Air Pollution Index: Understanding The Air We Breathe

The Air Quality Index (AQI) is a system used to communicate to the public about outdoor air quality and health. It is a tool developed by government agencies to inform the public about the current and forecasted level of air pollution. The AQI is measured daily and ranked on a scale of 0 for perfect air quality to 500 for air pollution levels that are immediately dangerous to the public. The higher the AQI value, the greater the level of air pollution and the greater the health concern. Different countries have their own air quality indices, corresponding to different national air quality standards.

How is the Air Quality Index (AQI) calculated?

The Air Quality Index (AQI) is a uniform way of reporting daily air quality conditions. It is calculated by converting measured pollutant concentrations to a uniform index based on the health effects associated with a pollutant. The AQI was developed by the United States Environmental Protection Agency (EPA) and is divided into six categories indicating increasing levels of health concern. The higher the AQI value, the greater the level of air pollution and the greater the health concern. For example, an AQI value of 50 or below represents good air quality, while an AQI value over 300 represents hazardous air quality.

The AQI is based on the concentrations of five pollutants: ozone, nitrogen dioxide, sulfur dioxide, PM2.5, and PM10. The breakpoints between index values are defined for each pollutant separately, and the overall index is defined as the maximum value of the index. Different averaging periods are used for different pollutants. The EPA has established National Ambient Air Quality Standards (NAAQS) for each of these pollutants to protect public health. The health benchmarks used for calculating the AQI are pollutant-specific and are established by the EPA through the NAAQS. The Clean Air Act requires the EPA to review these standards every five years.

An individual score (Individual Air Quality Index, IAQI) is calculated using breakpoint concentrations and a piecewise linear function to calculate intermediate values. The final AQI value can be calculated per hour or per 24 hours and is the maximum of these six scores. The score for each pollutant is non-linear, as is the final AQI score. An AQI of 300 does not mean twice the pollution of an AQI of 150, nor does it mean the air is twice as harmful.

AQI forecasts heavily depend on temperatures, precipitation, wind, and cloud cover. Weather affects pollution creation and transport from other areas. Fine-particle pollution is measured year-round in all reporting areas. Ozone pollution is monitored from April through October in all reporting areas except Grand Portage and Virginia. Carbon monoxide, sulfur dioxide, and nitrogen dioxide rarely influence the AQI and are only measured at a few sites.

How is the AQI communicated to the public?

The Air Quality Index (AQI) is a system used to communicate air quality to the public. It is designed to warn the public when air pollution levels are dangerous, with a particular focus on protecting vulnerable groups. The AQI is based on the five "criteria" pollutants regulated under the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Each pollutant has a national air quality standard set by the EPA to protect public health.

The AQI works like a thermometer that runs from 0 to 500, with six colour-coded categories indicating the level of health concern. The colours are often accompanied by a descriptor, such as "good", "moderate", "unhealthy", or "hazardous". For example, Code Green and Yellow mean the air is generally safe for everyone, while Code Red and Purple mean the air is unhealthy for everyone.

The AQI is communicated to the public through various channels, including newspapers, radio, television, and websites. Maps are also used to show how pollution levels change and move throughout the day, providing "real-time" information about current outdoor air quality. The public can access this information through websites such as AirNow.gov or mobile apps like AirNow. In addition to these sources, the public can also refer to Google Maps, which provides a map of all the air quality stations in a given area. However, it is important to note that the AQI level at a particular station may not reflect the exact AQI level at your specific location.

During periods of poor air quality, governmental agencies and public health organizations provide health recommendations to the public. For example, they may advise sensitive groups, such as the elderly, children, and those with respiratory or cardiovascular problems, to avoid outdoor activities. They may also recommend the use of masks outdoors and air purifiers indoors. In some cases, agencies may invoke emergency plans that require major emitters to curtail emissions until hazardous conditions improve.

What are the health implications of a high AQI?

The Air Quality Index (AQI) is a system used to warn the public about the level of air pollution and the associated health risks. The AQI scale ranges from 0 to 500, with 50 or below representing good air quality and an AQI over 300 indicating hazardous air quality. As the AQI value increases, so does the level of pollution and the potential for adverse health effects.

When the AQI value is between 101 and 150, or "Code Orange", the air quality is considered "unhealthy for sensitive groups". People with heart or lung disease, older adults, children, people with diabetes, and those of lower socioeconomic status are advised to reduce prolonged or heavy physical exertion. Even at moderate AQI levels, some individuals with unusual sensitivity may experience health issues.

As the AQI rises into the unhealthy range, the potential for health issues increases for everyone. High AQI levels can lead to respiratory problems such as coughing, wheezing, throat discomfort, and burning eyes. Prolonged exposure to high levels of air pollution can have broader health implications, including cardiovascular diseases, an increased risk of lung cancer, and exacerbation of pre-existing respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD).

Studies have shown that certain populations are more likely to be affected by particle pollution and experience health effects at lower AQI levels. These include children, older adults, people with asthma, and those with pre-existing respiratory or chronic illnesses. People in these sensitive groups are advised to limit their time outdoors and reduce physical activity on days with high AQI levels to minimise their exposure to air pollution and potential health risks.

How can people protect themselves from poor air quality?

The Air Quality Index (AQI) is a system used to warn the public about dangerous levels of air pollution. It is a valuable tool to help people stay safe. The AQI is divided into six colour-coded categories, with each category corresponding to a range of index values. An AQI value under 50 is considered good air quality and is safe for everyone to spend time outdoors. As the AQI number increases, so does the risk to health. Values over 100 are considered unhealthy, and an AQI over 300 is hazardous.

• Stay informed by checking daily air pollution forecasts in your area. Sources include local radio and TV weather reports, newspapers, and online at airnow.gov.
• Limit your time outdoors when air pollution levels are high. Move workouts indoors and limit the amount of time children spend playing outdoors.
• Even when air quality is good, avoid exercising near high-traffic areas as vehicles on busy highways can create high pollution levels.
• Reduce energy use in your home. Generating electricity creates air pollution.
• Use public transportation, walk, bike, or carpool instead of driving.
• Avoid burning firewood or trash.
• Use hand-powered or electric lawn care equipment instead of gasoline-powered tools.
• If you have asthma or respiratory disease, continue or start any controller medications as prescribed by your doctor.
• If you need to go outside when air quality is poor, wear an N95 or KN95 mask.
• Stay indoors with the windows closed and consider investing in an air purifier.

How does the AQI differ between countries and regions?

The Air Quality Index (AQI) is a tool used to communicate air quality to the public. It converts complex air quality data on various pollutants into a single, digestible number and colour. However, there is no unified air quality measurement system for the entire world.

Differences in AQI Standards

There are many different AQI standards around the world, which can make AQI numbers confusing. Countries like the US, China, and India all have their own AQI standards for measuring air pollution. A major difference between each country's AQI standard is the levels of PM2.5 deemed safe. The US has the strictest standard, with PM2.5 levels of 55 micrograms considered "unhealthy". China and India, on the other hand, consider PM2.5 levels of 35 micrograms as "good" and "satisfactory" respectively. The Chinese standard considers PM2.5 levels of up to 75 micrograms as good, which is far less strict than the US standard. India's standard is also more lenient than the US, with similar PM2.5 levels considered satisfactory.

Variations in Reporting Scales

Different countries and regions use different scales to report air quality based on local pollution and health considerations. For example, some states in Australia use a number-based system, while others use a category-based system. Canada, the US, and Japan each define separate air quality indexes, as does the European Environment Agency. The European AQI reports on six separate pollutants, while the Indian AQI includes ammonia (NH3) in addition to the other pollutants.

Averaging Times and Calculations

The averaging times for calculating AQIs vary across countries and regions. Google, for instance, calculates pollutant concentrations and AQIs on an hourly basis, while other commercial sensor network providers use different averaging times, such as 10-minute averages. The European AQI ranges from "Good" to "Extremely Poor" for each pollutant category, providing health advice based on the index level.

Socioeconomic Adjustments

The World Health Organization (WHO) provides guidelines on air quality, but these are sometimes adjusted for the socioeconomic characteristics of each country, resulting in specific air quality standards. For example, the WHO recommends a PM2.5 standard of 25 micrograms/m3, while India's standard is 60 micrograms/m3.

Frequently asked questions