Draft Ozone Procedures

For a prevention ofsignificant deterioration (PSD) application, if a project will emit 100

tons per year (tpy) or more ofVOC (volatile organic compounds) or NOx (nitrogen oxides)

emissions, an ozone impact analysis to demonstrate predicted compliance with the eighthour ozone standard is required (1). Preconstruction ambient air monitoring is required

as well, unless the applicant requests and receives a waiver. The Air Dispersion Modeling

Team (ADM'!') will use the attached screening procedure for the ozone impact analysis.

Determining Compliance with the Eight-Hour Ozone Standard

Procedure:

Step 1. Determine whethersite-specificmonitoring data orrepresentative monitoring data

will be used to obtain an ozone background concentration.

A site-specific monitoring program must last a minimum of at least 4-6 months up to 12

months during the ozone season before the application is submitted. Use the fourthhighest daily maximum 8-hour average ozone concentration monitored during a single

ozone season (1, 2). Or, up to a 3-year average of the annual fourth-highest daily

maximum 8-hour ozone concentration if data are available (3).

"Representative" monitoring data may be available from the ozone network in Texas.

Monitor in a different county: compare population and county-wide point, area, and

mobile source emissions to find a similar county with monitored ozone data. Use the 3-

year average of the annual fourth-highest daily maximum 8-hour ozone concentrations

if data are available (3).

Monitor in the same county: Use the 3-year average of the annual fourth-highest

daily maximum 8-hour ozone concentrations if data are available (3).

If the background concentration equals or exceeds 75 parts per billion (ppb), Step 2

cannot be used and approaches such as the applicant providing offsets or reducing VOC

or NOx emissions for the project below 100 tpy would be considered.

Step 2. Determine whetherthe site is VOC-limited orNOx-limited In VOC-fimited areas

(VOC to NOx ratioslessthan about4:1), minimizing orreducing VOC emissionsisthe most

effective means o{/imiting orlowering ozone concentrations. In NOx-limited areas (VOC to

NOx ratiosgreaterthan about15:1) minimizing orreducingNOx emissionsismost

effective.

Identif'y the total allowable emissions of VOC and NOx in tpy from the site. Include

requested increases from the project.

Multiply the ratio by 2.875. This factor adjusts the ratio to relate the emissions to molar

units consistent with ambient VOCjNOx ratios. It is derived by dividing moles of

methane (CH4) by moles of nitrogen dioxide (NOz).
If the adjusted ratio is 2:1 or less, the site is 03-neutral and the demonstration is

complete since there would not be a significant change to the current ozone levels in

the local area. Ifthe adjusted ratio is greater than 2:1, go on to Step 3.

Step 3. Contact the Ak Dispersion Modeling Team at 512-239-1250 for further guMance.

The applicant should be prepared to present and discuss options. Some options may

include the following:

Transport analysis using windrose andpollution rose data

Analysis of source type, for example low-level fugitive sources of VOC may not

signillcantlyimpact ozone concentrations

References:

(1) 40 CFR 52.21

(2) 40 CFR 58 Appendix D, 40 CFR 81

(3)40 CFR 50 Appendix I

Resources for monitoring and emissions data:

http:((www.epa.gov(oar(data(repsst.html?st-TX- Texas

http://www.tceq.state.tx.us/nav/data/aq_data.html