WESTAR Council & the University of Nevada Conference on Western Ozone Transport

1. WESTAR Council & the University of Nevada Conference on Western Ozone Transport October 10-12, 2012 Reno, NV

2. Increase our understanding of the science of ozone background and transport in the West Show how the science can help state regulatory agency decision making for: Nonattainment area planning Interstate transport assessments Conference Objectives

3. What are the source areas of ozone and what is the relevance of each to surface ozone in the western U.S.? Local/regional Western regional transport Long-range transport from Asia Stratospheric intrusions Wildfire Questions addressed at the Conference

4. What assessment techniques are being used to determine ozone? Ambient monitoring Ozonesondes Aerosol tracers Lidar Satellite Modeling Global Regional Questions addressed at the Conference

5. Clean Air Scientific Advisory Committee (CASAC) 2010 - Recommended 60 to 70 ppb EPA proposed 60-70 ppb but retained 2008 standard (75 ppb) Ozone NAAQS Background

6. EPA Ozone NAAQS 2012 Policy Assessment: “strong support” for tightening Ozone NAAQS CASAC review of the EPA Policy Assessment: “provides a strong rationale for consideration of ozone standards (8 hour averages) of 60 ppb and 70 ppb” “provides adequate justification for considering concentrations below 60 ppb, in the 50 to 60 ppb range.” Ozone NAAQS Background

7. The Problem typical U.S.“background” (model estimates) [Fiore et al., 2003; Wang et al., 2009; Zhang et al., 2011] U.S. National Ambient Air Quality Standard for O3 has evolved over time Future? (proposed) 75 ppb 2008 8-hr 84 ppb 1997 8-hr 120 ppb 1979 1-hr avg O3 (ppbv) Allowable O3 produced from U.S. anthrop. sources (“cushion”) 20 60 80 40 100 120 Lowering thresholds for U.S. O3 NAAQS implies thinning cushion between regionally produced O3 and background

8. Some challenges for WUS O3 air quality management Warming climate +in polluted regions [Jacob & Winner, 2009 review] + natural sources [recent reviews: Isaksen et al., 2009; Fiore et al., 2012] ? Transport pathways stratosphere Natural events e.g., stratospheric [Langford et al [2009]; fires [Jaffe & Wigder, 2012] lightning Rising Asian emissions [e.g., Jacob et al., 1999; Richter et al., 2005; Cooper et al., 2010] “Background” ozone X Wildfire, biogenic Pacific Asia Need process-level understanding on daily to multi-decadal time scales Western USA Today’s talk: 1) Intro: satellites + models 2) NASA AQAST Overview 3) Results for WUS from two collaborative AQAST projects 4) Air quality projections in a warming climate

9. Variability in springtime O3 background GFDL AM3 simulation with N. American anthrop. emissions shut off (1981-2007) MEAN OVER 27 YEARS STANDARD DEVIATION ppb ppb

10. Characteristics of background O3 • Wildfires: • Emery et al. (2012) found that modeled day-specific fires in the West can increase 8-hour ozone concentrations by 10-50 ppb. • Jaffe et al. (2008) determined that WUS seasonal mean ozone concentrations increased by ~ 9 ppb in years with high wildfire activity. • Stratospheric intrusions: • Lin et al. (2012) estimated that 8-hour ozone contributions from strong stratospheric intrusion events could range up to ~ 55 ppb in the WUS.     • Langford et al. (2010) noted that strong intrusion events are relatively straightforward to identify, but harder to quantify. • International transport: • Zhang et al. (2011) estimated that the worldwide anthropogenic methane plus intercontinental aNOX/aVOC contributions to 8-hour ozone is ~ 9 ppb at low-elevation sites and ~ 13 ppb at sites in the West. Also estimated mean contributions of 1-3 ppb from Canada and Mexico, with larger / more variable impacts in border regions. 10

11. Free tropospheric ozone trend above western North America All available data above western North America, regardless of transport history. An extension of the 1995-2008 ozone trend, adding years 2009, 2010 and 2011.

12. Estimates of background O3 in the U.S. Values are presented across the range of GEOS-Chem and CAMx results at all monitoring site locations with simulated MDA8 ozone concentrations above 55 ppb. Median values provide a more robust indicator than higher values of the distribution for the purpose of examining and comparing the regional and seasonal variability in NAB. The NAB predictions toward the higher end of the distribution (e.g., 75th and 95th percentiles) are more reflective of infrequent or atypical events. Due to the overall uncertainties and assumptions in the inputs to the two modeling systems, the higher percentage NAB predictions are likely to have a greater degree of uncertainty than the median values. (Henderson et al., 2012) 12

13. Trinidad Head, N. California O3 profiles: 1997-2009 • O3 is only regulated pollutant with positive gradient with height. • O3 is only regulated pollutant where background concentrations are more than 50% of the health threshold.

14. Average MDA8 at 10 Rocky Mtn CASTNET sites Great Basin • Avg MDA8 at these sites significantly correlated with elevation. • While there are site to site differences, interannual variations are significantly correlated across most sites (Jaffe 2011).

15. Elevated Ozone Reservoir (2011 data May - September)

16. Elevated Ozone Reservoir

17. Elevated Ozone Reservoir ? Frenchman Mt ~4020 ft Arden 4301 ft

18. Methods for estimating background O3 • Few true measurements of background ozone • Most, if not all, rural / remote monitoring sites in the US are affected, at least to some extent, by ozone from US anthropogenic emissions • Current scientific understanding of NA and U.S. background ozone is largely based on global / hemispheric photochemical models. These models have limitations: • Uncertainties in global emissions estimates • Uncertainties in chemistry important on global spatial and time scales • Uncertainty in mixing between the boundary layer and free troposphere • Limitations in capturing processes associated with episodic events • Much of the modeling to estimate background has relied upon a “zero-out” approach which may not properly capture the contribution of background sources to ozone under current ambient conditions. • Zero out runs are designed to answer a specific question. What would ozone be in the absence of these emissions? (Not “in-situ” contribution.) 18

19. Use of background O3 in NAAQS Implementation • Exceptional Events: • Existing rule establishes procedures and criteria by which air quality data affected by exceptional events can be excluded from regulatory decisions. • Among the criteria for defining an exceptional event is the determination that a violation would not have occurred “but for” the event. • Routine background contributions are not exceptional events. • 179B/International Transport: • Allows special treatment if projected air quality or air quality on the attainment deadline date would meet the NAAQS “but for” emissions from another country • Attainment demonstration guidance: • Consideration of boundary condition impacts on relative response factors? • Consideration of separate future-year boundary conditions? • Consideration of exceptional events in establishing baseline DV? • Will be an opportunity for State/Local review. 19

20. Summary • As ozone standards have tightened over time, background ozone is becoming more important and will need to be carefully considered in our efforts to attain NAAQS. • Recent modeling efforts have estimated that mean NAB contributions can range from 38-41 ppb in the intermountain Western U.S. • Background can be larger during episodic events associated with stratospheric intrusions, wildfires, or plumes of international emissions. • Recent modeling suggests U.S. anthropogenic sources are the largest contributor to most days with high O3 in most locations. • EPA policy and eventual State efforts will need to carefully consider ozone background in developing efficient and effective attainment strategies. 20

21. Cross section of isentropic potential vorticity in potential vorticity units at 18Z May 24, 2010, for latitude 39 degrees North across Colorado showing a tropopause fold descending to about 5 kilometers (MSL) over central Colorado. from the 18Z analysis run of the NAM12 on may 24, 2010. Patrick Reddy CDPHE 21

22. Develop standardized technical methods for analysis of Stratospheric Intrusions. Promote collaboration and data sharing between the states, academics and federal researchers. Promote archiving of key data sets. The workgroup will NOT specify criteria for approval of EE or make determinations of whether flagged data can be approved by EPA. Workgroup can NOT make recommendations on policy or how EPA could use this information. Stratospheric Ozone Workgroup