UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION IX 75 Hawthorne Street San Francisco CA 94105
July 20, 2011 

### Mr. James Goldstene Executive Officer California Air Resources Board 1001 I Street Sacramento, California 95814

Re: EPA Comments on Proposed Revisions to the StateImplementation Plan for SanJoaquin Valley 8-hour 0 one

EPAhas reviewed the Air Resources Board (ARB) staffsproposed revisions to the 2007 8-hour Ozone Plan for the SanJoaquin Valley. These revisions are in partthe result ofefforts by ARB and the San Joaquin Valley Air Pollution Control District to improve the emissions inventories. We applaud these efforts and have evaluated the potential implications ofthese recent inventory revisions on the Plan's attainment demonstration. Weunderstand that ARB is committed to achieving the reductions necessary to attain the 1997 8-hour ozone standard.

The SJV Ozone Plan, as adopted in 2007, includes modeling that indicates a need to reduce NOx emissions by 75 percent from the 2002 base year level to 160 tons perday (tpd) in orderto attain the 1997 8-hour ozone national ambient air quality standard. In the proposed revisions to the Plan, NOx emissions for the 2002 base year are revised downward by 12 percent to more accurately reflect the emissions in the base year, butthe Plan's attainment target of 160 tpd remains unchanged. Theextent of the base year emissions changes adds to the uncertainty inherent in determining the exact emissions level needed for attainment.

To address this uncertainty, EPArecommends that the ARB committo achieve a 75 percentreduction in NOxfrom the revised 2002 base year levels by 2023. A 75 percentreduction from the revised 2002 base year inventory equates to an attainmenttarget level of 141 tpd ofNOx emissions. We believe that the 75 percentreduction from the existing modeling provides the best available estimate ofthe NOxreductions needed to reach attainment. This rests on the reasonable assumption that the ozone decrease expected from a given relative emission decrease would be approximately the same were the base case to be remodeled, since the underlying chemical and atmospheric processes for the modeled episodes would remain unchanged. However, given that the actual emissions reductions needed for attainment could be differentbased on new modeling, we note this commitment could later be revised ifyou submit, and we approve through notice and corrimentrulemaking, a revision to the Plan based on a new modeling analysis demonstrating attainment ofthe 1997 8-hour ozone standard as expeditiously as practicable.

Based on our conversations with your staff, we agree that the preferred approach to reevaluating the attainment demonstration in light ofthe revised emissions estimates would be to perform new air quality modeling. We also recognize the time and effortinvolved in such modeling and appreciate ARB's commitment to complete new modeling within the next few years.Therefore, EPArecommends thatthe ARB commit to submit, by a specific date, a revised attainment demonstration including the attainment target for the 1997 8-hourozone standard for the SanJoaquin Valley. This revised attainment demonstration should bebased on new air quality modeling using the
mostrecent emissions estimates.

EPA believes that these recommendations are consistent with ARB's continuing aggressive commitments and efforts to achieve the emission reductions needed for attainment ofthe air quality standards in the SanJoaquin Valley and the rest ofCalifornia. Should you orARB staffwish to discuss this issue further, please call me orMatthew Lakin ofmy staffat415-972-3851.

Sincerely,

e all Jordan Director, Air Division

cc: Mr. Seyed Sadredin AirPollution Control Officer, SanJoaquin Valley AirPollution Control District Ms. Lynn Terry DeputyExecutive Officer, California AirResources Board Ms. Karen Magliano Chief, AirQuality DataBranch, California AirResources Board