Figure 8. Ozone Sites for OTAG Back-Trajectory Analysis

Analyses of Additional Low-Elevation Sites

While high-elevation monitoring sites provide ideal platforms from which to observe ozone transport aloft, they are limited primarily to the Appalachian Mountains and provide minimal representation of lower elevation exposures or to other areas of the OTAG region. Based on recommendations from members of the OTAG Air Quality Analysis workgroup and Ad Hoc Air Trajectory group, similar long-term trajectory data sets were developed for 17 additional low-elevation sites distributed throughout the OTAG domain. Locations for the current total of 23 high and low elevation sites are displayed in Figure 8 and Table 1.

Code Site Name Latitude Longitude Elev. (m) AIRS Site #

wfmn Whiteface Mtn., NY 44.36 73.90 1480 360310002

mglm Mt. Greylock, MA 42.64 73.17 1140 250034002

wtcn World Trade Ctr., NYC 40.71 74.01 503 360610063

shen Shenandoah NP, VA 38.52 78.44 1073 511130003

grbw Greenbriar County, WV 37.82 80.51 829 540250001

grsm Gt. Sm. Mt. NP, TN 35.63 83.94 793 470090101

benn Bennington, VT 42.90 73.25 216 500030004

ptcl Port Clyde, ME 43.92 69.26 9 230130004

rynh Rye, NH 43.00 70.75 10 330150012

ancr Ancora, NJ 39.67 74.86 35 340071001

seaf Seaford, DE 38.65 75.61 10 100051001(2)

graf Grafton, WI 43.43 87.92 299 550890008(5)

mktw Mark Twain SP, MO 39.47 91.79 213 291370001

nilw Nilwood, IL 39.40 89.81 201 171170002

fort Fortville, IN 39.94 85.84 265 180590003

boon Boone Cnty., KY 38.92 84.85 171 210150003

pthr Port Huron, MI 42.95 82.46 186 261470005

gran Granville Co., NC 36.14 78.77 91 370770001

semi Seminole Co., FL 28.75 81.31 18 121171002

lith Lithia Springs, GA 33.74 84.63 300 130970002

deso De Soto Co., MS 34.83 89.99 117 280330002

iber Iberville Par., LA 30.20 91.10 9 220470002

greg Gregg Co., TX 32.38 94.71 103 481830001

While none of the selected low-elevation sites were urban (all were rural or suburban), they all exhibit substantial diurnal variation. See, for example, the Figure 9 comparison of long-term average diurnal

Figure 9. Average Sumer 1989-95 Diurnal Ozone at Mt. Greylock, MA and Bennington, VT

ozone levels at high-elevation MT. Greylock, MA and the nearby low-elevation Bennington, VT site. To compare ozone levels and associated trajectories at different hours of the day from the low-elevation sites, we first calculated a long-term (7 summer) mean concentration for each site for each hour of day (3 AM, 9 AM, 3 PM, 9 PM), and then re-expressed each hourly ozone value as the deviation (in ppb) from the diurnal mean for that hour.

Figure 10 displays the hourly ozone levels at Bennington and Mt. Greylock during a 3-day period of increasing ozone concentrations during June, 1991. Concentrations increase at both sites, and both sites exhibit similar mid-afternoon peak levels. But while the mountaintop concentrations increase "smoothly", a strong diurnal pattern is evident at the Bennington site. The mid-afternoon concentration at Bennington on 6/24 is higher than the midnight concentration on 6/26. In Figure 11, the data from both sites have been re-expressed as the deviations from their diurnal mean concentrations. Now both sites exhibit relatively smooth increases; their nighttime levels are more comparable; and the 6/26 midnight value at Bennington is higher (and a positive deviation) than the mid-afternoon value on 6/24 (a negative deviation). Re-expressing (standardizing) the hourly data in this manner allows use of data (and trajectories) from different hours and from different sites on a more directly comparable basis.

Figure 10. Hourly Ozone at Mt. Greylock , MA
and Bennington, VT on 6/24-26/91

Figure 11. Ozone Deviations from Diurnal Means at
Mt. Greylock, MA and Bennington, VT on 6/24-26/91

Having "standardized" the ozone concentrations for each site as deviations from the average (for that site and hour of day), we next employed "trajectory-based sorting" for each receptor site to calculate average ozone deviations as a function of prior trajectory location. That is, for each of the 1440 grid squares, we calculate an average receptor site ozone deviation for all trajectories passing over that grid square en route to the receptor. The average is time-weighted, such that a trajectory residing for 8 hours over a square is given twice as much weight as a trajectory residing over the square for 4 hours. Average values are for squares characterized by less than 100 hours of total trajectory time (approximately equivalent to a minimum of 25 trajectories) are not displayed.

Currently available results using these methods (as presented at 7/96 OTAG meetings)have been processed into a series of 23 movie animations (one for each receptor site) which plot locations associated with trajectories resulting in low and high deviations from the site's mean ozone levels. Each movie has 62 frames; begins with locations (if any) associated with large negative deviations (15 ppb below the mean) and ends with locations (if any) associated with large positive deviations (15 ppb above the mean). Frame 31 of each movie shows all locations with trajectories associated with negative deviations (below average ozone concentrations) at the receptor, while frame 32 shows all locations associated with positive deviations (above average ozone) at the receptor. Movies are created in .avi format (viewable with CAPITA movie program or Microsoft Media Player). Movie names follow the form xxxxdev.avi, where xxxx is the 4-character site code listed in the first column of Table 1 (benndev.avi for Bennington, VT). All 23 single-site movies are compressed into the zipfile: 1sitedev.zip (1.2 Megs compressed; 3.3 Megs uncompressed) and posted on the OTAG AQA website.

Example frames 31 and 32 from the benndev.avi movie are pasted below in Figure 12. These show locations upwind of Bennington, VT for which trajectories are associated with below average (left) and above average (right) ozone deviations at Bennington.

Figure 12. Locations Associated with Negative (left) and Positive (right) Ozone deviations at Bennington, VT

Figure 13 a, b, c and d display example frames from 'Average Ozone Deviation' Movies for 4 sites:Pt. Huron, MI; Rye, NH; Mk. Twain SP, MO and Gt Smk. Mtn., NP, TN - in diverent sections of the OTAG domain (from 4sitedev.avi movie).Clockwise from upper left, frames show locations for which trajectories arriving at specified receptors are associated with ozone levels: a. Less than Average; b. Greater than Average; c. At least 5 ppb Greater than Average; d. At Least 10 ppb Greater than Average. Low ozone concentrations are associated with areas external to (North, South, East and West) of the OTAG domain, while high ozone levels are associated with trajectories internal to OTAG, with areas in the industrial Midwest being upwind of high ozone deviations at all 4 sites..

Figure 13a. Locations with Ozone Deviations of < Average	Figure 13b. Locations with Ozone Deviations of > Average
Figure 13c. Locations with Deviations at least 5 ppb > Avg.	Figure 13d. Locations with Deviations at least 10 ppb > Avg.