Global Sources of Local Pollution An Assessment of Long-Range Transport of Key Air Pollutants to and from the United States (2010) / Chapter Skim
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1 Introduction
1 Introduction
Pages 11-34
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We now know that atmospheric pollutants often have long-distance impacts on regional and continental scales (acid and nutrient deposition, atmospheric haze, particulate matter climate impact, persistent toxic
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There also is concern about international pollution transport as a source of continuing exposure to chemicals that have been banned in the United States and other countries (e.g., certain persistent organic pollutants, POPs)
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Air pollutants can be gaseous substances dispersed as individual mol ecules or very small condensed-phase liquid droplets or solid particles. The condensed airborne material is often collectively termed aerosol particles or particulate matter (PM)
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From an observational perspective, background (or baseline) concentrations are often estimated as the average weakly varying concentrations against which pollution plumes (events of enhanced pollutant concentrations)
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MOTIVATIONS FOR CONCERN Despite increasing growth and urbanization, air quality in developed countries generally has improved over the past 25 years because of serious efforts to set and meet air quality standards. However, air quality in much of the less developed world has declined due to increasing emissions from rapidly expanding and poorly regulated motor vehicle fleets, growing industrial and power generation activities, and domestic coal and biomass 1 Information on the committee's sponsors, its schedule, and its full statement of task are presented in Appendix A
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The conflict between increasing air pollutant levels in some parts of the world, and more stringent air quality standards in other parts of the world, leads to concerns that if even small fractions of the pollutants from Nation 1 reach Nation 2, Nation 2 may find it significantly more difficult to meet its mandated air quality goals. The cost of not meeting air quality standards on human health, agricultural production, and ecosystem viabilty can be high, so accepting higher pollution levels is an unattractive option.
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The effects of short-lived air pollutant species on regional and global climate, through both direct interaction with atmospheric radiation and indirect effects related to changes in cloud properties are a growing concern. More information about specific air pollutants and other environmental impacts is presented in the following four chapters.
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A brief overview of the dynamics of atmospheric air masses and their associated time and distance scales is presented below, and a more detailed explanation is provided in Appendix B Atmospheric Dynamics of Long-Range Transport Most meteorological phenomena that affect long-range pollutant transport occur in the troposphere, the lowest portion of the atmosphere, which extends from the surface to ~ 18 km in the tropics and ~ 8 km in polar regions.
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Air slowly rises out of the boundary layer, often Stratosphere Mixing Mixing Tropopause 8-18 km Tropopause folding Prevailing westerlies Free troposphere Mixing Mixing 1-2 km Boundary layer Advection Adve ction Lifting Subsidence H L H L Asia N America Europe FIGURE 1.1 Schematic of the dominant dynamical processes involved in long-range midlatitude pollution transport.
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Winds within both the boundary layer and free troposphere climatologically are from the west, thereby completing the global transport cycle. At lower latitudes the prevailing winds typically flow from east to west, while the prevailing midlatitude flows are from west to east; winds from northern Africa can bring Saharan dust to the Caribbean, Florida, and other Gulf Coast states.
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and hexachlorocyclohexane, which are persistent organic pollutants. The enhancements in the observed pollutants occured nearly simultaneously.
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can sequester reactive nitrogen oxides (NOx) in the cold free troposphere but releases it to form ozone when air masses subside and warm.
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More detailed examples of chemical transformation and removal processes are presented in subsequent chapters that discuss the production and transport of specific pollutant classes. Tools for Understanding Long-Range Transport It is challenging to detect and quantify the impact of long-range transport on local air quality that is dominated by local sources.
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This same study noted that assessing the adverse impact of long-range transport of pollution on North American air quality would require much improved emission inventories for the entire Northern Hemisphere. Emissions from regions with less experience in developing EIs are widely recognized to have even more serious problems, caused both by lack of basic emission data and inadequate institutional support for gathering and processing required data.
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INTRODUCTION BOX 1.3 Modeling Tools Used In the Study of Long-Range Transport of Pollution Chemical transport models (CTMs) are important tools that are used to explore pollution transport pathways and to assess the impact of long range transport on ambient pollution levels.
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GLOBAL SOURCES OF LOCAL POLLUTION BOX 1.3 Continued approach, wherein emissions from individual source regions are per turbed (or tagged) , and these perturbations are propagated forward throughout the modeling domain to future times (Wang et al., 1998; Wild et al., 2001; Derwent et al., 2004; Auvray and Bey, 2005; Sudo and Akimoto, 2007; Liu et al., 2007, 2008, 2009; Fiore et al., 2009; Saikawa et al., 2009)
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INTRODUCTION BOX 1.4 Pollutant Emissions Overview Emissions of the pollutants and pollutant precursors described in this report may be associated with both natural and anthropogenic (human caused) sources.
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Without accurate emission inventory data for both local and upwind emissions at required spatial and temporal resolutions, CTMs cannot be expected to correctly predict how pollutants will be transformed during long-range transport or to quantify either the absolute or relative impact of these pollutants on local air quality. Deficiencies in hemispheric and global emission inventories that affect assessments of long-range transport will be discussed in subsequent chapters.
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Specific policy contexts for each relevant pollutant class will be further discussed in Chapters 2-5. International Policy Context International action on long-range pollutant transport has revolved largely around the U.N.
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that is charged with advancing and assessing the state of knowledge with respect to the flows of air pollutants across the Northern Hemisphere to inform future policy negotiations under the Convention. A number of other existing bilateral, regional, and global agreements are potential vehicles for addressing the issue of long-range pollution transport, including • the U.S.-Mexico Border 2012 Program: LaPaz agreement on cooperation for the protection and improvement of the environment in the border area (addressing O3 and PM)
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that can affect air quality but are not reasonably controllable using techniques that local air agencies may implement. The EPA 2 The subsequent chapters include consideration of ambient air quality standards of other countries and WHO global-scale recommendations.
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and nitrogen oxides (NOx) across 28 eastern states, using an emissions trading system, in order to address the effect of an upwind state's emissions on a downwind state's ability to meet air quality standards for O3 and PM.
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Chapters 2-5 provide more detailed discussions about what is known and what needs to be learned for each of the main pollutant classes that we were asked to address in this study (ozone and its precursors, particulate matter and its precursors, gaseous and particulate mercury, and persistent organic pollutants)
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