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Course Outline/Key Points
What is Ozone?
What is ozone and where is it in the atmosphere?
Are high ambient ozone concentrations found only in urbanized areas?
How does atmospheric ozone affect human health?
Health Effects of Ozone in the General Population
Introduction
How are people exposed to ozone?
How does ozone react in the respiratory tract?
What are ozone's acute effects?
What effects does ozone have at the cellular level?
What are the other potential effects of short-term ozone exposure?
Hoes does response vary among individuals?
At what exposure levels are effects observed?
What are the effects of recurrent or long-term exposure to ozone?
Health Effects of Ozone in Patients with Asthma
Introduction
What is asthma?
Why are we concerned?
How does ozone affect people with asthma?
Patient Exposure and the Air Quality Index
Should I recommend that my patients reduce their exposure to ozone?
How can my patients reduce exposure to ambient ozone and the consequent health effects?
What is the Air Quality Index (AQI)?
What can I advise my patients to do when air quality is forecast to be unhealthy?
How effective are air quality alerts in reducing adverse effects in the real world?
Where can the daily AQI be found?
Where can I get more information?
Other Links
Clinical Scenarios
Frequent Questions
Review Questions
Patient Education Tools
References & Figures
Glossary
The links below go to the corresponding sections in the course.
What is Ozone?
What is ozone and where is it in the atmosphere?
- Ozone is a highly reactive gaseous molecule consisting of three oxygen atoms
- Ozone occurs naturally in the stratosphere (upper atmosphere)
- In the troposphere (lower atmosphere), ozone is formed primarily from photochemical reactions of man-made air pollutants
- Tropospheric ozone is also called "ambient" or "ground-level" ozone
Are high ambient ozone concentrations found only in urbanized areas?
- Ozone and its air pollutant precursors can be transported long distances, so high ground- level ozone concentrations may occur in rural as well as urban areas
- Ozone concentrations usually peak during afternoon hours when sunlight is strongest, but ozone peaks may also occur late in the day after wind has carried ozone and its precursors miles from their sources
How does atmospheric ozone affect human health?
- Ozone absorbs ultraviolet (UV) light, reducing exposure to harmful radiation that causes skin cancer and cataracts
- Ground-level ozone that is inhaled damages the respiratory tract, leading to a number of adverse health effects that are addressed in the following material
Health Effects of Ozone in the General Population
- Inhaling ground-level ozone can result in health effects that are observed in broad segments of the population, including respiratory symptoms, reduced lung function, and airway inflammation
- Respiratory symptoms can include coughing; throat irritation; pain, burning, or discomfort in the chest when taking a deep breath; chest tightness, wheezing, or shortness of breath
How are people exposed to ozone?
- Ozone exposure occurs when people inhale ambient air containing ozone
- The rate of exposure for a given individual is related to the concentration of ozone in the surrounding air and the amount of air the individual is breathing per minute
- Ozone concentrations are higher outdoors than indoors
- Increased physical activity increases a person's rate of ozone exposure
How does ozone react in the respiratory tract?
- Ozone reacts with chemical constituents of airway lining fluid throughout the respiratory tract, producing very reactive chemical intermediates
What are ozone's acute effects?
- Ozone or its reactive products stimulate airway neural receptors, resulting in respiratory symptoms and decreases in lung function
What effects does ozone have at the cellular level?
- Ozone or its products damage airway epithelial cells which results in inflammation, an increase in nonspecific airway reactivity, and an increase in epithelial permeability
- Over a period of days to a week, inflammation subsides and cell damage is repaired
What are the other potential effects of short-term ozone exposure?
- High daily ambient ozone concentrations are associated with increased school absence, increased hospital admissions for respiratory disease, and possibly increased mortality
Hoes does response vary among individuals?
- A wide range of responsiveness to ozone exists among otherwise healthy people
- With regard to lung function, young adults (teens to thirties) are more responsive than older adults (fifties to eighties)
At what exposure levels are effects observed?
- People of average sensitivity experience responses at levels as low as 0.08 ppm during extended exposures
- Asthma attacks seem to increase when 8-hour average concentrations rise above 0.06 to 0.08 ppm
What are the effects of recurrent or long-term exposure to ozone?
- Airway injury continues to occur with ongoing, recurrent exposure
- Some evidence suggests that long-term exposure may be related to the induction of new cases of asthma and that recurrent exposure of young children may result in abnormal development of their respiratory systems
Health Effects of Ozone in Patients with Asthma
- People with asthma are the only segment of the population to be the most acutely responsive to ozone exposure
- Younger adults (teens to thirties) experience larger lung function changes than older adults (fifties to eighties)
- Children likely do not have larger responses than young adults, though they may be at risk of higher exposure and larger acute responses because they tend to be more active and spend more time playing outdoors
- Very young children may be at special risk of effects upon respiratory system development
- Asthma is a chronic inflammatory disease of the airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and cough
- The majority of asthma is associated with allergic responses to common airborne allergens such as household dust mites, pollens, animal dander, and molds
- Induction of asthma refers both to the acquisition of immunologic sensitivity to allergens and the progression to a clinically detectable disease
- The prevalence of asthma has doubled in the U.S. in the last 20 years, with more than 20 million Americans now reporting having the disease
- Higher rates of asthma are reported among children under 17, minorities, and inner-city populations
- Illness associated with asthma accounts for an estimated 10 million patient visits and more than 470,000 hospital admissions annually, translating to an estimated loss of 3 million work days and 90 million days of restricted activity for people with asthma
- The costs related to asthma were estimated at $14 billion in the U.S. in 1996
How does ozone affect people with asthma?
- Ozone exposure is associated with exacerbation of existing asthma and other chronic lung diseases
- Respiratory symptoms and bronchodilator use are increased, and lung function is decreased, on days when ozone concentrations are high
- Numbers of emergency room visits and hospital admissions for asthma are increased on days when ozone concentrations are high
- People with asthma are likely affected by ozone in two ways: (1) they might be more sensitive to ozone than other people and experience lung function changes and respiratory symptoms at lower concentrations or with greater magnitude; (2) the injury, inflammation, and increased airway reactivity induced by ozone exposure may worsen a person's underlying asthma, increasing the probability of an asthma attack. The second mechanism is by far the greater concern.
Patient Exposure and the Air Quality Index
Should I recommend that my patients reduce their exposure to ozone?
- People working or exercising outdoors for long periods are at risk of having greater exposure to ozone than other people
- Evidence indicates that reducing a person's exposure to ozone will reduce the associated health effects
- People with asthma or other respiratory diseases will benefit most from exposure reductions
- Evidence also indicates that reducing ozone exposure reduces the public health impacts of associated asthma morbidity
- EPA recommends that health care providers counsel patients to reduce their ozone exposure when air quality is bad
How can my patients reduce exposure to ambient ozone and the consequent health effects?
- People can reduce their exposure by reducing: (1) the time they spend outdoors; (2) the level or duration of outdoor activity when ozone levels are high; or (3) a combination of (1) and (2)
- For example, people can exercise outdoors moderately rather than vigorously
What is the Air Quality Index (AQI)?
- The Air Quality Index, or AQI, is a nationally uniform index for reporting daily air quality in an area
- The AQI is a normalized scale that ranges from 0 to 500. The higher the AQI value, the greater the level of pollution and the greater the health concern
- When AQI values are above 100, air quality is considered to be unhealthy, first for sensitive groups (101-150), and then for the entire population (>150)
- When the air is forecast to be unhealthy, people should limit their outdoor activities as the AQI for ozone indicates, e.g., at 101-150, sensitive groups such as active children and adults, and people with respiratory disease, should limit prolonged or heavy exertion outdoors
What can I advise my patients to do when air quality is forecast to be unhealthy?
- Physicians should counsel their patients to use AQI forecasts to plan outdoor activities
- People can reduce their exposure to ozone by rescheduling outdoor activities to times of day when ozone levels are forecast to be lower (e.g., early morning), taking it easier when ozone levels are high, and spending less time engaged in vigorous outdoor activities when ozone levels are high
- People should pay attention to symptoms such as coughing, chest pain with a deep breath, chest tightness, and shortness of breath. These symptoms indicate that exposure reduction is warranted
How effective are air quality alerts in reducing adverse effects in the real world?
- The United States public is generally aware of the AQI, and people say they have taken steps to limit exposure when the air is forecast to be bad
- There is evidence that heeding air quality advisories reduces asthma morbidity
Where can the daily AQI be found?
AQI forecasts can be found in the following locations:
- With the weather forecasts in local newspapers, TV, and radio
- Through the national news media, including USAToday, The Weather Channel, and CNN
- On the EPA Web site http://www.epa.gov/airnow
Where can I get more information?
- Along with air quality forecasts and real-time air quality information, EPA's Web site http://www.epa.gov/airnow includes patient information materials physicians can use in their practice
- The site also includes a page for elementary school-aged children (http://www.epa.gov/airnow/aqikids_new) that has a guide for teachers
- Many of these materials are also available in the Patient Education section of this course
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