Air Quality Alert: Cities Choking On Smog

Air pollution is a serious health threat, causing asthma attacks and harming the development of children's lungs. The Air Quality Index (AQI) is a tool used by the U.S. Environmental Protection Agency (EPA) to communicate about outdoor air quality and health. The AQI is divided into six color-coded categories, each indicating a different level of health concern. An AQI value of 50 or below represents good air quality, while a value over 300 represents hazardous air quality. Nearly half of the people in the U.S. live in areas that received an F for air quality in 2025.

Air Quality Index (AQI)

The Air Quality Index (AQI) is a tool developed by the US Environmental Protection Agency (EPA) to communicate information about outdoor air quality and health. The AQI includes six colour-coded categories, each corresponding to a range of index values. The higher the AQI value, the greater the level of air pollution and the more serious the health concern. For instance, an AQI value of 50 or below indicates good air quality, whereas an AQI value over 300 represents hazardous air quality. AQI values at or below 100 are generally considered satisfactory. When AQI values exceed 100, the air quality is unhealthy, initially for certain sensitive groups of people, and then for everyone as values increase. Each category is assigned a distinct colour, enabling individuals to swiftly determine if the air quality in their communities is deteriorating.

The AQI is calculated based on the five major air pollutants regulated by the Clean Air Act: ground-level ozone, particle pollution, carbon monoxide, sulphur dioxide, and nitrogen dioxide. Each pollutant has a national air quality standard established by the EPA to safeguard public health. These standards define the maximum permissible levels of pollutants in the air to ensure the protection of human health and the environment.

Air pollution is a critical issue that can trigger asthma attacks, impair lung development in children, and even lead to fatalities. It is influenced by various factors, including industrial emissions, vehicle exhaust, wildfire smoke, and natural sources such as pollen and dust. Climate change exacerbates the conditions conducive to ozone pollution and complicates the task of improving air quality in areas with elevated ozone levels.

To address air pollution, policymakers must take decisive action. The Clean Air Act, enacted over 50 years ago, has been instrumental in driving pollution reduction. However, ongoing challenges, such as staffing and funding cuts threatening the EPA, underscore the need for continued vigilance and commitment to improving air quality.

Individuals can take proactive measures to protect themselves from the detrimental effects of air pollution. This includes checking the air quality forecast in their community and refraining from outdoor exercise or work when unhealthy air quality is predicted. Additionally, using air purification systems and wearing masks can help mitigate the impact of poor air quality. Staying informed about air quality data and advocating for environmental policies that prioritise clean air are also essential steps in combating this issue.

Air pollution's impact on health

Air pollution is a serious health threat, with the potential to trigger asthma attacks, harm lung development in children, and even be deadly. The main pathway of exposure from air pollution is through the respiratory tract. The health impact of air pollution depends on the duration and concentration of exposure, as well as the health status of the affected populations.

Short-term exposure to high levels of particulate matter can lead to reduced lung function, respiratory infections, and aggravated asthma. Long-term exposure to fine particulate matter, on the other hand, increases the risk of developing non-communicable diseases with longer onsets, such as stroke, heart disease, chronic obstructive pulmonary disease, and cancer. Ozone, a powerful lung irritant, can cause inflammation and damage to the lining of the small airways, impacting multiple body systems and even shortening lives.

Certain groups are more susceptible to the adverse effects of air pollution. These include children, pregnant women, older adults, and individuals with pre-existing heart and lung disease. People in low socioeconomic neighbourhoods and communities of colour may also be more vulnerable due to factors such as proximity to industrial sources of pollution, underlying health problems, poor nutrition, and psychosocial stress.

Maternal exposure to air pollution is associated with adverse birth outcomes, including low birth weight, pre-term birth, and small for gestational age births. Exposure to both ozone and particle pollution during pregnancy can further increase the risk of premature birth, low birth weight, and stillbirth.

To protect themselves from the harmful effects of air pollution, individuals can check the air quality forecast in their community and avoid outdoor activities when unhealthy air is expected. Policymakers and government agencies, such as the U.S. Environmental Protection Agency, also play a crucial role in regulating and improving air quality to safeguard public health.

The role of the EPA

The Environmental Protection Agency (EPA) is a US government agency with the mission to protect human health and safeguard the natural environment, including the air, water and land upon which life depends. The EPA works to protect public health and the environment while also restoring the American economy.

The EPA's role is to enforce federal laws that protect human health and the environment, ensuring that they are administered and enforced fairly and effectively as intended by Congress. The EPA also sponsors and conducts research, and develops environmental regulations. The EPA's Strategic Plan identifies measurable environmental and human health outcomes that the public can expect from the EPA and outlines how these results will be achieved.

The EPA works to reduce environmental risks based on the best available scientific information. For example, the EPA informs the public about activities through written materials and its website. The EPA also works to remediate contaminated sites and ensure clean drinking water, improving human health and the environment for all Americans.

The EPA's work is not limited to the US, as the worldwide EPA (Environmental Protection Agencies) has made the World Air Quality Index (AQI) possible. This project provides a real-time air pollution map for more than 80 countries, with data based on measurements of particulate matter (PM2.5 and PM10), Ozone (O3), Nitrogen Dioxide (NO2), Sulfur Dioxide (SO2) and Carbon Monoxide (CO) emissions. The AQI scale is based on the latest US EPA standard, and all measurements are taken hourly.

The EPA plays a critical role in protecting human health and the environment, both domestically and globally, through a variety of initiatives, regulations, and research.

Most polluted cities

Air pollution is a serious health threat that can trigger asthma attacks, harm lung development in children, and even be deadly. It is caused by a variety of factors, including ozone pollution, particle pollution, and climate change, which enhances the conditions for ozone pollution and makes it harder to clean up communities with high ozone levels. According to the World Air Quality Index (AQI), the following are some of the most polluted cities in the world:

Dhaka, Bangladesh

Dhaka, Bangladesh, tops the list of the most polluted cities in the world, with 114.5 µg/m3 of PM2.5. PM2.5 refers to particulate matter that is 2.5 micrograms or smaller in width, which is considered one of the more dangerous pollutants due to its ability to penetrate deep into the lungs and bloodstream.

Cities in China, India, and Pakistan

Of the 25 most air-polluted cities in the world, 10 were located in China, 8 in India, and 2 in Pakistan. The number of Indian cities on the list decreased from 9 to 8 since 2023, while China saw a significant jump from 4 to 10 cities. Other countries featured on the list include Bangladesh, Iraq, Tajikistan, Nepal, and the United Arab Emirates.

United States

In the United States, nearly half of the people live in areas where the air quality earned a failing grade in the "State of the Air" report for 2025. More than 156 million people live in counties that received a failing grade for either ozone or particle pollution, and more than 42 million people live in counties that received a failing grade for all three air pollution measures. The American Lung Association provides information on the most polluted cities in the United States, but the specific cities were not found.

Real-time air pollution maps

There are several real-time air pollution maps available online, such as those provided by AirNow.gov, IQAir, and WAQI.info. These maps can provide information on air quality for over 80 to 100 countries, with some, like IQAir, offering data for over 30,000 stations worldwide. The AirNow map, for example, includes data for the US, Canada, and Mexico, and provides forecasts for the day's overall AQI, with the option to view historical data. The map is interactive, allowing users to click on dots representing cities or reporting areas to access this information.

The WAQI.info map, on the other hand, provides real-time air quality data for over 10,000 stations globally. It uses the GAIA air quality monitor, which measures PM2.5 and PM10 particle pollution, two of the most harmful air pollutants. PM2.5 particles are particularly dangerous as they are small enough to be absorbed into the bloodstream when inhaled.

Similarly, the IQAir map offers a 3D animated real-time air pollution map, with additional features such as wildfire maps, air quality rankings for major cities, and a mobile app to stay updated on the air quality of your favourite places.

These maps are incredibly valuable for understanding the air quality in your area and can help inform decisions regarding outdoor activities, especially for individuals with respiratory issues. They also highlight the impact of human activities on air pollution, with manmade sources such as transportation, industrial businesses, and agriculture often being the leading contributors to poor air quality in cities.

Frequently asked questions