Weather Makes a Difference: 8-hour Ozone Trends for 1997-2005 State and Local Information for EPA Region 6


Weather Makes a Difference: 8-hour
Ozone Trends for 1997-2007

State and Local Information for EPA Region 6

Arkansas
Louisiana
Oklahoma
Texas

Composite trend for available sites in these states:

EPA Region 06 (selected sites)

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2004 2006

Year

U.S. Environmental Protection Agency

Office of Air and Radiation

Office of Air Quality Planning and Standards

April 2008

-------
Arkansas
Ozone

On average, ozone adjusted for weather conditions declined 13 percent between 1997 and
2007. These improvements in ozone are in response to both state and regional reductions
in NOx and VOC emissions. The level of ozone improvement varies from site to site.

Trends for 1997-2007 for rural sites and urban areas with complete ozone and
meteorology data are presented below. Ozone season (May 1 - September 30) averages
of daily maximum 8-hour ozone were adjusted to remove the influence of year-to-year
variability in weather conditions. The dotted line shows the trend in observed values at
monitoring sites, while the solid line illustrates the underlying ozone trend after removing
the effects of weather. The solid line serves as a m ore accurate ozone trend for assessing
changes in emissions. Typical weather conditions are determined by averaging
conditions (e.g., temperature, humidity, etc.) for the time period presented. The
information provided is useful for reviewing the weather influence for a particular ozone
season. The solid line represents ozone levels anticipated under typical weather
conditions.

Seasonal Average 8-hour Ozone Trends

Little Rock, AK 8-hr Ozone Trends

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Caddo Valley, AR

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1998

2000

2002
Year

2004

2006

-------
Louisiana

Ozone

On average, ozone adjusted for weather conditions declined 15 percent between 1997 and
2007. These improvements in ozone are in response to both state and regional reductions
in NOx and VOC emissions. The level of ozone improvement varies from site to site.

Seasonal Average 8-hour Ozone Trends

New Orleans, LA 8-hr Ozone Trends

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— Adjusted for Weather
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1998

2000

2002
Year

2004

2006

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Baton Rouge, LA 8-hr Ozone Trends

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1998

2000

2002
Year

2004

2006

-------
Oklahoma

Ozone

On average, ozone adjusted for weather conditions declined 11 percent between 1997 and
2007. Ozone trends vary from site to site.

Trends for 1997-2007 for rural sites and urban areas with complete ozone and
meteorology data are presented below. Ozone season (May 1 - September 30) averages
of daily maximum 8-hour ozone were adjusted to remove the influence of year-to-year
variability in weather conditions. The dotted line shows the trend in observed values at
monitoring sites, while the solid line illustrates the underlying ozone trend after removing
the effects of weather. The solid line serves as a more accurate ozone trend for assessing
changes in emissions. Typical weather conditions are determined by averaging
conditions (e.g., temperature, humidity, etc.) for the time period presented. The
information provided is useful for reviewing the weather influence for a particular ozone
season. The solid line represents ozone levels anticipated under typical weather
conditions.

Seasonal Average 8-hour Ozone Trends

Tulsa, OK 8-hr Ozone Trends

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Unadjusted for Weather

1998

2000

2002
Year

2004

2006

-------
Oklahoma City, OK 8-hr Ozone Trends

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Adjusted for Weather

Unadjusted for Weather

1998

2000

2002
Year

2004

2006

-------
Texas
Ozone

On average, ozone adjusted for weather conditions declined 6 percent between 1997 and
2007. There have been improvements in Dallas and Houston in recent years. These
improvements in ozone are in response to both state and regional reductions in NOx and
VOC emissions. Ozone trends vary from site to site.

Trends for 1997-2007 for rural sites and urban areas with complete ozone and
meteorology data are presented below. Ozone season (May 1 - September 30) averages
of daily maximum 8-hour ozone were adjusted to remove the influence of year-to-year
variability in weather conditions. The dotted line shows the trend in observed values at
monitoring sites, while the solid line illustrates the underlying ozone trend after removing
the effects of weather. The solid line serves as a more accurate ozone trend for assessing
changes in emissions. Typical weather conditions are determined by averaging
conditions (e.g., temperature, humidity, etc.) for the time period presented. The
information provided is useful for reviewing the weather influence for a particular ozone
season. The solid line represents ozone levels anticipated under typical weather
conditions.

Seasonal Average 8-hour Ozone Trends

San Antonio, TX 8-hr Ozone Trends

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Cl

0 80
c
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cd 60

-------
Austin, TX 8-hr Ozone Trends

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Dallas, IX 8-hr Ozone Trends

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Adjusted for Weather

Unadjusted for Weather

1998

2000

2002
Year

2004

2006

-------
Houston, TX 8-hr Ozone Trends

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1998

2000

2002
Year

2004

2006

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