|
What About
the Ozone Layer ???
I thought ozone was
helpful.
The
ozone layer is great - when it's way up there.
The
ozone layer protects life on earth from the sun's harmful ultraviolet
rays. But the ozone layer is 10 - 30 miles above the earth; this is far
above the air that we breathe. This protective shield becomes weaker when
certain gases are able to travel to the ozone layer and destroy the ozone
molecules. These destructive gases come from products like refrigerators,
air conditioners, cleansers, and aerosol cans (used for spray paint and
hairspray). The gases are called halons and CFCs - for chlorofluorocarbons.
Closer
to earth, ozone is an air pollutant that can be harmful. It is created and
hangs around in the layer of air near the ground (from 0 to 10 miles
high); where it affects everything it comes in contact with.
Things
That Affect Ozone Levels
The
amount of ingredient gases.
More
ingredient gases (VOC's and NO2) can mean more ozone.
Towns and cities that have more traffic or more industrial plants have a
higher potential for ozone formation, especially towns that also
experience many warm sunny days with little wind.
Weather
and Seasons: warm sunny days mean more ozone.
Since
sunlight and heat are the engines that drive ozone formation, warm sunny
days should have more ozone than cool or cloudy days. Wind can also play a
role. On windy days the wind can disperse the ozone, causing levels to
drop. Ozone pollution can be especially bad during summer heat waves when
the air does not mix very well and air pollution doesn't disperse.
Time
of Day: ozone levels build during the day.
On
a clear day, ozone levels can continue to rise all day long, and then
decrease rapidly after sunset. Since heat, sunlight, the ingredient gasses
each usually increase during the day, ozone formation also increases. When
the sun goes down, there is no energy for ozone formation and fewer
ingredient gases - so ozone levels drop.
Ozone
and Your Health
Why
ozone can hurt.
The
properties that make ozone a powerful cleaner, disinfectant, and bleaching
agent also make ozone dangerous to living tissues.
When
it comes in contact with living tissues, like our lungs, ozone attacks and
damages cells lining the airways, this causes swelling and inflammation.
Some
have compared ozone's effect to a sunburn ... inside your lungs.
|
Other health effects
include:
·
Irritation of the airway: a cough, an irritated throat, or
an uncomfortable feeling in your chest.
·
Reduced lung function: you may not be able to breath as
deeply or vigorously as you normally would.
·
Worsened Asthma: ozone can aggravate the effects of asthma
(see Asthma below).
·
Potential health effects: ozone may aggravate the effects
of emphysema and bronchitis, and may reduce the body's ability to
fight infections in the respiratory system.
|
Who
should watch out for ozone?
High
ozone levels can affect anyone.
Some
groups of people are particularly sensitive to ozone.
|
Sensitive Groups
·
Children
They spend more time outdoors, are more active, and their airways
are not fully developed.
·
Adults
exercising outdoors
Healthy persons engaged in physical activity breathe faster and
more deeply. This increases the amount of ozone flowing into the
lungs.
·
People
with respiratory disease
Ozone can further irritate the airways of persons who already have
diseases of the lung or airways.
|
Summertime
can be ozone time.
First,
there may be more ozone around. During the summer months high temperatures
and bright sunshine lead to increased ozone formation. Second, people may
spend more time outside engaged in physical activities.
Asthma
and ozone.
Ozone
can irritate the already sensitive airway of someone with asthma. When
ozone levels are high, more asthmatics have asthma attacks that require a
doctor's attention or the use of additional medication. One reason this
happens is that ozone makes people more sensitive to allergens, which are
the most common triggers for asthma attacks. (Allergens come from dust
mites, cockroaches, pets, fungus, and pollen.) Also, asthmatics are more
severely affected by the reduced lung function and irritation to the
respiratory system caused by ozone.
Ozone
-- Air Quality Index (AQI) and Health Concerns
Air Quality Index Values
|
|
Air Quality Descriptor
|
Health Effects
|
|
0 to 50
|
|
Good
|
No health effects are expected.
|
| |
|
51 to 100*
|
|
Moderate
|
Unusually sensitive individuals may experience respiratory effects from prolonged outdoor exertion if you are unusually sensitive to ozone.
|
| |
|
101 to 150
|
|
Unhealthy for Sensitive Groups
|
Member of sensitive group may experience respiratory symptoms (coughing, pains when taking a deep breath).
|
| |
|
151 to 200
|
|
Unhealthy
|
Member of sensitive group have higher chance of experiencing respiratory symptoms (aggravated cough or pain), and reduces lung function.
|
| |
|
201 to 300
|
|
Very Unhealthy
|
Members of sensitive groups experience increasingly severe respiratory symptoms and impaired breathing.
|
| |
* Generally, an AQI of 100 for ozone corresponds
to an ozone level of 0.075 parts per million (averaged over 8 hours).
|
|
Ozone
Concentrations and Your Health
Two of the most important factors are the concentration of ozone and duration of exposure. Numerous epidemiological studies show the relationship between health effects and specific ozone ranges. EPA has gathered information about health effects through research, studies comparing health statistics and ozone levels in the communities, and controlled testing of human volunteers.
The EPA has developed the Air Quality Index (AQI) for reporting the levels of ozone and other pollutants, and their effects on human health. The AQI scale has been divided in different categories, which range from 0 to 300. Each category corresponds to a different health impact (Table1). The NAAQS for ozone are 0.120 ppm averaged over 1 hour (Applies only in limited areas) and 0.075 ppm averaged over 8 hours.
0.116 (8-h) TO 0.404 (1-h) ppm (VERY UNHEALTHY)
At ozone concentrations from 0.116 to 0.404 ppm, sensitive people experience severe respiratory symptoms and impaired breathing.
Recent studies of humans exposed to these ozone concentrations have shown pulmonary function impairment during heavy exercise (7). Another study, conducted in Mexico City, shows that exposures from 0.170 to 0.250 ppm 1-h, increase the occurrence of respiratory symptoms, such as cough, phlegm, difficulty in breathing, and reduce PEFRs among children with mild asthma (2). In addition, ozone exposure to 0.30 ppm 1-h induces lower airway inflammation. This is manifested by PMN influx measured by bronchoalveolar lavage (3). Also, at this concentration with continuous exercise, FEV1 decreases.
0.096 to 0.115 ppm (UNHEALTHY)
1 HOUR EXPOSURE. A study conducted in Atlanta indicated that when the maximum 1-h ozone level equaled or exceeded 0.110 ppm, the number of emergency visits to the hospital for asthma or reactive airway disease increased in children. During this exposure, many children and adults progressively developed substernal pain on deep inspiration, coughing, and reduction of vital capacity and FEV1 (1). Other studies have associated 0.100 ppm ozone concentrations with increased respiratory hospital admission in elderly (12).
8 HOURS EXPOSURE. Reduction in lung function is observed with exposures of <0.12 ppm over 6-8 hours with moderate exercise, manifested by decrements in FEV1. (4,5). Also, 0.100 ppm ozone induces neutrophilic influx into the airway and resulting inflammation, and a decrease in forced expiratory volume (FEV1) and PEFR in asthmatic people (children and adults).
0.076 TO 0.095 ppm (UNHEALTHY FOR SENSITIVE GROUPS)
1 HOUR EXPOSURE. Sensitive people, active children and adults, and people with respiratory disease under
heavy outdoor exertion, may experience respiratory symptoms such as coughing or pain when taking a deep breath, and reduced lung function. However, in a study of 154 children aged
10-12 years in Tennessee, 0.078 ppm of ozone was associated with
decrements in FEV1 and FEF25-75 (5), and with 0.082 ppm an increase in
asthma-related hospitals visits was observed.
8 HOUR EXPOSURE.
In accordance with
AQI, sensitive people, active children and adults, and people with respiratory disease under prolonged outdoor exertion, may experience respiratory symptoms such as coughing or pain when taking a deep breath, and reduced lung function, which can cause some breathing discomfort.
A series of studies conducted in the USA (1,3,6) demonstrated that with 0.09 ppm ozone, the number of hospital visits for asthma increased and people undergoing moderate exercise increased their sensitivity to ozone.
In
addition, other studies (1,6,8) have demonstrated that ozone
concentrations at 0.080 ppm produce adverse effects on human health such
as PEFR decrements in asthmatic children (6), decrements in FEV1 with
intermittent exercise in healthy men (5,7), and increased hospital visits
for asthma (1,8).
0.060
to 0.075 ppm (MODERATE)
1 HOUR
EXPOSURE. In this specific range, based on the AQI standards, ozone
health effects are not expected. However, a study in Mexico suggests that
0.065 ppm ozone increases respiratory symptoms in asthmatic children. (5).
8 HOURS EXPOSURE. Sensitive people may experience respiratory
effects from prolonged exposure to ozone during outdoor exertion.
to 0.059 ppm (GOOD)
In accordance with NAAQS and AQI, at ozone levels from 0.000 to 0.059 no
health effects are expected and the air quality is considered
"GOOD". However, recent studies have demonstrated that at these
concentrations ozone can exert adverse health effects.
1 HOUR EXPOSURE. A study conducted in Brisbane, Australia by
Simpson et al. demonstrated an association between 0.030 ppm ozone and
daily mortality in the elderly (11). In a study in Mexico, the
relationship between ozone exposure in asthmatic children (5-13 years of
age) and mild asthma was evaluated. Exposure to 0.050 ppm increased the
occurrence of lower respiratory symptoms such as cough, phlegm and
difficulty breathing, and reduced PEFRs. (5).
8 HOURS EXPOSURE. No information available.
24 HOURS EXPOSURE. Sartor and co-authors (1994) analyzed low levels
of ozone and daily mortality in Belgium. This study demonstrated a
relationship between 0.050 ppm ozone, high temperatures, and the number of
daily deaths (9). An increase in elderly deaths with 0.034 ppm for 24-h
was also observed (9, 11). Schwartz utilized Medicare records for the
years 1986-1989 to study the association between ozone concentrations and
respiratory admissions among elderly. In this study a significant
relationship was observed between 0.050 ppm 24-h ozone concentration and
hospital admission for pneumonia. (12).
REFERENCES
White, M.C., et al. Exacerbations of childhood asthma and ozone pollution
in Atlanta. Environmental Research. 65: 56-58, 1994.
Romieu, I., et al. Effects of intermittent ozone exposure on peak
expiratory flow and respiratory symptoms among asthmatic children in
Mexico City. Archives of environmental health 52:5 Sep/Oct 1997. 368-375.
Frisher, T.M. et al. Ambient ozone causes upper airways inflammation in
children. American Review of Respiratory Disease. 148: 961-964, 1993.
Gielen, M.H., et al. Acute effects of summer air pollution on respiratory
health of asthmatic children. American Journal of Respiratory and Critical
Care Medicine. 155: 2105-2108, 1997.
American Journal of Respiratory and Critical Care Medicine. 153: 4-50,
1996.
Krzyanowski, M., et al. Relation of peak expiratory flow rates and
symptoms to ambient ozone. Archives of Environmental Health. 47: 107-115,
1992.
Mckittrick, T., et al. Pulmonary function response to equivalent doses of
ozone consequent to intermittent and continuous exercise. Archives of
Environmental Health. 50:2 153-158, 1995.
Cody, R.P., et al. The effects of ozone associated with summertime
photochemical smog on the frequency of asthma visits to hospital emergency
departments. Environmental Research 58, 184-194, 1992.
Sartor, F., et al. Temperature, ambient ozone levels, and mortality during
summer, 1994, in Belgium. Environmental Research. 70: 105-113, 1995.
Simpson, R.W., et al. Association between outdoor air pollution and daily
mortality in Brisbane, Australia. Archives of Environmental Health. 52:6
Nov/Dec 442-454, 1997.
Gerard, H. et al. Effects of ambient particulate matter and ozone on daily
mortality in Rotterdam, the Netherlands. Archives of Environmental Health.
52: 6 455-463, 1997.
Schwartz, J. PM10, ozone and hospital admissions for the elderly in
Minneapolis-St. Paul, Minnesota. 49:5 366-374, 1994.
www.epa.gov/airnow (environmental
Protection Agency).
Page content
Maria A. Fierro, M.D., Mary Kay
O'Rourke, Ph.D., and Jefferey L. Burgess, M.D., M.P.H.
The University of Arizona, College of Public Health
|
