OTAG Air Quality Analysis Workgroup
Workgroup Objective
Description of the Air Quality Analysis WG
Types of Analyses
Problem Statement
More counties are in nonattainment of the 80 ppb than the 120 ppb standard. Transport is also more important at the 80 ppb exceedance level.
Area source NOx emissions are highest near cities. Point sources dominate the center of OTAG.
The OTAG domain corners are at tropospheric O3 levels. The highest avg. O3 is over the megalopolis and Ohio Valley. There is an increasing trend from west to east.
Highest (90 %-ile) O3 occurs near urban areas. Lowest (10 %-ile) O3 is high in the center of the domain.
Northeast O3 exceedances have been declining. OTAG domain exceedances show less decline.
At slow wind speeds, O3 accumulates near source areas. At high wind speeds, O3 is dispersed from sources. The dispersion leads to long range transport and regional O3.
In the South, higher winds reduce O3, in the North it does not. In the Northeast, regional O3 is transported by synoptic and channeled flows while local O3 by near surface flows.
On high O3 days, the transport winds are slow with clockwise circulation around the south-center of the domain. On low O3 days, the swift transport winds are from outside the domain.
During regional episodes, air masses meander over the high emission regions and accumulate O3. The implied range of O3 transport is 150 - 500 miles. The ‘88,‘91,‘95 modeling episodes lasted 6-9 days.
The 4 episode avg. model concentration shows high O3 over the central section of the domain. The model O3 pattern roughly corresponds to the data.
The model under-predicts O3 in the North and over-predicts in the South by 10-20 ppb. The modeling periods over-represent O3 in the North and under-represent O3 in the South.
Transport winds during the ‘91,‘93,‘95 episodes are representative of regional episodes. OTAG episode transport winds differ from winds at high local O3 levels.
OTAG is a well defined control region. Low O3 air comes from outside, high O3 air from inside OTAG.
The transport winds on high O3 days are slow in the center of the domain. At many sites, the avg. O3 is higher when the wind blows from the center of the domain.
Emission changes do change O3 levels. 120 ppb exceedances are 3 times higher on Fridays than on Sundays.
Conclusions of the OTAG AQA Workgroup
Email: rhusar@mecf.wustl.edu