|
|
WHAT IS OZONE?
|
|
|
|
Ozone is formed in a photochemical reaction process. Other pollutants act on oxygen
at the earth's surface on warm days and in the presence of ultraviolet radiation to produce ground level ozone.
|
|
Source: Texas Air Control Board, Air Quality in Texas: Twenty Years
of Environmental Protection (1992), 8.
|
|
In the upper atmosphere, ozone (O3), an oxygen molecule with three, rather than two, oxygen atoms,
forms a layer that filters out ultraviolet radiation from the sun. Concern about the thinning of the atmospheric ozone layer has led to bans on the use of certain
chemicals, such as chlorinated fluorocarbons, that may destroy ozone.
Though atmospheric ozone helps sustain life, ozone formed near the ground may adversely affect plants,
animals, and humans. Ozone is produced when reactive hydrocarbons known as volatile organic compounds (VOCs) combine with nitrogen oxides and oxygen in the
presence of sunlight. Ozone problems are most common in the hot summer months because the warm air and sunlight speed ozone formation.
High levels of ozone can have serious human health effects. Ozone reacts with lung tissue and can cause
breathing problems, including an increased susceptibility to respiratory infection. Ozone may increase the risk of
asthma. For unknown reasons, about 10 to 20 percent of the population, sometimes referred to as "responders," are
especially sensitive to high ozone concentrations. This group, along with people with pre-existing respiratory diseases
and people who exercise outdoors, are particularly at risk from high ozone levels.*
People with asthma, chronic bronchitis, and emphysema in Texas are at risk of adverse health effects if they are
exposed to levels of ozone that have exceeded the national ambient air quality standards.* High ground levels of ozone
can also have negative environmental effects. High levels are believed to affect vegetation, including urban
ornamentals, crops, and forestry production, by damaging the cell walls of plants. In 1987 the East Texas Intensive
Research Site was established near Nacogdoches to investigate how pollutants affect the development of one- to
four-year-old shortleaf pines along coastal plains. The study subjected some trees to persistent exposure to ozone, and the trees showed loss of needles, stunted growth, and fewer stems.* Ozone also limits visibility in cities and national parks.
There are four major metropolitan areas in Texas which consistently have exceeded the one-hour ozone standards
(Houston/Galveston/Brazoria, Dallas/Fort Worth, El Paso and Beaumont/Port Arthur, while --during the 1990s-- the
Tyler/Longview/Marshall area has also exceeded standards. The Houston-Galveston-Brazoria metropolitan area reports
the highest number of days exceeding ozone standards in Texas. In general, the four metropolitan areas exceeding
standards have shown a decline over the past 20 years in the number of days exceeding national standards. In the
Houston-Galveston-Brazoria metropolitan area, however, the number of days first declined, rose again during the late
1990s and has since declined. On some years, Houston has even had more days exceeding the ozone standard than Los Angeles, the perennial leader.* In addition to the five metropolitan areas mentioned, other large Texas cities have
generally met the ozone standards since the early 1980s. Several of these metropolitan areas came close to violating
standards in the 1990s, although no metropolitan areas came close to matching Houston's highest ozone average.
|
NUMBER OF DAYS EXCEEDING ONE HOUR OZONE STANDARD, 1985-2000
|
|
|
'85
|
'86
|
'87
|
'88
|
'89
|
'90
|
'91
|
'92
|
'93
|
'94
|
'95
|
'96
|
'97
|
'98
|
'99
|
'00
|
'01
|
'02
|
'03
|
|
Dallas / Fort Worth
|
18
|
11
|
11
|
9
|
4
|
7
|
7
|
4
|
4
|
9
|
15
|
4
|
12
|
5
|
10
|
5
|
2
|
6
|
5
|
|
Tyler / Longview
|
1
|
0
|
0
|
0
|
0
|
2
|
0
|
1
|
1
|
0
|
4
|
0
|
1
|
5
|
4
|
4
|
0
|
0
|
0
|
|
El Paso
|
10
|
11
|
12
|
6
|
10
|
4
|
5
|
5
|
4
|
6
|
4
|
4
|
3
|
2
|
1
|
1
|
1
|
3
|
1
|
|
Beaumont / Port Arthur
|
0
|
8
|
3
|
7
|
9
|
5
|
9
|
5
|
0
|
2
|
8
|
0
|
3
|
4
|
3
|
4
|
2
|
3
|
4
|
|
Houston / Brazoria/ Galveston
|
58
|
48
|
54
|
59
|
37
|
52
|
37
|
28
|
28
|
30
|
56
|
28
|
50
|
38
|
41
|
40
|
31
|
24
|
30
|
|
San Antonio
|
0
|
1
|
1
|
1
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
2
|
0
|
2
|
0
|
0
|
0
|
2
|
0
|
|
Austin
|
2
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
Corpus Christi
|
0
|
0
|
2
|
0
|
0
|
1
|
0
|
0
|
1
|
1
|
1
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
0
|
|
Source: Texas Commission on Environmental Quality, High Ozone Averages, Available on Website, Accessed October 2003.
|
|
|
