Modeling Guidance and Examples for Commonly Asked Questions (Part 1) Rachel Melton and Matthew Kovar Air Permits Division Texas Commission on Environmental Quality Advanced Air Permitting Seminar 2014

Agenda Representative Background Monitor: – Selecting/Justifying a Representative Monitor – Calculating the Design Value 1-hr NO 2 NAAQS: – Treatment of Intermittent Emissions – Tier 3 Options for NO x -to-NO 2 Conversion

Purpose of a Representative Monitor The purpose of a representative monitor is to estimate existing ambient air quality at the project site and in areas which may be affected by emissions from the project.

What Is a Representative Monitor? A monitor that can capture nearby sources not explicitly modeled in an air dispersion modeling analysis – Nearby sources may include: mobile sources & non-stationary sources natural sources & unidentified sources

Selecting a Representative Monitor Factors to consider: – proximity of the monitor to the project site; – similarity of topography, meteorology, and land-use for the project and monitor site; – stationary source types and amount of emissions around the monitor compared to the project site; – emissions from mobile or other non-stationary source activities; and – meets completeness criteria

Resources for Selecting a Representative Monitor EPA AirData EPA Design Values Texas Air Monitoring Information System (TAMIS) Yearly Summary Reports

Justifying a Representative Monitor The applicant must justify why the monitoring data selected are representative of the existing air quality in the area of the project site – Qualitative assessment – Quantitative assessment

Qualitative Assessment: Monitor site relative to project site Proximity, topography, and land-use: – aerial photography Meteorology: – prevailing winds / influential sources

Quantitative Assessment: Monitor site relative to project site Population Harris County Jefferson County County wide comparison: – population – emissions: » similar source categories » mobile & other non-stationary source Houston Deer Park #2 monitor, highlighted RNs within 10kms Nearby emissions (10 km) comparison: Nearby emissions (10 km) comparison: – quantify emissions for RNs near the project site and monitor site

Example Project site Site located near Port Arthur in Jefferson County adjacent to various industrial sites; 786 TPY of reported PM 2.5 emissions near the site.

Example PM 2.5 monitor for use as a background The background monitor located in Harris County near Galveston Bay in a residential area with only a few industrial sites nearby; 282 TPY of reported PM 2.5 emissions near the monitor.

Example PM 2.5 monitor for use in justifying the SIL The monitor for SIL justification located in Harris County near industrial sites; 2765 TPY of PM 2.5 near the monitor.

Determine the Monitored Design Value EPA Completeness Criteria The representative background concentration should be in the form of the standard: Exceedance-based: – Example 1-hr CO:  H2H from most recent year Statistically-based: – Example 1-hr NO 2 :  3-year average of the 98 th percentile of the annual distribution of maximum daily 1-hr concentrations

Contact Information Rachel Melton – Air Dispersion Modeling Team – (512) – Matthew Kovar – Air Dispersion Modeling Team – (512) – Air Permits Division (512) Rachel Melton Air Permits Division (512) Matthew Kovar