Understanding Air Quality: Pollution Index Explained

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 calculated for major air pollutants, including ground-level ozone, particulates, sulfur dioxide, carbon monoxide, and nitrogen dioxide. It is often reported through colour codes, with code orange or purple/maroon days indicating poor air quality. The AQI is accessible through various platforms, such as AirNow, and plays a crucial role in helping individuals protect their health by providing real-time information on air pollution levels.

How is the Air Quality Index (AQI) calculated?

The Air Quality Index (AQI) is a system used to warn the public about dangerous levels of air pollution. 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 the maximum value of the index. The AQI is calculated either per hour or per 24 hours and is the maximum of six scores. The higher the AQI value, the greater the level of air pollution and the greater the health concern.

The United States Environmental Protection Agency (EPA) has developed an AQI that is used to report air quality. This AQI is divided into six categories indicating increasing levels of health concern: Good, Satisfactory, Moderately Polluted, Poor, Very Poor and Severe. Each category has a name, an associated colour, and advice. AQI values at or below 100 are considered satisfactory for almost everyone, while values above 100 are unhealthy, first for certain sensitive groups of people, and then for everyone as values get higher.

The EPA establishes an AQI for five major air pollutants regulated by the Clean Air Act: ground-level ozone, particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Each of these pollutants has a national air quality standard set by the EPA to protect public health.

Many countries monitor ground-level ozone, particulates, sulfur dioxide, carbon monoxide, and nitrogen dioxide, and calculate air quality indices for these pollutants. For example, in 2013, Hong Kong replaced the Air Pollution Index with the Air Quality Health Index, which is measured on a scale of 1 to 10+ and considers four air pollutants: ozone, nitrogen dioxide, sulfur dioxide, and particulate matter.

What are the health effects of air pollution?

The Air Quality Index (AQI) is a tool used to communicate about outdoor air quality and health. The AQI is a yardstick that runs from 0 to 500, with higher values indicating greater levels of air pollution and health concerns. An AQI value of 50 or below represents good air quality, while a value over 300 indicates hazardous air quality. The AQI is divided into six colour-coded categories, each indicating a different level of health concern.

Air pollution has a range of adverse health effects. Both short-term and long-term exposure to air pollutants can cause serious health problems. Particle pollution, or particulate matter (PM), is a mixture of tiny bits of solids and liquids in the air we breathe. PM2.5, a subset of PM, is 30 times thinner than a human hair and can be inhaled deeply into the lungs, contributing to serious health issues. Exposure to PM2.5 has been linked to an increased risk of mortality, with coal-sourced PM2.5 associated with a mortality risk twice as high as that from other sources.

Ozone, another pollutant, is a powerful lung irritant that can cause inflammation and damage to the lining of the small airways, impacting multiple body systems. High ozone levels can lead to breathing problems such as chest tightness, coughing, and shortness of breath, even in healthy young adults.

Air pollution is also associated with an increased risk of respiratory infections, heart disease, stroke, and lung cancer. It can worsen existing respiratory conditions such as asthma and chronic obstructive pulmonary disease (COPD). Additionally, air pollution has been linked to public health concerns such as cancer, cardiovascular disease, respiratory diseases, diabetes mellitus, obesity, and reproductive, neurological, and immune system disorders.

It is important to note that certain groups are more vulnerable to the health impacts of air pollution. These include children, people of colour, low-income communities, and individuals with pre-existing health conditions. Indoor air pollution, which tends to be overlooked, can also have significant health effects, especially for those who spend a significant amount of time indoors, such as the very young, older adults, and people with cardiovascular or respiratory diseases.

How can you protect yourself from air pollution?

The Air Quality Index (AQI) is a tool for communicating about outdoor air quality and health. It is a rating system that shows the severity of pollution in the air on a scale from 0 to 500. 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 indicates hazardous air quality.

• Check daily air pollution forecasts in your area. The color-coded forecasts can alert you when the air is unhealthy in your community. Sources include local radio and TV weather reports, newspapers, and online platforms.
• Avoid exercising outdoors when pollution levels are high. Move your workout indoors, such as walking in a shopping mall or using a gym.
• Limit the amount of time children spend playing outdoors if the air quality is unhealthy. Even with green forecasts, avoid exercising near high-traffic areas due to the high pollution levels caused by vehicles on busy highways.
• Protect your indoor air quality. Avoid indoor air pollutants such as cigarette smoke, incense, candles, and smoke from cooking.
• When outdoors, wear a well-fitting mask like an N95 or KN95 mask. Wear it in public spaces and on public transportation.
• When travelling by car, keep the windows closed and use air conditioning.
• Support national, state, and local efforts to clean up sources of pollution and reduce your energy usage at home, as generating electricity creates air pollution.

How does air pollution vary across different locations?

Air pollution is the contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. It is one of the leading risk factors for death and poor health across the world. The sources of air pollution are multiple and context-specific.

The burden of air pollution is not evenly shared and varies across different locations. Firstly, indoor pollution rates tend to be higher in low-income countries due to a reliance on solid fuels for cooking. For example, around 2.4 billion people are exposed to dangerous levels of household air pollution from cooking with open fires or simple stoves fuelled by biomass or coal. In contrast, outdoor air pollution tends to be higher in middle-income countries, as it increases as countries industrialize. Mobile sources, such as automobiles, and stationary sources, such as power plants, are significant contributors to outdoor air pollution. Wind can also transport air pollutants across borders, affecting areas downwind of pollution sources.

Socioeconomic factors also play a role in varying levels of air pollution across locations. Poorer people and some racial and ethnic groups are often exposed to higher levels of pollutants and may experience greater health impacts. Pollution sources tend to be located near disadvantaged communities, and people of colour are more likely to live in counties with higher levels of pollution. Additionally, low-income communities may have limited access to healthcare, healthy food, and clean energy alternatives, further exacerbating the health impacts of air pollution.

Furthermore, urban areas tend to have higher levels of air pollution due to increased industrial activity, traffic, and energy consumption. For example, cities with high populations of vehicles, such as cars and trucks, contribute to elevated ozone concentrations and particulate matter in the air.

Overall, the variation in air pollution across different locations is influenced by a combination of factors, including income, industrialization, energy sources, and geographic proximity to pollution sources. These factors contribute to disparities in the health impacts of air pollution on different populations.

What is the Air Quality Health Index (AQHI) and how is it different from the AQI?

The Air Quality Health Index (AQHI) is a scale that helps individuals understand the impact of air quality on their health. It is a health protection tool that provides information about the air quality and suggests ways to reduce exposure to air pollution. The AQHI is designed to help individuals make decisions to protect their health by limiting short-term exposure to air pollution and adjusting their activity levels during periods of increased air pollution. It also offers guidance on improving air quality by recommending behavioural changes to minimise the environmental footprint. This index is particularly useful for people who are sensitive to air pollution, such as those with asthma, cardiovascular disease, or respiratory issues. It provides them with tailored advice on safeguarding their health during various levels of air quality, ranging from low to very high health risks.

The AQHI measures three specific pollutants: ground-level ozone, particulate matter (PM), and nitrogen dioxide (NO2). Ground-level ozone is a significant component of smog during the summer, primarily originating from fuel combustion in vehicles and industrial activities. Particulate matter refers to tiny particles that can infiltrate deep into the lung alveoli, causing systemic inflammation and adverse effects on heart rate and blood pressure. Nitrogen dioxide is another critical air pollutant found in smog and acid rain, mainly produced by vehicle combustion, fossil fuel power plants, and industrial processes.

The AQHI provides a numerical value ranging from 1 to 10+, indicating the level of health risk associated with local air quality. On rare occasions, when air pollution levels are exceptionally high, the number may exceed 10 and be reported as 10+. The AQHI offers both current and forecasted values, allowing individuals to make informed decisions about their activities.

On the other hand, the Air Quality Index (AQI) is a tool used by government agencies to inform the public about the current and forecasted air pollution levels. The AQI focuses on individual air pollutants, providing information on the quality of the air compared to specific standards or criteria for pollutants. It is calculated based on the concentration of air pollutants over a specified averaging period, obtained from air monitors or models. The AQI values are typically categorised into ranges with corresponding descriptor codes and standardised public health advisories.

In summary, the key difference between the AQHI and the AQI lies in their respective goals and scope. The AQHI is designed to inform individuals about the health risks associated with a mixture of pollutants, providing a comprehensive understanding of the health implications of air pollution. On the other hand, the AQI focuses on reporting the current air quality based on specific levels of individual pollutants and providing corresponding health advisories. While the AQHI is a relatively new index specifically created to address health risks, the AQI has been traditionally used to convey air pollution levels to the public. Both indices serve important purposes in raising awareness about air quality and its potential impacts.

Frequently asked questions