Issue Title: Is attainment of an 8 hour 80 ppb ozone standard practical and feasible (working draft)

Contact: Steve Ziman, Chevron Research and Technology Company, (510-242-1530-phone; 510-242-5947-fax; sdzi@chevron.com) and David Chock, Ford (313-845-4777 phone, 313-549-2923-fax; dchock@smail.srl.ford.com)

Date December 20, 1996

I. Background:

EPA has proposed to implement a new ozone standard based on an 8 hour averaging period. The form of the standard will probably be the three year mean of the third highest concentration with either 85 ppb. or 81 ppb being the concentration for nonattainment designation. As part of the phase II efforts of the FACA Subcommittee and its workgroups, policies are being developed for implementation of the new standard. These policies may be assuming that the new standard can be attained by all nonattainment areas throughout the country. Inherent in these assumptions are suppositions that strategies which have resulted in reduction of the peak one hour values will provide similar results for peak 8 hour values. The present implementation policy and regulations explicitly adhere to the supposition that the one hour 120 ppb standard is attainable.

If the assumptions about feasibility of attainment of an 8 hour standard in the proposed form are not an adequate or accurate ones, based on technical analyses, then it is very important that this information be conveyed to those work groups and the Subcommittee prior to finalizing any decisions on specific implementation issues. As will be discussed below, some initial data analysis and photochemical modeling for the proposed new standard suggests that, from a practical aspect, attainment may not be a realistic assumption. More work will be required to further address this issue. With the present information, as well as availability of more information in the near future, the FACA groups can decide on how this body of information can be factored into other implementation issues which are now being discussed within those groups.

II. Hypothesis:

Overview on the Question of Feasibility of Attaining the Proposed 8 Hour standard: To date, there has been little analysis or photochemical modeling done to determine whether the proposed 8 hour 80 ppb ozone standard will respond to emissions reductions strategies in a manner similar to the present one hour standard. We provide some initial analyses which suggest that attainment of the proposed standard will be more difficult than the present one hour standard due to the form, the level and the availability of emissions reductions. Further analysis will be required to either support or refute the hypothesis that arises from the integration of these limited findings.

The hypothesis is that:

1. The present strategies are more efficient are reducing the higher concentrations of ozone than affecting concentrations less than 90 ppb. Thus, these strategies will continue to "shave the peaks", but will do little to reduce these lower values which are still above the standard.

2. The level of the proposed standard is set at 80 ppb; yet this level is not far from what has been observed as base line concentrations for peak 8 hour averages for clean sites in the US and other areas of the world. These peak levels can be higher than 60 ppb during summer time. Consequently, significant reductions of anthropogenic emissions must be made beyond those made for attainment of the present standard, especially if the present emissions reductions strategies are more effective at reducing the higher hourly concentrations.

3. The proposed standard has about the same stability as the present standard. It is an extreme value standard, and it track very well with the one hour standard with respect to effects due to meteorological variability. In order to attain the proposed standard, without bouncing in and out of attainment, the planning process will have to aim for emissions reductions capable of meeting a concentration level below the proposed 80 ppb level. This level, which is less than 80 ppb, averaged over 8 hours, is approaching the clean site base line level.

4. Taking these issues together, the implication is that very substantial anthropogenic emissions reductions will be needed to attempt to attain and maintain the proposed standard. For at least one area studied, the amount of reductions is estimated to be up to 90% of the anthropogenic emissions beyond that needed for attainment of the present one hour standard.

As noted in the recommendations section, more work should be undertaken to determine if this hypothesis is supportable.

III Technical Analyses:

a. Differences in How One Hour and 8 Hour Standard Respond to Emissions Reductions:

To date, not much analysis has been done to look at whether the one hour standard and 8 hour standard have responded in a similar manner to reductions made over the last 10 to 15 years. Further, even if both standards have shown similar trends, is the rate of progress a function of reduction of ozone across the range of hourly concentrations or only at the higher hourly concentrations?

Analysis done to date to look at the response of the present and proposed standards has been quite limited. Analysis was done on a site by site basis by Radian Corp. (personal communications, A. Hendler; Radian and Jim Price, Texas Natural Resources Conservation Commission) for potential nonattainment areas in Texas for different alternative forms of the peak 8 hour standard. This analysis used data from 1982 to 1995. Many of the sites showed some downward trend for the 8 hour 80 ppb average. But the rate of change is not large, and does not appear to reflect the larger rate of change for the one hour standard over the same period. For most sites, determination of the rate of improvement is complicated by meteorological fluctuations, even when a 3 year running average is used. What has not been done yet on a systematic basis is to understand whether the change in the 8 hour average is reflected in equal reductions in ozone concentrations at all levels above 80 ppb, or due mainly to reductions of the higher hourly concentrations in the 8 hour average. However, there is some information which may indicate that the higher hourly concentrations are being reduced preferentially, relative to those hourly concentrations less than 90 ppb.

The realization that the reduction of peak 1-hour ozone concentrations may have less impact on attaining an 8-hour standard for many areas of the country has been explored recently by an analysis by Lefohn (private communication). The hourly averaged ozone data in the U.S. EPA's AIRS and National Dry Deposition Network (NDDN) databases for the period 1993-1995 for all sites in the United States was used. Those design value sites that would violate the proposed 8-hour ozone standard using rounding conventions of 1 and 5 (i.e., violating sites having 3rd highest maximum 8-hr values 81 and 85 ppb) were identified. Using the county list of violators provided by the EPA, Lefohn identified 169 areas (i.e., CMSAs, MSAs, and remaining counties) that would violate the 81CB3 (third highest 8-hr 3-year average equal to or greater than 81 ppb) standard. Sixty-three percent of the violating areas experience design value sites where 4 or more of the 8 hours, making up the third highest 8-hr daily maximum exceedance of 81 ppb for a specific year, are less than 90 ppb. Attainment of the 80 ppb standard would require that these values between 81 and 90 ppb be reduced. However, this may be difficult. In many areas, regional upwind ozone levels are close to 80 ppb (and not much higher than observed for clean sites (see discussion below); consequently many of these area may have trouble attaining and maintaining the proposed standard. The present approach to control strategy, which focuses on reducing the peak one hour ozone concentrations (i.e., hourly average concentrations above 100 ppb), does not appear to have had the same effect on these lower concentrations. Lefohn estimates, using EPA's historical manner of nonattainment assignment, that a larger percent of all nonattainment areas than the previously mentioned 63% figure will have extreme difficulty in ever reaching attainment.

b. Background Ozone Concentrations:

In part a, we described the information which suggests that the emissions reductions made to date may preferentially reduce the higher hourly average concentrations. We have also noted that regional background in and around nonattainment areas can be at levels close to 80 ppb. Thus, it is important to understand whether it is possible to lower that regional background ozone concentration, and what types of reductions may be necessary. This section provides information about what concentrations should be expected for sites not affected by anthropogenic sources, and how those concentrations may set a lower bounds on what can be achieved.

Keeping in mind that the proposed 8-hour daily maximum standard is 80 ppb, it is important to investigate how low one might expect to reduce the 8-hour daily maximum hourly values. The U.S. EPA has defined background ozone as "the ozone concentration that would be observed in the U.S. in the absence of anthropogenic or biogenic emissions of VOCs and NOx in North America" (page 18-20 of the Ozone Staff Paper). The Staff Paper states that "based on the diurnal profiles presented for O3 at rural sites in Kelly et al. (1982, 1984), it is reasonable to estimate that the 8-hour daily maximum O3 during the summer is also in the range of 30 ppb to 50 ppb" (page 21 of the Ozone Staff Paper). However, using measurements at a remote site in South Dakota, Kelly et al. (1982) estimated the background O3 in air masses entering the Midwest and eastern United States to be 20-50 ppb, but did not take into consideration the generation of ozone from local, natural VOC emission sources. Altshuller and Lefohn (1996), using hourly averaged ozone data from remote sites in the western United States and Canada, reported that the current background at inland sites in the United States and Canada were in the range of 50 to 98 ppb for the April through October period. The maximum hourly concentrations at coastal sites ranged from 44 ppb to 80 ppb. The authors reported that this range suggests that background O3 is somewhat dependent on a number of conditions. Hourly average ozone data from background sites in the United States were presented in Tables 4.6 and 4.7 in the Ozone Criteria Document on pages 4-30 - 4-31 and 4-33. In separate testimony submitted to CASAC, Lefohn (1994) presented a table (Table 1) summarizing the top-10 8-hourly daily maximum values for the clean sites describes in the Criteria Document. The table was presented in written testimony to the Agency. Table 1 shows that the third highest maximum 8-hour daily maximum values ranged across years at the Theodore Roosevelt National Park (ND) from 55 to 62 ppb; for uster National Forest (MT), 60 to 69 ppb; and Yellowstone National Park (WY) from 54 to 68 ppb. The third highest daily maximum 8-hr concentrations occurring at inland clean sites in the United States are in the range of 55 to 69 ppb. Figure 1 shows that the percent of daily maximum 8-hr average concentrations greater than or equal to 40 ppb at the three clean sites is generally greater than 50%. Using the third highest values per year for the period 1993-1995, the third highest 8-hr daily maximum concentration averaged over 3 years was calculated for six clean sites in the United States. Figure 2 shows that the values ranged from 45 ppb to 61 ppb. Thus, it is clear that the assumed background value of 40 ppb by the Agency, which appears to be theoretically based, does not occur at the cleanest sites in the United States.. The number-40 ppb represents no anthropogenic and biogenic sources-an unrealistic situation

c: Estimate of Concentration Target to Ensure Attainment of an 8 Hour 80 ppb Standard Without Flip-flop:

The previous sections have stressed the need to reduce the hourly concentrations that may be less than 90 ppb. This need is complicated by the feasibility of approaching 8 hour ozone concentrations which represent clean site levels. As noted earlier, it is also complicated by meteorological fluctuation. Thus, the effects of meteorology must be accounted for in order to attain and maintain the proposed standard. That consideration, as described below, would require that the target ozone concentration to assure attainment of an 8 hour 80 ppb standard is less than 80 ppb.

Chock (presentation to STSWG) analyzed a data set supplied by EPA to explicitly show how attainment flip-flops make the standard extremely difficult to achieve unless the concept of attainment is modified. Specifically, he used 13 years of data from 1983 to 1995 and considered only counties with no missing design values for eleven consecutive three-year periods (1985-1995). Two hundred and sixty nine counties satisfied this constraint. The long-term mean of the design values for each county was defined as the average of the eleven design values. Table 2 shows the statistics of violation of a given ozone air quality standard for counties whose long-term means of the corresponding design values are less than the level of the standard. The forms and levels of the standard considered are given in the Table. Note that 40 to 60 percent of the counties with a long-term mean of the design values below the level of the standard actually violate the standard at least once over the eleven three-year periods. The percentage will likely increase with the length of time. Also, as the stringency of the standard increases, the percent of counties registering one or more violations of the standard will also likely increase. The long-term mean below which no violation of a given standard is observed is also presented in the Table. This value is the "effective" design value to assure compliance of the standard for the eleven consecutive three-year periods. As the length of time increases, this value will likely decrease and can get very close to the range of the observed natural or remote-area background ozone concentrations which is displayed in the last column of the Table. The range of the background concentrations corresponding to a given design value (e.g., the three-year average of the annual 3rd highest daily maximum 8h concentrations) are extracted from the data for monitors used recently by Altshuller and Lefohn to represent areas with background ozone concentrations. Clearly, in setting and implementing an air quality standard, its achievability must be considered. A long-term data base must be used in this consideration. The current practice of looking at the number of nonattainment areas or counties in one given three-year period is insufficient to reveal the achievability problem.

d. The above sections have tried to identify some very major issues with the attainment of the proposed 8 hour 80 ppb standard. Taken together, these issues suggest that significant anthropogenic emissions reductions above and beyond those needed to attain the present one hour standard will be required. However, none of the above sections allow one to estimate what levels of emissions reductions would be required. Photochemical modeling provides a frame work by which to predict the amount of reductions needed to approach an 8 hour 80 ppb standard. To this end, this section provides information on the projected emissions reductions required for one nonattainment area.

A study was done to estimate the costs associated with attaining the proposed ozone standard after the present one hour standard had been attained (Sierra Research, 1996). New modeling, based on previously modeled one hour peak episodes, was done to estimate the amount of reductions necessary to achieve the proposed 8 hour standard beyond those needed for the present one hour ozone standard for two areas of the country. The description of the study and the modeling done for it are given below. The findings of the study are significant. For the Lower Lake Michigan area, which includes Chicago, northern Indiana, southern Wisconsin and western Michigan, a 90% reduction of hydrocarbon emissions beyond that needed for attainment of the present standard was needed to reach 85 ppb (attainment based on rounding conversion for monitoring). While this may be considered a surprising finding, it does fall in line with the issues raised above. The finding suggests that much more reduction is needed to lower the hourly concentrations that lie below 100 ppb. This appears to be consistent with the need to reduce as much anthropogenic emissions as possible since the 8 hour proposed standard is approaching the clean site level. As noted below, about half of the needed reductions can not be identified.

The two study areas, the San Francisco Bay Area and the Lower Lake Michigan area were chosen because:

Photochemical modeling had been performed by the respective agencies for each of these areas to determine the emissions reductions needed for attainment of the federal one hour ozone standard.

The data bases used for the model simulations were derived from intensive data collection efforts. The Lake Michigan Ozone Study (LMOS) program provided the data for the UAM-V modeling performed by Lake Michigan Air Directors Consortium. The Bay Area Air Quality Management District (BAAQMD) September 1989 intensive ozone study provided the data for their UAM IV-modeling. Note that the LMOS work is now being used as one of the episodes for the OTAG effort.

Base year and future year emissions inventories for both areas were available or were improved with input from the respective agency

The Bay Area simulations represented an area that was minimally affected by upwind transport, and therefore should provide a lower bound estimate of emissions reductions needed for attainment. The Lower Lake Michigan area was affected by transport (treatment of upwind transport is described below), and its modeled peak one hour value was 16.4 pphm (over Lake Michigan) for the 26th of June, 1991. However, compared with other severe areas, its one hour design value is one of the lowest based on more recent ambient data (see table below).

Analyses showed that one hour episodes modeled were also typical of 8 hour peak ozone episodes in the range of the 3rd highest concentration.

Initial modeling was done to verify that the LADCO and BAAQMD results for their modeling of the federal one hour standard.. The model outputs for attainment of the one hour standard were then converted to 8 hour averages to determine the 8 hour modeling design values. This provided the starting point for determining what additional reductions are needed.. A series of twenty simulations were done with combinations of across the board percent reductions of hydrocarbons and NOx from the base case. This set of simulations was used to develop ozone isopleth response surfaces for the peak 8 hour site and a number of geographically diverse monitoring sites throughout the areas (Figures ). The analysis of the isopleths for each of the two areas allowed:

The information needed to choose an appropriate control strategy. In the case of the Bay Area, the 8 hour isopleths supported previous findings that the area is hydrocarbon limited. For the Lower Lake Michigan area, the results suggest that, depending on location, hydrocarbon reduction or NOx reduction was preferable. A hydrocarbon approach was taken as it appeared to provide the most benefits.

The information also allowed for a determination of the percent reduction of hydrocarbon needed to attain an 8 hour standard for the third highest concentration. For both areas, these reductions are those required beyond reductions needed for attainment of the present one hour standard. For the Bay Area, an additional 20% hydrocarbon reduction was estimated as necessary to attain. For the Lower Lake Michigan area, an additional 90% reduction was estimated (had a NOx strategy been pursued, similar reductions would have been required). Note that there can be downwind effects due to transported NOx. This situation, of a hydrocarbon limited urban area and a downwind area that responds to NOx reductions appears to be typical of a number of urban areas, based on OTAG and other modeling.

Analysis of all available control measures including those identified in some of the most stringent SIPs and FIPs nationwide was done. About one half of the reductions needed for the Lower Lake Michigan Area could be identified. A cap of $ 35,000 per ton was used as an upper limit on cost. No specific measures could be identified and quantified at higher costs. Thus, the costs may be low. These measures included stationary and area source controls, mobile source and transportation mitigation measures. It is very important to note that in the course of estimating the needed reductions, the upwind boundary precursor concentrations (both hydrocarbon and NOx) were reduced proportional to the reductions in the modeling region. This was done because the modeling domain did not include emissions for the upwind area (and future simulations need to be done with a much larger regional domain). The upwind ozone concentrations at the boundary was essentially equivalent to conditions observed in "clean areas" of the US. The emissions reductions needed within the Lower Lake Michigan region were not compensating for upwind conditions. Note also that because the upwind sources were not in the emissions inventory, no costs of reductions for these sources were included in the estimate of costs.

e. Implications of Results:

The Lower Lake Michigan area, particularly the Chicago CMSA, was classified as a severe area. However, review of both the frequency and intensity of the episodes over the past few years shows that it should have a much better chance of attaining the present one hour ozone standard than many of the other severe areas. Houston, for instance, continues to have multiple exceedances of the one hour standard at levels above 180 ppb. Certain areas in the northeast corridor also continue to see ozone levels well above the one hour standard. Some of these areas have already adopted many of the stringent controls that have previously been implemented in Los Angeles; yet they still can not show via modeling that the projected reductions will result in attainment of the present standard. It is not clear that the level of reduction beyond that needed for the present one hour standard can be identified, or even approached. For example, based on 1993-1995 data, the 8 hour ( 85 ppb) design value for a 3rd highest concentration for an number of areas with design values greater than 110 ppb are shown as contrast to the Lower Lake Michigan area. One should note however that Manitowoc, with its 123 ppb design value, was part of the modeling domain for the above referenced economics study; it had the highest observed ozone onshore concentration in that study.

Area Design Value 8-8-3 (1993-95 AIRS data) Chicago, Il-In-Wisc. CMSA 97 ppb Milwaukee CMSA 104 Atlanta 114 Baltimore 117 Greater Conn. 110 Houston CMSA 119 Manitowoc 123 New York-New Jersey 113 Philadelphia-Del-NJ 111 Los Angeles 167 Sacramento 110 San Diego 112 Ventura 119 San Joaquin Valley 121

As noted above, if areas must plan to reduce ozone levels well below an 80 ppb value in order to limit the probability of bouncing out of attainment, these reductions will be approaching the background levels measured in "clean areas. Thus, attainment for a number of areas does not appear to be feasible or realistic in the foreseeable future. This finding appears to be supported by EPA's recent ROM modeling analyses for the ozone Regulatory Impact Assessment. That analysis also acknowledge the need for very significant, as of yet unidentified emissions reductions in order to model attainment of two of the 8 hour alternatives (which bracket the proposed third highest concentration form). EPA notes that between 8 and 20 major areas will not attain the standard. Many of the areas in the above table are also identified in the EPA RIA.

If the inability to identify a large fraction of the anthropogenic emissions reductions for a number of areas is indeed the case, then requirements for attainment of a new standard are practically infeasible in the foreseeable future, This assumes that attainment will still rely on reducing the peak monitor to meet the form of the new standard. From the technical perspective, this suggests that any policy discussions of setting of attainment dates may not be realistic.

IV. Recommendations:

There are recommendations for both data analysis and modeling studies that should help refine the hypothesis presented at the beginning of this paper. In terms of data analysis, it is important to look at the trends for both the one hour and the proposed form of the 8 hour standard on a site by site basis over the last two decades (inception of the Clean Air Act amendments of 1977). Moreover, analysis of how the hourly values that make up the 8 hour averages have changed with time should be done. This information can tell us if the strategies used over the last two decades were preferential for high hourly concentrations. It could suggest that there will be difficulty reducing the hourly concentrations at or below 90 ppb.

Second, the seriousness of attainment flip-flops and its effects on the achievability of the proposed standard can no longer be ignored. Additional work may need to be done to support and confirm the analyses already done. If the proposed standard is to be adopted, one should take account of the year-to-year ozone concentration fluctuation in the compliance (or violation) test. This fluctuation, and the additonal amount of reduction that needs to be targeted to guarantee attainment must be considered as part of any implementation strategy development.

Third, there is a need to see what can be learned from photochemical modeling. There are a number of modeling studies being carried out now to meet the requirements of the 1994 one hour 120 ppb ozone demonstration SIPs. Where possible, the relevant agencies should be reviewing their modeling to determine the percent emissions reductions needed beyond the one hour standard to achieve an 8 hour 85 ppb three year mean of the third highest concentration. This should be done for areas that respond to hydrocarbon reductions, and those that respond to NOx reductions. In some cases, the urban core may respond differently than the downwind portion of the area. It is also very important to look at the impacts of upwind boundary conditions and the reduction of emissions of upwind sources to see if these upwind reductions will affect the needs for reductions in the downwind nonattainment area. The EPA ROM modeling for the RIA suggests that even with assumptions about regional controls, which should encompass the upwind areas, attainment will not be practically feasible for some areas.

If these recommended analyses substantiates the suppositions presented in this paper, then it is clear that any implementation policies which require attainment will not be realistic from a technical perspective. Consideration of approaches outlined in the issue paper on attainment need to be viewed in this light, as should other related issues. The findings of the Lower Lake Michigan study, and any others modeling or data analyses already done should be made available to the other workgroups and the Subcommittee prior to final decisions on relevant policy issues.

References:

Altshuller, A. P. and Lefohn, A. S., J. Air and Waste Man. Assoc., 46. 134 (1996)

Sierra Research, Report No. SR96-06-01, Socio-Economic Study of Possible Eight Hour Ozone Standard (1996)

other noted refereces are in EPA Criteria Document and Staff Paper.

12/20/96