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Patient Exposure and the Air Quality Index

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Should I recommend that my patients reduce their exposure to ozone?

Information from clinical, epidemiological, and animal studies summarized above indicates that exposure to ambient ozone is a risk factor for triggering short and long-term health effects. These include chest discomfort, cough, and shortness of breath in healthy people as well as those with lung disease; asthma attacks in people with asthma; the possible development of new cases of asthma and other respiratory disease in people exposed to ozone over many years; and possibly mortality in people with lung disease. For example, during and following days when ozone levels are high, people with asthma may experience worsening respiratory symptoms, need more medication, and be more likely to go to emergency rooms or be admitted to the hospital. As with most triggers, some people are more severely affected than others.

Because ambient ozone exposure is a risk factor for triggering both short- and long-term health effects, it is desirable, in general, for people to reduce both their short-term and their cumulative exposure to ozone. People with asthma or other respiratory diseases who know they are affected by ozone exposure will benefit the most from exposure reductions; others may experience little or no benefit.

Evidence also indicates that, across the population, reducing exposure to ozone will reduce the public health impacts. For example, the reduction in traffic congestion in Atlanta during the summer Olympic Games resulted in a prolonged reduction in ozone pollution and this reduction was associated with significantly lower rates of childhood asthma events. (Friedman et al., 2001) One of the main functions of the Air Quality Index (AQI) is to notify the public with advisories when ozone levels are, or are expected to be, unhealthy, thereby giving people the opportunity to reduce their own exposure to ozone.

In general, health care providers should recommend that patients reduce their ozone exposure on days when air quality is bad, especially people with asthma who know they are affected by ozone exposure. The Clinical Scenarios and Frequent Questions sections contain more clinically relevant interpretations of these data and suggestions for when and how to advise patients to reduce their exposure or increase medication usage.

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How can my patients reduce exposure to ambient ozone and the consequent health effects?

People can reduce their exposure by reducing the time they spend outdoors or by reducing the level or duration of outdoor activity during the times of the day that ozone levels tend to be high where they live. Ozone levels are typically highest in the warmer months (approximately May through September) and in the afternoon and early evening hours for most locations, but this can vary by location.

People can know when to reduce their exposure to ozone by paying attention to air quality reports and forecasts that notify the public when ozone levels are at unhealthy levels, thereby giving them the opportunity to plan activities accordingly. In the United States, State and local government agencies use EPA's AQI to provide these reports to the public.

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What is the Air Quality Index?

The Air Quality Index, or AQI, is a nationally uniform index for reporting and forecasting daily air quality. It is used to report the five most common ambient air pollutants that are regulated under the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI tells the public how clean or polluted the air is and how to avoid potential associated health effects.

AQI logo.
The AQI uses a normalized scale from 0 to 500. Since levels rarely exceed a value of 200 in the United States, in most cases only the range from 0 to 300 is shown. The higher the AQI value, the greater the level of pollution and the greater the health concern. An AQI value of 100 generally corresponds to the level of the National Ambient Air Quality Standard for the pollutant. AQI values below 100 are generally considered to be satisfactory. When AQI values are above 100, air quality is considered to be unhealthy, at first for members of susceptible populations, then for everyone as AQI values get higher.

The AQI is divided into six categories that correspond to different levels of health concern. For ozone, the breakpoints between these categories were selected based on a review of the health effects evidence. This evidence included concentration-response functions derived from a series of controlled human exposure studies.(Folinsbee et al., 1988; Horstmann et al., 1990; McDonnell et al., 1991) In these studies, healthy volunteers were exposed to ozone concentrations ranging from 0.08 to 0.12 ppm for 8 hours in environmental chambers. Activity patterns in these experiments were designed to simulate activities of a normal day, with periods of moderate activity interspersed with breaks for meals and for rest. Lung function and respiratory symptoms were recorded for each exposure and graded based on Table 1 (for healthy people) and Table 2 (for people with lung disease).

Click here to open a new window to view Table 1

Click here to open a new window to view Table 2

Air Quality Index
(AQI) values		 Levels of Health
Concern		 Colors
When the AQI
is in this range:		 ...air quality conditions are: ...as symbolized
by this color:
0 to 50 Good Green
51 to 100 Moderate Yellow
101 to 150 Unhealthy for Sensitive Groups Orange
151 to 200 Unhealthy Red
201 to 300 Very Unhealthy Purple
301 to 500 Hazardous Maroon
Figure 12: Air Quality Index (AQI) levels of health concern. This color-coded table shows generically how AQI values correlate with levels of health concern. For a copy of this AQI table, download the booklet, "Air Quality Index - A Guide to Air Quality and Your Health," that explains the AQI and the health effects of major air pollutants, at http://airnow.gov/index.cfm?action=aqibroch.index.
  • "Good" (0 - 50) Air quality is excellent and poses little or no risk.
  • "Moderate" (51 - 100) Air quality is acceptable; however, there may be some health concern for a small number of unusually sensitive individuals. We cannot identify groups of people that are at greater risk when air quality is in this range. However controlled human exposure studies indicate that there are individuals who experience health effects at more moderate levels of outdoor exertion or at lower ozone levels than the average person, and these individuals may experience effects when air quality is in the moderate range.
  • "Unhealthy for Sensitive Groups" (101 - 150) When air quality is in this range, people that are included in a sensitive group, whether the sensitivity is due to medical conditions, exposure conditions, or inherent susceptibility, may experience the effects described above when engaged in outdoor activities. However, exposures to ambient concentrations in this range are not likely to result in effects in the general population. For ozone, the sensitive group includes children and adults who are active outdoors because they are more likely to be at elevated ventilation rates for sufficiently long periods of time when ozone levels are high to experience effects. People with lung diseases are also included in this group because they often have poorer lung function to begin with, so that any additional reduction is more likely to result in symptoms, and also ozone can aggravate their underlying diseases. EPA's risk assessment (Whitfield et al., 1996) indicates that at this level for healthy individuals (adults and children) at moderate exertion: 1) approximately 18% are estimated to experience moderate or greater lung function impairment, 2) approximately 9% are estimated to experience large or greater lung function impairments, and 3) approximately 2% are estimated to experience moderate to severe aggravated cough.
  • "Unhealthy" (151 - 200) When air quality is in this range, any individual who is active outdoors may experience the respiratory effects described above. Members of sensitive groups are likely to experience more severe effects. EPA's risk assessment (Whitfield et al., 1996) indicates that at this level for healthy individuals (adults and children) at moderate exertion: 1) approximately 30% are estimated to experience moderate or greater lung function impairment, 2) approximately 15% are estimated to experience large or greater lung function impairments, and 3) approximately 5% are estimated to experience moderate to severe respiratory symptoms (i.e., chest pain with deep inspiration and aggravated cough).
  • "Very Unhealthy" (201 - 300) When air quality is in this range, it is expected that there will be widespread effects among the general population and more serious effects in members of sensitive groups. EPA's risk assessment (Whitfield et al., 1996) indicates that at this level for healthy individuals (adults and children) at moderate exertion: 1) approximately 50% are estimated to experience moderate or greater lung function impairment, 2) approximately 20% are estimated to experience large or greater lung function impairments, and 3) approximately 10-15% are estimated to experience moderate to severe respiratory symptoms (i.e., chest pain with deep inspiration and aggravated cough). Individuals with asthma or other respiratory conditions will likely be more severely impacted than healthy individuals, leading some to increase medication usage and seek medical attention, including increased emergency room and clinic visits, and increased hospital admissions.
  • "Hazardous" (301 - 500) If air quality gets in this range, it will trigger health warnings of emergency conditions and there will be widespread coverage in the media.

The AQI's levels of health concern correlate with pollutant-specific health and cautionary statements that suggest relatively simple measures people can take to reduce their exposure to air pollution. For example, when the AQI Index Value for ozone is between 101 and 150, or Code Orange, air quality is considered "unhealthy for sensitive groups," and active children and adults, and people with lung disease such as asthma, are advised to reduce prolonged or heavy exertion outdoors.

Index
Values		 Levels
of Health
Concern		 Cautionary Statements
0-50 Good None
51-100* Moderate
Unusually sensitive people should consider reducing prolonged or heavy exertion outdoors.
101-150 Unhealthy for Sensitive Groups
Active children and adults, and people with lung disease, such as asthma, should reduce prolonged or heavy exertion outdoors.
151-200 Unhealthy
Active children and adults, and people with lung disease, such as asthma, should avoid prolonged or heavy exertion outdoors. Everyone else, especially children, should reduce prolonged or heavy exertion outdoors.
201-300 Very Unhealthy
Active children and adults, and people with lung disease, such as asthma, should avoid all outdoor exertion. Everyone else, especially children, should avoid prolonged or heavy exertion outdoors.
301-500 Hazardous
Everyone should avoid all physical activity outdoors.
Figure 13: The AQI Guide for Ozone includes cautionary statements and actions people can take to reduce their risk from exposure to air pollution at different levels of health concern. This information can be found online at http://airnow.gov/index.cfm?action=static.aqi, along with AQI tables for other air pollutants.

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What can I advise my patients to do when air quality is forecast to be unhealthy?

As discussed above, the EPA recommends limiting outdoor activities as the AQI for ozone rises to unhealthy levels. The chances of being affected by ozone increase the longer a person is active outdoors and the more strenuous the activity is. If a patient is involved in an activity that requires moderate or heavy exertion, he or she can reduce the time spent on this activity or substitute another activity that requires less exertion (e.g., go for a walk rather than a jog). In addition, patients can plan outdoor activities when ozone levels are lower, usually in the morning or evening.

In general, controlled human exposure studies indicate that:

For most adults, activities that involve moderate exertion, with minute ventilation rates for adults that range from 25-45 liters/minute, include climbing stairs, playing tennis or baseball, simple garden or construction work, and light jogging, cycling, or hiking. Activities that involve heavy exertion, with minute ventilation rates greater than 45 liters/minute for adults, include playing basketball or soccer, chopping wood, heavy manual labor, and vigorous running, cycling, or hiking. Because fitness levels vary widely among individuals, what is moderate exertion for one person may be heavy exertion for another. No matter how fit a person is, cutting back on the level and/or duration of exertion when ozone levels are high will help protect him or her from ozone's harmful effects.

The appearance of respiratory symptoms when ozone levels are high is an indication that reduction of exposure is warranted. These symptoms can include:

In general, children are less likely to notice or report symptoms than adults, even when measures of peak flow are being affected.

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How effective are air quality alerts in reducing adverse effects in the real world?

For air quality advisories to have a positive effect on public health, they must be widely available and well-understood. Evidence indicates the AQI may indeed be helpful. In 2002, the Roper-ASW "Green Gauge" poll, based on interviews of 2,000 people from six Metropolitan Statistical Areas around the United States, found that more than 50% of those interviewed had heard of Code Red or Code Orange air quality days for ozone. Of those, more than 45% stated that they had taken measures to reduce their exposure to ozone. This poll indicates that approximately 25% of people living in areas where Code Orange or Code Red days are forecast have taken steps to reduce their exposure to ozone based on air quality alerts. With regard to reducing adverse health effects, a recent study of the economic impact of childhood asthma found a 4-7% reduction in pediatric hospitalizations for asthma attributable to parents taking action to protect their children in response to health advisories. (Neidell, 2002) A recent JAMA editorial on air pollution and childhood asthma expressed the view that parents should pay attention to AQI advisories to reduce asthma symptoms and morbidity. (Thurston and Bates, 2003)

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Where can the daily AQI be found?

In many areas, the local media - newspapers, television and radio - will provide AQI reports telling the public when ozone levels are predicted to be unhealthy. These reports generally occur during the weather forecasts. Some national media, such as USA Today, The Weather Channel, and CNN also provide daily air quality reports.

Photograph of Nick Walker of The Weather Channel giving air quality forecast. Figure 14: Nick Walker of The Weather Channel giving an air quality forecast. Look for the AQI with your daily weather report.

Air quality forecasts and real-time air quality information can be found on EPA's AIRNow Web site (http://www.airnow.gov). Ozone air quality forecasts for more than 350 cities across the country are posted daily by 4:30 PM during the summertime ozone season.

Click here for today's air quality forecast.

On-line map of the United States showing daily and next-day air quality forecasts for various pollutants by location. State and local agencies continually provide data for the forecasts, which are based on EPA's Air Quality Index (AQI). Figure 15: AQI forecast map. Same-day and next-day air quality forecasts for the United States can be found at http://www.airnow.gov/index.cfm?action=airnow.national. This on-line map shows forecasts for various pollutants by location. State and local agencies continually provide data for the forecasts, which are based on EPA's Air Quality Index (AQI). Clicking a spot on the actual forecast map links you to Web sites with information about air pollution in that location.

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Where can I get more information?

Along with air quality forecasts and real-time air quality information, at the AIRNow Web site (http://www.airnow.gov) there are patient information materials you can use in your practice. Your patients can find information about the health effects of ground-level ozone, as well as other pollutants such as airborne particles, and information about the AQI. There is even a Web page for elementary school-aged children (http://airnow.gov/index.cfm?action=aqikids_new.main) that includes a guide for teachers. These are also available in the Patient Education section of this course.

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