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
a.
b.
c.
d.
Air Quality Division
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
Introduction
• 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; BrownSteiner 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?
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Outline
• Two methods for estimating background
ozone in Houston, PCA and upwinddownwind: 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
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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.”
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Sites outside the red boundary are able to measure background ozone
reliably; sites inside often do not, due to influence from local sources.
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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.
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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).
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Background ozone drops during mid-summer due to transport from the
Gulf (Davis et al. 1998; Chan and Vet, 2010; Smith et al. 2013).
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Highest
concentrations
linked to
continental flow
Intermediate
concentrations
linked to coastal
flow
Lowest
concentrations
linked to Gulf of
Mexico flow
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95th background: -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).
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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
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Mean background is almost constant during ozone season; mean local
contribution peaks in early August
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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.
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Slope of annual median concentration is not significant (p = 0.39);
slope of annual 95th percentile concentration is significant (p = 0.038).
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Conclusions
•
•
•
•
•
•
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.
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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 overpredicting background
ozone.
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Contact information
• Mark.Estes@tceq.texas.gov
• (512) 239-6049
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Additional slides
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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
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95th MDA8: -2.33 ± 0.40 ppbv/yr, p = 0.00012
50th MDA8: -0.64 ± 0.33 ppbv/yr, p = 0.077
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95th local: -1.76 ± 0.26 ppbv/yr, p = 0.000029
50th local: -0.60 ± 0.18 ppbv/yr, p = 0.0062
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(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.
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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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