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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3 Particulate Matter
3 Particulate Matter
Pages 67-96
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From page 67... ...
Most attention has been focused on the fine fraction because it affects health, visibility, and radiative forcing. With lifetimes on the order of days to weeks, fine particulate matter can undergo long-range transport, producing global and regional in addition to local impacts.
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From page 68... ...
For modeling and monitoring purposes the composition of dry atmospheric PM is generally reduced to a few major categories. Commonly identified components include sulfates, nitrates, organic carbon, elemental or black carbon, sea salt, soil or crustal material, and specific elements of interest, such as Pb.
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From page 69... ...
It is important to bear in mind that water can be the dominant (and unmeasured) PM constituent above ~ 90 percent relative humidity and sampling and analysis difficulties are known to be present for elemental carbon, organic carbon, and nitrate species, making their routine quantification less certain.
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From page 70... ...
Figure 3.2 summarizes the global sources of major non dust PM components, including sources leading to secondary production of sulfate, nitrogen, and organic PM components. Secondary organic aerosol (SOA)
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From page 71... ...
In the column for organic carbon, dashed circles show the approximate contribution of secondary organic aerosol formed from precursors. Values are from Bond et al.
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From page 72... ...
Effects related to long-term exposure include increase in lower respiratory symptoms, reduction in lung function in children and adults, increase in chronic obstructive pulmonary disease, and reduction in life expectancy due mainly to cardiopulmonary mortality but also to lung cancer (WHO, 2006)
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From page 73... ...
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From page 74... ...
were linked with rapid secondary organic aerosol formation from anthropogenic sources (e.g. Robinson et al., 2007)
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From page 75... ...
(2008) have found that climate simulations using aerosol loadings projected to the year 2100 using the SRES A2 scenario produce regional patterns of surface temperature warming that do not follow the regional patterns of changes in aerosol emissions, tropospheric loadings, or radiative forcing.
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From page 76... ...
regulations, which are aimed at both limiting ambient levels of PM to protect human health and welfare and at controlling emissions from new and existing sources. At the present time welfare-based standards for pollutants apply only to visibility impairment and potential crop damage and not to direct or indirect radiative forcing impacts.
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From page 77... ...
In contrast to the NAAQS approach, which requires all areas of the nation to demonstrate that ambient pollutant concentrations are below a specified standard, the regional haze rule (passed in 1999) addresses only national parks and wilderness areas.
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From page 78... ...
KEY PM TRANSPORT PATTERNS AND EFFECTS ON SURFACE CONCENTRATIONS Local and regional emissions are responsible for most PM concentrations that exceed air quality standards, but it is now recognized that emis
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From page 79... ...
. Episodic highconcentration dust events are most frequently observed at the surface in springtime because of increased Asian dust mobilization and favorable transport pathways during that season (Wells et al., 2007)
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From page 80... ...
, but transport pathways vary seasonally. The direction of westward North African dust transport is tied to the shifts in position of the Bermuda high, with plumes affecting Amazonia in the Northern Hemisphere winter, and transport shifting northward during the summer months.
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From page 81... ...
suggested that European emissions dominate aerosol transport to the surface in the Arctic, whereas East Asian emissions dominate in the upper troposphere. MODELING AND ATTRIBUTION OF PM TRANSPORT AND TRENDS Trends in PM Concentrations Data from monitoring networks have been analyzed to attempt to discern trends in PM surface concentrations.
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From page 82... ...
Current experience suggests that PM2.5 surface concentrations are proportional to satellite aerosol observations for regions where aerosol composition and vertical profiles are relatively stable (e.g., eastern United States) , but this relationship weakens where aerosol composition and vertical profile have large variations (e.g., western United States)
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From page 83... ...
. There are also reviews focused on specific components of PM, for example, the review of secondary organic aerosol modeling by Kanakidou et al.
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From page 84... ...
Figure 3.5 summarizes the results from the model calculations in terms of the extent to which 20 percent perturbations in local and distant anthropogenic emissions of aerosol precursors and aerosol primary emissions contribute to mean surface PM2.5, total sulfate deposition, and sulfate column loadings over several receptor source regions: North America (NA) , Europe (EU)
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From page 85... ...
"SurfacePM" = surface concentrations of PM2.5; "DepSO4" = sulfate deposited to the surface; "TotColSO4" = total column sulfate loading.
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From page 86... ...
The increase in import sensitivity from surface concentrations to column loadings indicates the substantial role of aerosol transport above the planetary boundary layer in the long-range transport of PM. The column aerosol loadings play an important role in radiative forcing.
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From page 87... ...
8-hr O3 standard from 84 ppbv to 75 ppbv. FUTURE PROJECTIONS OF FACTORS INFLUENCING PM SURFACE CONCENTRATIONS A 20 percent increase in emissions in Europe, East Asia, and South Asia is estimated to change the annual PM2.5 concentrations at the surface in North America by ~ 0.02 µg m–3 (HTAP-TF, 2007)
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From page 88... ...
Large uncertainties in these estimates can be expected, due to imperfect understanding about the trajectories of economy and technology, and about the responses of forests and deserts. The values here are provided only to evaluate whether future changes in intercontinental transport could be expected to significantly affect PM budgets in the United States.
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From page 89... ...
In our estimates of future changes we neglect two of these: deforestation, which is a minor factor in most source regions, and prescribed fires, which depend on management policies. A warmer climate is expected to increase fire frequency and quantity (IPCC, 2007, Section 7.3.3.1; Spracklen et al., 2007)
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From page 90... ...
Thus, if PM lifetimes are decreased, export from source regions may remain unchanged or even decrease despite increasing future emissions. We also know that pollution export is dependent upon location (HTAP-TF, 2007)
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From page 91... ...
Ensemble studies of chemical transport models estimate that PM sources in Europe, South Asia, and East Asia contribute on average 0.05–0.15 µg m–3 to the continental U.S. annual mean surface PM2.5 concentration (obtained by scaling the 20 percent perturbation results by a factor of 5 to account for 100 percent of the foreign influence, ignoring any nonlinear effects)
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From page 92... ...
Modeling improvements that are particularly important in evaluation of long-range transport are the simulation of dust emissions, fire emissions, and production of secondary organic PM. Question: What are potential implications of long-range PM transport for meeting environmental goals?
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From page 93... ...
Increases in surface PM from episodic or persistent trans port are significant relative to other sources in places such as the Arctic and portions of the western United States, which do not have large local pollution sources. In particular, strategies to achieve compliance with the regional haze rule across the United States may be complicated by imported PM because existing U.S.
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From page 94... ...
Baseline and background changes tend to be regional (e.g., Northern Hemisphere; Arctic, Pacific, and Atlantic regions) , thus requiring corresponding regional strategies; • reevaluating the health burden resulting from imported PM, as better mechanistic understanding of PM-health links becomes available; • assessing the other impacts of imported PM, such as adverse consequences for ecological and agricultural systems, and conse quences for regional and global radiative forcing.
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From page 95... ...
Recommendation. Increase our ability to forecast the future signifi cance of imported PM by: • increasing understanding of how future climate will affect patterns of dust mobilization, fire frequency and intensity, and biogenic emissions; • understanding how regional perturbations in aerosols affect climate; • developing multipollutant emission inventories with high spa tial resolution that reflect economic growth, technological change, and incoming regulations; • improving the forecasting of changes in atmospheric dynamics that affect transport of pollution plumes, particularly boundary layer venting and precipitation, under changing climates; • designing effective observational networks that enable rigorous analysis of PM composition, trends, and other factors that relate to long-range transport.
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