Air Pollution: Outdoor Hazards And Health Risks

Outdoor air pollution is a complex mixture of pollutants from natural and anthropogenic sources, such as transportation, power generation, industrial activity, biomass burning, and domestic heating and cooking. It is a significant environmental and health problem affecting people in low-, middle-, and high-income countries. Outdoor air pollution is responsible for millions of premature deaths worldwide, with the greatest number of deaths occurring in low- and middle-income countries. It is a key risk factor for noncommunicable diseases, including cancer, asthma, cardiovascular disease, and chronic obstructive pulmonary disease. The mix of pollutants in outdoor air varies across space and time, influenced by diverse sources and atmospheric processes. Determining exposure to outdoor air pollution is complex, as it involves considering the amount and types of pollution, the number of people exposed, and the duration of exposure.

Natural and anthropogenic sources

Outdoor air pollution is a major environmental health problem, causing an estimated 4.2 million premature deaths worldwide in 2019. It is caused by a combination of natural and anthropogenic (human-caused) sources.

Natural Sources

Natural sources of air pollution include wind-blown dust, wildfires, and volcanoes. While these sources can sometimes be significant, they do not usually create ongoing air pollution problems. Natural processes that create air pollution include:

• Sulfur and chlorine gases from volcanic activity.
• Smoke and ash from wildfires.
• Dust storms.
• Biological decay.

Anthropogenic Sources

Most human-made air pollution comes from burning fossil fuels for transportation, electricity, and industry. Common pollutants produced by burning fossil fuels include:

• Carbon dioxide.
• Nitrogen oxides.
• Sulfur dioxide.
• Volatile organic compounds (VOCs).
• Particulates.

Other anthropogenic sources of air pollution include:

• Stoves, incinerators, and open burning, which produce carbon monoxide, carbon dioxide, and particulates.
• Chemicals that do not naturally occur in the atmosphere, such as chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), which are used as refrigerants.
• Fugitive sources, including VOCs and dust, which result from the leakage of gases from storage and handling facilities and the resuspension of dust, respectively.
• Vehicle emissions, which are the largest source of nitrogen dioxide pollution in the atmosphere.
• Stationary power generation, such as power plants, which emit large amounts of pollution from a single location.
• Industrial and agricultural emissions.
• Residential heating and cooking.
• The manufacturing, distribution, and use of chemicals.

Health effects

Outdoor air pollution has severe health effects, causing an estimated 4.2 million premature deaths worldwide in 2019. The mortality rate is higher in low- and middle-income countries, with 89% of premature deaths occurring in these regions. The health effects of outdoor air pollution vary depending on the level and mixture of pollutants in the air, exposure duration, individual susceptibilities, and other factors. Here are some of the specific health impacts:

Short-term effects: Short-term exposure to outdoor air pollution can exacerbate pre-existing respiratory and cardiovascular conditions. It can aggravate asthma, chronic obstructive pulmonary disease (COPD), ischemia, arrhythmias, and cardiac failure. This leads to increased hospitalization and emergency department visits. The Air Quality Health Index (AQHI) is a useful tool that indicates the health risk from air pollution, helping individuals, especially those with pre-existing conditions, to take necessary precautions.

Long-term effects: Long-term exposure to air pollution is associated with increased mortality and an increased incidence of lung cancer, pneumonia, and the development of atherosclerosis. It also increases the risk of respiratory infections, heart disease, stroke, and lung cancer. The fine PM2.5 particles are the most harmful pollutants, penetrating deep into lung passageways and contributing to excessive premature mortality.

Vulnerable populations: Children, the elderly, and people with low incomes are more susceptible to the health impacts of outdoor air pollution. Children are at risk because of their developing airways, higher breathing rates, and less developed immune systems. The elderly face increased harm due to the natural decline in lung function and a weaker immune response to inhaled contaminants. Additionally, people of color and those with pre-existing chronic conditions, such as asthma, diabetes, and heart disease, are more vulnerable to the health effects of air pollution.

Global health concern: Despite improvements in air quality in high-income countries, the adverse health effects of particulate air pollution remain a significant public health issue globally, even at relatively low pollution levels. Addressing air pollution is crucial for protecting public health, and it requires concerted action from policymakers and improvements in various sectors, including energy, transport, waste management, and urban planning.

Criteria pollutants

Outdoor air pollution is a major environmental health problem that affects people in low-, middle-, and high-income countries. It is estimated that in 2019, about 4.2 million premature deaths worldwide were caused by ambient (outdoor) air pollution. This mortality is due to exposure to particulate matter, which causes cardiovascular and respiratory diseases, and cancers.

The Environmental Protection Agency (EPA) regulates six pollutants as "criteria" air pollutants. These pollutants are common in outdoor air and can harm human health and the environment. They are referred to as "criteria pollutants" because the EPA regulates them by developing human health-based or environmentally-based criteria for setting permissible levels. The Clean Air Act requires the EPA to set National Ambient Air Quality Standards (NAAQS) for these pollutants. The six criteria air pollutants regulated by the EPA include:

• Particulate matter (PM) or particle pollution, which is made up of particles (solid or liquid) in the air. These particles can be big enough or dark enough to be seen, like smoke, or so small that they are invisible. PM10 irritates the eyes, nose, and throat, while PM2.5 is more dangerous as it can get into the deep parts of the lungs or even the blood.
• Ground-level ozone, which is one of the major constituents of photochemical smog. It is formed through the reaction with other gases in the presence of sunlight.
• Carbon monoxide (CO), a colourless, odourless, and tasteless toxic gas produced by the incomplete combustion of carbonaceous fuels such as wood, petrol, charcoal, natural gas, and kerosene.
• Nitrogen oxides, which are commonly released from the combustion of fuels in the transportation and industrial sectors. Breathing in high levels of nitrogen dioxide (NO2) can lead to respiratory problems, including coughing and wheezing, and an increased susceptibility to pulmonary infections.
• Lead, which can cause health issues such as developmental problems in children and cardiovascular issues in adults.
• Sulfur oxides, which are a group of regulated gases. The main sources of sulfur dioxide (SO2) emissions are power plants and industrial facilities that burn sulfur-containing fossil fuels. Exposure to sulfur dioxide can cause nose, throat, and airway irritation, coughing, wheezing, chest tightness, and shortness of breath.

The EPA is required to periodically review and update the NAAQS to reflect the latest scientific information on how outdoor air quality affects human health and the environment. In addition to the EPA's regulations, some states, such as California, have additional air quality regulations that are even stricter than those implemented by the EPA.

Air quality measurements

Outdoor air pollution is a major environmental health problem that affects people in low-, middle-, and high-income countries. According to the World Health Organization (WHO), outdoor air pollution caused an estimated 4.2 million premature deaths worldwide in 2019, with 89% of these occurring in low- and middle-income countries.

Air pollution levels are measured daily and ranked on a scale of 0 for perfect air quality and 500 for air pollution levels that pose an immediate danger to the public. This system is called the Air Quality Index (AQI). The AQI breaks air pollution levels into six categories, each with a colour and advice for the public. AQI values at or below 100 are considered satisfactory for almost everyone. Values above 100 indicate unhealthy air quality, with the risk to human health increasing as the number gets bigger.

The AQI is based on measurements of several pollutants, including particulate matter (PM2.5 and PM10), ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), and carbon monoxide (CO). These pollutants are common in outdoor air and can harm human health and the environment. PM2.5 and PM10 are considered some of the most harmful air pollutants.

There are many ways to measure exposure to outdoor air pollution. One way is to use ambient concentration data, which measures air quality at fixed outdoor locations. However, this method does not fully represent human exposure to air pollution, as people breathe air in various indoor and outdoor environments throughout the day. To fully understand an air pollution issue, information is needed on emissions sources, ambient air concentrations, exposures, and effects on exposed populations.

The US Environmental Protection Agency (EPA) collects data on outdoor air quality through outdoor monitors across the US. The EPA also issues year-round AQI forecasts, including maps that show how pollution levels change and move throughout the day. The World Air Quality Index project also provides a real-time air pollution map for more than 80 countries, using laser particle sensors to measure PM2.5 and PM10 particle pollution.

Reducing outdoor air pollution

Outdoor air pollution is a critical issue that has emerged as one of the leading causes of environmental health problems globally. It is caused by the presence of substances in the air at concentrations or durations above their natural levels, with the potential to produce adverse effects. These substances are known as air pollutants, and they can be classified as either gaseous or particulate matter (PM). PM is a common proxy indicator for air pollution and is composed of sulfates, nitrates, ammonia, sodium chloride, black carbon, mineral dust, and water.

• Reduce vehicle emissions: Vehicle exhaust is a major source of air pollution. To reduce emissions, drive less by carpooling, biking, using public transportation, or walking. When purchasing a new vehicle, opt for fuel-efficient models with good gas mileage, and keep your current vehicle well-maintained, including the emissions control systems.
• Limit idling: Turn off your engine whenever possible. Idling vehicles create unnecessary air pollution and waste fuel.
• Smart refueling: In hot summer months, refuel your vehicle during the early or late hours of the day when temperatures are lower. This helps reduce the evaporation of fuel, which contributes to air pollution.
• Energy conservation: Reduce your energy intake at home. Choose energy-efficient appliances and heating systems, and turn off electrical items when not in use. By consuming less power, you can help decrease the emissions from power plants.
• Avoid open burning: Burning trash and wood in low-temperature fires releases toxic air pollutants, including smoke, which can cause eye and lung irritation, headaches, and even more severe health issues.
• Plant and care for trees: Trees act as natural air filters, absorbing carbon dioxide and releasing oxygen into the atmosphere. They also help cool the surrounding area.
• Use electric or hand-powered equipment: Gas-powered lawn equipment, such as lawnmowers, leaf blowers, and snow blowers, often lack pollution control devices. Opt for electric or hand-powered alternatives to reduce emissions and air pollution.
• Support policy changes: Advocate for policies that promote cleaner transport, energy-efficient homes, sustainable power generation, improved waste management, and better industrial practices. These policies can significantly reduce key sources of outdoor air pollution.

By implementing these measures and supporting broader policy changes, we can effectively reduce outdoor air pollution, improve public health, and work towards a more sustainable future.

Frequently asked questions