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How Ozone Pollution Works
A) The weather report on the radio or TV tells you that it is going to be
sunny and hot and that an orange ozone alert has been issued. What is ozone?
What does an orange alert mean? Why should you be concerned about it? In this
article, we will examine what ozone is, how it is produced, what health hazards
it poses and what you can do to reduce ozone pollution.
B) Ozone is a molecule of three oxygen atoms bound together (O3). It is
unstable and highly reactive. Ozone is used as a bleach, a deodorizing agent,
and a sterilization agent for air and drinking water. At low concentrations, it
is toxic. Ozone is found naturally in small concentrations in the stratosphere,
a layer of Earth’s upper atmosphere. In this upper atmosphere, ozone is made
when ultraviolet light from the sun splits an oxygen molecule (O2), forming two
single oxygen atoms. If a freed atom collides with an oxygen molecule, it
becomes ozone. Stratospheric ozone has been called “good” ozone because it
protects the Earth’s surface from dangerous ultraviolet light.
C) Ozone can also be found in the troposphere, the lowest layer of the
atmosphere. Tropospheric ozone (often termed “ bad ” ozone) is man - made, a
result of air pollution from internal combustion engines and power plants.
Automobile exhaust and industrial emissions release a family of nitrogen oxide
gases (NOx) and volatile organic compounds (VOC), by-products of burning
gasoline and coal. NOx and VOC combine chemically with oxygen to form ozone
during sunny, high- temperature conditions of late spring, summer and early
fall. High levels of ozone are usually formed in the heat of the afternoon and
early evening, dissipating during the cooler nights.
D) Although ozone pollution is formed mainly in urban and suburban areas,
it ends up in rural areas as well, carried by prevailing winds or resulting from
cars and trucks that travel into rural areas. Significant levels of ozone
pollution can be detected in rural areas as far as 250 miles downwind from urban
industrial zones.
E) You can make ozone test strips to detect and monitor ozone levels in
your own backyard or around your school. You will need corn starch, filter paper
(coffee filters work well) and potassium iodide (can be ordered from a science
education supplier such as Carolina Biological Supply or Fisher Scientific).
Basically, you make a paste from water, corn starch and potassium-iodide, and
you paint this paste on strips of filter paper. You then expose the strips to
the air for eight hours. Ozone in the air will react with the potassium iodide
to change the color of the strip. You will also need to know the relative
humidity, which you can get from a newspaper, weather broadcast or home weather
station.
F) When you inhale ozone, it travels throughout your respiratory tract.
Because ozone is very corrosive, it damages the bronchioles and alveoli in your
lungs, air sacs that are important for gas exchange. Repeated exposure to ozone
can inflame lung tissues and cause respiratory infections.
G) Ozone exposure can aggravate existing respiratory conditions such as
asthma, reduce your lung function and capacity for exercise and cause chest
pains and coughing. Young children, adults who are active outdoors and people
with respiratory diseases are most susceptible to the high levels of ozone
encountered during the summer. In addition to effects on humans, the corrosive
nature of ozone can damage plants and trees. High levels of ozone can destroy
agricultural crops and forest vegetation.
H) To protect yourself from ozone exposure, you should be aware of the Air
Quality Index (AQI) in your area every day—you can usually find it in the
newspaper or on a morning weather forecast on TV or radio. You should also be
familiar with the U.S. Environmental Protection Agency (EPA) guide for
ozone-alert values.
I) What do the numbers in the AQI mean? The AQI measures concentrations of
five air pollutants: ozone, sulfur dioxide, particulate matter, carbon monoxide
and nitrogen dioxide. The EPA has chosen these pollutants as criteria
pollutants, but these are not all of the pollutants in the air. These
concentrations are compared to a standard set out in federal law. An index value
of 100 means that all of the criteria pollutants are at the maximum level that
is considered safe for the majority of the population. To reduce your exposure
to ozone, you should avoid exercising during afternoon and early evening hours
in the summer.
J) There are several ways you can help to decrease ozone pollution. Limit
using your automobile during afternoon and early evening hours in the late
spring, summer and early fall. Do not use gasoline-powered lawn equipment during
these times. Do not fuel your car during these times. Do not light fires or
outdoor grills during these times. Keep the engine of your car or boat tuned.
Make sure that your tires are properly inflated. Use environmentally safe
paints, cleaning and office products (some of these chemicals are sources of
VOC).
K) Besides personal attempts to reduce ozone pollution, the EPA has
initiated more stringent air-quality standards (such as the Clean Air Act and
its modifications) to reduce air pollution. Compliance with these standards by
industries, manufacturers and state and local governments has significantly
reduced the levels of many common air pollutants.
L) With continued conservation and reduction practices, adherence to
ozone-pollution warnings, research and government regulation, ozone-pollution
levels should
continue to fall. Perhaps future generations will not be threatened by this
environmental pollutant.
M) The thing that determines whether ozone is good or bad is its location.
Ozone is ‘‘good，，when it is in the stratosphere. The stratosphere is a layer of
the atmosphere starting at the level of about 6 miles (about 10 kilometers)
above sea level. The stratosphere naturally contains about six parts per million
of ozone, and this ozone is very beneficial because it absorbs UV radiation and
prevents it from reaching us.
N) Ozone is “bad” when it is at ground level. Ozone is a very reactive gas
that is hard on lung tissue. It also damages plants and buildings. Any ozone at
ground level is a problem. Unfortunately, chemicals in car exhaust and chemicals
produced by some industries react with light to produce lots of ozone at ground
level. In cities, the ozone level can rise to a point where it becomes hazardous
to our health. That’s when you hear about an ozone warning on the news.
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发表于 2018-5-31 22:48:19