1. Spatial and Temporal Variability in OMI NO 2 Observations and NO x Emissions Inventories in Eastern Texas Elena McDonald-Buller, Gary McGaughey, Yosuke Kimura, Mike Feldman, and David T. Allen Center for Energy and Environmental Resources The University of Texas at Austin Air Quality and Applied Sciences Team 6 th Semi-Annual Meeting January 15-17, 2014

2. Study Objectives Examine spatial and temporal trends in OMI tropospheric NO 2 column densities over eastern Texas sub-regions during 2005-2010. Compare relative changes in OMI NO 2 tropospheric column densities to those of ground-level NO 2 concentrations across the Dallas/Fort Worth and Houston-Galveston- Brazoria/Beaumont-Port Arthur areas during 2005-2010. Compare observed NO 2 trends between 2006-2010 to NO x emissions inventories for 2006 and 2012.

3. Datasets Tropospheric NO 2 Columns – Retrieved from OMI – Version 2.0.1 of DOMINO product http://www.temis.nl/index.php http://www.temis.nl/index.php – 1300 to 1400 LST; 2005-2010 – Criteria to retain data considered spatial location, product flags for row anomaly and cloud interference, surface albedo Ground-level NO 2 Concentrations – Hourly AQS measurements from TCEQ:http://www.tceq.texas.gov/a gency/data/aq-data.htmlhttp://www.tceq.texas.gov/a gency/data/aq-data.html – Dallas and Houston at 1300 LST; 2005-2010 Bottom-up NO x Inventories for June 2006 and 2012 – Developed by TCEQ in support of Dallas/Fort Worth SIP 10 Geographic Sub-Regions in Eastern Texas

4. Annual Mean of Monthly Average OMI Tropospheric NO 2 Column Densities 2006 (left) and 2010 (right)

5. Annual OMI Tropospheric NO 2 Column Densities in Dallas and Houston: 2005-2010 Box and whisker plot: horizontal bar represents the median, the box represents the 25 th and 75 th percentiles, and the whiskers represents the 5 th and 95 th percentiles. Annual Mean

6. Annual OMI Tropospheric NO 2 Column Densities in Austin/San Antonio, Tyler/Longview/Marshall/Corpus Christi/Victoria : 2005-2010 Box and whisker plot: horizontal bar represents the median, the box represents the 25 th and 75 th percentiles, and the whiskers represents the 5 th and 95 th percentiles. Annual Mean

7. Annual Mean OMI Tropospheric NO 2 Column Densities and Surface NO 2 Concentrations in DFW (left) and HGB/BPA (right): 2005-2010 Reductions between 2005 and 2010: DFW: 27% (OMI); 33% (surface) HGB/BPA: 15% (OMI); 19% (surface)

8. Daily Average NO x Emissions (tons/km 2 /day) and Relative Changes Between 2006 and 2012 by Eastern Texas Sub-Regions and Emissions Source Categories

9. Relative Changes in Annual Mean OMI Tropospheric NO 2 Column Densities (2006-2010) and in Average Daily NO x Emissions (2006- 2012) in Eastern Texas Sub-Regions (For DFW and HGB/BPA, relative changes in annual mean NO 2 at ground monitors (2006-2012) also shown)

10. Summary Spatial and temporal trends in OMI tropospheric NO 2 column densities were investigated for eastern Texas: – Between 2005 and 2010, NO 2 column densities declined over most eastern Texas areas, with pronounced reductions in the Dallas and Houston areas. – Annual average NO 2 concentrations across ground monitoring sites in DFW and HGB-BPA also declined. Relative changes in NO x emissions from mobile sources and, in certain sub-regions, oil and gas production activities are projected to be substantial between 2006 and 2012. Comparisons between inventories and observations suggest the need for further investigations in sub-regions outside of DFW and HGB/BPA – What are the uncertainties in these inventories? – Surface monitoring networks are not as dense; utility in using satellite observations to support analyses of air quality trends (e.g. top-down emissions estimates for informing emissions inventories) – Inter-comparisons among satellite data products