1. Eastern US Transport Climatology During Average, High and Low Ozone Days Bret A. Schichtel and Rudolf B. Husar Center for Air Pollution Impact and Trend Analysis (CAPITA) Washington University St. Louis, Missouri Presented at A&WMA's 91st Annual Meeting June 14 -18 1998

2. Objective Derive scales of airmass transport and directions from source impact regions Relate the transport conditions to local and regional high and low ozone concentrations Rational Source identification: Unique airmass pathways during high and low ozone levels, and common pathways for multiple regions (triangulation) Local vs regional contributions: Local sources have the largest contributions during stagnant transport conditions

3. Meteorological Data National Meteorological Centers Nested Grid Model (NGM) Time range: 1989 - 6/97 Horizontal resolution: ~ 160 km Vertical resolution: 10 layers up to 7 km 3-D variables: u, v, w, temp., humidity Surface variables include: Precip, Mixing Hgt,….

4. Single Plume - Noon July 5, 1995 Daily Plume - 12 plumes from 2 AM to midnight on July 5, 1995 St. Louis 5-day Plumes

5. Regional Impact Analysis Transport Wind Vector Source Region of Influence Encompasses 63% of mass vector from the source to the center of mass

6. Source Regions of Influence and Transport Wind Vectors, June – August, 1991 – 1995 St. Louis, MissouriAtlanta, Georgia

8. Ozone Data OTAG Domain Local Ozone - Average concentration within each NGM grid cell Regional Ozone - Average concentration with in OTAG domain

9. Transport Conditions During High (90%-ile) and Low (10%-ile) Local Ozone Days High local ozone in the Central East and Southeast occur during slow transport winds. In the north and west, high ozone is associated with strong winds. Low local ozone occurs on days with transport from outside the region. The regions of influence (yellow shaded areas) are also larger.

10. Transport Conditions During High (90%-ile) and Low (10%-ile) Regional Ozone Days High regional ozone is associated with slow meandering or recirculating transport over KY, TN and WV, with strong clockwise transport around this region. Low region ozone is associated with northerly transport in the Northeast, south - southwesterly transport in the South. and clockwise recirculation in the Northwest.

11. Conclusions High local ozone in the Central East (IL, IN, OH, and KY) and Southeast are associated with stagnant regional transport conditions. High local ozone levels in the northern and western parts of the Eastern US are more typically associated with higher speed and persistent regional transport conditions from inside the Eastern US. Regional transport in any direction from the Central East is associated with high local ozone levels in the neighboring areas. Low ozone is associated with swift regional transport from outside the US. High region ozone is associated with slow meandering or recirculating transport over KY, TN and WV, with strong clockwise transport around this region.

12. High speed transport occurring in all directions Low speed transport predominately to the east Equal Transport Vectors

13. Synoptic Scale Transport Analyses The analysis techniques characterize regional scale transport Cannot identify local flows or near by source influences Blumenthal et al., 1997