Weekend Effect Hypotheses

1. Weekend Effect Hypotheses Air Resources Board Cal/EPA Leon Dolislager Air Pollution Research Specialist Atmospheric Processes Section

3. Weekend Effect

4. WE Effect Working Group • Purpose • Investigation of cause(s) • Coordination of research • Sharing of results • Web Page - www.arb.ca.gov/ • aqd/weekendeffect/weekendeffect.html

5. Weekend vs. Control Strategy

6. Hypotheses of WE Effect • NOX-reduction • NOX-timing • Carryover near the ground • Carryover aloft • Increased weekend emissions • Decreased absorption of UV sunlight

7. NOX-reduction

9. NOX-reduction

10. NOX-timing

11. NOX-timing

12. Carryover near ground

13. Carryover aloft

14. Increased WE emissions

15. Decreased UV absorption

16. Summary • Plausible • NOX-reduction - likely • NOX-timing - likely • Carryover aloft • Increased UV - unlikely • Carryover at ground - unlikely • Not Plausible • Increased emissions