SBA Claim: The vast majority of PM2.5 from RICE travels less than 300m. Therefore, EPA should exempt 

rural engines from regulation and substantially reduce the benefits estimates. Justification for this claim 

includes a citation to the Zhu et al (2002) article examining ultrafine particles near roadways. 

• There is no data to suggest that a majority of stationary diesel RICE are rural. The available 

evidence shows that these engines are located in both rural and urban locations. The benefits 

estimates simulate a representative mixture of rural and urban emission locations across the 

country, including ground-level emissions and state-of-the science models for photochemistry 

and transport (U.S. EPA, 2006a). Even engines located in primarily rural areas would be upwind 

of more highly populated areas. 

• EPA has extensively modeled PM2.5 transport on similar on-road and non-road diesel engines 

and similar low-level sources for prior mobile source rulemakings, which all show that PM2.5 

emitted at ground-level can travel significant distances away from the source (U.S. EPA, 1999; 

U.S. EPA, 2000; U.S. EPA, 2004; U.S. EPA, 2008e; U.S. EPA, 2010c). In addition, independent 

publications have concluded that the impacts of ground-level mobile source emissions extend 

for hundreds of miles (Greco et al., 2007). 

• The recently finalized Integrated Science Assessment for Particulate Matter (U.S. EPA, 2009c), 

which is the compendium of known research regarding the science of PM, concludes that fine 

particles can travel hundreds to thousands of kilometers away from the emission source, 

whereas ultrafine and coarse particles travel less than 10km away from a source (Table 3-1, U.S. 

EPA, 2009c). Also, shown in Wilson and Suh (1997). 

• Most ultrafine particles accumulate to larger fine particles within minutes (U.S. EPA, 2009c; 

Kittelson, 1998; Zhu et al, 2002; Zhu et al, 2004; Barone and Zhu, 2008). Thus, ultrafines lose 

their identity as individual particles but still remain in the atmosphere as PM2.5 (Kittelson, 1998). 

Ultrafine particles generally represent only about 10% of PM2.5 mass (Mauderly and Chow, 2007; 

Morawska, 1998; Kittelson, 1998). Most diesel PM by mass is between 0.1 to 1 microns rather 

than ultrafine (below about 0.1 microns) (Kittelson, 1998). The benefits analysis is based on 

PM2.5 mass; as a result, conclusions about potential benefits of reductions in PM2.5 from RICE 

drawn from studies of ultrafine particles are not relevant. 

• Although some near-roadway studies show a steep gradient of concentrations for some 

pollutants away from the source, much of the drop in concentration is due to the dispersion, not 

deposition, of diesel pollutants (U.S. EPA, 2002; Horvath, 1988). In other words, concentrations 

fall as particles disperse across distances, which supports transport to a broader region as the 

explanation rather than deposition within a limited distance from the source. Many near 

roadway studies show either no significant pollution gradient for PM2.5 (Roorda-Knape et al, 

1998; Zhu et al, 2004; Zhu et al, 2006) or a significantly less steep gradient for PM2.5 (Tiitta et al, 

2002; HEI, 2010). Several studies identify evaporation, condensation, coagulation, and 

dispersion (dilution) as the primary mechanisms for the change in particle number 

concentrations and size distributions near roadways (Zhang and Wexler, 2004; Zhang et al, 2004; 

Zhang et al, 2005; Jacobson et al., 2005). 

• PM2.5 deposition rates are extremely slow because gravitational settling is overwhelmed by 

buoyancy and other resistive forces. A recent report from the Health Effects Institute on trafficrelated air pollution does not provide any evidence that elevated PM2.5 concentrations disappear 

after 300 meters (HEI, 2010). 
• The benefits estimates are based on PM2.5, which can have adverse health effects on people 

living far away from emission sources at very low concentrations (Pope et al, 2002; Laden et al, 

2006; Krewski et al, 2009). 

• The primary purpose of this rule is to control HAP emissions. The main HAPs from RICE are 

gaseous (i.e., formaldehyde, acetaldehyde, PAHs, and acrolein). EPA modeling (U.S. EPA, 2010b) 

shows that these pollutants can travel hundreds of kilometers away from the source. 

• We have already incorporated language suggested by DOE to address uncertainty in the PM cobenefits of the rule regarding the distance that PM2.5 travels from these engines because they 

have not been studied specifically. 

Studies sent to EPA for consideration: 

Zhu et al (2002) 

• Zhu et al (2002) primarily examined ultrafine particles, and only measured PM2.5 indirectly via 

light scattering, a method that EPA does not allow for regulatory measurement. Thus, the 

authors state that the PM estimates are only useful as indicators of general trends. 

• Zhu et al (2002) did not study deposition, but rather ambient concentrations of ultrafine 

particles. Neither the authors nor later mathematical modeling of the study domain suggest 

that deposition is a significant contributor to particle number gradients. 

• PM showed the shallowest gradient of all pollutants studied. 

• There are 3 main reasons for any gradient of ultrafine particles (in order of importance): 

formation of larger fine particles, dispersion, deposition through precipitation (U.S. EPA, 2009c). 

Roorda-Knape et al (1998) 

• The authors concluded that no clear near roadway gradient for PM2.5 was found. 

Mauderly and Chow (2007) 

• Less than 10% of the PM2.5 mass is ultrafine. 

• The benefits analysis is based on PM2.5 mass, not the number of particles. Reducing diesel PM 

emissions reduces ambient PM2.5 mass concentrations. 

Von Klot et al (2009) 

• Used a land use regression model to estimate air quality. Photochemical dispersion models, 

such as those used by EPA, are vastly superior models for estimating pollutant concentrations 

across large geographic areas. 

Language we have added to this RIA to address their concerns (excerpts): 

“The underlying emissions modeling and air quality modeling account for the current 

distribution of emissions sources, including both urban and rural sources. In addition, the air quality 

modeling included 14 vertical layers to simulate the differences between ground-level emissions and 

higher stack emissions (U.S. EPA, 2006a). The distance that particles travel primarily depends on the size 
of the particle and meteorological conditions, such as wind speed and precipitation. Fine particles can 

have an atmospheric half-life of days to weeks and travel hundreds to thousands of kilometers, whereas 

ultrafine and coarse particles travel less than ten kilometers (U.S. EPA, 2009c). Because we have not 

undertaken a study specific to emissions at ground level from RICE, with regard to transport issues and 

to size fraction of PM2.5 emissions (e.g., ultrafines and near ultrafines), there is uncertainty as to how far 

such emissions will travel and thus with regard to populations affected. Evidence from recent air quality 

modeling for mobile source rules with similar engines (U.S. EPA, 1999; U.S. EPA, 2000; U.S. EPA, 2004; 

U.S. EPA, 2008e; U.S. EPA, 2010c) shows that some fine particles can travel long distances in the 

atmosphere, but the proportion of such emissions from RICE that travel more than short distances is not 

yet definitively known.” 

“The distance that these HAPs travel away from the emission source depends on several factors. 

HAPs such as formaldehyde, acetaldehyde, PAHs, and acrolein are emitted as gases. Regional 

photochemical model simulations have shown that gaseous HAPs like formaldehyde and acetaldehyde 

can be transported hundreds of kilometers from their emissions source in distinct plumes (U.S. EPA, 

2010b). Further, these emissions can contribute to regional airmasses with elevated concentrations of 

gaseous HAPs. These polluted airmasses can be transported thousands of kilometers and affect 

locations well distant from the original emissions source. Some gaseous HAPs with higher molecular 

weight, such as toluene, can transform into particles in the atmosphere. For HAPs emitted as particles, 

such as metals, the travel distance primarily depends on the size of the particle and meteorological 

conditions, such as wind speed and precipitation. Fine particles can have an atmospheric half-life of 

days to weeks and travel hundreds to thousands of kilometers, whereas ultrafine and coarse particles 

travel less than ten kilometers (U.S. EPA, 2009c).” 

References 

Barone, Theresa and Yifang Zhu. 2008. The morphology of ultrafine particles on and near major 

freeways. Atmospheric Environment Volume 42, Issue 28, September, Pages 6749-6758. 

Greco, SL, Wilson AM, Spengler JD, Levy JI. 2007. Factors Influencing Mobile Source Particulate Matter 

Emissions-to-Exposure relationships in the Boston Urban Area Atmos Environ 41: 1011-1025. 

HEI Panel on the Health Effects of Traffic-Related Air Pollution. 2010. Traffic-Related Air Pollution: A 

Critical Review of the Literature on Emissions, Exposure, and Health Effects. HEI Special Report 17. 

Health Effects Institute, Boston, MA. 

Horvath, H; Kreiner, I; Norek, C; et al. 1988. Diesel emissions in Vienna. Atmos Environ 22:1255-1269. 

Jacobson, M. Z., D. B. Kittelson, and W. F. Watts. 2005. Enhanced Coagulation Due to Evaporation and 

Its Effect on Nanoparticle Evolution, Environ. Sci. Technol. 39, 9486. 
Kittelson, DB. 1998. Engines and nanoparticles: a review. J Aerosol Sci 29:575-588. 

Krewski D, Jerrett M, Burnett R T, Ma R, Hughes E, et al. 2009 Extended follow-up and spatial analysis of 

the American Cancer Society study linking particulate air pollution and mortality. HEI Research 

Report, 140, Health Effects Institute, Boston, MA. 

Laden, F., J. Schwartz, F.E. Speizer, and D.W. Dockery. 2006. Reduction in Fine Particulate Air Pollution 

and Mortality. American Journal of Respiratory and Critical Care Medicine 173:667-672. Estimating 

the Public Health Benefits of Proposed Air Pollution Regulations. Washington, DC: The National 

Academies Press. 

Mauderly, J.L. and J.C. Chow. 2008.). Health Effects of Organic Aerosols. Inhal. Toxicol., 20(3):257-288. 

Morawska, L., Bofinger, N. D., Kocis, L., and Nwankwoala, A. (1998). Submicrometer and 

Supermicrometer Particles from Diesel Vehicle Emissions, Environ. Sci. Technol. 32:2033–2042. 

Pope, C.A., III, R.T. Burnett, M.J. Thun, E.E. Calle, D. Krewski, K. Ito, and G.D. Thurston. 2002. Lung 

Cancer, Cardiopulmonary Mortality, and Long-term Exposure to Fine Particulate Air Pollution. 

Journal of the American Medical Association 287:1132-1141. 

Roorda-Knape MC, Janssen NAH, de Hartog JJ, van Vliet PHN, Harssema H, Brunekreef B. Air pollution 

from traffic in city districts near major motorways. Atmos Environ. 1998;32(11):1921–1930. 

U.S. Environmental Protection Agency (U.S. EPA). 1999. Regulatory Impact Analysis - Control of Air 

Pollution from New Motor Vehicles: Tier 2 Motor Vehicle Emissions Standards and Gasoline Sulfur 

Control Requirements. EPA420-R-99-023, December 1999. 

http://www.epa.gov/tier2/frm/ria/r99023.pdf. Accessed February 9, 2010. 

U.S. Environmental Protection Agency (U.S. EPA). 2000. Regulatory Impact Analysis: Heavy-Duty Engine 

and Vehicle Standards and Highway Diesel Fuel Sulfur Control Requirements. Prepared by Office of 

Air and Radiation. EPA420-R-00-026, December 2000. Available at 

http://www.epa.gov/otaq/highway-diesel/regs/2007-heavy-duty-highway.htm. Accessed February 

9, 2010. 

U.S. Environmental Protection Agency (U.S. EPA). 2002. Health Assessment Document for Diesel Engine 

Exhaust. U.S. Environmental Protection Agency, Office of Research and Development, National 

Center for Environmental Assessment, Washington Office, Washington, DC, EPA/600/8-90/057F. 

U.S. Environmental Protection Agency (U.S. EPA). 2004. Final Regulatory Analysis: Control of Emissions 

from Nonroad Diesel Engines. EPA420-R-04-007, May 2004. Prepared by Office of Air and 

Radiation. http://www.epa.gov/nonroad-diesel/2004fr/420r04007.pdf. Accessed February 9, 2010. 

U.S. Environmental Protection Agency (U.S. EPA). 2006a. Technical Support Document for the Proposed 

PM NAAQS Rule: Response Surface Modeling. Office of Air Quality Planning and Standards, 

Research Triangle Park, NC. February. Available on the Internet at 

<http://www.epa.gov/scram001/reports/pmnaaqs_tsd_rsm_all_021606.pdf>. 
U.S. Environmental Protection Agency. 2008e. Regulatory Impact Analysis: Control of Emissions of Air 

Pollution from Locomotive Engines and Marine Compression Ignition Engines Less than 30 Liters Per 

Cylinder. Prepared by Office of Air and Radiation. EPA420-R-08-001a, May 2008. 

http://www.epa.gov/oms/regs/nonroad/420r08001a.pdf. Accessed February 9, 2010. 

U.S. Environmental Protection Agency (U.S. EPA). 2009c. Integrated Science Assessment for Particulate 

Matter (Final Report). EPA-600-R-08-139F. National Center for Environmental Assessment – RTP 

Division. December. Available on the Internet at 

<http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=216546>. 

U.S. Environmental Protection Agency (U.S. EPA). 2010b. Air Quality Modeling Technical Support 

Document: Changes to the Renewable Fuel Standard Program, Office of Air Quality Planning and 

Standards, EPA 454/R-10-001. February. Available on the Internet at 

<http://www.epa.gov/OMS/renewablefuels/454r10001.pdf>. 

U.S. Environmental Protection Agency (U.S. EPA). 2010c. Renewable Fuel Standard Program (RFS2) 

Regulatory Impact Analysis. EPA-420-R-10-006, February 2010. Prepared by Office of Air and 

Radiation. http://www.epa.gov/OMS/renewablefuels/420r10006.pdf. Accessed February 9, 2010. 

von Klot, Stephanie; Gryparis, Alexandros; Tonne, Cathryn; Yanosky, Jeffrey; Coull, Brent A.; Goldberg, 

Robert J.; Lessard, Darleen; Melly, Steven J.; Suh, Helen H.; Schwartz, Joel. 2009. Elemental Carbon 

Exposure at Residence and Survival After Acute Myocardial Infarction. Epidemiology: July. Vol 20, 

Issue 4, pp 547-554. 

Wilson WE; Suh HH. 1997. Fine particles and coarse particles: concentration relationships relevant to 

epidemiologic studies. J Air Waste Manag Assoc, 47: 1238-1249. 

Zhang, K. Max and Anthony S. Wexler. 2004. Evolution of particle number distribution near roadways—

Part I: analysis of aerosol dynamics and its implications for engine emission measurement. 

Atmospheric Environment Volume 38, Issue 38, December, Pages 6643-6653. 

Zhang, K. Max, Anthony S. Wexler, Yi Fang Zhu, William C. Hinds, and Constantinos Sioutas. 2004. 

Evolution of particle number distribution near roadways. Part II: the ‘Road-to-Ambient’ process. 

Atmospheric Environment, Volume 38, Issue 38, December, Pages 6655-6665. 

Zhang, K. Max, Anthony S. Wexler, Debbie A. Niemeier, Yi Fang Zhu, William C. Hinds, Constantinos 

Sioutas. 2005. Evolution of particle number distribution near roadways. Part III: Traffic analysis and 

on-road size resolved particulate emission factors, Atmospheric Environment. Volume 39, Issue 22, 

July, Pages 4155-4166. 

Zhu, Y. F.; Hinds, W. C.; Kim, S.; Sioutas, C. 2002. Concentration and size distribution of ultrafine particles 

near a major highway. J. Air Waste Manage. Assoc. 52, 1032−1042. 

Zhu, Y. F.; Hinds, W. C.; Shen, S.; Sioutas, C. 2004. Seasonal trends of concentration and size distribution 

of ultrafine particles near major highways in Los Angeles. Aerosol Sci. Technol. 38, 5-13. 
Zhu, Y.; Thomas Kuhn, Paul Mayo, and William C. Hinds. 2006. Comparison of Daytime and Nighttime 

Concentration Profiles and Size Distributions of Ultrafine Particles near a Major Highway. Environ. 

Sci. Technol., 40 (8), pp 2531–2536.