|Caveat: The following information was first
published on SCAQMD's website in 1996 and is provided for historical
In addition to the health studies discussed below, there
are more recent, and ongoing, studies. For further information on
health studies, please
contact AQMD's Health Effects Officer, Dr. Jean Ospital by
e-mail or by phone at (909) 396-2582. Please also see the
health effects section --
Appendix I -- of the latest AQMP (pdf, 131kb*)
Also, the air quality standards mentioned in this historical data may
have been changed. To see the current air quality standards, visit the
California Air Resources Board website regarding
Quality Standards and
Health & Air
Pollution. See also the
of standards updated 6/7/12 by ARB. Also visit the
U. S. Environmental
Protection Agency website.
Table Of Contents
Sources of Smog
Historic Air Pollution Disasters
Health Effects Studies
Children and smog
Air quality standards and health
Smog episodes and what they mean
Informational Telephone number
The symptoms are familiar to all those who live in cities where the air
is polluted: aching lungs, wheezing, coughing, headache. Millions of
residents of the South Coast Basin (which includes Los Angeles, Orange, and
parts of San Bernardino and Riverside counties) breathe dirty air some
one-third the days of the year.
Ozone levels here, or what most refer to as smog, are often twice the
federal health standard. In 1995, the standard was exceeded on 98 days at
one or more Basin locations, most frequently in the east San Gabriel Valley.
What does all of this polluted air do to the body? The answer depends on
the situation. How long a person is exposed to pollution, the type and
concentration, the place, time and day, temperature, weather and more.
But one thing is certain: Smog is harmful to your health.
Lungs are ozone's primary target. Studies on animals show that ozone
damages cells in the lung's airways, causing inflammation and swelling. It
also reduces the respiratory system's ability to fight infection and remove
Ozone may pose a particular health threat to those who already suffer
from respiratory problems such as asthma, emphysema and chronic bronchitis.
About 10% of the basin's approximately 14 million residents fit into this
category. Ozone may also pose a health threat to the young, elderly and
Ozone affects healthy people as well. In 1990, the State Air Resources
Board established a new health advisory level in response to mounting
evidence that smog affects healthy, exercising adults at lower levels than
previously believed. Now, a health advisory is issued at .15 parts per
million (on the pollutant standards index) before a first stage smog alert
is called when ozone levels reach .20 ppm.
During a health advisory, everyone, including healthy adults and children
are advised to avoid prolonged, vigorous outdoor exercise. Susceptible
individuals, including those with heart or lung disease, should avoid
outdoor activities until the advisory is cancelled.
Currently, the federal Environmental Protection Agency is reviewing the
adequacy of the federal health standard for ozone and is considering
Sources of Smog
The sources of pollution include emissions from on-road vehicles,
non-road vehicles like planes, ships and trains, industries, and even small
businesses and households where polluting products are used.
Ozone, an invisible gas, is not emitted directly into the air, but forms
when nitrogen oxides from fuel combustion and volatile organic gases from
evaporated petroleum products react in the presence of sunshine. Ozone
levels are highest during the warm months when there is strong sunshine,
high temperatures and an inversion layer.
Nitrogen oxides are produced when fossil fuels are burned in motor
vehicles, power plants, furnaces and turbines.
Carbon monoxide is a by-product of combustion that comes almost entirely
from motor vehicles.
Fine particulates, which are emitted directly as smoke and diesel soot
and form in the air out of nitrogen oxides and sulfur oxides, obscure
visibility and can be inhaled deep into the lungs.
During the early years of World War II, Los Angeles residents began to
realize the consequences of an increasingly industrialized area.
Investigations began to determine the cause of resident's eye irritation,
crop damage, severe reductions in visibility and the rapid deterioration of
rubber products. "Smog" became a familiar word and everyday presence and
scientists and medical personnel began to look at its effects on public
In the mid-1950s, the state of California's Public Health division
started to step up its efforts to define the problem of how and where smog
forms, as well as address the health concerns associated with exposure to
smog. Ozone levels were reaching peaks of .68 parts per million, more than
six times the federal health standard. Early efforts to study the health
effects of exposure to air pollution focused on acute exposure episodes.
Only recently have the long-term exposure effects been addressed.
In a 1956 survey sent out by the Los Angeles County Medical Association,
physicians reported the following:
- 94.7% recognized the existence of a "smog complex" involving eye
irritation, irritation of the respiratory tract, chest pains, cough,
shortness of breath, nausea and headache;
- 56.1% have "authenticated cases of individuals leaving this area
solely because of smog";
- 43.3% have recommended that patients move from the area on account of
the effect of smog on their health;
- 86.7% have observed that patients with respiratory diseases are more
susceptible to smog than healthy adults;
- 68% believe that patients with cardiac diseases are more susceptible
to smog than healthy adults;
- 89.6% have noticed patients with allergies are more susceptible to
smog than healthy adults; and
- 81.3% believe that smog is a contributing factor to cancer of the
lungs and air passages.
Historic Air Pollution
There have been several episodes in history which illustrate the harmful
effects of acute short-term exposure to air pollution. Among those include:
Belgium's Meuse Valley
During a five-day fog in December 1930, 63 people died, most of the
deaths occurring on the fourth and fifth days. Older persons with previously
known diseases of the heart or lungs accounted for the majority of
fatalities. The signs and symptoms were primarily those caused by a
respiratory irritant. They include chest pain, cough, shortness of breath
and irritation of the eyes. Sulfur dioxide gas is suspected as the cause of
Twenty people died and approximately 7,000 or 50% of the population,
experienced acute illness during the week of Oct. 25, 1948, when temperature
inversion and air stagnation occurred. Persons of all ages became ill, but
those over 55 were more severely affected. Those with previous heart or
respiratory disease, particularly bronchial asthma, suffered most.
Symptoms were primarily respiratory and secondarily gastrointestinal, and
included cough, sore throat, chest constriction, shortness of breath, eye
irritation, nausea and vomiting. The onset of the illness for most persons
occurred on the evening of the third day. Of the 20 who died, 14 had some
known heart or lung disease.
Three episodes during which heavy fogs and air pollution were associated
resulted in the death of nearly 5,000 people - in 1948, 1952 and 1956.
The episode in December of 1952 alone, resulted in at least 3,000 deaths
more than expected for that time of year. Although the increase was present
in every age group, the greatest increase was in the age group of 45 years
and over. More than 80% of these deaths occurred among individuals with
known heart and respiratory disease.
During each of these incidents, comparable conditions were present:
limited air supplies as a result of low-lying temperature inversions and
faint winds, and a continuing heavy output of air pollution from multiple
Also, in none of the incidents was technology sophisticated enough to
properly monitor the air and diagnosis of the specific causes of the illness
and deaths were based on limited evidence gathered after the disasters.
Health Effects Studies
Since the 1950s, medical evidence chronicling the effects of air
pollution on the human body has continued to mount. Here are summaries
of some of the most recent medical studies:
- A 1989 study funded by AQMD and conducted by Dr. Jane Hall of Cal
State Fullerton found that meeting federal clean air standards for ozone
and fine particulates in the South Coast region would provide $9.4 billion
in health-related benefits each year. The study found that 98% of the
four-county basin's population of 13 million is exposed to unhealthful
air, with children especially vulnerable. In addition, 1,600 people die
prematurely as a result of exposure to air pollution, according to the
- In 1991, as a follow up to the study, Hall looked at how air quality
impacts minority communities. The study showed that minorities as a whole
were shown to be exposed more often to poor air quality since they tend to
live in more polluted air where housing is affordable. African-Americans
and Hispanics generally breathe the worst air, partly because they tend to
work in outdoor occupations.
- Children are the focus of a study funded by the California Air
Resources Board that began in spring 1992 and will track 9,600 fourth,
eighth and twelfth grade students for up to 10 years to assess the
potential health damage from continued exposure to ozone, fine
particulates and atmospheric acidity. The lead scientist on the project is
Dr. John Peters of the University of Southern California.
- David Abbey, Ph.D., of Loma Linda University, studied a group of 6,340
Seventh Day Adventists living throughout California (62% lived in the
Basin). Results of the study suggest a relationship between long term
exposure to air pollution and the development of specific chronic
diseases. Residents living in areas which exceeded state and federal
standards for suspended particulates on 42 days or more per year had
higher risks of respiratory diseases, including a 33% greater bronchitis
risk and 74% greater asthma risk. In addition, women living in those high
particulate areas had a 37% higher risk of developing some form of cancer.
- In 1987, Drs. Russell Sherwin and Valda Richters of USC examined the
health of 152 young people, between the ages of 15 and 25, who died
suddenly from accidents or homicide. In lung autopsies of over 100 of the
subjects, slight lung airspace inflammation was found in 75% of the group,
with severe damage in 27%. In addition, all of the youths examined had
some degree of airway inflammation, while 39% had severe illness in the
bronchial glands and 29% had severe illness in their bronchial linings.
Combined, about 54% of the youths examined had at least one site of severe
illness. While no evidence has been found to deter-ine the levels of
smoking or other contributing factors that could have affected their
health, these youths appear to have provided the first positive proof of
health damage from long-term exposure to poor air quality.
- A study conducted by Dr. Roger Detels of UCLA on chronic obstructive
respiratory disease (CORD) looked at residents of three Southern
California areas (Long Beach, Glendora and Lancaster) with different types
and levels of air pollution.
Participants aged 7 to 59 were questioned about lifestyle habits and
examined using lung function tests and histories to record exposures to
pollutants from workplaces and personal habits, such as smoking.
Researchers followed those participants for more than five years and found
that the residents who lived in the more polluted areas, Long Beach and
Glendora, which experience numerous days of unhealthful air, had more
symptoms of respiratory diseases such as bronchitis and asthma, while the
residents of Lancaster had measurably fewer symptoms of those illness.
- Athletes may be relatively young, healthy, physically fit and
nonsmokers, but they may be among the most vulnerable to the effects of
inhaled ozone (and other environmental pollutants), according to Dr. Henry
Gong of UCLA. Endurance studies suggest that athletic performance may
begin to suffer at the .12 ppm level of ozone (the federal health
standard), and is very likely at .20 ppm for most athletes exercising
heavily for one or more hours.
- Fine particulate pollution -- even at levels below the federal health
standard -- can shorten lifespans by two years, according to a 16-year
study by Harvard University researchers. In a study of 8,111 residents of
six U.S. cities, particle pollution was strongly associated with excess
deaths from lung cancer and heart disease -- even when other lifestyle
risks such as cigarette smoking were factored out.
The six cities studied -- Watertown, Mass., Harriman, Tenn., St. Louis and
Steubenville, Ohio, Portage, Wis. and Topeka, Kan. -- all have PM10 levels
below the federal health standard. In contrast, the South Coast Air Basin
has some of the worst PM10 pollution in the nation, nearly twice the
federal health standard.
- A study by C. Arden Pope III, Ph.D., of Brigham Young University found
that particulate pollution reduces the average life expectancy by one to
three years in some of the most polluted cities.
There have been many Environmental Protection Agency studies looking at
health effects. Some findings include:
- A study of 10 adult men exposed to .12 ppm ozone for 6.6 hours
(including five hours of moderate exercise), found that lung function
decreased and respiratory symptoms (coughing and breathing discomfort)
increased over the more than six hours of exposure.
- In a study done on rats, continuous low level exposure to ozone caused
restrictive lung disease. Removal of the rats from the ozone environment
to one of clean, filtered air appeared to reverse the disease state back
to normal. However, the study indicated that since people do not breathe
filtered air, ozone exceedances in numerous cities would appear to promote
- In a field study of children during normal activities at summer camp,
lung function measurements were taken before, during and after ozone
levels reached above .12 ppm on four days and .18 ppm on one day. Lung
function failed to return to its pre-episode level for many days after the
ozone episode had passed.
- An acute exposure of humans to .40 ppm ozone initiates biochemical
changes in the lung resulting in the production of components which
contribute to inflammation and acute lung damage and which can lead to
long term effects such as fibrosis. A study was initiated to determine if
prolonged exposure to low levels of ozone would produce similar
biochemical changes. Non-smoking males were randomly exposed to filtered
air and either .10 ppm or .08 ppm of ozone for 6.6 hours with moderate
exercise. The study concluded that exposure of humans to low levels of
ozone is sufficient to cause an inflammatory reaction in the lungs.
Children and smog
A 1984 study conducted by Dr. Kay Kilburn, M.D., Professor of Medicine at
USC showed that children raised in the South Coast Air Basin suffer a 10% to
15% decrease in lung function compared to children who grow up where the air
is less polluted.
The California Air Resources Board has concluded that "since the lungs of
children are not fully developed, early damage to the respiratory tract
could increase the risk of respiratory disease in adult life."
Jane Hall's 1989 study on the health effects of air pollution on
residents of the South Coast Air Basin estimated that school-age children,
who represent only 20% of the basin's population, experience more than 40%
of the symptoms associated with exposure to ozone.
Because of their physiology, children are much more likely than adults to
develop smog-related lung damage. For their body size, children inhale
several times more air than adults, and they breathe faster, particularly
during strenuous physical activity. In addition, they spend more time
outdoors than any other segment of the population according to the AQMD
Dr. Robert F. Phalen, Ph.D., professor of community and environmental
medicine and director of the Air Pollution Health Effects Laboratory at the
University of California, Irvine, says that when children exercise, they
tend to breathe through their mouths.
According to Phalen, mouth-breathing bypasses the natural filtering of
air pollutants by the nose and allows large volumes of polluted air to
affect the more sensitive areas of children's lungs which are still
Studies show that children exposed to summer ozone pollution year in,
year out, have a greater susceptibility to respiratory infections because
chronic exposure to smog impairs their immune system.
Research findings also suggest that, even if children do not show
symptoms while exercising in unhealthful air, they are likely to suffer a
loss in lung function compared to youngsters who grow up where the air is
Air quality standards and
State and federal governments have set health standards for pollutants,
specifying levels beyond which the air is unhealthful.
California's state standards for air pollutants are more stringent than
the federal government's. It is up to each individual state to determine if
they want to set tougher standards.
Standards are set to provide an adequate margin of safety in the
protection of public health. Under the federal Clean Air Act, EPA must base
standards solely on health considerations and not economics or technology.
The standards for pollutants in California include:
Ozone (one-hour average)
Federal = Not to exceed .12 ppm (parts per million) more than one
day per year. That means no more than .12 of a volume of ozone per million
volumes of air.
State = Not to equal or exceed .09 ppm
Federal = Not to exceed 35 ppm for one-hour average; 9.4 ppm for
State = Not to exceed 20 ppm for one-hour average; 9 ppm for
PM 10 (particles 10 micrometers (millionths of a meter) or less in
Federal = 150 micrograms per cubic meter of air for 24-hour
average (arithmetic mean); 50 micrograms per cubic meter of air for annual
average (arithmetic mean)
State = 50 micrograms per cubic meter of air for 24-hour average;
30 micrograms per cubic meter of air for annual average (geometric mean).
Federal = .52 ppm for one-hour average
State = .25 for one-hour average
Smog episodes and what they
Various levels of smog episodes are reported for the pollutant ozone. The
declaration of a first, second or third stage smog alert is based on the
degree of health risk. The protective actions help to reduce exposure to
unhealthful levels of ozone, but those who are especially sensitive should
contact their physician for more specific advice.
Generally, in the event of a smog alert, outdoor activities should be
scheduled for morning or early evening hours to avoid the mid-day peak when
ozone levels are at their highest.
Hourly updates on air pollution levels are available to the public
through the AQMD's toll-free, taped telephone information service at