MEMORANDUN (2/11/04)

SUBJECT: API comments regarding relation between ozone 1 - hour and 8 - hour trends FROM: Fred Dimmick, Group Leader

Air Quality Trends Analysis Group API offered the following comment on the 8 - hour NAAQS implementation proposal. First, the 8 - hour standard is more stringent than the 1 - hour standard and that past air quality trends information for 11 metropolitan areas show that, on average, 8 - hour average ozone concentrations declined over the 1980 - 2002 period at about half the rat e that 1 - hour averages declined. API concludes that attainment for areas with 8 - hour values a certain percentage above the standard to take relatively more time to attain the 8 - hour standard than areas with 1 - hour values the same percentage above the 1 - ho ur standard would take to attain the 1 - hour standard. In API comments on the 6/2/03 notice, they provided the figure below as a comparison for selected metropolitan areas of median decadal trends in annual maximum 1 - hour and 4 th - highest maximum daily 8 - hour ozone concentration, 1980 through 2002.

API notes that for all areas, 8 - hour design values decrease at a slower rate than the 1 - hour values. API goes on to find, on average 8 - hour values have decreased at about half the rate as 1 - hour values, attesting to the fact that the 8 - hour standard will be much more difficult to attainResponse

First, from a program implementation perspective, it is not necessarily informative to project future program effectiveness based on an analy sis of progress from the 1980's to 2002. Programs designed to address the 1 - hour ozone NAAQS were not necessarily designed to reduce 8 - hour ozone levels at some prescribed rate. See Figures 1 and 2 for long - term national trends. Note, the relationship b etween 1 - hour and 8 - hour trends for recent years differs from the relationship early in this 20 - year comparison. The 1 - hour ozone programs were most effective in the early years. In the most recent 10 - years, neither the 1 - hour nor the 8 - hour ozone levels have decreased as they did in the first 10 years. Also, different rates of improvement occurred at different locations; program effectiveness varied across the country -- more or less NOx and VOC bringing about differing program needs/results. The EPA is currently focusing on NOx reductions as needed to address the lingering 8 - hour ozone problems 1 . In the 1980s and 1990s, the focus was on VOC reductions (which can be seen in national emission trends where NOx was reduced considerably less than VOC). W ith the emerging national ozone program s addressing NOx much more than previously, the rate of progress for 8 - hour (contrasted to 1 - hour) is not expected to be well related to previous progress. Second, the technical analyses provided do not support a b roadly applicable percentage such as the 50% suggested. The API developed a ratio of 50% for comparisons using the 1 - hour ozone design values compared to 8 - hour ozone design value for identified metropolitan trends; in the same figure, they showed widely varying rati os for the identified metropolitan trends. Georgia DNR's performed a similar analysis for their comments found a different relationship. With this variability it is hard to say that the 50% ratio represents a broadly applicable relationship. The ratio of 8 - hour to 1 - hour ozone levels changes over time, approaching a ratio of 8/10 for 90th percentile 8 - hour ozone levels to 1 - hour ozone levels. By comparing the annual 2 nd (1 - hour) and 4 th (8 - hour) maxima at the higher ozone levels across the country, Figures 3 and 4 show how they have compared over time. Figure 4 focus es on the most recent 10 years and show s the kind of relation that occurred as the 1 - hour ozone programs were implemented . If this pattern continues, and the 1 - hour ozone pro gram does not adapt to an 8 - hour ozone program, then there may well be a constant relationship and both 8 - hour and 1 - hour would make similar progress over time. On the other hand, with the emerging ozone program addressing NOx much more than previously, t he rate of progress for 8 - hour ozone levels (contrasted to 1 - hour ozone levels) would not be well related to previous progress.

1 In developing the NOx SIP call, EPA followed work done by the Ozone Transport Assessment Group (OTAG), which was active from 1995 - 1997 and consisted of repr esentatives from the 37 States in that region; the District of Columbia; EPA; and interested members of the public, including industry and environmental groups. The OTAG completed the most comprehensive analysis of ozone transport that had ever been condu cted, developing technical data, including up - to - date inventories and state - of - the - art air quality modeling, to quantify and identify the sources of interstate ozone transport. The OTAG concluded that regional NOx emissions reductions are effective in pro ducing ozone benefits, while VOC controls are effective in reducing ozone locally and are most advantageous to urban nonattainment areas.In summary, the suggested “percent” adjustment does not address current program

direction; would be difficult to develop anal ytically (considering the wide variations found), and therefore does not appear to represent a broadly applicable relationship. 1hr

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Mean 10th% 90th% Linear (Mean)

Figure 1. Plot of 20 - year trend for 1 - hour ozone (annual 2 nd max) national air quality levels 8hr

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Mean 10th% 90th% Linear (Mean)

Figure 2. Plot of 20 - year trend for 8 - hour ozone (annual 4th max) national air quality levelsRatio of 8-hr to 1-hr Ozone Levels

0.6 0.65 0.7 0.75 0.8 0.85

1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 90th% 10th% Mean

Figure 3. Plot of Ratio of 10 th %, Mean, and 90 th % ozone levels for 20 years. Mean Ozone Levels 10-yr Trend

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16

1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002ppm 1hr 8hr Ratio/10 Ratio of 8-hr ozone to 1-hr ozone concentrations divided by 10 Figure 4. Plot of trend of mean ozone 1 - hour and 8 - hour levels with ratio of the two levels.