12
WIND
X
Upwind
Site
X
Downwind
Site
Of the sixteen sampling days, five days did have wind-persistent conditions that allowed
for a upwind /downwind analysis. The sampling data obtained for each of the five days
for key target compounds has been presented in Figure 4 along with wind roses (wind
frequency distribution) that depict the associated wind direction data. Figure 4 also
provides for each target compound the average value obtained from the five samples for
the wind positive site and the wind negative site and the calculated percent difference
(wind positive to wind negative). The Figure 4 wind roses illustrate the site impacts,
Bensenville located southwest of the airport impacted by winds from the north to east,
and Schiller Park located east of the airport impacted by winds from the southwest to
northwest.
The data analysis demonstrated that O’Hare Airport emissions had an impact in the areas
adjacent to the airport for several key target compounds, including acetaldehyde,
benzene, formaldehyde, polycyclic organics and lead. All these compounds are Urban
Air Toxics and have been identified as associated with airport operations. The
downwind concentration of acetaldehyde was found to be 45.6% higher than upwind,
formaldehyde was 32.8% higher, benzene was 34.1% higher, polycyclics (PAHs) were
65.9% higher and lead was 87.5% higher. An impact from airport operations was not
unexpected as airport operations, including aircraft takeoffs, landings, taxiing, refueling
and use of support equipment, result in significant emissions of volatile organics and
target air toxic compounds. The resulting airport emissions should have had, as the
monitoring data shows, some impact in the areas adjacent to the airport. While the
downwind concentrations were found to be higher, the results showed that the levels
found at O’Hare Airport are still in the “typical urban” range and lower than levels found
in other large urban areas.
Appendix IV provides a detailed summary of the meteorological conditions which were
present on each of the sampling days. The appendix also includes a summary table that
provides for each sampling day the frequency distribution of hourly wind data, which has
also been plotted in a wind rose shown in Figure 5. As can be seen from that summary
table, the most prevalent wind directions on sampling days were winds from the west
southwest, west and the northeast. These three wind directions provided the opportunity
for frequent impact of airport emissions on the two O’Hare area monitoring sites.
EMISSION
SOURCE
