Results of 2010/2015 Post-CAIR Ozone Source Apportionment Modeling

1. Results of 2010/2015 Post-CAIR Ozone Source Apportionment Modeling August 2005 OAR/OAQPS/EMAD/AQMG

2. Ozone Source Apportionment Modeling Results • The following slides show the relative contribution of different groups of emissions sources to ozone levels at times and places where exceedances of the 8-hour standard are projected to occur in 2010 and 2015. This information can be useful in considering potential control strategies. However, a key consideration in weighing alternative strategies is which types of emissions are cost effective and practical to control, a consideration not addressed by the source apportionment modeling.

3. What is source apportionment in the context of AQ modeling? • The Comprehensive Air Quality Model w/ Extensions (CAMx) contains a source apportionment tool which can be used to estimate how emissions from individual source areas and regions affect modeled ozone concentrations over space and time. • This is achieved by using multiple tracer species to track the fate of ozone precursor emissions (VOC and NOx) and the ozone formation caused by these emissions within a CAMx simulation.

4. How was source apportionment used in this particular application? • Two base cases were considered, both based on the Clean Air Interstate Rule CAMx ozone modeling. For more information on CAIR-specific ozone source apportionment, please see the CAIR modeling Technical Support Document • 2010 projection, after application of CAIR controls • 2015 projection, after application of CAIR controls • This analysis used the Anthropogenic Precursor Culpability Assessment (APCA) option for the CAIR source apportionment modeling. • Allocates all ozone production to manmade precursor emissions, when interaction between manmade emissions and biogenic emissions.

5. How was source apportionment used in this particular application? • Contributions were calculated from 39 source areas: • 37 eastern US States within the modeling domain • Canada • Gulf of Mexico • Contributions were calculated from 6 major source sectors: • EGU Point, • Non-EGU Point, • Stationary Area, • On-Road Mobile, • Non-Road Mobile • Wildfire emissions (generally shown to be negligible)

6. How was source apportionment used in this particular application? • Source area/sector contibutions were calculated over those nonattainment areas that are projected to be residual nonattainment areas in the 2010 and 2015 future year modeling: • 16 projected post-CAIR ozone nonattainment areas in 2010 • 6 projected post-CAIR ozone nonattainment areas in 2015 • See next slide for a map of the specified receptor regions • Modeling source apportionment results can be summarized via multiple metrics. This analysis focuses on a single metric: episodic-average contribution over only those time periods in which the model projects future 8-hour ozone exceedances. • NOx and VOC emissions were tracked separately but combined in the final analysis.

8. 2010 Results • Each of the next 16 plots provides information about the source sectors and source regions that are estimated to be contributing to residual nonattainment in 2010 over various eastern U.S. areas. • Pie chart: • Shows average contribution to model ozone “exceedances” • (i.e., 8-hour ozone concentrations >= 85 ppb) • 18 different “contributors”: 6 source sectors x 3 region types. • For simplification purposes, the 39 source areas were subjectively aggregated into three types of regions for each receptor: “local”, “nearby”, and “other”. The specific definitions of the regions associated with each receptor are listed on the last slide. • Top bar chart – Percentage Contribution by State • Only top eight contributing States are plotted • Bottom bar chart – Percentage Contribution by Source Sector

25. 2015 Results • Same format/metrics as 2010 • Six nonattainment areas are projected to remain in 2015: • Philadelphia, • New York City, • Houston, • Milwaukee, • Chicago • Baltimore

32. CAIR 2010/2015 Ozone Source Apportionment • Definition of local areas (i.e., multi-state nonattainment areas) • New York City: NY, NJ, CT • Philadelphia: PA, DE, MD, NJ • Washington DC: MD, VA • Definition of “nearby” areas • Atlanta: AL, FL, NC, SC, TN Houston: AR, LA • Baltimore: DE, PA, VA, WV Kent/Queen Anne: DE, PA, VA, WV • Beaumont: AR, LA, OK Milwaukee: IA, IL, IN, MI • Buffalo: PA New York City: DE, MA, PA • Chicago: IA, IN*, MI Philadelphia: VA, WV • Cleveland: IN, MI, PA, WV Providence: CT, MA, NY • Dallas: AR, LA, OK Sheboygan: IA, IN, IL, MI • Detroit: IN, OH Washington DC: DE, PA, WV • Questions? Contact Pat Dolwick: dolwick.pat@epa.gov