Air Pollution Index: Understanding The Severity Of Air Quality

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. It is a yardstick that runs from 0 to 500, with higher values indicating greater levels of air pollution and health concerns. The AQI is based on the measurement of particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions. WHO provides technical support to its member states, offering guidance, tools, and advice on health issues related to air pollution and its sources. WHO also monitors and reports on global trends and changes in health outcomes associated with actions taken to address air pollution.

The Air Quality Health Index (AQHI)

The AQHI pays special attention to individuals who are particularly sensitive to air pollution, providing them with tailored advice on protecting their health during varying levels of air quality, ranging from low to very high health risks. This index is a valuable resource for vulnerable populations, enabling them to take proactive measures to mitigate the potential health consequences of air pollution.

The AQHI is measured on a scale from 1 to 10, with higher values indicating a greater health risk associated with air quality. When the level of air pollution becomes extremely high, the number is reported as 10+. This simplified scale makes it easy for individuals to quickly assess their level of risk and take appropriate action.

The AQHI is calculated based on measurements of several key pollutants, including particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO) emissions. These pollutants are monitored by the Environmental Protection Agencies (EPA) and play a significant role in determining the overall air quality and its potential health implications.

The AQHI is an essential tool for individuals to proactively manage their health and well-being in relation to air quality. By understanding the index and following its recommendations, people can effectively reduce their exposure to harmful pollutants and minimize potential health risks associated with air pollution. It empowers individuals to take control of their respiratory health and make informed decisions about their daily activities, especially during periods of heightened pollution levels.

Particulate matter

The relationship between elevated air pollution, especially fine particulate matter, and compromised health has been well documented. Negative consequences of ambient air pollution include decreased lung function, chronic bronchitis, asthma, and other adverse pulmonary effects. Long-term exposure to fine particulate matter increases premature death risk among people age 65 and older, even when exposure is at levels below the National Ambient Air Quality Standards. These harmful particles can be directly emitted from sources such as forest fires, or they can form when gases emitted from power plants, industrial operations, and automobiles react in the air. Minority populations and those living in poverty are more likely to be exposed due to practices like redlining, which has historically segregated neighbourhoods.

The WHO's air quality database compiles data on ground measurements of annual mean concentrations of particulate matter, including PM2.5 and PM10. The database currently hosts data for 4300 human settlements in 108 countries and is updated regularly. The data is used as input to derive the Sustainable Development Goal Indicator 11.6.2, Air quality in cities, for which the WHO is the custodial agency.

Carbon monoxide

The World Health Organization (WHO) has established indoor air quality guidelines for carbon monoxide. These guidelines specify the acceptable concentration of carbon monoxide in the air for different durations: 15 minutes (100 mg/m3), 1 hour (30-35 mg/m3), 8 hours (10 mg/m3), and 24 hours (7 mg/m3). The guidelines aim to address the risk of long-term exposure to carbon monoxide, which can have harmful effects on human health.

In homes, particularly in developing countries, the burning of biomass fuels and tobacco smoke are significant sources of indoor carbon monoxide exposure. Other sources include clogged chimneys, wood-burning fireplaces, decorative fireplaces, gas burners, and supplementary heaters without proper safety features. Incomplete oxidation during combustion can lead to high concentrations of carbon monoxide in indoor air. Tobacco smoke and vehicle exhaust from attached garages can also contribute to indoor carbon monoxide levels.

To ensure the safety of the public, organizations like the United States Environmental Protection Agency (EPA) set standards and monitor data to help state and local agencies maintain safe levels of carbon monoxide in the air. These standards are established under the Clean Air Act to control and reduce CO pollution.

Ozone

The Air Quality Index (AQI) is a scale used to communicate air quality to the public. It is based on the health effects of individual pollutants, with higher AQI values indicating greater air pollution and health risks. The AQI is calculated using the five "criteria" pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide.

The AQI for ozone is calculated using the maximum 8-hour average ozone concentration within a 24-hour period. This is visualised on maps using contouring methods, with each monitor displaying the highest AQI value among ozone, PM2.5, and PM10 pollutants. The breakpoints between index values are defined separately for each pollutant, and the overall index is the maximum value among them.

Nitrogen dioxide

Sources of NO2 include emissions from cars, trucks, and buses, as well as power plants and industrial facilities. The highest levels of NO2 pollution are often found in large cities and urban areas worldwide, with the most affected regions being North Africa, the Middle East, high-income countries, and Central and Eastern Europe.

The effects of NO2 on human health are concerning. Breathing air with high NO2 concentrations can irritate the airways and aggravate respiratory diseases, especially asthma. Prolonged exposure may also contribute to the development of asthma and increase susceptibility to respiratory infections. Scientific evidence further suggests potential harm to the heart and lungs, adverse effects on pregnancy and birth outcomes, and a possible association with kidney and neurological damage, autoimmune disorders, and cancer.

Indoor sources of NO2 include tobacco smoke and the use of gas, wood, oil, kerosene, and coal-burning appliances such as stoves, ovens, and heaters. In homes, the use of a gas stove and combustion space heaters significantly influence indoor NO2 concentrations.

According to the World Health Organization (WHO), nitrogen dioxide is one of the seven oxides of nitrogen that may be present in ambient air. Nitric oxide (NO) and nitrogen dioxide (NO2) are the two principal nitrogen oxides associated with combustion sources. These gases can exceed a total concentration of 500 μg/m3 in dense urban areas.

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