1. 1 Ozone Transport Assessment Imperial County Gayle Sweigert, Manager Air Quality Analysis Section Air Resources Board

2. 2 Project Objectives  Evaluate transport impacts on ozone violations in Imperial County  Use results to select high ozone periods (episodes) for attainment demonstration  Make sure attainment demonstration captures all types of transport conditions

3. 3 Study Area Mexicali-UABC Mexicali-ITM Calexico East El Centro Calexico-Ethel Calexico-Grant Mexicali-Cobach Westmorland Niland Alpine-Victoria Dr. Tijuana Palm Springs

4. 4 Complex Process  Transport occurs both at surface and upper atmosphere  Political boundaries don’t prevent transport  Weather and distribution of emissions are very important  Remaining emissions and ozone from previous day can also be a factor

5. 5 Transport Classifications   Classify all ozone exceedance days in Imperial County for transport potential – –Overwhelming – –Shared

6. 6 Methods for Assessing Transport  Distribution of ozone violations  Change in wind speed and direction over time  Time of day that ozone violations occur  Estimating the path of an air parcel during, before, and after violations

7. 7 Putting It All Together  Map measured air quality to determine spatial extent of ozone violations  Graph hourly concentrations to determine time of day of ozone peaks  Take hourly weather data to determine prevailing wind speed and direction  Use trajectory program to estimate the air pathway 36 hours prior to each ozone violation

8. 8 Map of Ozone Concentrations June 3, 2007

9. 9 Hourly Ozone Concentrations Selected Sites: Mexico and Imperial County 7/4/2007

10. 10 Transport Findings (2005 – 2007)   Transport impacts originate from 3 areas: – –South (Mexicali) – –North (South Coast and Coachella Valley) – –West (San Diego and/or Mexico)   Overwhelming impact from Mexico on all Calexico exceedance days   El Centro & Westmorland, results are more varied

11. 11 Assessment Results

12. 12 Overwhelming Transport: Mexico Calexico-East 6-03-07 Palm Springs Westmorland El Centro Calexico-East Calexico-Ethel Mexicali Ontario

13. 13 Shared Transport: Mexico Westmorland 5-09-06 Ontario Palm Springs Westmorland El Centro Calexico Ethel Calexico East Mexicali

14. 14 Overwhelming Transport: South Coast Westmorland 6-07-05 Ontario Palm Springs Westmorland El Centro Calexico East Calexico Ethel Mexicali

15. 15 Shared Transport: Mexico & South Coast Westmorland 5-31-05 Ontario Palm Springs Westmorland El Centro Calexico Ethel

16. 16 Shared Transport: West El Centro 5-09-07 Ontario Palm Springs Westmorland El Centro Calexico Ethel

17. 17 Results (2005 – 2007) El Centro & Westmorland Transport Pattern Exceedance Site Total El CentroWestmorland Overwhelming (MEX)505 Overwhelming/Share (MEX) 505 Share (MEX)178 Share (WEST)369 Overwhelming (SC)033 Share (mixed)347 Total172037

18. 18 Limitations of Method   Doesn’t capture what is going on in the upper atmosphere   Doesn’t capture large difference in emissions between Mexico and Imperial County   Uncertainty related to transport from the west

19. 19 Next Steps   Model three different ozone episodes   Episodes capture all transport scenarios identified   Final conclusions will integrate results from data analysis and photochemical modeling   Summarized in ozone attainment plan

20. 20 Questions? Contact:Gayle Sweigert gsweiger@arb.ca.gov (916) 322-6923