Air Quality Index

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Air Quality Index The Air Quality Index (AQI) was established by the EPA as a simple indication of how clean the air is on a given day and what precautions, if any, need to be taken in carrying out daily activities.27 The AQI can be viewed as a yardstick to measure the cumulative effects of the criteria air pollutants on human health. It is calculated based on a number of factors such as ambient air temperature, wind conditions, and concentrations of various pollutants. The value of 100 is arbitrarily assigned to air which barely meets the national air quality standards. A value lower than 100 means acceptable air quality and successively lower values mean comparatively cleaner air. Values above 100 signify unhealthy air. The higher the AQI number, the more health risks to individuals. Under these conditions, sensitive groups such as children, the elderly, and adults with heart disease, asthma and other respiratory complications are at higher risk and must limit their outdoor activities. When the AQI climbs above 200, everyone is affected. AQI above 300 is considered hazardous and everyone should avoid prolonged outdoor exposure (See Table 8-3). In the United States, the AQI is usually below 100 for most communities, but may exceed this value a few times a year. In recent years, the AQI has rarely gone beyond 200. Similar standards are set in other major cities around the world (Figure 8-14). Table 8-3 Air Quality Index Table 8-2. Guidelines for Common Pollutants WHO US EPA Pollutant Exposure time Concentration (μg/m3) CO 15 min 30 min 1 hour 8 hours 100,000 60,000 30,000 10,000 --- --- 40,000 10,000 NO2 1 hour 1 year 400 40 --- 100 SO2 10 min 24 hour 1 year 500 125 50 --- 365 80 O3 1 hour 8 hour 175 110 235 157 PM2.5 24 hours 1 year --- --- 65 15 PM10 24 hours 1 year --- --- 50 50 Lead 1 quarter 1 year --- 0.5 1.5 --- 27 Environmental Protection Agency,


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