UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
September 09, 2009
EPA-CASAC-09-014
The Honorable Lisa P. Jackson
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, N.W.
Washington, D.C. 20460
Subject: Comments and Recommendations Concerning EPA's Proposed Rule for the Revision of
the National Ambient Air Quality Standards (NAAQS) for Nitrogen Dioxide
Dear Administrator Jackson:
The Clean Air Scientific Advisory Committee (CASAC) Oxides of Nitrogen Primary National
Ambient Air Quality Standards (NAAQS) Review Panel held a public teleconference on August 10, 2009
to discuss the Environmental Protection Agency's (EPA) Proposed Rule for the Revision of the NAAQS
for Nitrogen Dioxide (NO2) published in the Federal Register on July 19, 2009 (74 FR 34404-34466). In
that notice, EPA proposed to retain the current annual standard and institute a new one-hour standard
based on a two-tier (area-wide and near-road) monitoring network. The proposal also described an
alternative approach to setting a new one-hour standard, which would be based on area-wide monitors
only.
Prior to reviewing the proposed rule, CASAC had provided advice to EPA on its Integrated
Science Assessment (ISA) for Oxides of Nitrogen - Health Criteria and on EPA's draft Risk and Exposure
Assessment (REA) to Support the Review of the NO 2 Primary National Ambient Air Quality Standard.
The REA synthesized available scientific information discussed in the ISA to characterize NO2 exposures
and the associated risks with different profiles of exposure, but did not discuss the alternative monitoring
scenarios described in EPA's July proposed rule. In reviewing the REA, CASAC supported a short-term
standard for NO2 and in reviewing the proposal, CASAC supports the proposed one-hour averaging time
in EPA's proposed rule.
Since EPA's REA did not address NO2 monitoring issues, the CASAC panel discussed
monitoring issues, EPA's proposed monitoring approach, and proposed alternative approach extensively
during the August teleconference. There was a split view on the two approaches among both CASAC and
CASAC panel members with a majority of each favoring the Agency's proposed two-tiered monitoring
network because they thought this approach would be more effective in limiting near-roadway exposures
that may reach levels in the range at which some individuals with asthma may be adversely affected.
Other members acknowledged the need for research and development of near-road monitoring data for
criteria pollutants in general but favored retention of EPA's current area-wide monitoring for NO2
regulatory purposes, due to the lack of epidemiological data based on near-roadway exposure
measurements and issues related to implementing a near-road monitoring system for NO2. CASAC panel
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members agreed to present these different views in this letter, as there was not consensus. Enclosure A
provides further comments about approaches to near-road monitoring.
Assuming that the Agency proceeds with the proposed two-tier monitoring approach, CASAC
recommends the following:
1) retention of the current annual NO2 standard.
2) establishment of a one-hour standard with the following characteristics:
• use of NO2 as the appropriate indicator.
• a form based on a three-year average. The 98th percentile is preferred by CASAC
for the form, given the likely instability of measurements at the upper range and the
absence of data from the proposed two-tier approach.
• the level of the one-hour NO2 standard should be within the range of 80-100 ppb and
not above 100 ppb. In its letter of December 2, 2008, CASAC strongly voiced a
consensus view that the upper end of the range should not exceed 100 ppb, based on
evidence of risk at that concentration. The lower limit of 80 ppb was viewed as
reasonable by CASAC; selection of a value lower than 80ppb would represent a
policy judgment based on uncertainty and the degree of public health protection
sought, given the limited health-based evidence at concentrations below 100 ppb.
If the alternative monitoring approach is selected, CASAC recommends that a one-hour NO2
standard be set in the range of 50 to 75 ppb, if protection is to be approximately equivalent to the range of
80-100 ppb with the two-tier approach.
CASAC members recognize that the Agency is moving quickly to promulgate the new NAAQS
for NO2 on a court-ordered schedule. However, the proposed rule involves a substantially new approach
to monitoring that might have benefited from a more in-depth review by CASAC than was possible with
the schedule for comments. In the enclosure, CASAC comments on the need for a comprehensive
approach to developing a near-roadway network that would involve other pollutants, in addition to NO2.
This letter summarizes the main recommendations from the CASAC, while the enclosed
comments (Enclosure A) provide further detail. Enclosure B provides a panel roster. We hope that our
comments will prove useful as you evaluate the current NAAQS for NO2. If you have questions about
our advice, please do not hesitate to contact me.
Sincerely,
/Signed/
Dr. Jonathan Samet, Chair
Clean Air Scientific Advisory Committee
Enclosures
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NOTICE
This report has been written as part of the activities of the EPA's Clean Air Scientific Advisory
Committee (CASAC), a federal advisory committee independently chartered to provide
extramural scientific information and advice to the Administrator and other officials of the EPA.
CASAC provides balanced, expert assessment of scientific matters related to issues and
problems facing the Agency. This report has not been reviewed for approval by the Agency and,
hence, the contents of this report do not necessarily represent the views and policies of the EPA,
nor of other agencies within the Executive Branch of the federal government. In addition, any
mention of trade names of commercial products does not constitute a recommendation for use.
CASAC reports are posted on the EPA website at http://www.epa.gov/CASAC.
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Enclosure A
General Comments on Proposed NOi Monitoring Requirements
A number of issues were identified by CASAC that are specific to roadside monitoring
and the use of data from near-roadway monitors to determine attainment.
1. Support for EPA's two-tiered monitoring network for NO; regulatory monitoring
A majority of CASAC panelists supported the Agency's proposed two-tiered monitoring network
because they thought this approach would be more effective in limiting near-roadway exposures that may
reach levels in the range at which some people with asthma may be adversely affected, as indicated in
clinical and controlled human exposure studies. Members also indicated support for near-road monitoring
if EPA took steps to address concerns outlined in Section 2 of this enclosure.
Panel members also supported the proposed two-tiered approach because basing
regulations on area-wide monitoring alone was problematic. Such an approach would require
EPA to embed uncertainties and assumptions about the relationship between area-wide and road-
side monitoring into the area-wide standard. Panel members supported the two-tiered approach
as a means to start gathering specific information about roadside exposures that will be used for
public health protection.
The area-wide monitoring utilizing existing sites should continue as proposed. The area-
wide monitoring would provide a link to historically observed concentrations. It would thus
support showing progress in reducing NOX for NC>2, ozone and PM control programs and would
also continue to support health analyses. In contrast, new roadside measurements of NC>2 alone
would provide minimal information on near-road multi-pollutant exposures and may have
limited value in supporting future health studies.
2. Support for alternative area-wide monitoring only for NO; regulatory monitoring [EPA
solicited comment on a lower range of levels (>50 to <75 ppb) to provide a similar degree of
public health protection to that intended by the proposed approach and proposed range of
levels (in conjunction with the same forms as those proposed]
As noted in the Federal Register (July 15, 2009, pg. 34436): "In making judgments
regarding the weight to place on the scientific evidence and exposure/risk information, the
Administrator has considered the results of epidemiologic studies, controlled human exposure
studies, and exposure/risk analyses as well as the uncertainties associated with this evidence and
these analyses. Specifically, she notes the following: "The ISA concluded that epidemiologic
studies provide the strongest support for the relationship between short-term exposure to NCh
and respiratory morbidity." While it is recognized that the epidemiologic studies likely included
people exposed along roadways among those affected populations, those epidemiologic studies
that are relied upon by the Administrator (e.g., those displayed in Figures 4 and 5 of the Federal
Register) did not generally use near-roadway exposure data, but instead usually relied upon
conventional area-wide monitoring in developing their reported NC>2-health effects associations.
As such, in the face of a lack of sufficient near-roadway health effects studies to develop direct
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exposure-health effects relationships, it would be better to set the standard on the same area-wide
monitoring basis as employed in the epidemiologic studies upon which it now relies.
Several CAS AC panel members noted the difficulty of designing a roadside monitoring
network for NC>2 at this time. Roadside monitors will be more likely to experience excursions of
concentrations to very high values than area-wide monitors because they are nearer to sources
and more susceptible to periods of high episodic emissions, low dispersion and other events that
could lead to high peak monitored levels that are not reflective of more widespread levels (e.g.,
heavy congestion near a monitor, and trucks idling near the monitor). In the absence of more
detailed roadside data collection, it will be difficult to identify the causes of extreme near-road
NC>2 concentrations or to understand how such concentration values are reflected in exposures of
nearby urban populations. Further data collection and analyses are needed to determine the
causes and frequency of extreme concentrations monitored by near-road monitors and to
understand how such peak concentrations relate to those measured in the current, population-
oriented network.
The concentrations monitored will be very sensitive to the specific location of near-road
monitors, including exact distance from the roadway, height of monitor inlet, orientation with
respect to prevailing wind directions (during peak traffic periods), and other likely factors.
Differences in the microscale environments of different roadside monitors may result in one area
being out of attainment even though the area actually has similar, and possibly lower, maximum
NC>2 levels than other areas. This possibility also exists for area-representative monitoring, but
the likelihood of such non-representative values is reduced because the monitoring approach is
not intended to capture the extreme upper end of the distribution. Various logistical
considerations are likely to further constrain the options for establishing new roadside
monitoring sites. Practical siting considerations could mean that selected locations will not be
reflective of the maximum concentrations in the target area. Unless siting criteria are very
tightly constrained, data may not be directly comparable across different cities or sites within
cities.
To identify the locations with maximum NC>2 levels will be difficult, and the proposed
approach may miss the locations where the maxima occur. The proposed approach to
identification of monitor sites may be unsatisfactory in many locations, because it is based
primarily on traffic count. Diesel trucks emit more NOX than cars, and it would be expected that
the actual maximum levels would be found in areas of high diesel activity (including rail yards
and shipping) with reduced dispersion (e.g., street canyons). Open freeways that have high
usage by light duty vehicles would not necessarily have the highest levels. In the design of a
network to identify the maximum NC>2 levels in an area, we would support a more broad
assessment to predict the locations having the likely highest NC>2 levels based upon investigation
of model results [e.g., Community Multiscale Air Quality (CMAQ) and Land Use Regression
(LUR) modeling, and Gaussian plume models, if available] and also emissions inventories. For
example, CMAQ results, if available at a 4 or 12 km resolution, could be used to help inform
analyses directed at identifying locations with likely higher area-wide NC>2 levels, although such
analyses would be less informative on locations with the highest NC>2 levels in a city. The
Agency could also use diesel truck activity. We note that the traffic data bases include activities
by various classes of vehicles. Thus, we strongly support further analysis of the current NC>2
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data, diesel truck activity data, model results, and emissions inventories, as well as vehicle
activity data, to identify where area-representative sites might be placed to capture broad areas
with higher NO2 levels.
The use of diesel particle filters (DPFs) adds complexities to siting and to data
interpretation. DPFs can lead to significant increases in the fraction of NO2 in NOX emissions.
This phenomenon has been observed in London, England, where there have been NO2 increases
in areas where DPFs are being used, and it may increase the potential to have local NO2 "hot
spots" in locations with more presumably "cleaner" diesel vehicles in use. This phenomenon
also will impact how near-road observations are related to more general population exposures.
CASAC is further concerned by the suggestion in the proposal that building tops may be
used for monitor placement. This placement should be done with caution as building tops may
not be informative of much higher NO2 concentrations at lower heights where dispersion is
limited.
The expected high spatial variability of roadside NO2 concentrations also raises questions
about the spatial representativeness of roadside monitor results. How large a non-attainment area
is defined by a roadside violation? What population (if any) is assumed to be affected by the
roadside concentrations? What is the public health message in presenting the results? Will the
daily AQI for the county be driven by the relatively highest measurement from among
neighborhood-scale (8-hr) ozone, (24-hour) PM2 5 monitors and roadside 1-hour NO2 - the latter
of which by design does not represent the populations covered by the PM2 5 and Os monitors?
Would an effective control strategy be to reroute traffic from the high-speed urban freeway (with
the monitor) onto low speed urban residential streets (without monitors)?
If the Administrator decides to adopt the alternative approach, monitoring issues remain.
1. Preferably the NO/NO2 monitoring would be done in locations that include CO, ozone
and PM species monitoring as well.
2. EPA should follow the CASAC recommendation in regard to the level of the standard.
3. Having the state/local air quality managers assess how the current network satisfies the
goal of providing data representative of area-wide (not maximum) concentrations is
appropriate. As noted above, the population threshold may be too low (it is not apparent
that all cities with a population above 350,000 will have NO2 levels approaching the
potential revised standards), and such a choice needs further support and review. One
could consider requiring that removal of NO/ NO2 monitors not be allowed, and
repositioning would need to have approval by the Regional Administrator. Further, each
state could be required to have at least one NO2 monitor sited to represent areas with
higher NO2 exposures. Giving the Regional Administrator discretion to require
additional monitoring to address community impacts is justified based on appropriate
analyses (e.g., using modeling and emissions data).
4. The definition of "area-wide" is not very specific, though it reflects the realities of
monitoring. It would be useful to specify a minimum distance that a monitor could be
placed from a major facility (including freeways and highways), e.g., that a monitor that
is representative of area-wide NO/ NO2 should not be placed within 100 m of a major
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facility (with a further definition of major facility in terms of expected NOX emissions;
for roads this could be in terms of NOX per 100m).
3. Characterizing near-road exposures for multiple pollutants
If EPA undertakes near-road monitoring, the Agency should proceed with care and seek
advice and review of the design of the network by technical experts, such as those in the CAS AC
Ambient Air Quality Monitoring Subcommittee.
A smaller roadside network with more comprehensive measurements to better
characterize near-road exposures to and gradients for a complex mixture of mobile source
pollutants may provide more information than a new roadside monitoring network with hundreds
of sites having only NOX monitors and meteorological instrumentation. In addition to
characterizing NO2 and NO and meteorology, such monitoring should include CO, continuous
PM, with speciation as possible (e.g., including elemental carbon or black carbon, continuous
nitrate and sulfate, as possible, and possibly CO2 and gaseous VOCs). Such an alternative
network, as discussed below, would not be designed to have all monitors necessarily placed in
locations with the highest NO2 concentrations, but would also include locations that are impacted
by heavy duty vehicle emissions, light duty vehicle emissions and suspended road dust
Consideration would need to be given to the extent to which the network is designed with
orientation towards areas with minimal dispersion (street canyons). Another siting criterion
should be whether there is a location of interest near the roadway (e.g., a school, hospital, park,
etc.) that may be attended or inhabited by persons in susceptible or vulnerable subpopulations.
The need to have a more comprehensive set of measurements is highlighted by the likelihood of
more extensive use of DPFs. If only NO2 observations were available, it might appear that air
quality was deteriorating, when in actuality significant reductions in particulate matter are
occurring. This would affect how such observations might be used in assessing the impact of
controls and associating pollutant concentration changes to health outcomes.
CASAC is very strongly supportive of a special-purpose monitoring network oriented
towards roadside monitoring that is not used for attainment purposes at this point but for
research. It would be designed to characterize pollutants in areas with high exposure to traffic-
derived pollutants of all types, including heavy duty and light-duty vehicle emissions, tire and
brake wear and road dust, and would include pollutants beyond NO and NO2 as discussed above.
Detailed meteorological measurements would be well justified at these more intensive sites, as
would automatic traffic counters.
Further, such a special network would specifically include variability in terms of site
location (different distances to the facility, different highway characteristics) and type of
monitoring to provide the type of data that would better inform our understanding of pollutant
dynamics, control strategy effectiveness, and how a future road-side network should be designed
for use in attainment decisions and standard setting. Such a network should go in quickly to
capture the changes in emissions that are occurring in response to various controls. Funding for
such special purpose monitoring may have to come predominantly from EPA. One approach for
establishing the monitoring would be through competitive grants to state and local agencies. The
network would likely be limited in scope, possibly on the order of 20 to 50 sites and it could
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evolve over time as information is gained. A single city might have multiple near-road special-
purpose monitors to address issues in siting near-road monitors and to understand relationships
between roadside concentrations and larger population exposures. Cities with various
characteristics should be chosen for assessing near-road monitoring issues. This approach
appears to fit well with a recent EPA document, "Ambient Air Monitoring Strategy for State,
Local, and Tribal Air Agencies," which states:
"With this background, EPA's Strategy currently recognizes (1) the importance of near
roadway exposures, and (2) the need for further exploration of the meaning of these
exposures to both NAAQS-oriented monitoring networks and air toxics networks.
Monitoring near roadways has, to date, been limited to research-level monitoring. As
monitoring networks evolve, it is vital that monitoring near roadways be further
investigated and eventually integrated into the monitoring networks. Currently, EPA and
others continue to evaluate strategies for incorporating this monitoring into the other
components of the monitoring Strategy primarily as a means of determining health risks
and impacts on urban attainment. EPA intends to consult with SLTs and other
stakeholders about the eventuality of developing the near-roadway component of ambient
monitoring. The primary consideration would be to operate a small number of sites
spaced in varying geographical areas of the country in an initial attempt to address near-
roadway issues. Outcomes from EPA's Office of Research and Development's (ORD)
near-roadway studies that began in 2006 and extend through 2009 or 2010 would heavily
influence where, how, and when a near-roadway monitoring pilot would occur."
If there is a mechanism to begin more comprehensive roadside monitoring but not
include such data in attainment determination, then a two-tier monitoring approach is potentially
attractive for support of health studies that could be used in future NAAQS reviews. However,
as discussed above, such monitoring should not be limited to NO and NO2 only, but also include
CO, continuous PM mass, and continuous total carbon/elemental carbon (or black carbon).
Without this additional data, the results would be significantly less informative. If, as part of the
current CO and PM reviews, a network of roadside monitoring of all of these species was
proposed and implemented, the data could potentially be used in supporting a future NAAQS
revision for those species. The data would be more readily used in a multi-pollutant air quality
control program and for the determination of the effectiveness of control measures. Monitoring
of NO/NO2 alone would not be as informative, particularly given the changing make-up of both
light and heavy duty fleets, applied controls, and the change in traffic volumes.
4. Additional issues
The CAS AC panel determined that the proposed data quality objectives are appropriate.
The chemiluminescent approach is appropriate. It would be good to improve and extend
the technique to give both true NO2 as well as NOy. However, that would not be viable within
the time frame of this rulemaking.
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The justification for the meteorological measurements is unclear in regard to assessing
attainment. The need for and uses of such data should be better supported. We agree that such
monitoring would be very useful at comprehensive monitoring sites.
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Enclosure B
ROSTER
U.S. Environmental Agency
Clean Air Scientific Advisory Committee
Oxides of Nitrogen Primary National Ambient Air Quality Standards Panel
CHAIR
Dr. Jonathan M. Samet, Professor and Chair, Department of Preventive Medicine, University
of Southern California, Los Angeles, CA
CASAC MEMBERS
Dr. Joseph Brain, Philip Drinker Professor of Environmental Physiology, Department of
Environmental Health, Harvard School of Public Health, Harvard University, Boston, MA
Dr. Ellis B. Cowling, University Distinguished Professor At-Large Emeritus, Colleges of
Natural Resources and Agriculture and Life Sciences, North Carolina State University, Raleigh,
NC
Dr. James Crapo, Professor of Medicine, Department of Medicine, National Jewish Medical
and Research Center, Denver, CO
Dr. H. Christopher Frey, Professor, Department of Civil, Construction and Environmental
Engineering, College of Engineering, North Carolina State University, Raleigh, NC*
Dr. Donna Kenski, Data Analysis Director, Lake Michigan Air Directors Consortium,
Rosemont, IL*
Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering ,
Georgia Institute of Technology, Atlanta, GA
CONSULTANTS
Prof. Ed Avol, Professor, Preventive Medicine, Keck School of Medicine, University of
Southern California, Los Angeles, CA
Dr. John R. Balmes, Professor, Department of Medicine, Division of Occupational and
Environmental Medicine, University of California, San Francisco, CA*
Dr. Terry Gordon, Professor, Environmental Medicine, New York University School of
Medicine, Tuxedo, NY
Dr. Dale Hattis, Research Professor, Center for Technology, Environment, and Development,
George Perkins Marsh Institute, Clark University, Worcester, MA
*Unable to participate in the August 10, 2009 CASAC Public Teleconference
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Dr. Rogene Henderson, Senior Scientist Emeritus, Lovelace Respiratory Research Institute,
Albuquerque, NM
Dr. Patrick Kinney, Associate Professor, Department of Environmental Health Sciences,
Mailman School of Public Health , Columbia University, New York, NY
Dr. Steven Kleeberger, Professor and Lab Chief, Laboratory of Respiratory Biology, National
Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle
Park, NC
Dr. Timothy V. Larson, Professor, Department of Civil and Environmental Engineering,
University of Washington, Seattle, WA
Dr. Kent Pinkerton, Professor, Regents of the University of California, Center for Health and
the Environment, University of California, Davis, CA*
Dr. Edward Postlethwait, Professor and Chair, Department of Environmental Health Sciences,
School of Public Health, University of Alabama at Birmingham, Birmingham, AL
Dr. Richard Schlesinger, Associate Dean, Department of Biology, Dyson College, Pace
University, New York, NY
Dr. Christian Seigneur, Director, Centre d'enseignement et de recherche en environnement
atmospherique (CEREA), Ecole nationale des ponts et chaussees (ENPC), Universite Paris-Est,
CEREA - ENPC, Marne la Vallee,, France
Dr. Elizabeth A. (Lianne) Sheppard, Professor, Biostatistics and Environmental &
Occupational Health Sciences, School of Public Health, University of Washington, Seattle, WA
Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. George Thurston, Professor, Environmental Medicine, NYU School of Medicine, New
York University, Tuxedo, NY
Dr. James Ultman, Professor, Chemical Engineering, Bioengineering Program, Pennsylvania
State University, University Park, PA
Dr. Ronald Wyzga, Technical Executive, Air Quality Health and Risk, Electric Power
Research Institute, Palo Alto, CA
SCIENCE ADVISORY BOARD STAFF
Dr. Angela Nugent, Designated Federal Officer, 1200 Pennsylvania Avenue, NW
1400F, Washington, DC, Phone: 202-343-9981, Fax: 202-233-0643, (nugent.angela@epa.gov)
*Unable to participate in the August 10, 2009 CASAC Public Teleconference
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