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Regional background ozone in Texas: Recent research and future needs. Mark Estes a , Shaena Berlin b , Andrew Langford c , Melody Dong d , Jim Smith a , Fernando Mercado a , David Parrish c Presented to AQAST Meeting, Rice University January 16, 2014.

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regional background ozone in texas recent research and future needs

Regional background ozone in Texas: Recent research and future needs

Mark Estesa, Shaena Berlinb, Andrew Langfordc, Melody Dongd, Jim Smitha, Fernando Mercadoa, David Parrishc

Presented to AQAST Meeting, Rice University

January 16, 2014

Texas Commission on Environmental Quality, Austin, TX

Massachusetts Institute of Technology, Cambridge, MA

NOAA ESRL Chemical Sciences Division, Boulder, CO

Dept. of Bioengineering, University of California, San Diego

Air Quality Division

  • Measured background ozone trend on US west coast is upward; linked to increasing Asian emissions (Jacob et al. 1999; Jaffe et al. 1999, 2003; Cooper et al. 2010, 2012; Parrish et al. 2009; Reidmiller 2009; Brown-Steiner and Hess 2011; Lin et al. 2012; Zhang et al. 2008, 2011; Widger et al. 2013; Pfister et al. 2013)
  • Question: What is the regional background ozone trend in HGB and DFW? What factors affect background ozone in the eastern half of Texas?
  • Two methods for estimating background ozone in Houston, PCA and upwind-downwind: Berlin, S., A. Langford, M. Estes, M. Dong, and D. Parrish (2013), Magnitude, decadal changes and impact of regional background ozone transported into the greater Houston, Texas area, Environ. Sci. Technol., 2013, 47 (24), pp 13985–13992, DOI:10.1021/es4037644
  • Seasonal variations in background ozone
  • Transport effects upon background ozone
  • Trends in regional background ozone
  • Both Houston-Galveston and Dallas-Fort Worth
definition of regional background ozone
Definition of regional background ozone
  • For these analyses, regional background ozone is the ozone transported into the area such that local emissions have little influence upon the ozone concentrations.
  • Generally not equivalent to “natural background” or “policy-relevant background.”

Sites outside the red boundary are able to measure background ozone reliably; sites inside often do not, due to influence from local sources.


Estimated HGB background ozone for every day

from April 1, 2000 to October 31, 2012

Median background ozone: 30 ppbv

Mean: 32.6 ppbv

95th percentile: 58 ppbv

Clearly, there are systematic variations in background ozone during the ozone season.


Peak and background ozone are correlated, though correlation is not causation. Conditions suitable for high background are also suitable for high local production (i.e., clear skies, light winds, high temperatures).


Background ozone drops during mid-summer due to transport from the Gulf (Davis et al. 1998; Chan and Vet, 2010; Smith et al. 2013).


Highest concentrations linked to continental flow

Intermediate concentrations linked to coastal flow

Lowest concentrations linked to Gulf of Mexico flow


95thbackground: -0.58 ± 0.19 ppbv/yr (p = 0.011)

50th background: -0.071 ± 0.25 ppbv/yr (p = 0.78)

Flat or downward trend consistent with Cooper (2012), Oltmans (2012), Parrish (2012), and Lefohn (2010, 2013).


Estimated DFW background ozone for every day from April 1, 2001 to October 31, 2012

DFW Median background ozone: 41 ppbv

Mean: 41.3 ppbv

95th percentile: 63 ppbv

HGB Median background ozone: 30 ppbv

Mean: 32.6 ppbv

95th percentile: 58 ppbv


Mean background is almost constant during ozone season; mean local contribution peaks in early August


Flow from DFW gives high ozone.

Flow from E and NE gives high ozone, like HGB, but with somewhat different source regions.

Flow from south gives lower ozone, but not as low as HGB.


Slope of annual median concentration is not significant (p = 0.39); slope of annual 95th percentile concentration is significant (p = 0.038).

  • Regional background ozone concentration trends are flat or decreasing in both HGB and DFW. The increase observed on the US west coast due to Asian emissions is not apparent in eastern Texas.
  • In both cities, background ozone varies with transport pattern, especially in Houston. In Houston, background ozone trends vary with transport direction, with flow from the Gulf of Mexico having zero trend, and flow from continental US having a downward trend (Berlin et al. 2013).
  • Regional background ozone in DFW is on average higher than in HGB.
  • Peak daily 8-hour ozone concentrations in Houston and DFW are positively correlated with regional background ozone.
  • In Houston, background and local ozone vary with season; highest total ozone tends to occur when both peak. In DFW, background ozone is nearly constant; local contribution and total ozone peak in early August.
  • Analyses imply that much of the seasonal ozone variation is contributed by large-scale spatial and temporal patterns.
future needs
Future needs
  • This analysis focuses upon averages, not case studies or exceptional events. Studies of days with high regional background ozone and/or high local ozone production would be useful.
  • Quantifying sources of regional background ozone: within Texas, within US, outside US, natural and anthropogenic. Quantifying the effects of changes in precursor emissions. Quantifying the effects of different meteorological patterns.
  • Improved modeling of regional background ozone, both over ocean and over land—in general, models are overpredictingbackground ozone.
contact information
Contact information
  • (512) 239-6049
method details background ozone estimation at upwind sites
Method details: Background ozone estimation at upwind sites
  • Select sites in the Houston area that are capable of measuring background ozone, given the proper conditions. These sites are not located near large emission sources
  • Calculate peak daily 8-hour ozone for each site.
  • Select the minimum peak daily 8-hour ozone from the subset of background sites.
  • Ozone season defined as April 1 – Oct 31.
  • Number of sites selected varied from 6 to 19, greatly increasing after 2002.

85 ppbv NAAQS

75 ppbv NAAQS

*2013 DV not finalized


95th MDA8: -2.33 ± 0.40 ppbv/yr, p = 0.00012

50th MDA8: -0.64 ± 0.33 ppbv/yr, p = 0.077


95th local: -1.76 ± 0.26 ppbv/yr, p = 0.000029

50th local: -0.60 ± 0.18 ppbv/yr, p = 0.0062


(a) Trends in the highest MDA8 O3 reported by one of the 6 CAMS stations used in the PCA analysis (Max 6 CAMS) and by all HGB CAMS (Max HGB). The number of ozone exceedance days (2008 NAAQS) at the 6 CAMS stations is also shown.

(b) and (c) Trends in mean MDA8 ozone and background and local contributions from the 6-station PCA and the TCEQ methods, respectively. The solid lines indicate the linear least-squares fits; the parameters of the fits with 95% confidence intervals are annotated.


Slope of annual median peak ozone is not significant (p = 0.57); slope of annual 95th percentile peak ozone is significant (p = 0.0062), as is the slope of annual maximum peak ozone (p = 0.0054).

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