Air Pollution: When Does It Become Deadly?

Air pollution is a mix of hazardous substances from both human-made and natural sources, and it is a major environmental health problem affecting everyone in low-, middle-, and high-income countries. According to the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year, and 99% of the global population breathes air that exceeds WHO guideline limits. The Air Quality Index (AQI) is used to warn the public when air pollution levels pose an immediate danger to the public, with levels ranked on a scale of 0 for perfect air up to 500 for dangerous levels of air pollution. So, what level of air pollution is dangerous?

Air pollution sources

Air pollution is defined as the contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. There are four main types of air pollution sources: mobile, stationary, area, and natural sources. Mobile sources include cars, buses, planes, trucks, and trains. These sources account for more than half of all air pollution in the United States, with automobiles being the primary contributor. Stationary sources, such as power plants, oil refineries, industrial facilities, and factories, emit large amounts of pollution from a single location. Area sources consist of smaller pollution sources that collectively contribute significantly, including agricultural areas, cities, and wood-burning fireplaces. Natural sources, such as wind-blown dust, wildfires, and volcanoes, can also contribute to air pollution, but they usually do not create ongoing pollution problems.

Motor vehicles are a significant source of air pollution, with tailpipe emissions from cars and trucks contributing to elevated ozone concentrations and releasing gases such as carbon dioxide, carbon monoxide, nitrogen oxides, and sulfur oxides. The combustion of fossil fuels in vehicles, factories, power plants, and other industries also produces particulate matter (PM), a common proxy indicator for air pollution. PM includes fine particles such as sulfates, nitrates, carbon, or mineral dusts. These particles can penetrate the lungs and bloodstream, causing serious health issues such as respiratory and cardiovascular diseases, and even contributing to premature deaths.

Industrial processes and power generation are major sources of air pollution. In addition to emitting gases and PM, industries produce volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs). VOCs vaporize at or near room temperature and are found in paints, cleaning supplies, pesticides, and even craft materials. PAHs are organic compounds containing carbon and hydrogen, and they are widespread in the environment due to industrial processes such as iron, steel, and rubber product manufacturing.

Another source of air pollution is residential and recreational wood burning. While many other sources of pollution are declining, wood smoke pollution has been increasing, with residential burning accounting for a significant portion of fine particle emissions. This is particularly concerning as wood smoke contains PM and contributes to the health risks associated with air pollution. Additionally, agricultural activities, including the use of equipment and combustion processes, emit pollutants into the air, impacting air quality and human health.

Natural sources of air pollution, such as wildfires, can have significant impacts on air quality. Wildfire smoke can linger for days and pollute the air with particulate matter over extensive areas. Climate change-fueled droughts and dry conditions increase the risk of wildfires, further exacerbating air pollution. Additionally, climate change intensifies smog by increasing heat and ultraviolet radiation, creating a greater health risk for vulnerable individuals.

Air pollution levels

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is a familiar environmental health hazard, and the climate crisis threatens to worsen air pollution problems significantly. According to the World Health Organization (WHO), air pollution kills an estimated seven million people worldwide every year.

The WHO Global air quality guidelines (AQG) offer global guidance on thresholds and limits for key air pollutants that pose health risks. These guidelines are developed through a transparent, evidence-based decision-making process. The AQG provides interim targets to promote a gradual shift from high to lower concentrations and their associated health benefits. For example, through the achievement of interim target one (35 µg/m3), around 300,000 deaths would be saved worldwide annually.

The Air Quality Index (AQI) is a system used to warn the public when air pollution is dangerous. The AQI tracks ground-level ozone (smog) and particle pollution (tiny particles from smoke, power plants, factories, vehicle exhaust, and other sources), as well as four other widespread air pollutants. The AQI breaks air pollution levels into six categories, each with a name, an associated color, and advice. AQI values at or below 100 are considered satisfactory for almost everyone. When AQI values are above 100, air quality is considered unhealthy, and the higher the number, the more people are at risk of health harm.

Particulate matter (PM) is a common proxy indicator for air pollution and has strong evidence for its negative health impacts. PM includes fine particulate matter (PM2.5), which is 30 times thinner than a human hair and can be inhaled deeply into lung tissue, contributing to serious health problems. PM2.5 accounts for most health effects due to air pollution in the US. Sources of PM2.5 include wildfires, wood-burning stoves, coal-fired power plants, diesel engines, and other sources.

Other pollutants of major public health concern include carbon monoxide, nitrogen dioxide, and sulfur dioxide. Ozone (O3) is also a significant pollutant, formed at ground level when emissions from combusting fossil fuels react with sunlight. It can irritate the eyes and throat and damage the lungs, especially those of children, the elderly, and people with asthma or allergies.

Health risks

Air pollution is a major threat to global health and prosperity, and it is the second-highest risk factor for non-communicable diseases. It is responsible for approximately seven million deaths per year, with nine out of ten people breathing polluted air. The health risks of air pollution vary depending on age, location, underlying health, and other factors.

One of the most significant health risks of air pollution is its impact on respiratory health. Fine particulate matter in the air, such as soot, can penetrate deep into the lungs, causing irritation and inflammation and damaging the lining of the respiratory tract. This can lead to respiratory infections, trigger asthma attacks, and worsen existing respiratory conditions such as bronchitis and chronic obstructive pulmonary disease (COPD). Children who live in high-ozone communities or near busy roads are more likely to develop asthma. Additionally, air pollution has been linked to an increased risk of lung cancer.

Air pollution also poses cardiovascular risks. The tiny airborne particles in soot can enter the bloodstream, increasing the risk of heart attacks and abnormal heart rhythms. Exposure to air pollution has also been associated with lowered levels of good cholesterol in older individuals, increasing their risk of cardiovascular disease. Pregnant women exposed to air pollution are at a higher risk of developing hypertensive disorders, which can lead to pre-term birth, low birth weight, and maternal and fetal illness and death.

Furthermore, air pollution has been classified as a human carcinogen by the International Agency for Research on Cancer of the World Health Organization (WHO). It is associated with oxidative stress and inflammation in human cells, which can contribute to the development of chronic diseases and cancer. Exposure to certain air pollutants, such as PM2.5, has been linked to an increased risk of mortality.

The effects of air pollution are not limited to physical health. It can also have economic impacts, particularly in vulnerable communities. Residents in areas with high air pollution may face higher medical costs and may be unable to work due to illness or air quality conditions. Additionally, communities of color and low-income communities are disproportionately affected by air pollution due to historical racist zoning policies and discriminatory lending practices, resulting in environmental injustice.

Preventative measures

Air pollution is a serious issue that affects the health of millions worldwide. It is defined as the contamination of the indoor or outdoor environment by any chemical, physical, or biological agent that modifies the natural characteristics of the atmosphere. While the World Health Organization (WHO) has developed guidelines and targets for reducing dangerous levels of air pollution, it is important for individuals to also take preventative measures to protect their health and the environment. Here are some key strategies:

• Limit backyard fires in urban areas: Smoke from fires can negatively impact the health of people with asthma or lung conditions, especially during stagnant weather. If you must have a campfire, keep it small and brief, and only burn dry firewood.
• Plant and care for trees: Trees act as natural air filters, absorbing carbon dioxide and releasing oxygen into the atmosphere, helping to improve air quality.
• Reduce the use of gas-powered lawn equipment: Small gas-powered engines, like those on lawnmowers, often lack pollution control devices and contribute to air pollution. Opt for electric or hand-powered alternatives instead.
• Conserve energy: Choose energy-efficient appliances and heating systems, and turn off electrical devices when not in use. This reduces the demand for power generation, which is a significant source of outdoor air pollution.
• Support local initiatives: Engage with local businesses, city offices, and schools to promote programs that reduce air pollution and encourage sustainability. This can include initiatives such as GreenStep Cities, which aim to educate residents about best practices.
• Choose active or public transportation: Walking or cycling instead of driving can significantly reduce air pollution and congestion. Public transportation, such as buses or trains, also helps reduce your carbon footprint and improve air quality.
• Advocate for policy changes: Support policies that promote cleaner technologies, improved waste management, and increased access to affordable clean energy solutions. These policies can help reduce industrial emissions, capture methane gas, and improve energy efficiency in buildings.

By implementing these preventative measures, individuals can play a crucial role in reducing air pollution, protecting their health, and contributing to a cleaner, healthier environment for all.

Air Quality Index (AQI)

Air pollution is a serious issue that affects the health of millions of people worldwide. The World Health Organization (WHO) reports that 99% of the global population breathes air that exceeds WHO guideline limits and contains high levels of pollutants. Outdoor and indoor air pollution can cause respiratory and other diseases and are significant sources of morbidity and mortality. Fine particulate matter (PM2.5) is a dangerous and prevalent air pollutant, widely considered one of the most harmful to human health. It can penetrate the lungs and bloodstream, worsening respiratory conditions and even leading to heart attacks.

To help communicate about outdoor air quality and health risks, the United States Environmental Protection Agency (EPA) uses the Air Quality Index (AQI). The AQI is an index for reporting air quality that consists of six color-coded categories, each representing a range of index values. These categories are:

• Good: AQI value of 50 or below, indicating little to no health risk.
• Moderate: AQI values between 51 and 100, considered satisfactory but may be unhealthy for sensitive groups.
• Unhealthy for Sensitive Groups: AQI values above 100, indicating potential health concerns for certain sensitive individuals.
• Unhealthy: AQI values above 150, suggesting unhealthy air quality for the general public.
• Very Unhealthy: AQI values above 200, representing significant health risks for everyone.
• Hazardous: AQI value over 300, indicating extremely dangerous air quality.

The AQI provides valuable information for the public and policymakers to make informed decisions about protecting public health and improving air quality. It is important to note that the AQI values are general guidelines, and individual sensitivity to air pollution can vary. Therefore, it is always advisable to prioritize your health and take precautions when necessary, even if the AQI indicates moderate levels.

Frequently asked questions