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WRAP Technical Comments concerning the EPA PM NAAQS proposal of January 17, 2006
DRAFT February 21, 2006 DRAFT
Summary: The Western Regional Air Partnership has several concerns and suggestions with regard to
the proposed changes to the PM NAAQS related to its mission to help western states and tribes achieve
reasonable progress toward the national visibility goal and implement the Regional Haze Rule.
Specifically WRAP has the following comments.
1. WRAP believes that a secondary standard for the PM2.5 NAAQS is necessary to protect urban visibility, as
was considered but not included in the proposal, and will provide the additional benefits of reduced haze
levels in many proximate and distant downwind federally-protected areas by further reducing emissions that
are transported out of western urban areas. EPA should modify the proposal to include nationally-
applicable secondary standards as recommended by CASAC, for a short-term maximum value of 20 μg/m3
to 30 μg/m3 to reduce urban as well as remote area haze levels.
2. WRAP is concerned that the rationale for limiting the PMcoarse NAAQS to urban areas is problematic.
WRAP believes that the EPA assertion that PMcoarse in rural areas are composed of benign materials is
unfounded/not well-founded. Limited compositional analysis using the IMPROVE network PM10 filters and
other western monitoring programs show PMcoarse to be composed of complex mixtures of components that
vary regionally and are not necessarily benign. The highest concentrations of coarse mass are in areas
where playas and terminal lakebeds that are naturally enriched with soluble salts and heavy metals are the
principal emission sources. EPA should modify the proposal to make the PMcoarse NAAQS and the
supporting monitoring networks applicable to rural and urban locations across the nation, not just in large
population centers.
3. The collective experience of WRAP members with PM monitoring since the inception of the federal Clean
Air Act tells us that the recently proposed monitoring plan for PMcoarse is short-sighted and inappropriate
because it would restrict monitoring to urban areas and does not include speciation. PMcoarse is known to
travel hundreds of kilometers without significant loss. Without a national network that monitors PMcoarse to
assess regional events and without speciated PMcoarse to aid in assessing the source types and health threat,
chances of ever having an adequate understanding of the PMcoarse impacts will be severally hampered. EPA
should modify the proposal to endorse the use of IMPROVE Network PMcoarse monitoring and to expand its
capabilities to include routine speciation so that it would be the rural counterpart to the urban monitoring
conducted by state and local air agencies. Include charts from Lydia Wegman’s presentation and map of
IMPROVE and IMPROVE protocol sites.
4. WRAP is concerned that the proposal to both eliminate the PM10 NAAQS and replace it with an urban-only
PMcoarse standard, which includes exemptions for agricultural and mining emissions, will result in the
removal of current and planned emission control measures for substantial primary PM source activities
throughout the western U.S. Progress in meeting the regional haze goals for many western Class I areas
would be jeopardized if dust contributions, which are already substantial in some areas, were to increase due
to loss of a federal standard and the resulting backsliding. EPA should promulgate a 24-hour PMcoarse
secondary NAAQS that would apply nationwide with a 98th percentile standard in the range from 50μg/m3
to 135μg/m3 and with no exemptions for any source type or industry.
Documentation: This section briefly documents rationale for the four numbered recommendations
summarized above. Some of the information supports more than one of the recommendations.
Visibility impairment is caused by both PM2.5 & PMcoarse (supports recommendations 1 and 4)
Light extinction effects of PM have been known for many decades through laboratory and field
measurements, and are precisely predicted by Mie Theory calculations. The EPA “Guidance for
Tracking Progress Under the Regional Haze Rule” includes an algorithm used to estimate haze levels
for the Regional Haze Rule that has both PM2.5 and PMcoarse terms. PMcoarse is not as efficient on a per
unit mass concentration basis as the various PM2.5 components, but at some locations and times the
high concentrations of PMcoarse compared to the PM2.5 makes PMcoarse the single largest contributor to
haze. This can be seen in the map in Figure 1 that shows the fraction of IMPROVE samples where
dust contribution to light extinction is the largest of component (other components include sulfate,
nitrate, organic mass and black carbon). In this map dust includes light extinction from PMcoarse plus
PM2.5 soil, but the PMcoarse is generally 80% to 90% of the dust extinction.
The percentage of sampling days when dust dominated aerosol light extinction is as high as ~ 50 –
70% in some of the sites. “Dominated” means that it caused more light extinction than any of the
other major categories -- SO4, NOx, EC, and OC. 3
Figure 1. Percentage of IMPROVE sample days between 1997 and 2002 when haze from dust (coarse
mass plus fine soil) is the largest component.
The Regional Haze Rule is particularly concerned with the 20% worst haze days based on monitoring
data. Figure 2 shows that the PMcoarse contributes substantially at Saguaro National Park (near Tucson
Arizona and typical of a number of southwestern class I areas). The worst days in these stacked bar
plots are labeled with a W at the top. This plot shows that PMcoarse (light gray at the top of the bars) is
a major contributor on most of the worst haze days. Similar plots can be seen for many federally
protected areas in the southwestern U.S. by using the composition tool on the VIEWS web site at:
http://vista.cira.colostate.edu/views/web/AnnualSummaryDev/Composition.aspx.
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Figure 2. Stacked bar plots showing the six components of light extinction for Saguaro National Park in
Arizona.
A more restrictive nationally-applicable secondary PM2.5 NAAQS for urban visibility leading to
urban emissions source reductions will have beneficial effects on proximate downwind areas with
federal visibility protection (supports recommendation 1)
Western metropolitan areas such as the Colorado Front Range (Denver and other cities) and the
Phoenix area have adopted urban visibility indices1,2 because former and current secondary PM
NAAQS do not protect scenic views and welfare effects within and across their urban regions.
Federally–protected Class I areas are contiguous and/or proximate to a large number of metropolitan
areas in the West, see for example Class I areas proximate to the Phoenix and Tucson urban areas.
Figure 3. Arizona state map showing the proximity of visibility-protected Class I areas to the Phoenix
and Tucson metropolitan areas.
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WRAP has prepared emissions analyses for 50 kilometer buffer zones around western Class I areas.
See the example of Saguaro National Park’s West Unit contiguous to the Tucson urban area.
Emissions in the Tucson area are important contributors to the visibility impairment observed at
Saguaro National Park. Therefore a secondary PM2.5 NAAQS set between 20μg/m3 and 30μg/m3 to
reduce urban haze would result in improved haze in nearby class I areas.
Near Emissions Project Home Page
http://wrapair.org/forums/class1/near/htmlfiles/main.html
The maps and data on this site are intended to illustrate the general landscape of emissions in and near WRAP Class I areas.
For purposes of this illustration, "near" is defined as a 50 km area surrounding the borders of the Class I areas. Because in
several cases areas are adjacent and have similar characteristics, some areas are analyzed and displayed together as a single
group. There are 82 groups representing 117 areas. Start here to review maps and tables for a particular Class I area.
All emissions are derived from WRAP emission databases for the year 1996. Their spatial allocation to the analysis areas,
however, are based on several data sets (e.g., population density, land use/cover, etc.) which span a few different years over
the 1996 period. Additional details on the methods and data sources can be obtained by clicking on the "About" links on
other pages within this site.
A survey of local officials in each Class I group was conducted to ensure reasonableness of the data and to identify
activities, trends, and proposed projects which may affect emissions but which may not be apparent in the emission
databases. Results of this survey are available upon request.
Figure 4. Map showing that the Tucson metropolitan area is within 50km of the western unit of Saguaro
National Park.
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Table 1. Emissions within 50km of the West Unit of Saguaro National Park.
1996 Emissions (tons) Near WRAP Class I areas
Group 54: Saguaro (West)
Source Category VOC NOx SO2 PM10 PM2.5 NH3
Point Sources 189 8,147 2,805 5,124 942 2
Area Sources (excluding windblown dust) 18,978 4,117 387 7,617 2,740 1,847
Residential Wood Combustion 478.2 30.6 4.4 298.0 298.0 0.0
Other Fuel Combustion 55.3 3,950.4 348.9 89.6 54.7 10.0
Industrial Processes 10.7 0.0 0.0 714.6 170.9 0.0
Construction Dust 0.0 0.0 0.0 4,284.5 1,428.2 0.0
Solvent Utilization 14,138.7 0.0 0.0 0.0 0.0 0.0
Petroleum Storage and Transport 3,509.6 0.0 0.0 0.0 0.0 0.0
Waste Disposal and Recycling 785.4 136.1 34.1 557.6 469.9 149.6
Agricultural Activities (except burning) 0.0 0.0 0.0 1,672.5 318.6 1,687.6
Fires 2 1 0 4 4 0
Management Fires 2.1 1.0 0.3 4.3 3.7 0.2
Wildfires 0.0 0.0 0.0 0.0 0.0 0.0
On-Road Mobile Sources 22,143 19,574 354 2,185 827 455
Light-Duty Vehicle Emissions 20,821.5 13,053.8 258.7 250.6 191.4 441.7
Heavy-Duty Vehicle Emissions 1,321.3 6,520.0 95.8 355.3 332.2 13.0
Fugitive Dust - Paved Roads 0.0 0.0 0.0 660.0 165.0 0.0
Fugitive Dust - Unpaved Roads 0.0 0.0 0.0 919.2 137.9 0.0
Off-Road Mobile Sources (excluding airports
and commercial marine vessels) 6,400 8,116 806 558 513 40
Lawn & Garden Equipment 4,956.4 546.8 48.9 149.4 137.5 10.6
Recreational Equipment 160.7 7.0 0.6 0.8 0.7 0.2
Commercial and Industrial Equipment 667.8 909.5 67.3 63.0 58.1 18.3
Construction and Mining Equipment 405.2 1,956.1 270.5 212.6 195.5 3.7
Agricultural Equipment 18.7 105.8 13.2 16.3 15.0 0.2
Recreational Marine Vessels 0.0 0.0 0.0 0.0 0.0 0.0
Locomotives and Railroad Equipment 190.8 4,591.0 405.9 115.7 106.4 7.1
Logging Equipment 0.0 0.0 0.0 0.0 0.0 0.0
Total 47,711 39,955 4,353 15,488 5,026 2,344
PMcoarse concentrations are regionally highest in areas impacted by suspended dust from certain
desert playas that are enriched in salts and heavy metals that cannot be assumed to be benign.
Regions with substantial agricultural dust emissions do not exceed the annual 98 th percentile level
proposed for the urban only standard. (supports recommendations 2, 3 and 4).
PMcoarse data from the IMPROVE Network for 2002 through 2004 were used to determine the highest
annual 98th percentile values for each site. The mean values of these are shown in Figure 5. This
shows that the region of highest coarse mass is in southern NM and west TX.
Table 2 shows the sites with the largest three-year mean of annual PMcoarse 98th percentile
concentrations. None of these sites would violate the proposed PMcoarse NAAQS. The five highest
concentrations are at sites influenced by suspended dust from desert playas and those in or near urban
areas. The Cherokee Nation site with a mean 98th percentile concentration of 41ug/m3 is the highest is
in an agricultural area. Again, none of these sites exceed the proposed urban PMcoarse standard of
70μg/m3.
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Figure 5. Map of the average 2002-04 98th percentile PMcoarse concentration values for the IMPROVE
Network sites. (prettier map to follow)
Table 2. PMcoarse 98th percentile concentrations for sites with three year mean values above 30 μg/m3.
Site State 2002 2003 2004 Mean Max
Guadalupe Mountains NP TX 41.72 109.00 56.71 69.14 109.00
Birmingham AL 54.51 54.51 54.51
Phoenix AZ 57.18 55.00 35.08 49.09 57.18
Salt Creek NM 39.89 73.75 24.67 46.10 73.75
Douglas AZ 43.63 43.63 43.63
Cherokee Nation OK 32.23 50.77 40.21 41.07 50.77
Virgin Islands NP VI 37.44 39.12 43.63 40.06 43.63
Saguaro West AZ 34.17 58.95 22.92 38.68 58.95
El Dorado Springs MO 54.78 35.35 25.43 38.52 54.78
Queen Valley AZ 31.08 55.02 27.87 37.99 55.02
Dome Lands Wilderness CA 36.07 28.39 41.30 35.26 41.30
Walker River Paiute Tribe NV 30.75 37.20 33.98 37.20
Cedar Bluff KS 48.56 29.23 23.61 33.80 48.56
San Gabriel CA 65.11 18.14 17.16 33.47 65.11
Omaha NE 29.70 34.11 31.91 34.11
Death Valley NP CA 41.77 20.63 32.77 31.72 41.77
Spokane Res. WA 38.68 34.58 21.58 31.61 38.68
Sycamore Canyon AZ 34.88 31.96 27.78 31.54 34.88
Viking Lake IA 28.75 35.87 27.87 30.83 35.87
Blue Mounds MN 23.80 38.26 28.47 30.17 38.26
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Agricultural emissions of PMcoarse are significant and should not be exempted from possible controls
for their contributions to the NAAQS or regional haze. (supports recommendation 4)
Figure 6 shows a map of wind-blown dust emissions in the western U.S. developed using a model of
wind suspension of dust with soil characteristics and land-use data coupled to a wind field model. The
results may seem counter-intuitive in that the region of largest emissions is not the deserts of the
southwest, but the agricultural regions where soil tillage and harvesting periodically disturbs and
exposes bare soil to wind erosion. While the relative contributions of dust to haze are largest in the
desert southwest and these locations experience some of the highest extremes (as seen in Figure 5), the
absolute dust contribution to annual haze levels are larger in the areas influenced by agricultural
emissions. This is clearly seen in Figure 7 that shows that the annual PMcoarse concentrations as
measured by the IMPROVE network is high in the agricultural center of the country and Central
Valley of California. Any exemption for agriculture emission controls for PMcoarse could adversely
affect the long-term success of the regional haze rule. Blanket exemptions for mining emission
controls could have similar effects on a more local scale.
Figure 6. Map of the model-estimated wind-blown dust emissions for 2002.
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Figure 7. Map showing the annual PMcoarse concentration from the IMPROVE network for 2004.
A PMcoarse secondary standard set no higher than 135μg/m3and applicable nationwide is needed to
prevent backsliding resulting from the rescinding of the PM10 NAAQS.
WRAP’s Dust Emissions Joint Forum recently sponsored research conducted by Midwest Research
Institute on the PM2.5 fraction of PM10 emissions from fugitive dust sources (unpaved roads,
agriculture, et cetera) employing a variety of soil material suspended under laboratory wind-tunnel
conditions. This work is documented in a peer-reviewed project report3 and recommended changes to
the PM2.5 to PM10 ratio4 in AP-42 (EPA’s emissions guidance document). This work shows that 80%
to 90% of the PM10 is PMcoarse for fugitive emissions sources. Table 1 below from the report on
proposed revisions to AP-42 shows that these values differ from currently used values in AP-42, which
show a smaller PMcoarse fraction of PM10. The difference is principally due to the use of a sharper cut,
ambient particle sampler instead of the cyclone samplers that were used in the measurements that were
the basis of AP-42.
Using the 90% value as the basis for setting the level of a secondary PMcoarse NAAQS that would be
equivalent to the current primary PM10 NAAQS of 150μg/m3 give a value of 135 μg/m3 (90% of 150 is
135). The photographs (not yet produced) show computer simulated haze conditions at Saguaro
National Park under typical conditions, worst haze conditions, and typical PM2.5 conditions but with
135 μg/m3, 100 μg/m3, 70 μg/m3, and 50 μg/m3 of PMcoarse. These clearly show the added benefit for
haze of having a smaller secondary PMcoarse NAAQS.
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Table 3. Proposed particle size ratios for AP-42.
AP-42 PM2.5/PM10 Ratio
Fugitive dust source category
Section Current Proposed
Paved Roads 13.2.1 0.25 0.15
Unpaved Roads (Public & Industrial) 13.2.2 0.15 0.1
Construction & Demolition – 0.208 1 0.1
0.1 (traffic)
Aggregate Handling & Storage Piles 13.2.4 0.314
0.15 (transfer)
Industrial Wind Erosion 13.2.5 0.40 0.15
Agricultural Tilling – 0.222 2 0.2 (no change)
Open Area Wind Erosion – - 0.15
Notes:
1
AP-42 Section 13.2.3 suggests using emission factors for individual dust
producing activities, e.g., materials handling and unpaved roads. The WRAP
Fugitive Dust Handbook recommends using a fine fraction ratio of 0.208 from a
report prepared for the US EPA, Estimating Particulate Matter Emissions from
Construction Operations (MRI, 1999).
2
Agricultural tilling was dropped from the 5th edition of AP-42. The WRAP
Fugitive Dust Handbook recommends using a fine fraction ratio of 0.222 from
Section 7.4 of the California Air Resources Board’s Emission Inventory
Methodology (CARB, 2003).
References:
1
Colorado Department of Public Health and Environment. Denver Metropolitan Area Visibility
Standard Index. http://apcd.state.co.us/psi/main.html
2
Arizona Department of Environmental Quality. Phoenix Metropolitan Area Visibility Index. 2003.
http://www.phoenixvis.net/vis-index.html#m
3
Cowherd, C. and J. Donaldson. 2005. Analysis of the Fine Fraction of Particulate Matter in
Fugitive Dust. Final report prepared for the Western Governors’ Association, Western Regional Air
Partnership (WRAP), MRI Project No. 110397, October 12, 2005.
4
Proposed Revisions to Fine Fraction Ratios Used for AP 42 Fugitive Dust Emission Factors by
Chatten Cowherd of Midwest Research Institute for the Western Regional Air Partnership (WRAP),
MRI Project No. 110397, November 7, 2005
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