6576750 

UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

 WASHINGTON D.C. 20460 

 

OFFICE OF THE ADMINISTRATOR 

SCIENCE ADVISORY BOARD 

March 6, 2009 

EPA-CASAC-09-005 

The Honorable Lisa P. Jackson 

Administrator 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

Subject: Consultation on Ambient Air Monitoring Issues Related to the Ozone NAAQS 

Dear Administrator Jackson: 

The Clean Air Scientific Advisory Committee (CASAC) Ambient Air Monitoring & 

Methods Subcommittee held a public teleconference on February 10, 2009, to consult with staff 

from EPA’s Office of Air Quality Planning and Standards (OAQPS) on monitoring network 

design issues related to the National Ambient Air Quality Standards (NAAQS) for ozone (O3) as 

promulgated in March 2008. The final rule revised both the primary and secondary standards 

and set identical, 8-hour standards of 0.075 ppm for both public health and welfare. The Agency 

is developing separate rules to support changes in the monitoring network requirements based on 

the revisions of the primary and secondary NAAQS and considering changes to the required 

ozone monitoring seasons. 

The CASAC uses a consultation as mechanism for technical experts to provide comments 

to the Agency on the issues under consideration. In general, the Subcommittee is supportive of 

the Agency’s efforts to increase the number O3 monitors; however, as noted in the individual 

comments enclosed with this letter, outlying issues with deployment, siting, and state-specific 

coverage remain. As this is a consultation, we do not expect a formal response from the Agency. 

We thank the Agency for the opportunity to provide advice in the NAAQS review process. 

Sincerely, 

 

 /Signed/ 

Dr. Armistead (Ted) Russell, Chair 

CASAC AAMMS 

Enclosures 
Enclosure A 

U.S. Environmental Protection Agency 

Clean Air Scientific Advisory Committee 

Ambient Air Monitoring and Methods Subcommittee

CASAC MEMBERS 

Dr. Armistead (Ted) Russell (Chair), Professor, Department of Civil and Environmental 

Engineering, Georgia Institute of Technology, Atlanta, GA 

Dr. Donna Kenski, Data Analysis Director, Lake Michigan Air Directors Consortium, 

Rosemont, IL 

SUBCOMMITTEE MEMBERS 

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA 

Dr. Judith Chow, Research Professor, Desert Research Institute, Air Resources Laboratory, 

University of Nevada, Reno, NV 

Mr. Bart Croes, Chief, Research Division, California Air Resources Board, Sacramento, CA 

Dr. Kenneth Demerjian, Professor and Director, Atmospheric Sciences Research Center, State 

University of New York, Albany, NY 

Dr. Delbert Eatough, Professor of Chemistry, Department of Chemistry and Biochemistry , 

Brigham Young University, Provo, UT 

Dr. Eric Edgerton, President, Atmospheric Research & Analysis, Inc., Cary, NC 

Mr. Henry (Dirk) Felton, Research Scientist, Division of Air Resources, Bureau of Air Quality 

Surveillance, New York State Department of Environmental Conservation, Albany, NY 

Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical 

Engineering, Clarkson University, Potsdam, NY 

Dr. Rudolf Husar, Professor, Mechanical Engineering, Engineering and Applied Science, 

Washington University, St. Louis, MO 

Dr. Kazuhiko Ito, Assistant Professor, Department of Environmental Medicine, School of 

Medicine, New York University, Tuxedo, NY 

Dr. Thomas Lumley, Associate Professor, Biostatistics, School of Public Health and 

Community Medicine, University of Washington, Seattle, WA 

 2 
Dr. Peter H. McMurry, Professor and Head, Department of Mechanical Engineering, 

University of Minnesota, Minneapolis, MN 

Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, Department of 

Environmental Conservation, Vermont Agency of Natural Resources, Waterbury, VT 

Dr. Kimberly A. Prather,* Professor, Department of Chemistry and Biochemistry, University 

of California, San Diego, La Jolla, CA 

Dr. Jay Turner, Visiting Professor, Crocker Nuclear Laboratory, University of California, 

Davis, CA 

Dr. Warren H. White, Research Professor, Crocker Nuclear Laboratory, University of 

California - Davis, Davis, CA 

Dr. Yousheng Zeng, Air Quality Services Director, Providence Engineering & Environmental 

Group LLC, Baton Rouge, LA 

Dr. Barbara Zielinska, Research Professor, Division of Atmospheric Sciences, Desert Research 

Institute, Reno, NV 

SCIENCE ADVISORY BOARD STAFF 

Ms. Kyndall Barry, Designated Federal Officer, 1200 Pennsylvania Avenue, N.W. (Mailcode 

1400F), Washington, DC, Phone: 202-343-9868, Fax: 202-233-0643, (barry.kyndall@epa.gov) 

*Dr. Prather did not participate in this CASAC AAMM Subcommittee activity.

 3 
Enclosure B 

Comments received:

Mr. George Allen .......................................................................................................................... 5 

Dr. Judith C. Chow....................................................................................................................... 8 

Mr. Bart Croes............................................................................................................................ 15 

Dr. Delbert J. Eatough................................................................................................................ 18 

Mr. Dirk Felton........................................................................................................................... 21 

Dr. Phil K. Hopke........................................................................................................................ 24 

Dr. Rudolf Husar ........................................................................................................................ 27 

Dr. Kazuhiko Ito ......................................................................................................................... 28 

Dr. Donna Kenski........................................................................................................................ 31 

Dr. Thomas Lumley.................................................................................................................... 34 

Dr. Peter H. McMurry................................................................................................................ 37 

Mr. Richard L. Poirot................................................................................................................. 40 

Dr. Armistead Russell................................................................................................................. 44 

Dr. Jay R. Turner........................................................................................................................ 46 

Dr. Warren H. White.................................................................................................................. 49 

Dr. Yousheng Zeng ..................................................................................................................... 50 

Dr. Barbara Zielinska................................................................................................................. 52

 4 
Mr. George Allen 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

Yes, these changes should result in an urban network that is “minimally adequate”. Most urban 

areas are “ozone holes” due to NO scavenging; exceptions to this are very large urban areas such 

as NYC and LA. Still, urban ozone is an important monitoring need. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

While it is desirable to deploy network changes sooner than later, State, Local and Tribal Air 

Agencies (“SLT”) are presently under substantial pressure to meet other required new 

monitoring such as NCore. At the same time, these agencies are under severe budgetary 

constraints that effect staffing levels, and this is expected to continue for the near future. To the 

extent that it does not adversely impact compliance designation, a staggered deployment 

schedule that extends the period for another year would probably be helpful to air agencies. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three non-urban 

ozone monitors to meet certain objectives (described above). Considering the stated objectives 

of the non-urban ozone monitoring requirements, is three required monitors per state sufficient? 

Specifying this on a per state basis may not be the best way. Three may be excessive for RI and 

insufficient for TX. There are additional variables that could drive this need on a regional basis 

such as regional transport, transport over large bodies of water (allowing formation without 

sinks), etc. In general, for a pollutant like ozone that is often regionally transported, requiring 

any component of network siting design on a state by state basis may not be the best approach. 

A design that is relatively ignorant of state boundaries may be better. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

Site elevation and over-water transport are two factors that may need to be considered. Distance 

downwind from major precursor sources could be another. 

 5 
3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

In these resource constrained times, a careful balance between meeting network objectives and 

the resources required to implement additional monitoring must be met. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

Setbacks from roadways or other local sources that may impact measured ozone may need to be 

increased, since non-urban ozone site are presumably regional in spatial scale. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Any existing or future “third party” ozone sites should meet all siting and operational QC 

requirements required of SLT sites if data from those sites is going into AQS and would be used 

for meeting required network design goals and NAAQS compliance purposes. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

First, for something like the 50 largest cities, or perhaps locations of the 54 core STN sites, 

ozone should be measured year round for use in health effect studies. NCore will presumably 

provide this. For other sites, it may be difficult to determine an appropriate season from existing 

data if there are no year-round or extended season site data presently available that represent a 

given area. In these cases, an analysis of several year’s worth of start and end ozone season 

months’ data is the best that can be done; if there is a reasonable chance of an exceedance 

occurring outside of the current season, then the required monitoring season should be extended 

by at least one month. In the northeast US for example, it is clear that March needs to be 

included in the revised season. March has substantial solar radiation, and “leaf-out” does not 

occur until early May. These and perhaps other factors contribute to high observed ozone levels 

during that month from the limited year-round network currently in place. It is less likely that 

October needs to be included for this northeast example, since solar radiation is less than in 

 6 
March. Still, for some northeast states, October may be appropriate to include in the ozone 

monitoring season. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

It might be informative for certain sites such as high-elevation transport locations to run yearround. Stratospheric intrusion can occur, and there is a level of ozone present that is of interest 

(from a non-compliance perspective) even in the winter. Another possible need for year-round 

monitoring might be the situation observed in Wyoming’s Upper Green River Basin, where there 

are intensive natural gas wells in valley locations. It appears that the reported winter ozone is 

real and not an interference with the UV monitoring method; situations like these have the 

potential for increasing our understanding of ozone formation in non-traditional scenarios like 

this with cold temperatures and decreased incoming solar radiation. A related issue here is the 

lack of a viable commercial instrument for the EPA ozone reference method (chemiluminescent 

ethylene). Perhaps it is time for EPA to consider a new reference method that is reasonably free 

from interferences (Hg, VOCs, water vapor, etc) and is commercially available. Finally, if an 

ozone monitor is at a site where other monitors are run year-round, the incremental cost to 

continue ozone for the full year is relatively small, and the potential value for non-compliance 

use may turn out to be substantial. The significant cost-savings of turning off an ozone monitor 

for a few months is limited to sites where ozone is the only pollutant measured. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

Yes it is reasonable. For existing monitors, extending the season by a month or two does not 

have a large impact on SLT agency resources. 

 7 
Dr. Judith C. Chow 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

Figure 1 of the Ozone monitoring document shows that there are many populated but 

unmonitored areas. Many of these areas have experienced substantial population and traffic 

growth, especially in the western and southeastern U.S. There is ample evidence that O3 is 

transported over long-distances, as well as being locally generated, and that elevated 

concentrations can be found nearly everywhere (Bertschi and Jaffe, 2005; Choi et al., 2008; 

Dabdub et al., 1999; Goldstein et al., 2004; Guttorp et al., 1994; Hudman et al., 2004; Rao et al., 

2003; Rosenthal et al., 2003; Spicer et al., 1979; Wolff et al., 1977). Elevated O3 can also be 

generated by non-urban sources such as plantlife (Marr et al., 2002; Pun et al., 2002; Tao et al., 

2003), fires (Bertschi and Jaffe, 2005; Preisler et al., 2005), and livestock (Howard et al., 2008). 

It is entirely appropriate to lower the population threshold for monitoring to protect urban public 

health. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

Maximum flexibility should be allowed for the addition of monitoring locations. It is better to: 

1) thoroughly evaluate the potential measurement locations, 2) procure and install the best 

equipment, 3) train operators in its use, and 4) have an adequate shakedown period than to rush 

the process. It often takes a year or more to obtain the funding, permits, and infrastructure when 

a new air quality site is installed. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three non-urban 

ozone monitors to meet certain objectives (described above). Considering the stated objectives 

of the non-urban ozone monitoring requirements, is three required monitors per state sufficient? 

It is not clear whether or not this would require three monitors in addition to those identified in 

Figure 2 of the Ozone monitoring document or would include those monitors. Perhaps columns 

could be added to Table 2 of the Ozone monitoring document that would include the number of 

current monitors in each state that are: 1) federal lands with sensitive ecosystems; 2) small towns 

(micropolises?); and 3) non-urban locations with expected high concentrations. Would this also 

 8 
include existing monitors from non-compliance networks (e.g., the National Park Service’s 2B 

O3 monitors http://www.nature.nps.gov/air/Studies/portO3.cfm)? Looking at the large 

differences in areas of different states, the complex terrain in some states as opposed to others, 

and the existing densities of monitors in Figures 1 and 2 of the Ozone monitoring document, it 

would seem that a more refined allocation of monitoring locations based on a conceptual model 

of O3 precursor locations, formation potential, and transport corridors might be more useful than 

an allocation of three monitors per state. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

Factors for measurement location should include: 1) presence of species susceptible to damage 

(Legge et al., 1995; Miller and McBride, 1999; Musselman et al., 2006; Paoletti, 2006; Prinz, 

1985); 2) potential for high O3 levels (transport, upslope/downslope flows, local generation) (Lee 

et al., 2007; Wager and Baker, 2006); and 3) logistics and cost-effectiveness. It might be more 

logical and cost-effective to extend the NPS network to additional IMPROVE 

(http://vista.cira.colostate.edu/views) sites where some infrastructure already exists. It would 

also be useful to think “beyond compliance” (Chow and Watson, 2008) and not require a fullscale compliance monitoring site at some of the remote locations. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

Additional objectives should include: 1) tracking trends in O3 and precursors to evaluate 

accountability and relationships to other pollutants for O3 SIPs (Cohan et al., 2007; Foley et al., 

2003); 2) increasing understanding of O3 chemistry and transport (Blanchard et al., 1999; 

Blanchard and Fairley, 2001; Blanchard and Stoeckenius, 2001; Milford et al., 1989; Milford et 

al., 1994; Sillman et al., 1997; Sillman, 1999; Sillman, 2001); 3) defining non-attainment areas 

according to established criteria (Clark County Department of Air Quality and Environmental 

Management, 2004; Seitz, 2000); and 4) forecasting effects of climate change on O3

concentrations (Grewe, 2007; Jacob and Winner, 2009; Zeng et al., 2008). 

Additional monitors might be needed at some locations for NO2 and certain VOCs to better 

attain these objectives. For some remote forest exposure locations it might be more effective to 

use passive O3 monitors (Bernard et al., 1999; Grosjean and Williams, II, 1992; Manning et al., 

1996; Paoletti, 2006; Skelly et al., 2001). 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances from 

roadways). Are these requirements (that have been developed for urban monitors) appropriate 

for non-urban ozone monitors? What changes, if any, should be considered? 

 9 
No. O3 monitors within the forest measure lower values than those outside or above the forest 

canopy because of the plant uptake (which also causes the damage). Both measurement types 

are important, as the difference indicates the exposure, so two nearby sites with different middlescale to neighborhood-scale characteristics might be considered. Monitors within the shallow 

nighttime surface inversion often experience NO titration, even when they are somewhat distant 

from a roadway, due to the overnight trapping of pollutants. Monitors on a hilltop, tall building, 

or towers may better indicate O3 exposure and carryover than surface-based monitors. It is 

difficult to locate sites very distant from some type of roadway as the sites need to be accessed 

regularly. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

All available data should be compiled and used for the defined objectives. As noted above, the 

information needed and acquired should dictate the number of monitors rather than an arbitrary 

assignment of a certain number of monitors to each state. Where a number of different networks 

or monitor types are used, there should be a comparison and evaluation of the operating 

conditions, including evidence of regular calibration, auditing, maintenance, precision, accuracy, 

and comparability. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

Some of the remote sites may not be easily accessible during winter owing to snow, and this 

should be considered. High O3 concentrations can occur in winter, however, owing to reflection 

of sunlight from snowcover and concentration of precursors during the day within a shallow 

layer over the snow. O3 is also correlated with HNO3 (Aneja et al., 1994; Bottenheim and Sirois, 

1996) that is a precursor to wintertime PM2.5 nitrate levels and can be useful as part of a multipollutant control strategy development where PM2.5 concentrations are also excessive. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

O3 monitors should be operated year round wherever practical to evaluate multi-pollutant 

approaches and to determine the extent of elevated levels during winter. This is the case already 

 10
at most multi-pollutant monitoring sites. There may be instances at remote locations where 

access is denied due to weather, and it is probably not cost-effective to take extreme measures 

for such locations. At a minimum they should be operated year-round in areas that experience 

excessive PM2.5 and O3 concentrations. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

The same argument applies as above. It is better to phase in the changes in a logical manner than 

to set a mandate that will compromise quality and the utility of the data. It is probably less of a 

burden to extend the monitoring period than it is to locate new sites, but additional staff, training, 

and possibly instrumentation may be needed that will require some lead time. 

References

Aneja, V.P.; Claiborn, C.S.; Li, Z.; Murthy, A. (1994). Trends, seasonal variations, and analysis 

of high elevation surface nitric acid, ozone, and hydrogen peroxide. Atmos. Environ., 28(10): 

1781-1790. 

Bernard, N.L.; Gerber, M.J.; Astre, C.M.; Saintot, M.J. (1999). Ozone measurement with passive 

samplers: Validation and use for ozone pollution assessment in Montpellier, France. 

Environ. Sci. Technol., 33(2): 217-222. 

Bertschi, I.T.; Jaffe, D.A. (2005). Long-range transport of ozone, carbon monoxide, and aerosols 

to the NE Pacific troposphere during the summer of 2003: Observations of smoke plumes 

from Asian boreal fires. J. Geophys. Res. -Atmospheres, 110(D5): 

Blanchard, C.L.; Lurmann, F.W.; Roth, P.M.; Jeffries, H.E.; Korc, M. (1999). The use of 

ambient data to corroborate analyses of ozone control strategies. Atmos. Environ., 33(3): 

369-381. 

Blanchard, C.L.; Fairley, D. (2001). Spatial mapping of VOC and NOx-limitation of ozone 

formation in central California. Atmos. Environ., 35(22): 3861-3873. 

Blanchard, C.L.; Stoeckenius, T. (2001). Ozone response to precursor controls: Comparison of 

data analysis methods with the predictions of photochemical air quality simulation models. 

Atmos. Environ., 35(7): 1203-1215. 

Bottenheim, J.W.; Sirois, A. (1996). Long-term daily mean mixing ratios of O-3, PAN, HNO3, 

and particle nitrate at a rural location in eastern Canada: Relationships and implied ozone 

production efficiency. J. Geophys. Res. -Atmospheres, 101(D2): 4189-4204. 

Choi, Y.; Wang, Y.; Zeng, T.; Cunnold, D.; Yang, E.S.; Martin, R.; Chance, K.; Thouret, V.; 

Edgerton, E. (2008). Springtime transitions of NO2, CO, and O-3 over North America: 

Model evaluation and analysis. J. Geophys. Res. -Atmospheres, 113(D20): 

Chow, J.C.; Watson, J.G. (2008). New directions: Beyond compliance air quality measurements. 

Atmos. Environ., 42(21): 5166-5168. doi:10.1016/j.atmosenv.2008.05.004. 

Clark County Department of Air Quality and Environmental Management (2004). Nevada air 

quality designations boundary recommendations for the 8-hour ozone NAAQS for Clark 

County, Nevada. prepared by Clark County Department of Air Quality and Environmental 

 11
Management, Las Vegas, NV, 

http://www.epa.gov/ozonedesignations/documents/clark/NV/boundary.pdf

Cohan, D.S.; Boylan, J.W.; Marmur, A.; Khan, M.N. (2007). An integrated framework for 

multipollutant air quality management and its application in Georgia. Environmental 

Management, 40(4): 545-554. 

Dabdub, D.; DeHaan, L.L.; Seinfeld, J.H. (1999). Analysis of ozone in the San Joaquin Valley of 

California. Atmos. Environ., 33(16): 2501-2514. 

Foley, G.J.; Georgopoulos, P.G.; Lioy, P.J. (2003). Accountability within new ozone standards. 

Environ. Sci. Technol., 37(21): 392A-+. 

Goldstein, A.H.; Millet, D.B.; Mckay, M.; Jaegle, L.; Horowitz, L.; Cooper, O.; Hudman, R.; 

Jacob, D.J.; Oltmans, S.; Clarke, A. (2004). Impact of Asian emissions on observations at 

Trinidad Head, California, during ITCT 2K2. J. Geophys. Res. -Atmospheres, 109(D23): 

Grewe, V. (2007). Impact of climate variability on tropospheric ozone. Sci. Total Environ., 

374(1): 167-181. 

Grosjean, D.; Williams, E.L., II (1992). Field tests of a passive sampler for atmospheric ozone at 

California mountain forest locations. Atmos. Environ., 26A(8): 1407-1411. 

Guttorp, P.; Meiring, W.; Sampson, P.D. (1994). A space-time analysis of ground-level ozone 

data. Environmetrics, 5(3): 241-254. 

Howard, C.J.; Yang, W.; Green, P.G.; Mitloehner, F.; Malkina, I.L.; Flocchini, R.G.; Kleeman, 

M.J. (2008). Direct measurements of the ozone formation potential from dairy cattle 

emissions using a transportable smog chamber. Atmos. Environ., 42(21): 5267-5277. 

Hudman, R.C.; Jacob, D.J.; Cooper, O.R.; Evans, M.J.; Heald, C.L.; Park, R.J.; Fehsenfeld, F.; 

Flocke, F.; Holloway, J.; Hubler, G.; Kita, K.; Koike, M.; Kondo, Y.; Neuman, A.; Nowak, 

J.; Oltmans, S.; Parrish, D.; Roberts, J.M.; Ryerson, T. (2004). Ozone production in 

transpacific Asian pollution plumes and implications for ozone air quality in California. J. 

Geophys. Res. -Atmospheres, 109(D23): D23S10. doi:10.1029/2004JD004974. 

Jacob, D.J.; Winner, D.A. (2009). Effect of climate change on air quality. Atmos. Environ., 

43(1): 51-63. 

Lee, S.M.; Fernando, H.J.S.; Grossman-Clarke, S. (2007). MM5-SMOKE-CMAQ as a modeling 

tool for 8-h ozone regulatory enforcement: application to the state of Arizona. Environmental 

Modeling & Assessment, 12(1): 63-74. 

Legge, A.H.; Grunhage, L.; Nosal, M.; Jager, H.J.; Krupa, S.V. (1995). Ambient ozone and 

adverse crop response: An evaluation of North American and European data as they relate to 

exposure indices and critical levels. Journal of Applied Botany-Angewandte Botanik, 69(5-

6): 192-205. 

Manning, W.J.; Krupa, S.V.; Bergweiler, C.J.; Nelson, K.I. (1996). Ambient ozone (O3) in three 

Class I wilderness areas in the northeastern USA: Measurements with Ogawa passive 

samplers. Environ. Poll., 91(3): 399-403. 

Marr, L.C.; Noblet, G.S.; Harley, R.A. (2002). Formation of photochemical air pollution in 

central California 2. Impact of revised emissions on Eulerian model predictions. J. Geophys. 

Res., 107(D6): 6-1-6-11. 

Milford, J.B.; Russell, A.G.; McRae, G.J. (1989). A new approach to photochemical pollution 

control: Implications of spatial patterns in pollutant responses to reductions in nitrogen 

oxides and reactive organic gas emissions. Enivron. Sci. Technol., 231290-1299. 

 12
Milford, J.B.; Gao, D.; Sillman, S.; Blossey, P.; Russell, A.G. (1994). NOy as an indicator of the 

sensitivity of ozone to ROG and NOx emissions. J. Geophys. Res., 99(D2): 3533-3542. 

Miller, P.R.; McBride, J.R. (1999). Oxidant Air Pollution Impacts in the Montane Forests of 

Southern California. A Case Study of the San Bernardino Mountains. Ecological Studies 

134; Springer-Verlag: New York. 

Musselman, R.C.; Lefohn, A.S.; Massman, W.J.; Heath, R.L. (2006). A critical review and 

analysis of the use of exposure- and flux-based ozone indices for predicting vegetation 

effects. Atmos. Environ., 40(10): 1869-1888. 

Paoletti, E. (2006). Impact of ozone on Mediterranean forests: A review. Environ. Poll., 144(2): 

463-474. 

Preisler, H.K.; Grulke, N.E.; Bytnerowicz, A.; Esperanza, A. (2005). Analyzing effects of forest 

fires on diurnal patterns of ozone concentrations. Phyton-Annales Rei Botanicae, 45(4): 33-

39. 

Prinz, B. (1985). Effects of air pollution on forests - Critical review. J. Air Poll. Control Assoc., 

35(9): 913-915. 

Pun, B.K.; Wu, S.Y.; Seigneur, C. (2002). Contribution of biogenic emissions to the formation of 

ozone and particulate matter in the eastern United States. Environ. Sci. Technol., 36(16): 

3586-3596. DOI: 10.1021/es015872v. 

Rao, S.T.; Ku, J.Y.; Berman, S.; Zhang, K.S.; Mao, H.T. (2003). Summertime characteristics of 

the atmospheric boundary layer and relationships to ozone levels over the eastern United 

States. Pure and Applied Geophysics, 160(1-2): 21-55. 

Rosenthal, J.S.; Helvey, R.A.; Battalino, T.E.; Fisk, C.; Greiman, P.W. (2003). Ozone transport 

by mesoscale and diurnal wind circulations across southern California. Atmos. Environ., 

37S51-S71. 

Seitz, J.S. (2000). Boundary guidance on air quality designations for the 8-hour ozone national 

ambient air quality standards. prepared by U.S. Environmental Protection Agency, Research 

Triangle Park, NC, 

Sillman, S.; He, D.; Cardelino, C.A.; Imhoff, R.E. (1997). The use of photochemical indicators 

to evaluate ozone-NOx- hydrocarbon sensitivity: Case studies from Atlanta, New York, and 

Los Angeles. J. Air Waste Manage. Assoc., 47(10): 1030-1040. 

Sillman, S. (1999). The erroneous use of receptor modeling to diagnose O3-NOX-hydrocarbon 

sensitivity. Atmos. Environ., 33(14): 2289-2291. 

Sillman, S. (2001). Comment on 'The impact of an 8h ozone air quality standard on ROG and 

NOX controls in southern California' by Chock et al. Atmos. Environ., 35(19): 3367-3369. 

Skelly, J.M.; Ferdinand, J.A.; Savage, J.E.; Jagodzinski, J.M.; Mulik, J.D. (2001). A 13-week 

comparison of passive and continuous ozone monitors at forested sites in north-central 

Pennsylvania. J. Air Waste Manage. Assoc., 51(9): 1280-1287. 

Spicer, C.W.; Joseph, D.W.; Sticksel, P.R.; Ward, G.F. (1979). Ozone sources and transport in 

the northeastern United States. Enivron. Sci. Technol., 13(8): 975-985. 

Tao, Z.N.; Larson, S.M.; Wuebbles, D.J.; Williams, A.; Caughey, M. (2003). A summer 

simulation of biogenic contributions to ground-level ozone over the continental United 

States. J. Geophys. Res. -Atmospheres, 108(D14): 

Wager, D.J.; Baker, F.A. (2006). Ozone concentrations in the Central Wasatch Mountains of 

Utah. J. Air Waste Manage. Assoc., 56(10): 1381-1390. 

 13
Wolff, G.T.; Lioy, P.J.; Wight, G.D.; Meyers, R.E.; Cederwall, R.T. (1977). An investigation of 

long-range transport of ozone across the midwestern and eastern United States. Atmos. 

Environ., 11797-802. 

Zeng, G.; Pyle, J.A.; Young, P.J. (2008). Impact of climate change on tropospheric ozone and its 

global budgets. Atmos. Chem. Phys., 8(2): 369-387. 

 14
Mr. Bart Croes 

These comments also reflect input from California Air Resources Board (ARB) staff responsible 

for implementing U.S. EPA monitoring requirements and using the data in ozone data analyses 

and health studies. 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

The requirement for one monitor to be placed in MSAs of population between 50,000 and less 

than 350,000 is clearly warranted in locations where there is the absence of a design value, 

primarily because of the large number of people potentially affected by any standard 

exceedances. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

Based on the experience in California, 18 months is adequate if funding is provided and 

implementation can be accomplished with existing staff. If funding and staff resources are not 

adequate, a staggered deployment schedule that extends over the following year should be 

considered. While attainment designations would be delayed by a year, this may not adversely 

affect control programs as any nonattainment areas with populations of this size are likely to be 

affected by ozone transport from larger, upwind cities, and will already be receiving the benefit 

of control programs in these areas. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

The choice of three non-urban monitors per state appears arbitrary with no acknowledgement of 

geographic size differences, potential for transport from upwind area or ozone severity. 

USEPA’s impressive ozone modeling capabilities could be used to identify broad geographic 

areas where additional non-urban ozone monitoring is warranted. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

 15
Factors that relate to the potential for higher ozone levels should be considered. These include 

proximity to upwind source regions, size of the source region, mixing ratios recorded at upwind 

monitors, smaller potential for deposition losses (shorter transport distances, transport over water 

bodies or areas with less vegetation), higher elevations (decoupled from night-time surface NOX

sources), and sunnier areas with higher photolysis rates. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, affect the minimum number of non-urban required monitors? 

The resources available for equipment, shelters, operations and personnel should be considered. 

Non-urban ozone monitoring may be useful for ozone transport analyses and ozone model 

evaluation. Monitoring near ozone sensitive vegetation, especially areas where forest health or 

ecosystem monitoring is occurring, should be considered. I do not think these considerations 

should affect the minimum number of non-urban required monitors. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

Yes, they are still applicable to maintain uniform siting criteria throughout the entire network 

(urban and non-urban). Monitoring at higher elevations with snow during the winter needs to be 

seasonal to facilitate site access. More attention needs to be placed to setbacks from trees and 

other vegetation because of the potential for ozone deposition. And to setbacks from roadways 

as there is unlikely to be co-located NOX monitoring to identify episodes of ozone titration. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Other agencies would need to become part of their local Primary Quality Assurance 

Organization (PQAO) and follow uniform procedures, have staff take similar training, maintain 

same standard traceability, and submit data to USEPA’s Air Quality System (AQS). 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

Provisions for high elevation sites with only seasonal access should be considered. 

 16
2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

The Health Effects Institute or other representations of the air pollution epidemiology 

community should be consulted as to where year-round ozone measurements would be useful for 

epidemiologic cohort studies. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

Yes, it is a reasonable schedule as the logistics are relatively straightforward. 

 17
Dr. Delbert J. Eatough 

The subject of this charge is not my area of expertise. I have responded only to those questions 

where I think I can give useful input. 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

The proposed changes seem reasonable and adequate. The existence of Class 1 monitors covers 

many non-urban areas already and the NCORE site activation will give a reasonable year round 

data set. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

If the final rulemaking is completed this year, increasing the deployment on a staggered basis, 

depending on the available data, to either two or three years (i.e., a one year extension for some, 

identified lower probability sites) seems reasonable. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three non 

urban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

The criteria for the three sites seems reasonable. The inclusion of a wilderness site as one might 

be relaxed if such sites already exist in the state. What happens if a state has no unmonitored 

MSA which models and other reasonable estimations indicates will be likely to exceed the 85% 

value? 

WY is certainly an outlier in the data set. The observation that the high ozone concentrations in 

WY appear to be associated with VOC emissions from oil and gas recovery during winter 

inversions has implications for other areas. I have made an additional comment on this below. 

 18
2. What factors should be considered in the siting of ozone monitors to assess impacts on 

ozone sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the 

consideration of additional objectives, if any, effect the minimum number of non-urban 

required monitors? 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) 

include requirements for station and probe siting (e.g., vertical distance of inlets, set-back 

distances from roadways). Are these requirements (that have been developed for urban 

monitors) appropriate for non-urban ozone monitors? What changes, if any, should be 

considered? 

5. We believe that States should have the option of designating that existing non-urban 

ozone monitors that are potentially operated by another agency (e.g., CASTNET 

monitors operated by the National Park Service) be utilized for meeting certain non-urban 

minimum monitoring requirements. What factors should States use to determine if such 

monitors are appropriate to include in their networks?

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

There is evidence that even at low Ozone concentrations, there is photo oxidation of material 

during the winter which leads to high PM levels during inversions in high mountain valleys. 

This is seen, for example, in our studies on the composition and apportionment of PM in the Salt 

Lake City area during winter inversions (Long et al., 2003, 2005) Identifying some of these 

regions for year round joint ozone monitoring and fine particulate speciation would be useful. 

Salt Lake is one such location. Boise could well be another. Including some PM studies in the 

WY region where high winter ozone has been observed could be useful. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside Ncore? 

See response to 1 in this section. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

 19
Yes. 

References:

Russell W. Long, Norman L. Eatough, Nolan F. Mangelson, Wesley Thompson, Kyle Fiet, Scott 

Smith, Rachel Smith, Delbert J. Eatough, C. Arden Pope, William E. Wilson (2003). “The 

Measurement of PM2.5, Including Semi-Volatile Components, in the EMPACT Program: 

Results from the Salt Lake City Study and Implications for Public Awareness, Health 

Effects, and Control Strategies.” Atmospheric Environment, 37; 4407-4417. 

Russell W. Long, William K. Modey, Phillip S. Smith, Rachel Smith, Cristina Merrill, Joshua 

Pratt, Andrew Stubbs, Norman L. Eatough, Delbert J. Eatough, William C. Malm, and 

William E. Wilson. (2005) “One- and Three-Hour PM2.5 Characterization, Speciation, and 

Source Apportionment Using Continuous and Integrated Samplers.” Aerosol Science and 

Technology, 39:238-248. 

 20
Mr. Dirk Felton 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

The requirement to add monitors in MSAs as small as 50,000 may be burdensome to some 

monitoring agencies. One element that should be added to the regulation is the ability to waive 

the monitoring requirement if the State designates the MSA as non-attainment. With the new 

lower NAAQS, the non-attainment areas in some states cover large areas and several MSAs. It 

is quite possible that upwind, rural or transport oriented monitors and monitors in adjacent MSAs 

can adequately justify the determination of non-attainment for small MSAs without a monitor. 

The RA should also have the discretion of waiving additional monitors that either can’t meet 

siting requirements in certain urban areas or where the cost to install a monitor is excessive and 

out of the reach of the monitoring agency. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

The schedule is appropriate only if monitoring agencies already have a suitable facility to install 

additional monitors. For these existing locations, the monitoring agencies will need calendar 

year 2010 to modify their network plan, to modify budgets and to purchase and install new 

equipment. The timeline should establish a start date of 2012 for completely new installations. 

This extra year will be needed because monitoring locations are very difficult to site in urban 

areas. In these areas, conventional monitoring shelters are usually either banned by building 

codes or can’t be sited properly due to the cost of property and the density of tall structures. In 

some of these situations, monitoring agencies have to go to the expense of modifying existing 

buildings whether public or private to accommodate monitoring equipment. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

The plan to require three monitors per state is a bit too cookie cutter to adequately meet the 

monitoring needs in each state. Many states have multiple rural areas, some separated by 

mountains, that are distant from each other and are affected by separate upwind sources. It is 

likely that the plan for three non-urban monitors will only be adequate for a few states. The EPA 

 21
must be flexible and should encourage periodic discussions between OAQPS, the EPA Regional 

Offices, monitoring agencies and perhaps other stake holders such as health researchers to 

determine the minimum number and location of additional monitors. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

The importance of altitude and local terrain is often overlooked in monitor siting. Rural 

monitors could be situated on a mountain top, on an elevated plateau or in a deep valley. These 

terrain features will affect local Ozone concentrations and could detrimentally reduce the scale of 

the monitor. Monitoring is expensive and rural monitors should be sited to represent large 

scales. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

Transport is another objective that could be served by a suitably placed rural monitor. The 

installation of a transport monitor can be very important if it is used to help with attainment 

planning for downwind areas. The states that have non-attainment areas or whose emissions 

contribute to non-attainment areas should be provided with the resources to establish monitoring 

networks that exceed the minimum requirements. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

The set-back distances from roads and other local sources for non-urban, rural monitors should 

be increased to the extent possible. Rural monitors should represent large spatial scales and 

influences such as NOx scavenging from nearby sources will alter the apparent Ozone 

concentration for the entire area represented by the monitor. Ideally, the monitor should be 

situated in a “typical” spot in the area to be represented by the new monitor. If the area is a 

nearly roadless Class 1 wilderness area, the monitor should be quite far from a road. If the nonurban monitor is actually representing a suburban commuter area outside of a larger MSA then it 

is acceptable to be closer to a roadway or other typical local sources. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

It has yet to be demonstrated that CASTNET can reliably meet the QA requirements that would 

make their data comparable to state and local monitoring networks. The CASTNET network is 

operated by a contractor who is selected through a competitive bidding process. It is possible 

 22
that as the contract is awarded in future years to the same or another vendor, the data quality 

could vary. 

State and local monitoring agencies should carefully evaluate the data quality of all of the 

monitors in their area. States should be permitted to audit the operation of either CASTNET or 

NPS monitors that potentially could be included as a component of a comprehensive state 

monitoring network. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

In states with cold winters, seasonal roads or high altitude monitoring locations, it may not be 

possible to initiate monitoring on the proposed earlier start dates at every location. The EPA 

should permit reasonably delayed start dates if access to a monitoring location is prohibited or 

delayed due to snow or mud conditions. 

Population exposure monitors should be given the highest priority for initial startup at the 

beginning of the monitoring season. The EPA should consider not changing the monitoring 

season for the non-urban and ecosystem oriented monitors. The data from these sites is likely to 

be less valuable when air temperatures are still relatively cold and sensitive vegetation is 

dormant or snow covered. Monitoring agencies utilize the period in between monitoring seasons 

to perform instrument maintenance, re-certify calibrators and train staff. Permitting delayed start 

dates for the non-urban monitors will also ease the difficulty of starting many monitors on the 

same date. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

Due to the nature of NCore siting, most NCore sites will not be located where the Ozone 

concentrations are the highest. It would be appropriate to also monitor year round at one of the 

highest Ozone concentration sites for each non-attainment area. This will provide context for the 

NCore data. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

A 2010 start date for a longer monitoring season for existing monitors would be acceptable if the 

regulation was finalized before the end of the first Quarter of 2009. 

 23
Dr. Phil K. Hopke 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

At least one monitor in each MSA with more than 50,000 is certainly warranted. I suggest a key 

consideration here has to be that the concentration of ozone is also critically important in control 

of PM given the role of oxidants in the formation of secondary particles. It is time we looked at 

the problem from a multiple pollutant perspective both in terms of the health effects and in terms 

of the control strategies. To do and fully protect public health requires that we have adequate 

measurements of all of the key pollutants in any area of reasonable population. 

I would second George Allen’s comment that we really should have a commercially available 

ethylene chemiluminescence monitor to use as a QA reference. It does not make a lot of sense to 

have as the FRM as monitor that no one can actually buy and use. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

At this point, state and local agencies are hard pressed for funding. At the same time, one would 

suggest that from a public health protection standpoint, it would be important to deploy the 

monitors as quickly as possible. However, there should be resources made available to the state, 

local, and tribal agencies to defray the costs of the redeployment or the acquisition of additional 

monitors. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

We consider Montana and Rhode Island equivalent in the need of monitors per unit area? This is 

clearly a very strange idea. We can certainly apply appropriate models and look at the real needs 

to monitor and where they will need to be placed in order to meet the underlying objectives. 

Given the disparity in the size of states, the distribution of population centers and where 

transported ozone represents a significant regional control problem, this requirement appears 

arbitrary. There are a number of small eastern states where this would not appear very sensible 

and other states where it will clearly be inadequate. Who is to decide whether or not to exceed 

 24
the minimum number? There needs to be a clearer definition of the criteria for siting the 

monitors and that would define the minimum number per area. We have adequate modeling 

capabilities that can provide good indications of the numbers of different ozone regions that exist 

in a state. We can also think about monitors located in contiguous states to potentially serve to 

cover an area as well. We need to be less fixated by the number of monitors and more ties to the 

underlying motivations for the monitoring and our best understanding of the atmospheric 

processes to deploy limited resources to provide the most benefit. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

We need to look at cumulative indices of exposure for the plants. We can estimate these 

exposures from appropriate modeling efforts and given the nature of the ecosystem, estimate the 

likely damage. If we are really interested in protecting the vegetation, then it is worth the effort 

to customize the plans for each major area of the country having significantly different types of 

vegetation. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

Clearly, a major concern for monitoring in rural areas is to provide critical data for model testing 

and validation. They also can provide some additional data for warning of pending ozone 

episodes in areas downwind of the monitor. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

Even in rural areas, there could be significant NO sources and one would want to site well away 

from such sources. We still want glass and Teflon inlets, etc. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Clearly the monitoring locations have to meet the needs identified under question 2 above. The 

key issue is whether or not they can be operated with the same level of quality assurance as the 

SLAMS monitors. If so, fine.

 25
Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

Again, we need to think in multiple pollutant terms. Secondary aerosol is still formed in the 

winter. Exposures to ozone and other pollutants occur. We will never sort out the requirements 

to protect health from the exposure mixture that the atmosphere produces without making year 

round measurements. If the SLAMS site is monitoring other pollutants, then the incremental 

cost of running that monitor all of the year is pretty minimal and well worth the extra effort and 

expense. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

Again, one needs to look at the needs for understanding the behavior of the suite of pollutants 

and whether ozone data would provide critical information needed to make the management 

judgments needed to adequately protect public health. 

 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors?

It is not clear that it would be useful to do this uniformly across the country. It might make more 

sense to phase these into those areas that are most sensitive and where the data would prove most 

useful. 

 26
Dr. Rudolf Husar 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

I think that mandating a month-by-month fine tuned monitoring season to each state is 

unnecessary. If such adjustments for the shoulder seasons are in fact made, the states that have a 

short ozone season should be monitored less. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

Regional/continental background sites and/or high elevation sites. These would document the 

spring stratospheric ozone, trans-continental (Asian) ozone transport and other larges-scale 

processes. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

No comment. It is a feasibility issue.

 27
Dr. Kazuhiko Ito

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas?

EPA may need to accommodate the concerns expressed by State air monitoring agencies and 

multi-state air planning organizations that these requirements ignore the needs that States and 

localities have for additional monitors to measure ozone levels in areas with populations under 

350,000. Judging from the figure in the white paper, it looks like there may be about 20 MSAs 

with less than 350,000 people that may be near the border of non-attainment. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

It seems to me that there is no need to delay the deployment for the larger MSAs with existing 

sites even if setting up additional sites may take additional time, unless EPA needs to relocate 

some of the existing sites. I don’t see disadvantage of a staggered deployment schedule if they 

are necessary. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

There must be something like “Data Quality Objectives” (DQO) to determine whether or not 

some specific number of monitors is sufficient to achieve the goal. Without knowing the goal in 

some numerical manner, this question cannot be concretely answered. I suppose the following 

questions are more specific. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

I am not familiar with the quantitative relationships (i.e., linear or non-linear?) between ozone 

and the effects on sensitive vegetations, but the siting of the monitors should consider: (1) the 

known quantitative relationship between ozone and the sensitive vegetation; (2) the spatial 

distribution of such vegetations; and, (3) prediction model of ozone concentrations over the areas 

where sensitive vegetations exist. The siting should be done to minimize the uncertainty 

 28
associated with the ozone prediction over the areas that are densely populated with such 

vegetations. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

I don’t personally use them, but there are models (e.g., CMAQ) out there that predict air 

pollution levels including ozone. I imagine that prediction and model validation of these models 

rely on the locations of existing monitors. If EPA uses these models, why not also consider 

siting monitors where the model performance would improve. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

I took a quick look at Appendix E of 40 CFR part 58. Regarding the probe height, it says: “The 

probe or at least 80 percent of the monitoring path must be located between 3 and 15 meters 

above ground level.” I am not sure if this height requirement is appropriate in determining the 

exposure of sensitive vegetation. Perhaps it needs to be lower, but one needs to know the 

concentration gradient (profile) of ozone near the ground to take into consideration scavenging 

of ozone by the surface characteristics including those of vegetations. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

I am not familiar with the difference in the procedures, analytical methods, or siting requirements 

between the CASTNET monitors vs. EPA monitors, so I cannot provide specific comments, but 

if they are comparable, then any CASTNET monitors that meet requirements in Questions 2, 3, 

and 4 above should be included. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

I am generally opposed to restricting the available data for research purposes. If the change 

results in shorter sampling periods, such decision needs to take into consideration the balance 

between the possible information to be lost vs. the information gained by additional sampling 

 29
locations (because you trade these two for a fixed budget, I assume). It should be noted that, as 

far as the health effects are concerned, the current NAAQS is NOT based on a clear-cut 

threshold below which we don’t observe any effects. This means that, if we shutdown ozone 

monitoring for areas and periods we observe levels below the current standard, then we are 

eliminating the future data for research from which we will base our future standards! However, 

based on the EPA’s presentation during the conference call, the only one state would have a 

shorter ozone season. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

If the spatial variation of ozone is not easily predicted in a MSA, additional year-round monitors 

may be needed to characterize such variations. Also, the seasonal cycles and the relationship 

between ozone and other pollutants must be different from city to city or region to region. 

Also, as far as air pollution epidemiological studies are concerned, I sense that the more 

emphasis will be placed in multi-pollutant evaluation. Then, the NAAQS will also have to 

emphasize multi-pollutant context. If this happens, then, the longer the ozone sampling period, 

the better for the multi-pollutant evaluation. Based on the EPA’s presentation during the 

conference call, many states would have longer ozone sampling seasons. I welcome this change. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors?

I am not familiar with the operational aspect of changing (extending) the ozone monitoring 

season, but given that the monitors are continuous analyzers, I don’t imagine it would be 

unfeasible to do this for existing monitors ahead of the deployment schedule. 

 30
Dr. Donna Kenski 

Urban Network Design Requirements:

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to 

ensure a minimally adequate network in urban areas? 

I support the proposed change to require monitoring in MSAs of populations between 50,000 and 

350,000, although I suggest that this requirement be tempered by an allowance to reduce 

monitoring if the data show little or no potential for exceeding the NAAQS. For example, if an 

area has a recent design value (within the last 5 years) less than 85% of the current NAAQS, the 

requirement for a new monitor could be waived (as Table D-2 of 40CFR part 58 App. D 

currently permits). Similarly, after 3 years of monitoring in these new areas, a resulting design 

value less than 85% of the standard should allow the states to remove or relocate the monitor in 

that area. The intent, as in Table D-2, is to characterize ozone concentrations in areas with 

significant population, but not insist on permanent monitors in areas where the data demonstrate 

little evidence of health impacts. In a few locations, from the map given, it looks like there are 

existing monitors very near the MSAs. EPA might consider substituting those on a case-by-case 

basis, if a state can provide supporting evidence (e.g., modeling or previous monitoring) that a 

nearby existing monitor can provide data that is representative of the MSA. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking 

will be completed in 2009. Is this schedule appropriate or should EPA consider 

providing an additional year for new monitors to be deployed (or relocated)? What 

would be the advantages or disadvantages of a staggered deployment schedule? 

EPA should allow the states at least a 1 year period from the time of rulemaking to the required 

operation of monitors. The proposed timeline seems adequate, assuming the states are allotted 

funding early in the process so they can make purchases of new equipment with sufficient lead 

time. A staggered deployment schedule might be useful for those few states with a lot of new 

sites (Texas?) but most states with only 2 or 3 new monitors would probably find it more 

efficient to make these changes at the same time; staggering deployment would unnecessarily 

complicate the process. Of course, when you combine the required new urban monitors with the 

new non-urban monitors, the numbers start to add up for all the states, in which case staggering 

deployment starts to make more sense. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban 

ozone monitors to meet certain objectives (described above). Considering the 

stated objectives of the non-urban ozone monitoring requirements, is three required 

monitors per state sufficient? 

 31
Certainly three is sufficient for most states, but surely too many for some (RI? CT? NJ?) and 

perhaps not enough for others. Can there be a more equitable distribution based on area? Or 

better yet, could we distribute them based on where we know vegetation is sensitive, and 

consider the non-urban monitors that we already have? It seems somewhat heavy-handed to 

make a blanket requirement for every state regardless of size, existing monitors, and sensitive 

vegetation. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on 

ozone sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

Expected concentration and the presence of sensitive species. One might want to consider the 

practical aspects like ease of access to the site, collocated equipment, etc. But ozone has harmful 

effects on agricultural and ornamental vegetation as well, so let’s not restrict our ozone 

monitoring in nonurban areas to wilderness areas. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the 

consideration of additional objectives, if any, effect the minimum number of non-urban 

required monitors? 

This network really ought to consider geographic distribution without trying to parse equal 

numbers of monitors to each state. Plot the existing nonurban monitors (including state 

monitors, CASTNET and IMPROVE), find the holes, and add enough monitors to fill in the 

gaps. Terrain and likelihood of higher concentrations could also be factored in (we probably 

don’t need as many monitors in North Dakota as in Texas). There’s nothing inherently wrong 

with using some carefully modeled ozone data to estimate where highest concentrations in 

currently unmonitored areas might be. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) 

include requirements for station and probe siting (e.g., vertical distance of inlets, set-back 

distances from roadways). Are these requirements (that have been developed for urban 

monitors) appropriate for non-urban ozone monitors? What changes, if any, should be 

considered? 

These non-urban monitors might be sited more like the IMPROVE monitors with respect to 

distance from any potential sources. 

5. We believe that States should have the option of designating that existing non-urban 

ozone monitors that are potentially operated by another agency (e.g., CASTNET 

monitors operated by the National Park Service) be utilized for meeting certain non-urban 

minimum monitoring requirements. What factors should States use to determine if such 

monitors are appropriate to include in their networks? 

These other network monitors should absolutely be considered in developing a non-urban 

network, and efforts toward harmonizing the various networks should continue. The presence 

of stable, long-term funding is probably the most important factor to consider, followed closely 

 32
by an adequate quality assurance program and some kind of network intercomparison to ensure 

reliable, comparable data with the other state monitors. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses 

of the patterns of ozone exceedances and occurrences of the Moderate level of the Air 

Quality Index, during periods outside of the currently required seasons. What other 

factors should be considered, if any, in the determination of the length of the required 

monitoring season for each State? 

Thank you for posting the additional information on the Camalier ozone season analysis. It 

seems to be a reasonable approach and I concur with the conclusion to increase ozone season in a 

number of states. Another approach, or factor to examine, is to look at the timing of exceedances 

or values >0.06 ppm throughout the year and statistically predict how likely those concentrations 

might occur before the start of the monitoring season. That is, if Wisconsin has recorded an 

ozone concentration of 0.076 as early as April 20 in the past, how are likely is it that a similar 

concentration might occur 6 days earlier, before the official season begins? The work of Rasmus 

Benestad in predicting extreme events seems like a promising approach (Benestad, R., EOS, 

Trans. AGU 89:41, 7 Oct 2008). 

2. We believe that ozone monitors that are located at NCore stations should be operated on 

a year-round monitoring schedule. Under what circumstances might it be appropriate to 

require year-round monitoring at other stations beside NCore? 

EPA should encourage, but not require, year-round monitoring at ozone sites. The NCore sites 

will provide a sufficient base of year-round monitoring and will include the collocated species 

that make it more useful for health and chemistry studies. Of course more data is always better, 

but it comes at a cost. At this point, I don’t think there is sufficient added value to expanding the 

pool of year-round monitors (i.e., requiring all sites to monitor year-round) to justify the 

additional cost. If future health data demonstrate a pressing need for winter ozone data from 

additional sites, we could revisit this, but right now I don’t think the need is there. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for 

newly required ozone monitors. Is this schedule reasonable for existing monitors? 

Yes. 

 33
Dr. Thomas Lumley 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

The addition of monitors in lower-population areas is an important step in ensuring that the 

NAAQS protect the US population. I believe the current density of monitors in larger urban 

areas is sufficient if they are appropriately located in places where higher ozone concentrations 

are expected. A useful way to confirm this would be to summarize how many excedances of the 

proposed threshold in large urban areas were detected by only a single monitor 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

I have no relevant expertise on the feasibility of deploying monitors by 1/2011. If this schedule 

is feasible then postponing the deployment will significantly reduce the amount of data available 

in smaller urban areas by the next revision of the standards. My non-expert reading of economic 

forecasts suggests that state budgets are likely to still be strained by the current recession in 

2010, so later deployment may be helpful for cost reasons. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

It is not clear to me that the number of monitors in each state should be the same. States may 

differ greatly both in the amount of publically significant ozone-sensitive vegetation and in the 

likelihood of high ozone levels. It seems more appropriate to customize the requirements to the 

actual risks. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

The likelihood of adversely high ozone concentrations; the sensitivity of the vegetation; the 

importance of the vegetation ecologically, as a public attraction, and as part of a more-or-less 

pristine wilderness area. In particular, since vegetation (unlikely human health) can safely be 

 34
assumed to be unaffected by natural background levels of ozone, monitoring should focus on 

areas where anthropogenic ozone impacts are likely to cause vegetation damage. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, affect the minimum number of non-urban required monitors? 

I have no suggestions on this issue. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

Increasing required distances from roads may be appropriate. In an urban setting there are 

constraints on required distance from roads that are not present in non-urban areas. In addition, 

important ozone-sensitive vegetation is likely to live further from main roads than the typical 

member of the urban population. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

This seems appropriate. The monitors should be operated on the same schedule and have 

accuracy comparable to the urban monitors, and they should be sited so as to capture the 

potential ozone impacts that the standards protect against. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

I can’t think of any. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

Year-round monitoring at NCore stations plus extension of the monitoring season to capture 

`Moderate’ ozone levels at other stations seems sufficient. 

 35
3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable. 

I have no relevant expertise on this issue. 

 36
Dr. Peter H. McMurry 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

Based on my reading of the document and comments from other committee members who are 

more knowledgeable than I on this topic, it seems reasonable to me. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

It is my understanding that the new ozone monitors would need to be operational at the 

beginning of the 2011 ozone monitoring season, not necessarily on January 1. This seems 

reasonable. Committee members pointed that given states’ current financial difficulties, some 

flexibility may be advisable. I am sympathetic to this concern. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

I am among the group of Committee members who are perplexed by this specification. I agree 

with others that the focus needs to be on achieving adequate coverage. After studying Figure 1 I 

was only able to find one state (Montana) that currently has fewer than three sites (I recognize 

there may be other states whose sites do not meet the constraints defined by this proposal.) 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

Ozone may be a sentinel for climate change in some remote areas. Temperature changes will 

lead to changes in rainfall and vegetation. Biogenic emissions of compounds that react to 

produce ozone will be affected by those changes. Ozone concentrations might also be affected by 

temperature, which affects rates of reactions that produce ozone. If these processes were to affect 

ozone concentrations, long periods (years) of continuous monitoring (not only during the ozone 

NAAQS season) would be required to detect them. I am not expert on this topic, but certainly 

others are. I recognize that this is not a topic that falls within the primary ozone NAAQS, but it 

should be a consideration. 

 37
3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Wherever possible, an effort should be made to qualify ozone monitors in other networks 

(CASTNET, NPS, etc) as FRM monitors. Also, ozone monitors should be located at sites where 

other species are also being measured. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

The clear message needs to be communicated to states that there is substantial value in operating 

ozone monitors year round, not only during the primary NAAQS ozone monitoring season. The 

potential value of such measurements in supporting model evaluation, assessing climate change 

impacts, etc., should be communicated so that states are aware of the benefits. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

There are compelling arguments for making year-round measurements wherever possible. These 

include (1) the possibility that instruments operate better when they are operated continuously, 

(2) the possibility that data can be used for many purposes other than meeting NAAQS 

requirements. EPA should communicate to state agencies the ways in which continuous ozone 

data could be of value. These include model evaluation, assessment of climate change on ozone 

concentrations, assessment of unanticipated impacts of new sources (e.g., emissions from 

Wyoming’s energy industry), assessment of multi-pollutant health impacts when ozone is below 

NAAQS levels, etc. It should be emphasized that there is no known lower threshold for ozone 

health effects. 

 38
3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors?

I defer. 

 39
Mr. Richard L. Poirot 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

The proposed change is probably “sufficient” to ensure a minimally adequate network in urban 

areas, and the “logic” of affording “protection” to populations in smaller MSAs is reasonable. 

However, population levels – especially for cities as small as 50,000 – may not be the best 

predictor of (currently unmonitored) locations where exceedances of the new NAAQS are most 

likely, nor is a new monitor necessarily the best means to afford “protection” to a given 

population. Considering that the primary and secondary NAAQS are the same, and given the 

“suburban” nature of many existing monitoring sites, it can also become difficult to distinguish 

between urban and rural monitoring sites and objectives, and it might be more useful to think 

more in terms of an urban/rural continuum rather than separate networks with separate 

objectives. 

Rather than deploying new monitoring “urban” sites strictly according to a MSA populationbased formula, other desirable monitoring objectives that might be considered include: 

• Minimize spatial interpolation errors and uncertainties – both for real-time mapping and 

for estimating longer-term exposure metrics for both health and sensitive vegetation, 

• Improve forecasting ability (are there key locations - or kinds of locations - that the 

forecasters would like to see to help improve their forecast accuracy?), 

• Evaluate/improve forecast (or SIP backcast) models (local, regional, continental, global), 

• Evaluate/improve satellite estimates, 

• Enhance consideration of multi-pollutant exposures and effects (and atmospheric 

chemistry) through collocation with other pollutant & meteorological measurements, 

• Provide better indication of ‘true’ human exposure levels in inner city locations, 

• Evaluate effects of control strategies or of projected population or industrial growth, 

• Improve estimates of regional, transboundary and transcontinental transport, as well as 

regional and “policy-relevant” background concentrations. 

For these reasons, EPA and the states should be encouraged to exercise substantial flexibility in 

implementing the new “urban” monitoring requirements. For example, I strongly endorse Dirk’s 

suggestion to wave monitoring requirements for smaller MSAs which the state has designated 

nonattainment. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

 40
States are currently under severe budgetary constraints. Given this and the difficulty that can be 

associated with establishing new monitoring sites in urban areas (as opposed to adding ozone 

monitors at existing monitoring sites), a 1/1/11 deadline may be overly ambitious. A phased 

schedule that provides more time is likely to result in better data quality in the long-term, 

especially if new site locations need to be established. 

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three nonurban 

ozone monitors to meet certain objectives (described above). Considering the stated objectives of 

the non-urban ozone monitoring requirements, is three required monitors per state sufficient? 

While 3/state is an arbitrary proposal, the number generally seems about right given your stated 

multiple objectives (and/or is difficult to judge without knowing which existing “non-urban” 

sites may meet these criteria). In addition to the stated monitoring objectives, some of the 

additional objectives listed above for “urban” monitoring might also be considered in selecting 

new “rural” sites. 

Sites at higher (relative) elevation can be especially valuable for evaluating transport 

contributions and model performance, but in many regions will also tend to measure higher 

concentrations. So some states may be reluctant to sample at such locations without specific 

incentives or perhaps special designation as “research sites” not subject to compliance 

determinations. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

As always, substantial value is added if ozone measurements are collocated with other 

measurements, and so adding ozone at IMPROVE sites would provide useful new information. 

It can also be noted that EPA research on effects of ozone on sensitive vegetation has been quite 

limited in recent years (decades), and so it could be valuable for EPA to form partnerships with 

Agencies like NPS, Forest Service and with academic groups to better coordinate monitoring and 

effects research activities. See for example the NPS “Ozone Risk Assessment for Vital Signs 

Networks” http://www.nature.nps.gov/air/Permits/ARIS/networks/ozoneRisk.cfm

Some emphasis might also be placed on monitoring (and/or effects research) in locations with 

high densities of ozone-sensitive plants or where ozone effects have been observed (such as 

foliar injury in FHA surveys), but where current ozone standards are not expected to be 

exceeded. Also, given CASAC recommendations in the last 2 ozone NAAQS reviews to adopt a 

more biologically relevant cumulative seasonal secondary standard, some emphasis might be 

placed on the kinds of locations where a SUM06 or W126 metric would be high relative to the 8-

hour daily maximum. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? 

 41
How would the consideration of additional objectives, if any, effect the minimum number of nonurban required monitors? 

See answers to previous questions. In addition, final decisions on the numbers of required new 

sites need to be balanced with considerations of alternate monitoring priorities – such as longer 

monitoring seasons. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

Given the blurred distinctions between urban and rural sites (& monitoring objectives), and for 

reasons of consistency, I think station and probe siting requirements should generally be the 

same for rural and urban monitors 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Monitors not operated by State Agencies should be subject to the same QA/QC requirements 

imposed on state-operated sites. 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

The various anomalies in the page 20 map of proposed ozone season requirements by state look a 

little silly from a science perspective, and for various reasons, it might make more sense to 

require (or provide some incentives for) year-round sampling at some sites in all states. It would 

be useful to develop some estimates of the incremental costs of extending the ozone monitoring 

season – especially at sites where other monitoring demands year-round attention. I would think 

the incremental cost of running year-round at such sites would be relatively small (and there can 

also be problems & costs associated with shut-down/start-up operations). Additional data from 

these sites would also have the added value of providing useful information on multi-pollutant 

exposures and effects and on atmospheric chemistry. I think there’s still much we don’t 

understand about the (multiple) causes for the general springtime maxima, intercontinental 

transport, winter photochemistry, stratospheric intrusion, etc. 

 42
2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

I would think many of the NCore sites might not be sited to measure peak ozone levels (in any 

season – but especially) in cooler months, and/or might not be ideally sited to help indicate broad 

spatial patterns. Possibly it would be useful to require at least 1 rural site per state for year-round 

sampling. Also, it seems likely that the site characteristics to record maximum concentrations 

may be different in warm & cool seasons. For example, higher elevation / ridge top or “near 

water” sites often see highest concentrations in summer, while in-land valley locations might see 

higher concentrations in winter. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

This seems reasonable in most cases. Some rural sites – especially at higher elevation – can be 

inaccessible in winter. Allowances should be made for such sites (which are also not likely to 

record the highest concentrations in cooler months). 

 43
Dr. Armistead Russell 

Urban Network 

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

I would not be overly aggressive in setting a schedule. First, I would ask the question as to what 

objective a specific cite addresses. Next, I would ask if the siting, and system could benefit from 

more thought than is allowed with the given schedule. Overall, I would argue for thoughtful 

flexibility. 

Non-Urban Network 

1. We are considering a new requirement that each State operate a minimum of three non-urban 

ozone monitors to meet certain objectives (described above). Considering the stated objectives 

of the non-urban ozone monitoring requirements, is three required monitors per state sufficient? 

My first reaction to this requirement was quite negative until reading about the proposed 

flexibility, and even that may not be enough. Given the large variety of resources that inform us 

about ozone across the US, I am not sure that we need three non-urban monitors in each state. I 

would look at the various available products (satellite data, annual modeling simulations, nonroutine monitoring results (including special study monitors), the size of the state, population, 

etc., and use these to determine how many and where the monitors should go. As stated above, I 

would argue for thoughtful flexibility. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on ozone 

sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

My view is that the agency, along with the states, should look at where information is critically 

missing. Use the modeling results (of more than just ozone), statistical analysis, satellite data (of 

more than just ozone) and current monitoring results to figure out where adding an ozone 

monitor to the network, preferably at a pre-existing (likely PM) monitoring site. I would hesitate 

to site any new ozone monitor where there is not some other monitor already. The information 

typically is not as valuable as it would be if information on more pollutants is available at the 

same site. 

 44
3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

I would be less worried about the modeling end (as a modeler)... we make too little use of the 

ones we have. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

Every city (> 350,000) should have at least one monitor going and reporting all year round. In 

regards to other monitors, 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors?

Yes. 

 45
Dr. Jay R. Turner 

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas? 

Monitoring should be conducted in all MSAs below 350,000 population to at least establish 

ozone air quality conditions. This is important given the role of ozone monitoring not only for 

NAAQS compliance determinations but also for AQI reporting. There should be flexibility in the 

timeline to deploy new monitors in such areas and the requirements to maintain monitoring in 

these smaller MSAs depending on the observed ozone levels. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

What three-year period will be used for the first round of designations under the May 2008 

NAAQS revisions? If the new data are expected to inform the decision-making on 

nonattainment area boundaries, then every effort should be made to get these monitors operating 

on a schedule consistent with the designation process. This might be particularly important for 

monitors being sited near the fringe areas of existing nonattainment areas or monitors being sited 

in smaller MSAs in counties near, but currently outside, existing nonattainment areas. MSAs 

smaller than 350,000 population and currently without ozone monitoring could have staggered 

implementation to provide the monitoring agencies with flexibility in allocation of resources (it 

would be shame to buy ozone monitors for each of smaller MSAs only to find that sustained 

monitoring in many such areas would not be a priority) and mindful of the additional burden on 

personnel to establish and operate these new sites.

Non-Urban Network Design Requirements

1. We are considering a new requirement that each State operate a minimum of three 

nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

With the pattern towards ratcheting down the ozone standard, I am concerned about the low 

density of non-urban monitoring downwind of (generally large) urban ozone nonattainment 

areas, especially in the Midwestern United States. It is not clear to me that we are capturing the 

spatial extent of the ozone impact in such cases. For example, a largely rural county at the 

downwind edge of a nonattainment area (but perhaps still within the MSA) might have the 

highest ozone design value; in this case, it should be determined whether the plume is causing 

 46
NAAQS violations further downwind. While these areas might have relatively low population, 

people living in these areas are impacted. (I respect the philosophical issues this might create 

with respect to a given urban area’s impact on air quality in the immediate downwind counties in 

light of larger scale, regional transport and the complexities in attributing observed burdens to 

emission source regions, but the urban plume patterns should be a consideration at least in areas 

with geographically isolated nonattainment areas.) Given this need, together with the need for 

monitoring with respect to objectives relevant to the secondary standard, three non-urban 

monitors per state might be sufficient in some but not all cases. 

2. What factors should be considered in the siting of ozone monitors to assess impacts on 

 ozone sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

Existing estimates of ozone concentration fields should be used to prioritize areas. States should 

be allowed to capitalize on existing monitoring conducted by other networks (e.g. CASTNET) to 

fulfill this monitoring objective. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

See #1 above, which encourages placing additional emphasis on non-urban areas downwind of 

large urban ozone nonattainment areas. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

No comments at this time. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

See #2 above; States should determine whether existing non-urban ozone monitors that are 

potentially operated by another agency are in locations consistent with their prioritized list of 

sites based on estimated ozone levels. The daily maximum 8-hour average might not be best 

ozone metric for prioritizing such areas and other metrics should be considered (e.g. reflecting 

upon analyses and considerations for the secondary standard that were part of the mostrecent 

ozone NAAQS review process). 

 47
Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

The analysis used to support adjustments to the state-specific ozone seasons seems reasonable. 

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

Ozone monitors at NCore sites should be operated year-round. Many data analyses, including but 

not limited to health effects studies (including studies which might not be focused on ozone but 

include it as a possible confounder), would benefit from year-round data. Also, ozone data can be 

useful when validating performance of certain portions of chemical transport models that might 

be run for purposes other than ozone (e.g. fine PM).

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors?

What three-year period will be used for the first round of designations under the May 2008 

NAAQS revisions? This information is important when considering the timelines for phasing in 

changes to the monitoring season. 

 48
Dr. Warren H. White 

Ozone monitoring season – general comments

An indication of the incremental cost of extending an existing seasonal site to year-round 

operation is missing from the materials provided for discussion. The AAMMS does not need to 

know the actual dollars involved, but does need an approximate “exchange rate” between 12-

month operation and, say, 8-month operation. What are typical marginal costs as a fraction of 

fixed costs? 

I appreciate that a lot of experience and history has gone into the map of ozone monitoring 

seasons, but does it really have to be so complex and spatially resolved? Wyoming, for example, 

scheduled to start monitoring year-round, is entirely surrounded by states still scheduled to 

hibernate every winter. Is there any scientific rationale for creating this island defined by 

political rather than climatological or topographical boundaries? Note that Schnell et al. (2009) 

“suggest that similar ozone production [to that observed in Wyoming] during wintertime is 

probably occurring around the world under comparable industrial and meteorological 

conditions.” I would prefer a uniform monitoring season everywhere, if only on aesthetic 

grounds, and would prefer it to be as long as we can afford, year-round if possible. 

I don’t feel strongly about extending the monitoring season at ozone-only sites, where nothing 

else is measured, because we wouldn’t know how to interpret the resulting cold-weather data as 

an indication of other photochemical products and their aggregate effect on health and welfare. 

The NAAQS is set for ozone as “the indicator for a mix of O3 and other photochemical oxidants” 

(Arnold et al., 2007), and the composition of the winter mix may differ from that of the summer 

mix on which most current evidence for ozone-related health effects is based. The presence of 

monitors for other variables should discourage shutting down a monitor for ozone. 

 

References:

J. Arnold, Q. Meng, J. Pinto and W. Wilson (2007) Atmospheric chemistry and physics used in 

Integrated Science Assessments. Presented to the Human Health Risk Assessment 

subcommittee of the Board of Scientific Counselors, Bethesda, 

http://www.epa.gov/OSP/bosc/pdf/hhraltg3abstracts.pdf.

R.C. Schnell, S.J. Oltmans, R.R. Neely, M.S. Endres, J.V. Molenar and A.B. White (2009) Rapid 

photochemical production of ozone at high concentrations in a rural site during winter. 

Nature Geoscience, doi:10.1038/NGEO415. 

 49
Dr. Yousheng Zeng 

Urban Network Design Requirements

In my opinion, it is appropriate to require at least one monitor in a small MSA (population 

50,000-350,000) where no design value exists. However, if after a period of monitoring, the 

results are far below the ozone NAAQS, state agencies should be allowed to discontinue 

monitoring in the area. I would propose the following monitoring requirements in a sliding 

scale. In a MSA with population between 50,000 and 350,000, a minimum of one ozone 

monitoring station be required to collect valid monitoring data for at least one ozone season. If 

the maximum concentration during this season is below 50% of NAAQS, agencies may 

discontinue the monitoring until the MSA is bumped up to the next MSA category (i.e., 350,000-

4,000,000) based on decennial MSA redefinition. If the maximum is equal to or above 50% of 

NAAQS, the monitoring must be continued for at least 3 years (3 seasons) to establish a design 

value for the MSA. The screening value of 50% of NAAQS is proposed as an example. Another 

screening value similar to this one may be established based on a static analysis on probability of 

design value being higher than 85% of NAAQS if one year maximum is below that screening 

value. If the design value is below 85% of NAAQS, the monitoring may be discontinued as EPA 

currently proposed. If the design value is equal to or above 85% of NAAQS, the monitoring 

must be continued until the design value drops below 85% of NAAQS for additional 3 

consecutive years. 

In regard to deployment schedule, I would propose the beginning of ozone season in 2011 

instead of Jan. 1, 2011. This will give some agencies more time to install the monitoring stations 

without losing usable data. I also strongly support the idea of staggered deployment schedule. 

Agencies should be required to deploy at least one newly required monitoring station in the first 

required season within their jurisdiction (and one in each subsequent season if there is more than 

one newly required station). In combination with above proposed sliding scale, if an agency 

deploys the first station and the result for the first season is below 50% of NAAQS, the agency 

can relocate the station to the next newly required station. With this requirement and 

deployment approach, transportable monitoring trailers can be used to maximize resources and 

minimize cost. 

Non-Urban Network Design Requirements

I agree with Dr. Hopke. It does not make sense to require a small state like Rhode Island and a 

large state like Montana with large non-urban areas to have equal number of monitors. EPA 

should develop different network design criteria and guidelines. They should include 

considerations of geographic coverage and level of ozone precursor emissions in the area. I 

would also add the concept of sliding scale and staggered deployment schedule outlined above. 

To cover large non-urban areas, EPA should consider requirements that would incentivize state 

agencies to use transportable (or even mobile) monitoring platforms. For example, a state 

agency can use one or two transportable monitor(s) to cover a large area by rotating them at predetermined locations, one location per ozone season. If the monitoring result of a season at a 

location is below 50% of NAAQS, this location is screened out. With a combination of the 

 50
above proposed sliding scale and staggered deployment schedule, state agencies can assess large 

areas in a very cost effective manner. 

I support the option of using existing monitoring stations (e.g., CASTNET monitors) to fulfill 

part of the new requirement. 

Ozone Monitoring Season

I support the proposed increase in length of monitoring period. The monitoring period should be 

long enough so that there should not be ozone exceedances outside of the monitoring period. My 

only question is how confident EPA is in making this proposed requirement when only 45% of 

year-round monitoring data was analyzed. 

I strongly agree that ozone monitors at NCore stations should be operated year-round. I don’t 

know if PAMS stations are required to be operated year-round. There is some value to operate 

PAMS monitors year-round. This is not limited to ozone monitors at PAMS sites, but also 

applies to other pollutants. For example, if speciated VOC, along with ozone, are monitored 

year-round, it may provide some insight in ozone study, which is a major objective of PAMS 

network. In non-ozone season, stationary industrial sources of VOC typically emit at the level 

comparable to that of ozone season. These VOC may have a longer lifetime in the atmospheric 

during non-ozone season than during ozone season. Without strong atmospheric photochemical 

processes, the monitoring data during non-ozone season may preserve sources’ characterization 

and influence better. 

Making the change to monitoring period effective in 2010 for existing monitors seems feasible to 

me. However, more weight should be given to several AAMMS members who are more 

involved in SLAMS operations and may know some practical challenges. 

 51
Dr. Barbara Zielinska

Urban Network Design Requirements

1. Considering the ozone minimum monitoring requirements that are already promulgated 

through 40 CFR Part 58, is the considered change to these requirements sufficient to ensure a 

minimally adequate network in urban areas?

The proposed addition of one ozone monitor in urban areas with population between 50,000 and 

350,000 is clearly appropriate in locations where there is an absence of an ozone design value. 

However, if after 3 years of monitoring a resulted design value is lower than 85% of the 

standard, the state should be allowed to remove or relocate the monitor in such areas. 

2. We are considering a timeline that would require newly required ozone monitors to be 

operational no later than January 1, 2011, based on the expectation that final rulemaking will be 

completed in 2009. Is this schedule appropriate or should EPA consider providing an additional 

year for new monitors to be deployed (or relocated)? What would be the advantages or 

disadvantages of a staggered deployment schedule? 

I am in favor of a staggered deployment schedule, especially when a new monitoring site is 

required. It is better to allow more time for purchasing adequate equipment, operator training, 

establishing QA/QC procedures, shake down period, etc. 

Non-Urban Network Design Requirements 

1. We are considering a new requirement that each State operate a minimum of three nonurban ozone monitors to meet certain objectives (described above). Considering the stated 

objectives of the non-urban ozone monitoring requirements, is three required monitors per state 

sufficient? 

This depends on the specific State - one size does not fit all. Considering differences in a State 

geographic locations, presence or absence of protected areas downwind of major urban 

populations, sensitive vegetation, etc, , three non-urban ozone monitors may be sufficient for 

some States, but for some – may not. I suggest more detailed analysis; similar to that EPA has 

done for changes to required ozone monitoring season (Table 2 of the ozone review document).

Variable patters of ozone temporal distribution in complex mountain terrain point to a need for 

higher number of monitoring sites in such areas than in other areas (Van Ooy and Carroll, 1995). 

2. What factors should be considered in the sitting of ozone monitors to assess impacts on 

ozone sensitive vegetation in national parks, wilderness areas, and other ecosystems? 

One of the most important factors is to consider the presence of the most ozone sensitive species 

in these areas. For example, Ponderosa pine, which is the main tree species in Sierra Nevada 

Mountains, is very sensitive to ozone exposure (Bytnerowicz et al., 2003). Thus, it is important 

to situate the monitors in proximity of these species during their physiological activity and active 

 52
uptake of gases. In addition, factors such as transport from large urban areas, enhanced 

photochemical activity in some areas, logistics, etc., should be considered. 

3. In addition to the objectives that have been described for non-urban ozone monitors, what 

other objectives should be considered in the final network design? How would the consideration 

of additional objectives, if any, effect the minimum number of non-urban required monitors? 

Additional objectives may include testing and evaluation of ozone models, ozone forecasting 

improvements and better understanding of policy relevant ozone background values. 

4. Current ozone monitoring regulations (described in Appendix E of 40 CFR part 58) include 

requirements for station and probe siting (e.g., vertical distance of inlets, set-back distances 

from roadways). Are these requirements (that have been developed for urban monitors) 

appropriate for non-urban ozone monitors? What changes, if any, should be considered? 

The additional requirements for non-urban ozone monitors may include appropriate distance 

from high trees and local roadways, placement of the monitors in open terrain and in proximity 

of sensitive vegetations. 

5. We believe that States should have the option of designating that existing non-urban ozone 

monitors that are potentially operated by another agency (e.g., CASTNET monitors operated by 

the National Park Service) be utilized for meeting certain non-urban minimum monitoring 

requirements. What factors should States use to determine if such monitors are appropriate to 

include in their networks? 

These monitors should meet the required technical quality and be able for continuous ozone 

monitoring. Integrated methods (such as passive ozone monitors), are convenient is some 

situations and may help in selection of “hot spots” where real time monitors should be placed 

(Arbaugh and Bytnerowicz, 2003). Diurnal variations in ozone concentrations are important in 

assessment of the ozone impact on sensitive vegetations. Real-time monitors which can be 

placed in remote locations (light, reliable, battery-operated; not requiring AC), such as 2B 

Technologies, Boulder CO, should be considered. 

 

Additional comment: Efforts leading to a development of more biologically relevant ozone 

secondary standard, such as those taking currently place in Europe should be considered 

(Matyssek et al., 2007). 

Ozone Monitoring Season

1. We are considering changes to the required ozone monitoring seasons based on analyses of 

the patterns of ozone exceedances and occurrences of the Moderate level of the Air Quality 

Index, during periods outside of the currently required seasons. What other factors should be 

considered, if any, in the determination of the length of the required monitoring season for each 

State? 

Some sites, especially at high elevations, may have only seasonal access. 

 53
 54

2. We believe that ozone monitors that are located at NCore stations should be operated on a 

year-round monitoring schedule. Under what circumstances might it be appropriate to require 

year-round monitoring at other stations beside NCore? 

The year-round data from some urban monitoring sites may be important for ozone health effect 

study. 

3. We are considering that changes to the required ozone monitoring season be applicable to 

existing monitors beginning in 2010, one year ahead of the deployment schedule for newly 

required ozone monitors. Is this schedule reasonable for existing monitors? 

Yes, it seems reasonable. 

References:

Arbaugh, M. J., Bytnerowicz, A. (2003) Ambient ozone patterns and effects over the Sierra 

Nevada: synthesis and implications for future research. In: A. Bytnerowicz, M. Arbaugh, R. 

Alonso (eds), Ozone Air Pollution in the Sierra Nevada: Distribution and Effects on Forests, 

Developments in Environmental Science, vol. 2, Elsevier, Amsterdam, 249-261. 

Bytnerowicz, A., M.J. Arbauch and R. Alonso (2003): Ozone Air Pollution in the Sierra Nevada: 

Distribution and Effects on Forest, Elsevier, 402 pp. 

Matyssek, R., Bytnerowicz, A., Karlsson, P.-E., Paoletti, E., Sanz, M., Schaub, M., Wieser, G.: 

2007, Promoting the O3 flux concept for European forest trees. Environmental Pollution, 

146 (3): 587-607. 

Van Ooy, D. J., Carroll, J. J. 1995. The spatial variation of ozone climatology on the western 

slope of the Sierra Nevada, Atmos. Environ. 29, 1319–1330.