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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They also include secondary pollutants that are created in the atmosphere by chemical reaction sequences that begin with primary pollutants. Important secondary pollutants include atmospheric oxidants like ozone and hydrogen peroxide, sulfuric and nitric acids, and chemically diverse secondary smog particles.
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REPORT GENESIS Federal, state, and local agencies are faced with the need to understand and manage the current impact of long-range transport of pollution on health and well-being (relative to the impacts of local pollution sources) , as well as the need to develop measurement methods and models to track pollution transport trends and project their future levels and impacts.
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KEY CONCLUSIONS Both observational and modeling studies confirm that significant quantities of the pollutants considered in this study are transported over long distances, both to and from North America. Meteorological conditions off the east coasts of both Asia and North America are conducive to lofting pollutants into the midlatitude free troposphere, where strong winds aloft can rapidly transport polluted Asian air masses to North America and polluted North American air masses to Europe.
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in key source regions; • frequent satellite observations (and associated analyses) of a range of important primary and secondary pollutants with adequate horizontal and vertical resolution in order to identify long-range transport events and to verify regional emissions estimates with inverse modeling; • more capable in situ monitoring of multipollutant ground-level and vertical profile concentration measurements at judiciously chosen receptor sites with measurement capabilities designed to fingerprint pollutants from foreign sources and provide key pollutant ratios and other data necessary to establish trends and allow source attribution calculations; • periodic intensive field measurement campaigns designed to track long-range transport events, better characterize chemical and physical transformations of key pollutants, and identify and quantify mechanisms that transport pollutants from the surface into the free troposphere and back; and • improved chemical transport models capable of using inversion techniques (wherein pollutant emissions are derived from measured atmospheric concentrations)
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These plumes are observed in the free troposphere over affected regions, but less frequently at the surface due to dilution in the boundary layer. • Multimodel studies calculate that a 20 percent reduction in ozone precursor emissions from any three of the four major industrial regions of the Northern Hemisphere will reduce surface O3 in the fourth region by about one part per billion (ppb)
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• Chemical transport models are increasingly being used to estimate long-range transport contributions to atmospheric PM concentrations. Uncertainties in model estimates result from factors such as lack of observational constraints, particularly in the free troposphere, where much of the transport occurs; poorly constrained or unknown emissions of some primary particles and the emissions and conversion of PM precursors (especially secondary organic PM)
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Transpacific atmospheric transport of POPs to the continental United States is relatively well characterized, but other potentially important transport pathways are not. • There is evidence that atmospheric concentrations of historically used pesticide-related POPs are declining due to global regulations, while concentrations of combustion-related POPs, as well as some chemicals currently in use that have the potential to be considered POPs, are increasing due to growing emissions.
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Emission Inventories and Projections To enhance our ability to understand, forecast, and manage changing emission sources, and thus adequately model long-range pollutant transport events, the Committee recommends designing field experiments that not only confirm emission totals but also link them to the fundamental sources and processes that generate them; improving the accuracy, timeliness, spatial and temporal resolution, multipollutant coverage, and inter-comparability of Northern Hemisphere
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Meteorologists and atmospheric chemists, including both modelers and measurement specialists, should collaborate on efforts to develop better measurement techniques and improved numerical models that will enable us to adequately quantify the role of distant sources on local air quality. Ship and Air Transport Emissions It is necessary to better understand how emissions from ocean shipping and transport aircraft affect atmospheric composition, and can complicate the detection and characterization of long-range atmospheric pollutant transport from traditional land-based sources.
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CONCLUDING THOUGHTS The pollutants discussed in this study do not represent all species of concern, but they do illustrate the variability of pollutant composition and behavior and provide focused examples for analyzing the phenomenon of long-range pollutant transport. Present global socioeconomic scenarios predict that adverse air quality impacts from distant sources of pollution are likely to grow and cause increasing concern in the United States and other nations that are determined to provide clean air for their citizens and their ecosystems.
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