1. 1 Modeling challenges in policy-relevant PM assessments in the U.S. Air Quality Applied Sciences Team 10th Semi-Annual Meeting, January 5-7, 2016 James T. Kelly Office of Air Quality Planning & Standards U.S. Environmental Protection Agency, Research Triangle Park, NC

2. 2 Purpose Fundamental aerosol research Parameterization & incorporation into grid models Policy-relevant assessments based on grid modeling Regulatory decision-making Targeted improvements in aerosol modeling would strengthen policy- relevant assessments (PRAs) and be beneficial for decision making Common challenges in applying aerosol models in PRAs may not be clear to those conducting fundamental research or parameterizing this research for 3D grid models The purpose of this presentation is to communicate some common challenges faced in conducting PRAs involving aerosol modeling to the air quality research community Idealized flow of information to inform regulatory decision-making

3. 3 Examples of Policy-Relevant Assessments Involving Aerosol Modeling State Implementation Plan (SIP) attainment demonstrations o Identify emissions controls that would lead to attainment of PM 2.5 NAAQS o Modeling includes simulating recent- and future-year PM for reference and emission control scenarios to develop PM response factors to project measurements to future Regulatory Impact Analysis (RIA) o Assess the benefits and costs anticipated to result from the proposed regulatory action and alternative regulatory actions (e.g., alternative PM 2.5 NAAQS revisions) o Modeling steps are similar to SIPs, but the control strategies are “illustrative”, analysis is usually at the national scale, and multiple standard levels may be considered Cross-state contribution assessments o Assess whether upwind states contribute significantly to nonattainment and/or interfere with maintenance of NAAQS attainment in downwind states in “good neighbor” SIP/FIP o Modeling is used to identify nonattainment/maintenance monitors and estimate contributions of sources in upwind states to monitors in downwind states Risk and Exposure Assessment (REA) o Estimate the health/welfare risk and/or population-based exposure for existing PM levels and for levels just meeting alternative standard(s) o Modeling involves characterizing recent-year PM levels and PM at alternative levels that meet targets; could potentially use high resolution info (space/time/composition/size)

4. 4 Inorganic Aerosol Model performance is good for secondary inorganic aerosol in some areas and seasons Face challenges in areas of west with complex terrain, diverse emissions Model performance challenges also exist for primary PM 2.5 components (e.g., from fugitive dust) Comprehensive model development programs that cut across emissions, meteorology, and chemistry communities and leverage field campaign data would be beneficial

5. 5 Secondary Organic Aerosol To date, control strategies in SIPs and RIAs have not directly focused on SOA due to limitations in science and model representations SOA modeling approaches that can be applied with reasonable confidence in regulatory assessments will be of increasing importance as the sources contributing to inorganic PM and primary OM are increasingly controlled As new SOA modeling approaches are incorporated into models, clarity is needed on the degree of confidence in their predictive capabilities, particularly when processes are not explicitly represented and/or depend heavily on uncertain parameters Pye et al. (2015) ES&T

6. 6 Sensitivity Modeling PRAs often require or would benefit from knowledge of the sensitivity of aerosol to changes in emissions or other variables; fast turn-around, reduced-form sensitivity models would be valuable in many applications DDM and adjoint sensitivity modeling approaches described in the literature show promise for such applications However, they are rarely applied in PRAs involving aerosol due to the lack of availability of all approaches in regional models, numerical instabilities, need to substantiate results with additional modeling, etc. Good agreement in single-source sulfate impacts from brute-force and DDM. Agreement is poor for nitrate cases (not shown; see Kelly et al., 2015, Atmos. Environ. 111:10-19)

7. 7 Source Contribution Regulatory assessments often require or would benefit from knowledge of source contributions to aerosol levels ( e.g., regional/international transport, regional haze, sector studies, RIAs) Explicit source tracking approaches and lumped reactive tracer approaches have been developed Limitations on their use in PRAs include availability in all grid models, computational constraints, and challenges in fully testing and evaluating approaches Good agreement in source contributions from CMAQ-ISAM and brute-force for a primary PM case. It is more difficult to test/evaluate results for secondary PM cases (e.g., Kelly et al., 2015, Atmos. Environ. submitted)

8. 8 Fire and Dust Events Estimating the impacts of fire and windblown dust events on air quality can be important in regional haze planning and exceptional event demonstrations Modeling has the potential to play a role in such assessments due to its comprehensive spatial and temporal coverage and source apportionment capabilities Improvements in the scientific basis and technical credibility of fire modeling is needed and will likely require fundamental insights from intensive field studies (e.g., FIREX) and other approaches Without Fires Emissions With Fires Emissions 24-hr Avg. PM 2.5 Credit: Mathur et al. (2011) CMAS Conference

9. 9 Fine and Global Scales Fine-scale o Population-based exposure assessments could potentially improve interpretation of earlier health studies and inform new studies o Exposure models can apply information on hourly PM levels at fine spatial scales over urban areas for a range of metrics, e.g.,  PM 2.5, PM 10-2.5, ultrafine PM, components, etc. o Adequately modeling aerosols at these scales is challenging Global-scale o There is increasing interest in characterizing current and possibly future-year contributions of large-scale transport to local PM levels o Need clarity on the degree of confidence in global model predictions, improvements in global emissions inventories and projections, and greater consistency between global and regional models

10. 10 Closing Thoughts Robustness of numerical methods and computational efficiency are key in regulatory assessments Studies that rigorously test algorithms, mechanisms, and instrumented approaches and incorporate them into regional models are valuable Results of application-oriented studies using research grade and/or outdated emissions and models are difficult to use It is important to consider the spatial and temporal scales that are appropriate for a specific assessment Recognizing the need to highlight new developments, clarity on limits of state-of-the-science is helpful Aerosol modeling challenges are often due to challenges in adequately representing model inputs, e.g., o Meteorology in areas of complex terrain in the west o Bottom-up emissions of NH 3, NOx, iVOCs/SVOCs, RWC, fires, etc.

11. 11 Disclaimers and Acknowledgments Acknowledgments: This presentation was informed by helpful conversations with Rich Scheffe, Pat Dolwick, Norm Possiel, Kirk Baker, Heather Simon, Brian Timin, and Tyler Fox Disclaimer: This presentation has been subjected to Agency review and approved for distribution. The views and interpretations in this presentation are those of the authors and are not necessarily attributable to their organizations.