally dominates the NOX emission inventory. Standards for NO2 emissions from vehicles are in place in both Canada and the United States, and have led to substantial reductions in emissions per vehicle over the past twenty years. However, because these progressive reductions have been outweighed by the increased number of vehicles and their increased use in many regions, total NO emissions have not been much affected. In the case of some large stationary sources, several pilot and full-scale projects have demonstrated that significant reductions in NOX emissions can be achieved through substitution of oxygen for air in the combustion process and through catalytic treatment of stack emissions.

Nitrogen dioxides and hydrocarbons are the main precursors to the formation of tropospheric (i.e. ground-level) ozone. Growing concern over sustained acidification of sensitive ecosystems and the effects of increased ozone levels in many parts of Canada and the United States has led to discussion of the need for additional NOX emission reductions. Nevertheless, strategies are being developed in many areas to address ozone and other pollutants. As these strategies are implemented, steps to reduce NOX emissions will likely be taken as well.

1.5.3 Acid Rain

Reductions in SO2 emissions have been central to lowering the acidity of rain on both sides of the Canada­United States boundary. Recent evidence suggests that, with the advent of sulfur dioxide reduction programs, the nitrate component of acid rain, largely influenced by NO2, has assumed more importance. Reductions in NOX emissions have been more difficult to achieve than for SO2, largely because of the importance of the transportation sector as an emission source. The research conducted since the problem of acid rain was first widely recognized in the early 1970's has led to a much better understanding of its impact on forest species and forest growth and on freshwater resources.

1.5.4 Tropospheric Ozone

Ground-level ozone is formed by a complex series of reactions that occur when NOX and hydrocarbons co-exist in the presence of sunlight. Ozone formation was first recognized in Los Angeles in 1952. The problem was initially thought to be confined to that region, but for the past twenty years it has been recognized as a significant concern in every part of the world. Ozone, as well as its precursors, exists long enough in the atmosphere to allow major transboundary transfers to occur: it is thought to be capable of traveling as far as 750 km (460 miles) from the major source of its precursors.

Ozone is an intense oxidizing agent. It is capable of causing inflammation in the human lung when breathed at concentrations as low as 0.08 parts per million (ppm). Epidemiological studies have shown that emergency room visits and admissions for acute respiratory disease in all age groups are associated with ozone levels at concentrations currently experienced in many portions of the U.S. and Canada. Field studies of children at summer camps have demonstrated that ambient ozone levels cause a measurable decline in lung function. Similar effects have been found in fruit pickers in the Fraser Valley working ten-hour days in atmospheres of less than 0.08 ppm of ozone. Several studies have also found that ozone levels are associated with increased daily mortality.

Many crops are sensitive to ozone exposure during the growing season, and the economic impact of ozone at current levels in some regions is thought to be considerable. Native forest species are also sensitive to ozone, although there has been some difficulty in distinguishing which effects on natural forests are ascribable to ozone and which to acid species.

It is now recognized that a reduction in the emissions of both hydrocarbons and NOX is necessary to limit ozone formation. In some regions, natural hydrocarbons from trees are believed to be responsible for as much as 30 per cent of the ozone formed. In completely urban regions, hydrocarbons are largely derived from gasoline fugitive emissions and certain chemical processes. In Los Angeles and the northeastern United States, requirements for vapor recovery technology have been imposed to limit hydrocarbon emissions when automobiles are refueled. The NO2 contributions to ozone formation are primarily the result of anthropogenic emissions from stationary and mobile sources.

1.5.5 Particulate Pollution and Haze

Particulate pollution originates from windblown dust, smoke, and direct emissions of particles from mobile and stationary sources. It also originates from the formation of secondary aerosols, particularly organics, nitrates and sulfates, from reactions of contaminants such hydrocarbons, NOX and SO2 emitted to the atmosphere. Although all particles less than 10 microns in diameter (PM10) are respirable into the human lung and therefore potentially capable of causing adverse effects, it has recently been recognized that particles less than 2.5 microns in diameter (PM2.5) may constitute the fraction most responsible for demonstrated adverse health effects. Because PM2.5 is capable of traveling long distances, transboundary atmospheric transport is inevitable.

There is now a large body of epidemiological data indicating that daily mortality, particularly from respiratory and cardiac causes, is associated with PM10 and PM2.5 levels. These studies have now been reported from 30 different regions on three continents with very different climatic conditions and with differing associated pollutants. Other indicators of significant adverse health effects are the diminished lung function of children, hospital admissions for respiratory disease (both acute and chronic), aggravation of asthma, and possibly the risk of lung cancer.

The detailed biological mechanisms of these very diverse effects and the components of PM2.5 responsible for them are not yet fully understood. There is some indirect evidence that particles from diesel engines may be more toxic than others and that particles from the earth's crust are less toxic. Until the nature of the toxic particles is more precisely known, however, it is generally considered appropriate to treat all PM10 and PM2.5 particles, regardless of their origin, as potentially harmful.

Regional haze is associated with fine particulate matter (PM2.5 or smaller). Depending on their origin in North America, these particles can be dominated by secondary sulfates, nitrates, carbon, or soil-related materials. Visibility-reducing particles may come from large combustion sources, vehicle emissions, forest fires, road dust, mining operations, or residential wood burning. On both sides of the border, regional haze is monitored according to protocols established by the Interagency Monitoring of Protected Visual Environments (IMPROVE) network developed by the U.S. National Park Service. The United States has 69 IMPROVE or IMPROVE 'protocol' sites in many of the 156 Class 1 protected (parks and wilderness) areas. The number of IMPROVE sites will increase to 108 should pending national regional haze rules receive Congressional approval.

In July 1997, the U.S. Environmental Protection Agency (EPA) proposed regional haze rules that would use deciviews as the standard visual index for the 156 protected areas. The deciview reflects perceived visual changes: a one-deciview change represents a change in scenic quality that would be noticed by most people.

In the United States under the pending legislation, state implementation plans (SIPs) would be required to control particles causing regional haze in order to attain the national visibility goal of no impairment in designated areas. As haze is often formed in areas some distance from the source of the original pollution, the Board encourages the formation of regional partnership groups to deal with downwind emissions that reduce visibility in another state.

1.6 Receptors

Along the Canada­United States border, regional pollutants of concern (ozone, PM, PM2.5, and acid rain) are currently affecting sensitive receptors. These receptors include both natural resources and human populations, especially sensitive groups such as asthmatics, children and the elderly. Visibility, the ability to see scenic vistas, is also subject to being degraded in parks, wilderness areas, and refuges. In controlling regional pollutants, streams, lakes, fisheries, grassland, alpine and forested ecosystems, and wildlife would also benefit. An emerging natural resource issue is the effect of nitrogen inputs to estuaries and coastal ecosystems, where eutrophication can result in oxygen depletion and other negative effects on fisheries and water quality. These sensitive receptors are found in all regions along the border, without reference to political boundaries.

Recommendations

Recognizing the need to manage the transboundary region in as seamless a manner as possible, the Board recommends the following:

  • The Commission propose to governments that the Canada­United States border region (extending far enough on either side to capture transport distances for at least the common air pollutants) be segmented into Transboundary Air Pollution Transport Regions (TAPTRs) as a focus of further joint effort by the governments. The Board commits itself to provide continual advice and guidance to the Commission as the governments consider this approach and attempt its implementation.
  • Within each of the TAPTRs, the Commission should advocate the generation of common harmonized data sets, including emission inventories and monitoring data. Monitoring networks and methodologies and transport models should be continually examined to determine the comparability of their outputs. These data resources should be used to develop truly borderless air quality representations for the transboundary regions.
  • For pollutants transported over great distances, such as mercury and POPs (Persistent Organic Pollutants), the Board should continue to identify source regions that contribute significantly to Canada­United States transboundary pollution and review the effectiveness of the governments' control programs in reducing emissions in these regions. These actions will support a broader continental effort led by the Commission for Economic Cooperation (CEC) in North America. Source regions of these PTSs may in some instances be subsets of the TAPTRs or may be located beyond the boundaries of the TAPTR border zone.