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Two neighboring pines of the same species respond differently to ozone, exhibiting genetic variability. The pine on the left shows needle damage from ozone and the one on the right appears healthy.
© NPS photo
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Ozone is made of three joined oxygen atoms, and it
is found both in the Earth's upper atmosphere and at
ground level. Ozone can be helpful or harmful,
depending on where it is found:
Good ozone occurs naturally
in the Earth's upper atmosphere (stratosphere)-
10 to 30 miles above the Earth's surface - where
it shields us from harmful ultraviolet rays.
Bad ozone forms near the
ground (troposphere) when pollutants from cars,
power plants, and other sources react chemically.
Sunlight provides the energy that drives this
chemical reaction, so the amount of ozone in the
atmosphere is highest on summer afternoons.
Ozone may be the most damaging pollutant here.
Individual ponderosa and Jeffrey pine trees that are
ozone-sensitive show extensive injury to their
foliage at present ozone levels. For example, one
study found that nearly 90% of Jeffrey pines in or
near the Giant Forest showed visible signs of ozone
injury. Compared to ozone-resistant individuals,
ozone-sensitive pines have lower photosynthetic
rates, lose their needles earlier, and have
diminished annual ring growth. In contrast to pines,
mature giant sequoias seem to be relatively resistant
to present ozone levels. However, newly emerged
sequoia seedlings are suspected to be more vulnerable
to ozone injury.
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These pine needles demonstrate chlorotic mottling (or a yellowing effect), characteristic of ozone damage. Ozone damages chlorophyll in the needles, reducing or destroying their ability to photosynthesize (or make food for the plant).
© NPS photo
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We humans are very
vulnerable to ozone damage too. It can irritate the
human respiratory system causing coughing, irritation
in the throat, and/or an uncomfortable sensation in
the chest. The elderly and those with pre-existing
respiratory problems (e.g. asthma, bronchitis) are
more vulnerable to these effects.
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A technician collects data at the air quality monitoring site on the western edge of Giant Forest in Sequoia National Park.
© NPS photo
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For further information, visit the Environmental
Protection Agency AirNow Web Site.
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