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Transboundary influences on US background ozone

Transboundary influences on US background ozone. Huiqun Wang 1 (hwang@cfa.harvard.edu) Philippe Le Sager 2 (plesager@seas.harvard.edu) Rokjin Park 3 (rjpark@snu.ac.kr) Daniel Jacob 2 (djacob@fas.harvard.edu). Smithsonian Astrophysical Observatory Harvard University

aubrey-phillips
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Transboundary influences on US background ozone

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  1. Transboundary influences on US background ozone Huiqun Wang1 (hwang@cfa.harvard.edu) Philippe Le Sager2 (plesager@seas.harvard.edu) Rokjin Park3 (rjpark@snu.ac.kr) Daniel Jacob2 (djacob@fas.harvard.edu) • Smithsonian Astrophysical Observatory • Harvard University • Seoul National University Funding from DOE

  2. Tightening the standard has large impact

  3. NA background from GEOS-Chem CASTNet sites observations GEOS-Chem at CASTNet Background ozone is important for setting the standard Fiore et al. [JGR 2003b] March-October 2001 Background is not directly measurable, and need to be estimated from models

  4. NA background – No anthropogenic emissions in North America US background – No anthropogenic emissions in the US The national totals of CAN & MEX are small, but there are non-negligible emission sources near the boarder.

  5. NA background (without NA anthropogenic emissions) JJA mean based on daily-8h-max US background (without US anthropogenic emissions)

  6. Canadian and Mexican Influences (ppb) JJA mean based on daily-8h-max sites Enhancement to NA background is concentrated in the northeast and southwest US

  7. Sites JJA mean daily-8h-max Canadian enhancement in the northeast (ppb) The largest JJA mean Canadian enhancement is 8.8 ppb (among all US gridboxes).

  8. Sites JJA mean daily-8h-max Mexican enhancement (ppb) The max JJA mean Mexican enhancement is 13.1 ppb among all US gridboxes.

  9. Modeled v.s. observed surface ozone at selected sites Northeast r=0.76 Southwest r=0.60

  10. Probability distribution of daily8hmax surface ozone in the U.S. (JJA, 2001) NA-background (PRB) Standard-run US-background 20 40 60 O3 (ppb) US background is several ppb higher than NA background

  11. Time series at Unionville, MI r = 0.85 Observation Std-Run US-backgroundNA-backgroundCANMEX Episodic enhancements to NA background increase US background to >40 ppb

  12. CAN contributes 59% to O3 precursors on peak ozone days at Buffalo Slide from EPA presentation

  13. At different locations, transboundary pollutions contribute differently to surface ozone. CAN influence > 10 ppb on some peak ozone days (>80ppb) CAN influence > 10ppb does not occur when ozone > 80ppb

  14. Time series at Alpine, CA r = 0.64 Observation Std-Run US-backgroundNA-backgroundCANMEX Larger mean enhancement, but less episodic. US background is frequently above 30 ppb

  15. Canadian pollutions influence the northwest through frontal systems Some fronts reach far into the U.S.

  16. Max 90% 75% 50% 25% Min US background and NA background statistics for successive 10ppb ozone bins Statistics are for all US gridboxes with JJA mean enhancement >= 3ppb Southwest has higher background ozone Max background occur when ozone is 50 – 70 ppb

  17. Canadian influence is >10ppb on some peak ozone days (>80ppb) Canadian influence is always <10ppb on peak ozone days(>80ppb) Untagged color boxes have max surface ozone < = 80 ppb Color background : JJA mean Canadian influence as before Canadian influence is important for the areas near the lakes and northeast coast Max Canadian contribution on peak ozone days is 23 ppb among the boxes indicated by

  18. Canadian influence is >10ppb on some peak ozone days (>75ppb) Canadian influence is always <10ppb on peak ozone days(>75ppb) Untagged color boxes have max surface ozone < = 75 ppb Color background : JJA mean Canadian influence as before

  19. Canadian influence is >10ppb on some peak ozone days (>70ppb) Canadian influence is always <10ppb on peak ozone days(>70ppb) Untagged color boxes have max surface ozone < = 70 ppb Color background : JJA mean Canadian influence as before

  20. Contribution of CAN pollutions to non-attainment for different choices of ozone standard 28 cases Y > 10ppb & X > 80ppb 93 50 cases Y > 5ppb & X > 80ppb 138 Y: 527 280 70 75 854 cases X> 80ppb 1679 X: 2936 15180 data points: all JJA timeserises at US gridboxes within [36N-48N, 88W-66W].

  21. Mexican influence is >10ppb on some peak ozone days (>80ppb) Mexican influence is always <10ppb on peak ozone days(>80ppb) Untagged color boxes have max surface ozone <= 80ppb Color background : JJA mean Mexican influence as before Max Mexican contribution on peak ozone days is 18 ppb among the boxes indicated by Mexican influence is important for southern California

  22. Mexican influence is >10ppb on some peak ozone days (>75ppb) Mexican influence is always <10ppb on peak ozone days(>75ppb) Untagged color boxes have max surface ozone <= 75ppb Color background : JJA mean Mexican influence as before

  23. Mexican influence is >10ppb on some peak ozone days (>70ppb) Mexican influence is always <10ppb on peak ozone days(>70ppb) Untagged color boxes have max surface ozone <= 70ppb Color background : JJA mean Mexican influence as before

  24. Contribution of MEX pollutions to non-attainment for different choices of ozone standard 28 14 cases Y > 10ppb & X > 80ppb 53 49 cases Y > 5 ppb & X > 80ppb Y: 271 109 413 cases X > 80ppb 70 75 X: 1002 2453 34960 data points : all JJA timeserises at US gridboxes within [26N-42N,120W-90W]

  25. US bkg 50 40 30 US background = NA background + CANMEX Enhancement CANMEX enhancement All US JJA time series included NA background CANMEX enhancement maximizes when NA background is 10 – 20 ppb

  26. US background = NA background + CANMEX Enhancement 50 40 30 20 For peak ozone cases (>80 ppb) in the US, Transbounrary pollutions are large (>10ppb) when NA background is 10 – 30 ppb. They can increase US background to levels >30 ppb.

  27. Conclusion • Transboundary pollutions from Canada and Mexico increase the background surface ozone in the US by 1-13 ppb. • The max JJA Mean Canadian enhancement is 8.8ppb, with episodic maximum of 34 ppb (at Unionville) in daily-8h-max time series. • The max JJA mean Mexican enhancement is larger (13.1ppb), but the maximum in daily-8h-max time series is smaller (21ppb, not shown). • The median US background in the southwest is 30-40ppb, and that in the northeast is 20-25ppb. • The maximum US background in the southwest is near 55ppb, and that in the northeast is near 50ppb. They occur when the surface ozone is 50-70ppb. • Canadian and Mexican enhancements maximize when NA background is 10–30ppb. • For peak ozone cases, the US background can be > 30 and even 40 ppb due to transboundary influences. • Transboundary pollutions can contribute significantly (up to 23 ppb in the northeast and 18 ppb in the southwest) to peak ozone levels (>80ppb) sometimes.

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