Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 1 

### Supplemental Analysis for Recommended 8-Hour Ozone Designations

The following analyses and data are provided in res ponse to EPA questions and are additive to the State of Colorado Technical Support Document (TSD) for the Recommended 8-Hour Ozone Designations, dated March 9, 2009.

Factor #2: Emissions Data (pages 12 and 13 of TSD )

The TSD provided summary NOx and VOC emissions for the 9-County Nonattainment Area for thirteen source categories. The EPA has requested that Electric Generating Units (EGUs) be separated out as a separate source category in Tabl es 1-2 and 1-3 of the TSD. EPA further requested summary emission totals for each source c ategory in the 9-County area and surrounding area. Tables 1 and 2 provide the reque sted information.

Table 1: 2006 NOx and VOC emission inventory for 9 -County Nonattainment Area

Table 2: 2006 NOx and VOC emission inventory for c ounties surrounding the 9-County

Nonattainment AreaAdditional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 2

Factor #3: Population Density and Degree of Urbaniz ation (pages 17, 18 and 19 of TSD)

The TSD provided a number of maps from the US Censu s Bureau, Denver Regional Council of Governments, and North Front Range Metropolitan Pla nning Organization that graphically indicated population density in the 9-county nonatt ainment area and surrounding counties. The EPA has requested that we supplement the maps with population density data at the county level. In Table 3, the Division has prepared a table indic ating county level population, land area and calculated population density

Table 3: County-level Population and Calculated Po pulation DensityAdditional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 3

Factor #4: Traffic and Commuting Patterns (pages 20 thru 23 of the TSD)

The TSD included a number of major roadway maps (de veloped by CDOT) that included annual average daily trips (2007). The EPA requested that traffic data be provided in table format by county and include growth projections for years 201 0, 2015 and 2020. Table 4 provides the requested information except that the data is expre ssed as vehicle miles travelled (VMT) rather than average daily trips.

Table 4: County-level Annual Average Vehicle Miles Travelled

The TSD provided a projection of the number of work ers commuting between the Denver Region and the surrounding counties (Figure 1-17, based on 2000 Census). The EPA requested information on the number of workers commuting betw een counties within the Denver Region,Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 4

specifically Adams, Arapaho, Boulder, Broomfield, C lear Creek, Denver, Douglas, Gilpin and Jefferson Counties. Table 5 provides detail on the number of workplace trips for counties within the Denver Region.

Table 5: Number of Trips between Residence and Wor kplace for Counties within the Denver Region

Factor #6: Meteorology (page 29 of TSD)

The TSD includes a HYSPLIT back trajectory analyses (map) of the four highest days for each year in 2006-2008 for the Fort Collins West, Rocky Flats and Chatfield monitors. The EPA has requested that the elevation of the back trajectory points be included to better understand interpretation of the map. Figure 1 includes a rev ised back trajectory map that includes the elevation contours in color. The trajectory point altitudes above ground level do not necessarily reflect the deep vertical mixing that is often occu rring. While HYSPLIT may show trajectories following the terrain, the atmosphere may in fact b e deeply mixed during the transit period.Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 5

Figure 1: Hourly Back Trajectories Points for FTCW, RFLAT and CHAT Monitoring Sites

Associated with above map (Figure 1), the EPA has a lso requested that the trajectory points within the domain be numerically characterized to better u nderstand the relative spatial density of areas around the 9-County Region. Figure 2 provides a co unt of back trajectory points in each grid cell to help identify relative densities of back traject ory points.Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 6

Figure 2: Trajectory Points per Grid Cell (analyse s based on Figure 1)

Similar to the HYSPLIT back trajectory analyses in Figure 1 (highest ozone days for each year in 2006-2008 for the Fort Collins West, Rocky Flats an d Chatfield monitors), the EPA has requested a similar back trajectory map for days with ozone val ues between 76ppb to 79 ppb. Figure 3 provides the back trajectory analysis for high ozon e days (76-79 ppb) at the Fort Collins West, Rocky Flats and Chatfield monitors for years 2006-2 008.Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 7

Figure 3: Hourly Back Trajectories Points for FTCW, RFLAT and CHAT Monitoring Sites

The above analysis (76-79 ppb) indicates back traje ctory patterns very similar to Figure 1, which depicts the back trajectories for the highest days in 2006-2008. It is difficult to visually ascertai n differences between the back trajectory plots, so a comparison of the number of back trajectory points per grid cell is necessary to quantify the s patial differences. In Figure 4 below, the number of back trajectory points per grid cell are based t he 76-79 ppb back trajectory analysis. In comparing Figures 2 and 4, it appears that the dist ribution of plus “+” signs appear to be pretty similar around the three metro-area monitoring site s.Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 8

Figure 4: Trajectory Points per Grid Cell (analyse s based on Figure 3 back trajectories)

Expanded Meteorology Conclusions: (page 30 of TSD)

The EPA requested additional explanation of any rel ationship between elevation and ozone concentrations for counties on the edge of existing non attainment area. The following paragraphs respond to the issue:

Decades of weekly ozonesondes in Boulder, recent ai rcraft profiles of ozone over the Front Range, and research in other places in the United States - show that ozone concentrations in the boundary layer often increase with altitude above ground. O ne of the main reasons is that ozone near the ground is diminished by reactions with nitric oxide emitted near the surface by mobile and point sources. Ozone at ground level is also reduced to some extent by oxidation reactions with vegetation and other materials on the surface. Ozo ne near the top of the boundary layer may alsoAdditional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 9

be elevated because of complex re-circulation effec ts, residual layer processes, and prolonged

residence times that allow for an accumulation of o zone aloft.

High ozone concentrations are possible in the highe r terrain of the Front Range. It is known that

individual concentrations in excess of the new stan dard have been measured at NOAA’s Niwot Ridge Tundra monitor at 11,500 feet in Boulder Coun ty (located in the existing 8-hour ozone nonattainment area) and a short-term exploratory monit or operated by the United States Forest Service (USFS) for one season at Kenosha Pass in Pa rk County. The Niwot Ridge Tundra site uses an "equivalent" analyzer, but to our knowledge the NOAA air monitoring does not meet the QA/QA requirements as set forth in 40CFR58, Appendix A. At Kenosha Pass, the USFS used the 2B-Tech analyzer. This monitor is not designated as a "ref erence" or "equivalent" analyzer as set forth in 40CFR53, and the monitoring effort did not meet the QA/QA requirements as set forth in 40CFR58, Appendix A. Presently, there is no federa l reference method data that show that ozone

concentrations are in violation of the standard in Clear Creek, Gilpin, or Park Counties

In response to the possibility of elevated ozone in the higher elevations or the Front Range foothills, where public exposure to elevated ozone is of particular concern, the Division has added two ozone monitors, one is located at Aspen Park (e levation 8,095 feet - near Conifer) and the other is located in Rist Canyon (elevation 6,750 fe et - west of Fort Collins). Both monitors started operations this spring and as data is gathered over the summer, we should have a better sense of the relationship between ozone concentrations and e levation in the Front Range foothills.

In addition to the long-term federal reference meth od ozone monitor located near Longs Peak at an elevation of about 9000 feet in Rocky Mountain N ational Park, the National Park Service (NPS) also operates a portable ozone monitor located alon g Trail Ridge Road in Larimer County just above tree line. The monitor was in operation for a part of a summer in 2008, and is back online

for data collection this summer. The data from thi s site is not of federal reference method quality, but it should provide us with more information on o zone concentrations at high elevation sites.

While it is certainly possible that high concentrat ions may occur at high altitudes in these counties, it is important to note that the primary source for this ozone is most likely the urbanized area of the plains to the east. Anthropogenic emis sions from these mountain areas are expected to have an insignificant contribution to NAA ozone

Factor #7: Geography/Topography (page 31 of TSD)

The EPA requested a revised 3-D map of Denver Basin (see Figure 1-25, TSD dated March 9, 2009) with less vertical exaggeration. In Figure 5, the topographic elements of the Denver Basin are defined with color variations indicating difference s in elevation. The gray line depicts the current ozone non-attainment area and the names of major to wns/cities are identified.Additional Analysis and Data for Ozone Recommendations – June 24, 2009 Page 10Figure 5: Topographic Illustration of Physical Barriers that define the Denver BasinAdditional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 11

Expanded Summary Conclusions for Denver MetroArea/N orth Front Range 8-hour Nonattainment Area: (page 35 of TSD)

The preceding additional analysis and data provides information in support for retention of the existing boundary for the Denver Metro Area/North F ront Range (DMA/NFR) Ozone Nonattainment Area. In response to the potential i nclusion of additional areas that would expand the existing Ozone Nonattainment Area, the followin g considerations are offered:

(1) Extend the existing nonattainment area boundary to the north to include all portions

of Larimer and Weld Counties:

The northern portions of Larimer and Weld Counties are rural and sparsely populated with most areas having a population density fewer than five p eople per square mile, as indicated in the Figure 1-8 of the TSD. There are only three statio nary point sources with ozone precursor air pollutant emissions above 100 tons/year located nor th of the existing nonattainment area boundary. Expanding the nonattainment area to incl ude these three point sources would not enhance the States regulatory authority, although a ny future major modifications to these facilities

would be affected.

The estimated 2006 emissions (all source categories ) for the northern portion of Larimer County are: NOx ≈ 2,936 tons/year and VOC ≈ 2,968 tons/yea r. The estimated 2006 emissions (all source categories) for the northern portion of Weld County are: NOx ≈ 279 tons/year and VOC ≈ 864 tons/year. More detail on emissions data can also be found in the TSD under Factor #2 Section.

Depending on the severity of the future ozone nonat tainment area classification, requirements associated with the existing ozone nonattainment ar ea may change from voluntary to mandatory, such as vehicle Inspection/Maintenance Program. Co nsequently, the potential inclusion of these

rural areas into the nonattainment area could resul t in requiring residents with vehicles to be subject to mandatory vehicle inspections. The emis sion reduction benefit associated with a mandatory I/M program targeting rural residents oft en located far from an inspection station is negligible.

The above back trajectory analysis (reference Figur es 2 and 4) indicates that the northern portions of Larimer and Weld Counties are infrequen t contributors to air quality in the DMA/NFR nonattainment area. This is indicated by the very low number of trajectory points in the grid cells over the northern portions of Larimer and Weld Coun ties.

In summary, the inclusion of the northern portions of Larimer and Weld Counties into the ozone nonattainment area is not warranted because of spar se population, low degree of urbanization, low precursor emissions, and infrequent contributio ns to air quality in the DMA/NFR.

(2) Expand the existing nonattainment area boundary further west to include Clear Creek and Gilpin Counties:

The counties of Clear Creek and Gilpin are lightly populated areas located in high elevation mountainous terrain outside of the existing ozone n onattainment area. Based on the informationAdditional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 12

in Table 3, above, the estimated 2007 population de nsity for Clear Creek and Gilpin Counties are 23.8 and 34.3 people per square mile respectively. The total estimated 2007 population residing in Clear Creek and Gilpin Counties is 9,408 and 5,1 44 people respectively. Compared to the 3.27 million (2007) people residing in the existing DMA/ NFR nonattainment area, these two counties represent less than 0.5 percent of the total popula tion for the area.

The combined ozone precursor emissions (NOx and VOC ) for both counties are about 4,000 tons/year from all source categories. There are no stationary point sources in Clear Creek or Gilpin Counties with ozone precursor emissions over 100 tons/year.

The estimated 2007 annual average vehicle travel fo r Clear Creek and Gilpin Counties is 1,980,603 and 192,315 vehicle miles travelled (VMT), respecti vely, based on the information provided in the

above listed Table 4. The total estimated 2007 ann ual average VMT for DMA/NFR nonattainment area is about 82,470,000. The VMT for Clear Creek and Gilpin Counties represent about 2.6 percent of the total VMT in the metro area. The hi gher VMT identified in Clear Creek County is

associated with the I-70 corridor and some from the mountain casinos. Most of the mountain casino vehicle traffic originates from Jefferson Co unty as listed in the above Table 5 which is located in the existing ozone nonattainment area.

The above back trajectory analysis (reference Figur es 2 and 4) indicates that Clear Creek and Gilpin Counties are infrequent contributors to air quality in the DMA/NFR nonattainment area. This is indicated by the low number of trajectory p oints in the grid cells over Clear Creek and Gilpin Counties.

In summary, the inclusion of Clear Creek and Gilpin Counties into the ozone nonattainment area is not warranted because of low population, low degree of urbanization, very low precursor emissions, and infrequent contributions to air qual ity in the DMA/NFR.

(3) Expand the existing nonattainment area boundary both east and west to include the urbanized portions of Elbert County (Towns of Eliza beth and Kiowa) and Park County (Town of Bailey):

The counties of Elbert and Park are lightly populat ed areas outside of the existing ozone

nonattainment area. Based on the information in Ta ble 3 above, the estimated 2007 population density for Elbert and Park Counties are 12.5 and 7 .7 people per square mile respectively. The total estimated 2007 population residing in Elbert and Park Counties is 23,093 and 17,006 people respectively. Compared to the 3.27 million (2007) people residing in the existing DMA/NFR nonattainment area, these two counties represent le ss than 1.3 percent of the total population for

the area.

Information from the State Demography Office indica tes that the 2007 population estimates for the towns of Elizabeth and Kiowa are 1,456 and 610 persons respectively. Bailey is an unincorporated town that is not tracked as a munici pality by the State Demography Office, although a Google search yielded population data fo r 2009 indicating that 9,080 people reside in the Bailey ZIP code (80421).Additional Analysis and Data for Ozone Recommendati ons – June 24, 2009 Page 13

The combined ozone precursor emissions (NOx and VOC ) for Elbert and Park Counties are about 2,700 tons/year and 1,900 tons/year from all source categories respectively. There are no stationary point sources in Elbert or Park Counties with ozone precursor emissions over 100 tons/year.

The estimated 2007 annual average vehicle travel fo r Elbert and Park Counties is 644,878 and 606,542 vehicle miles travelled (VMT) respectively based on the information provided in the

above listed Table 4. The total estimated 2007 ann ual average VMT for DMA/NFR nonattainment area is about 82,470,000. The VMT for Elbert and P ark Counties represent about 1.5 percent of

the total VMT in the metro area.

The above back trajectory analysis (reference Figur es 2 and 4) indicates that Elbert and Park Counties are infrequent contributors to air quality in the DMA/NFR nonattainment area. This is indicated by the very low number of trajectory poin ts in the grid cells over Elbert and Park Counties, particularly over the urbanized areas of concern.

In summary, the inclusion of the urbanized areas of Elbert and Park Counties into the ozone

nonattainment area is not warranted because of low population, low degree of urbanization, very low precursor emissions, and infrequent contributio ns to air quality in the DMA/NFR.

(4) Expand the eastern nonattainment area boundary to include Morgan County:

Morgan County is a rural area outside of the existi ng ozone nonattainment area. Based on the information in Table 3 above, the estimated 2007 po pulation density for Morgan County is 22.2 people per square mile. The total estimated 2007 p opulation residing in Morgan County is 28,577. Compared to the 3.27 million (2007) people residing in the existing DMA/NFR nonattainment area, Morgan County represents less than 0.9 percen t of the total population for the area.

The ozone precursor emissions for Morgan County are NOx ≈ 7,794 tons/year and VOC ≈ 2,270 tons/year from all source categories. The NOx emis sions from one Electric Generating Unit represent over half of the total NOx in the county. There are five stationary point sources in Morgan County with ozone precursor emissions over 1 00 tons/year.

The estimated 2007 annual average vehicle travel fo r Morgan County is 1,072,728 VMT based on the information provided in the above listed Table 4. The I-76 corridor represents a substantial total of the VMT in Morgan County. The total estim ated 2007 annual average VMT for Denver Metro/North Front Range nonattainment area is about 82,470,000. The VMT for Morgan County represents about 1.3 percent of the total VMT in th e metro area.

The above back trajectory analysis (reference Figur es 2 and 4) indicates that Morgan County is an infrequent contributor to air quality in the DMA/NF R nonattainment area. This is indicated by the very low number of trajectory points in the grid ce lls over Morgan County.

In summary, the inclusion of Morgan County into the ozone nonattainment area is not warranted because of low population, low degree of urbanizati on, low precursor emissions, and infrequent contributions to air quality in the DMA/NFR.