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N emissions and the changing landscape of air quality

N emissions and the changing landscape of air quality. Rob Pinder US EPA Office of Research and Development Atmospheric Modeling & Analysis Division. Global nitrogen and carbon cycles: much of the anthropogenic impacts start in the atmosphere.

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N emissions and the changing landscape of air quality

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  1. N emissions and the changing landscape of air quality Rob Pinder US EPA Office of Research and Development Atmospheric Modeling & Analysis Division

  2. Global nitrogen and carbon cycles:much of the anthropogenic impacts start in the atmosphere Source: Gruber and Galloway, An Earth-system perspective of the global nitrogen cycle, Nature, 2008

  3. Questions: • What are the trends in reactive nitrogen atmospheric concentrations? • How is the atmospheric reactive nitrogen chemical composition changing? • What aspects of the atmospheric reactive nitrogen budget are poorly constrained?

  4. Sources of reactive nitrogen

  5. Rapid dry deposition | Slow Dry Deposition

  6. Less Water Soluble | More Water Soluble

  7. Atmospheric Modeling Tools • Use the air quality model to understand fate and transport of reactive nitrogen • CMAQ: Community Multi-scale Air Quality • Emissions • Advection / dispersion • Chemistry • Aerosol thermodynamics • Wet and dry deposition

  8. Outline • Can models and observations constrain the • Trends in NO2 and NH3? • Aerosol and gas phase reactive nitrogen? • Soluble reactive nitrogen in the free troposphere? • What additional information is needed?

  9. Trends in NO2 and NH3

  10. Trend in space-based observations of NO2 A. Richter et al., Increase in tropospheric nitrogen dioxide over China observed from space, Nature, 437 (2005)

  11. SCIAMACHY 2003 2004 2005

  12. SCIAMACHY 20032004 2005

  13. SCIAMACHY 20032004 2005

  14. OMI 20052006 2007 2008 molecules NO2× 1015

  15. OMI 20052006 2007 2008 molecules NO2× 1015

  16. OMI 2005 2006 2007 2008 molecules NO2× 1015

  17. OMI 20052006 2007 2008 molecules NO2× 1015

  18. OMI trend for summer NO2 Trend in polluted areas: 5-6% per year reduction in NO2 column density

  19. NH3 is not well constrained, but deposition measurements indicate anupward trend

  20. Satellite retrieval of NH3 Source: Clarisse et al., Global NH3 distribution derived from infrared satellite observations, Nat. Geo., 2009

  21. February 2009 to February 2010 • CAMNet NH3 monitoring sites match-up with TES overpass • Two week integrated samples • Sited away from livestock operations to be representative of TES footprint • Allows detection of spatial variability and seasonal trends TES NH3 Comparison Example : Transects over North Carolina USA Acknowledge: John Walker, Karen Cady-Pereira, Mark Shephard, Daven Henze, Ming Lou

  22. AMoNNH3 surface measurements from Dec. 2007 - today CMAQ compared with all sites error: 60% bias: -6.4% Low bias: overall amount of emissions is reasonable High error: spatial and temporal distribution of emissions are uncertain

  23. Conclusions about NO2 and NH3 • Trend in NO2 is reasonably well constrained by satellite observations • Appears to be consistent with emission changes • Wet deposition NH4+provides the best constraint on NH3 trend • Surface monitoring and satellite NH3 retrievals are under development

  24. Rapid dry deposition | Slow Dry Deposition Trends in Aerosol and Gas Phase

  25. CMAQ represents spatial distribution of nitrate decrease summer 2002 – 2005 Change in total nitrate, μg m-3

  26. Acknowledge: Wyat Appel

  27. Acknowledge: Wyat Appel

  28. Decrease in nitrate at CASTNet sites

  29. Conclusions about aerosol and gas phase reactive nitrogen • Significant decreases in total nitrate and aerosol nitrate • CMAQ captures these trends well • Increase in the fraction in the aerosol phase: subtle effect on spatial distribution • Need co-located measurements of NH3 and NH4+ to understand trend in reduced nitrogen

  30. Trends in Long-lived Reactive Nitrogen Less Water Soluble | More Water Soluble

  31. Half of reactive nitrogen is in the free troposphere Acknowledge: Ken Pickering, Dale Allen, Barron Henderson

  32. Important contribution from NO produced from lightning Acknowledge: Ken Pickering, Dale Allen, Barron Henderson

  33. Chemical partitioning between soluble forms of oxidized nitrogen in the free troposphere has biases Acknowledge: Ken Pickering, Dale Allen, Barron Henderson

  34. CMAQ simulation with lightning NO production successfully reproduces wet deposition flux

  35. Conclusions: long-lived reactive nitrogen • Long-range transport is controlled by chemical state of oxidized nitrogen • The vertical profile of soluble oxidized nitrogen is not well simulated by CMAQ • CMAQ is able to simulate wet deposition in the eastern US • Little is known about reduced nitrogen in the free troposphere • CalNex study will be very helpful

  36. Conclusions • Trends in measurements, CMAQ simulations, and emissions of oxidized nitrogen are consistent • Oxidized nitrogen is decreasing • Reduced nitrogen is increasing • CMAQ simulations of the aerosol and chemical partitioning of oxidized nitrogen are sufficiently consistent with observations to • assess the regional budget (in the East) • estimate impacts of future emission scenarios • Need more observational constraints of sources, transport and fate of reduced nitrogen

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