1. A regional-to-global perspective on attaining the new U.S. ozone NAAQS Panel on Meeting the New Ozone Standard Energy Summit 2015 University of Wisconsin, Madison, WI October 13, 2015 Arlene M. Fiore Acknowledgments: George Milly, Lukas Valin (LDEO) Harald Rieder (U Graz, Austria) Lok Lamsal (NASA GSFC) 83520601

2. Ground-level O 3 is produced photochemically in the atmosphere, from both natural and anthropogenic sources O3O3 + CH 4 NMVOC NO x Fuel local-to-regional ozone pollution episodes Raises background ozone levels Observed surface ozone includes background plus any ozone produced from local-to-regional emissions

3. 1950s Present 1980s NMVOCs+ NO x + CH 4 ?? U.S. ozone abatement strategies evolve with our understanding of the O 3 problem Abatement Strategy: O 3 smog recognized as an URBAN problem: Los Angeles, Haagen-Smit identifies chemical mechanism Smog considered REGIONAL problem; role of biogenic VOCs discovered A GLOBAL perspective: role of intercontinental transport, background

4. Lower O 3 NAAQS level likely expands non-attainment regions Cooper et al., Science, 2015 2011-2013 ozone design values at EPA approved ozone monitoring sites

5. Cleaner U.S. air is visible from space Satellite (OMI) tropospheric NO 2 columns c/o Lok Lamsal & Bryan Duncan, NASA GSFC New OMI NO 2 website: airquality.gsfc.nasa.govairquality.gsfc.nasa.gov

6. Tropospheric column NO 2 higher on weekdays vs. weekends, mainly attributable to weekly cycle in diesel NO x emissions WEEKENDWEEKDAY Mid-2000s Following NO x emission controls, current weekday tropospheric NO 2 columns look more like past weekends Early 2010s Luke Valin LDEO, in prep.

7. Similar patterns occur in surface ozone 90 th % summer afternoon surface ozone (U.S. EPA AQS)  Additional diesel NO x controls would lower weekday surface ozone (and tropospheric NO 2 columns)  Implies regional NO x -sensitive ozone production WEEKDAY WEEKEND Luke Valin LDEO, in prep. Mid- 2000s Early 2010s

8. 2001-2005 2021-2025 (RCP8.5) # DAYS OBSERVEDOBSERVED + MODELED Future projections in the context of the revised O 3 NAAQS Number of summer (JJA) days with MDA8 O 3 > 70 ppb at CASTNet sites APPROACH 1. Use chemistry-climate model (GFDL CM3) to estimate regional-scale changes 2. Apply modeled changes at each percentile to observed distribution at each site Rieder et al., in prep, 2015 40% decrease in EUS NO x emissions over near-term (2020-2005) leads to 3 or fewer summer days with MDA8 O 3 > 70 ppb at all but 5 sites ?

9. Future projections in the context of the revised O 3 NAAQS: a monitoring site in Dodge County, WI 2001-2005 OBSERVED 2021-2025 OBSERVED + MODEL (RCP8.5) REGIONAL CHANGES AT EACH PERCENTILE  Moving from 75 to 70 ppb doubles # days > NAAQS level  Projected regional-scale O 3 decreases suggest near-term attainment of new standard possible H. Rieder

10. The “tightening vise” of ozone management Ozone concentration Historical Future (alternate view) Hemispheric background Regional Local Standard Future Keating, T. J., J. J. West, and A. Farrell (2004) Prospects for international management of intercontinental air pollutant transport, in A. Stohl, Ed., Intercontinental Transport of Air Pollution, Springer, p. 295-320.  Future may require concerted efforts to lower background

11. Reducing methane lowers hemispheric background ozone (plus climate co-benefit)  ~ 1 ppb across the northern hemisphere [Fiore et al., JGR, 2009; TF HTAP, 2007, 2010; Wild et al., ACP, 2012]  7700-400,000 annual avoided cardiopulmonary premature mortalities in the N. Hemisphere uncertainty in concentration-response relationship only [Casper Anenberg et al., ES&T, 2009] Range over 18 models Global mean avoided warming in 2050 (°C) [WMO/UNEP, 2011] CLIMATE OZONE AIR QUALITY Benefits of ~25% decrease in global anthropogenic methane emissions North America Europe East Asia South Asia

12. Estimated in a model (GEOS-Chem) by turning off N. American anthropogenic emissions Background over the U.S.A. is highest in the west (at altitude) and in spring Latest background estimates (recent years, higher resolution) support general conclusions; emphasis now on episodic background events e.g., Wu et al., 2008; Wang et al., 2009; McDonald-Bueller et al. 2011; Mueller & Mallard, 2011; Zhang et al., 2011; 2014; Emery et al., 2012; Lin et al., 2012ab; Fiore et al., AtmEnv, 2014 Summer 1995 afternoon average background ozone [Fiore et al., JGR, 2002] 12 20 28 37 Ozone (ppb) [Fiore et al., JGR, 2003] Monthly afternoon mean ozone over the Northeast U.S.A., 2001 J F M A M J J A S O N D Month of 2001 Ozone (ppb) OBS. Model Background

13. Setting achievable standards requires accurate knowledge of background levels 120 ppb 1979 1-hr avg 84 ppb 1997 8-hr 75 ppb 2008 8-hr 40 6080 100120 O 3 (ppbv) 20 U.S. National Ambient Air Quality Standard for O 3 has evolved over time typical average U.S. “background” (model estimates) [ Fiore et al., 2003; Wang et al., 2009; Zhang et al., 2011] “Allowable” O 3 produced from U.S. anthrop. sources (“cushion”) Lowering U.S. O 3 NAAQS levels implies thinning cushion between regionally produced O 3 and background background events over WUS [e.g., Lin et al., 2012ab] 70 ppb 2015 8-hr Adapted from D.J. Jacob & NAS, 2009

14. An Air Quality Management Challenge: NATURAL EVENTS How to detect and attribute accurately? Fiore et al., EM 2014 (NASA AQAST special issue) Examples of how satellite, in situ measurements and models can be combined to detect and attribute exceptional events WILDFIRES STRATOSPHERIC INTRUSIONS

15.  Downward ozone trend as EUS NO x emission controls are implemented  Decreasing NO x emissions reduces sensitivity of O 3 to temperature; continued controls should guard against climate-driven increases [e.g., Bloomer et al., 2009; Rasmussen et al., 2012; Brown-Steiner et al., 2015] Observations at U.S. EPA CASTNet site Penn State, PA 41N, 78W, 378m July mean MDA8 O 3 and July mean daily maximum temperature An Air Quality Management Challenge: CLIMATE CHANGE Will warmer temperatures worsen O 3 pollution? G. Milly Figure 6a of Fiore, Naik, Leibensperger, JAWMA, 2015

16. Attaining the new U.S. ozone NAAQS: A regional-to-global perspective Continued regional NO x decreases should facilitate attainment with new standard (NO x -sensitive ozone production) over the eastern U.S.A. Background contributions to U.S. surface ozone vary in space and time Exceptional events may become more common with respect to a tighter standard and under climate change (e.g., wildfires) Trans-boundary transport could increase if foreign emissions rise (see next panel) Methane emission reductions would lower hemispheric background ozone levels (and also decrease climate forcing)