Air Toxics: What's The Deadliest Pollutant?

Air pollution is responsible for millions of premature deaths worldwide, with over 99% of the global population living in areas where the air pollution levels exceed the World Health Organization's (WHO) air quality guidelines. Hazardous air pollutants are substances that cause or are suspected of causing cancer, birth defects, and other serious health issues. These pollutants can be gases, such as hydrogen chloride, benzene, and nitrogen dioxide, or compounds and metals such as asbestos, cadmium, and mercury. While there are many dangerous air pollutants, this article will focus on the most toxic among them and the sources from which they originate.

Nitrogen oxides, including nitrogen dioxide (NO2) and nitrogen monoxide, are toxic air pollutants

Nitrogen oxides are a group of air-polluting chemical compounds. Nitrogen dioxide is the most harmful of these compounds and is generated from the combustion of fuel engines and industrial activities. It can damage the human heart and lungs and reduce atmospheric visibility at high concentrations. It is also a critical precursor to the formation of ground-level ozone. Breathing air with a high concentration of NO2 can irritate the airways in the human respiratory system. Exposure to high levels of NO2 over short periods can aggravate respiratory diseases, especially asthma, leading to respiratory symptoms such as coughing, wheezing, or difficulty breathing.

Longer exposures to elevated concentrations of NO2 may contribute to the development of asthma and potentially increase susceptibility to respiratory infections. Scientific evidence suggests that exposure to NO2 could likely cause asthma in children. In addition, nitrogen dioxide is associated with a higher likelihood of emergency department and hospital admissions. It is important to note that everyone is at risk from the health impacts of nitrogen dioxide pollution, but those who live near emission sources are at higher risk.

Nitrogen oxides are produced from burning natural gas (methane) both outdoors and indoors. Outdoors, this includes gas-fired power plants and facilities that extract, process, or transport oil and gas. Indoors, appliances such as stoves, dryers, and space heaters that burn natural gas, liquefied petroleum gas (including propane and butane), and kerosene can produce substantial amounts of nitrogen dioxide. If these appliances are not fully vented to the outside, levels of NO2 can build up to unhealthy levels indoors.

To reduce exposure to nitrogen dioxide and improve indoor air quality, it is recommended to properly maintain gas-powered appliances and ensure adequate ventilation.

Black carbon, or soot, is a short-lived climate pollutant and a component of PM2.5

Black carbon, or soot, is a short-lived climate pollutant. It is formed by the burning of fossil fuels, biofuels, wood, and other biomass fuels, as well as waste. Black carbon is a component of PM2.5, which refers to fine particles that are 2.5 microns or less in diameter. These particles are many times smaller than a grain of table salt and can penetrate deep into the lungs, facilitating the transport of toxic compounds into the bloodstream.

The health impacts of black carbon are significant. It has been linked to respiratory and cardiovascular illnesses, including chronic lung diseases such as bronchitis, aggravated asthma, acute respiratory infections, and an increased risk of dementia. It is also a leading environmental cause of premature deaths, with approximately 4 million deaths associated with long-term exposure to PM2.5 air pollution each year.

Black carbon emissions are particularly high in Asia, Africa, and Latin America, with residential solid fuels and kerosene used for cooking, lighting, and heating contributing significantly to global emissions. In Europe and North America, diesel engines are a major source of black carbon emissions.

Reducing black carbon emissions can have important climate and health benefits. Due to its short atmospheric lifetime, targeted methods to reduce emissions can deliver results within a relatively short duration. Studies have shown that decreasing black carbon emissions can reduce near-term warming of the climate, increase crop yields, and prevent premature deaths.

Black carbon is also known as "soot," and it enters the air when fossil fuels and biofuels, such as coal, wood, and diesel, are burned. Soot can come in solid, liquid, or gaseous aerosol states and is capable of penetrating the lungs and bloodstream when inhaled. The term "soot" also refers to a type of particle pollution composed of various pollutants, such as chemicals, acids, metals, or soils, suspended in the air after emission.

Ground-level ozone is formed from the reaction of pollutants from cars, power plants, etc. in sunlight

Ozone (O3) is a naturally occurring gas found in the Earth's upper atmosphere, where it helps block out harmful ultraviolet light from the sun. Ground-level ozone, on the other hand, is a harmful air pollutant and is the main ingredient in "smog". Ground-level ozone is not emitted directly into the air but is formed by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC).

These reactions occur when pollutants emitted by cars, power plants, refineries, and other sources react in the presence of sunlight. Sources of VOCs include chemical plants, gasoline pumps, oil-based paints, auto body shops, and print shops. Nitrogen oxides are produced primarily by high-temperature combustion, with significant sources including power plants, industrial furnaces and boilers, and motor vehicles.

The formation of ground-level ozone depends on the presence of heat and sunlight, resulting in higher concentrations during the summer months. However, high ozone levels have also been observed in cold months under specific conditions, such as in high-elevation areas with high VOC and NOx emissions, even when temperatures are near or below freezing.

Ground-level ozone has detrimental effects on human health and the environment. Exposure to ozone pollution is associated with immediate and long-term health risks. Immediate problems include breathing difficulties and an increased need for medical treatment for individuals with lung diseases like asthma or COPD. Long-term exposure to ozone has been linked to respiratory illnesses, metabolic disorders, nervous system issues, reproductive problems, and increased cardiovascular-related mortality.

Ozone is recognised as one of the six common air pollutants identified in the Clean Air Act, and efforts are being made to reduce emissions that contribute to its formation. These include implementing state implementation plans to improve air quality in non-attainment areas and adopting cleaner technologies in power plants, industrial sites, and on-road vehicles.

Methane, largely from agriculture, contributes to global warming and chronic respiratory illnesses

While there are many toxic air pollutants, methane (CH4) is a significant contributor to global warming and chronic respiratory illnesses. Methane is a powerful greenhouse gas, second only to carbon dioxide (CO2) in its heat-trapping ability. However, methane is more than 28 times as potent as carbon dioxide at trapping heat, making it a critical contributor to global warming.

Methane has various sources, both natural and human-induced. Natural sources include wetlands, lakes, and thawing permafrost, particularly in Arctic regions. On the other hand, human activities are responsible for about 60% of today's methane emissions. The largest human-induced sources of methane are agriculture, fossil fuels, and the decomposition of landfill waste. Within agriculture, livestock farming is a primary contributor, accounting for around 40% of global methane emissions.

Methane contributes to global warming by trapping heat in the atmosphere. According to scientists, the increase in methane concentrations over the past 200 years is responsible for 20-30% of climate warming since the Industrial Revolution. This warming has led to extreme weather events, including stronger storms, more intense wildfires, and prolonged droughts. These events further degrade air quality and create conditions that worsen respiratory illnesses.

Additionally, methane plays a role in forming ground-level ozone, which is toxic to humans. Ground-level ozone is created when methane reacts with other pollutants in the presence of sunlight. This ozone, along with other toxic chemicals released alongside methane, contributes to chronic respiratory illnesses. These illnesses include asthma, heart disease, cancer, and strokes.

To mitigate the impacts of methane on global warming and respiratory health, efforts should focus on reducing emissions from the oil and gas industry, agriculture, and waste sectors. Improving waste management practices, implementing common-sense oil and gas industry standards, and promoting healthier livestock practices can help reduce methane emissions and improve overall air quality.

Particulate matter (PM) refers to inhalable particles of varying sizes, with PM2.5 being the most common

Particulate matter (PM) is a mixture of solid particles and liquid droplets found in the air. Some particles, like dust, dirt, soot, or smoke, are large or dark enough to be seen, while others are so small they can only be detected using an electron microscope. PM is not a single pollutant but a mixture of many chemical species. It is composed of solids and aerosols composed of small droplets of liquid, dry solid fragments, and solid cores with liquid coatings. These particles vary widely in size, shape, and chemical composition and may contain inorganic ions, metallic compounds, elemental carbon, organic compounds, and compounds from the earth’s crust.

PM10 and PM2.5 are two types of PM defined by their diameter for air quality regulatory purposes. Particles with a diameter of 10 microns or less (PM10) are inhalable into the lungs and can induce adverse health effects. PM2.5 refers to fine particles that are 2.5 microns or less in diameter. These particles are so small that they can be inhaled and cause serious health problems. They can get deep into the lungs, and some may even enter the bloodstream. PM2.5 is the more common of the two and poses the greatest risk to health.

PM2.5 is produced from a wide range of industrial processes, including bulk material handling, combustion, and minerals processing. Industries that use these processes include brickworks, refineries, cement works, iron and steelmaking, quarrying, and fossil fuel power plants. Particulates are also released from diffuse sources, such as lawn mowing, wood stoves, fires, and wind-generated dust. Natural sources of PM2.5 include bushfires, dust storms, pollen, and sea spray. Vehicles are another source of PM2.5, with particulates generated from the burning of fuels, especially in diesel-powered vehicles, and from tyre wear or vehicle-generated air turbulence on roadways.

The health effects of exposure to PM2.5 are well-documented. Short-term exposures (up to 24 hours) have been linked to premature mortality, increased hospital admissions for heart or lung causes, acute and chronic bronchitis, asthma attacks, emergency room visits, respiratory symptoms, and restricted activity days. Long-term exposure (months to years) has been associated with premature death, particularly in people with chronic heart or lung diseases, and reduced lung function growth in children. Older adults with chronic heart or lung disease, children, and asthmatics are the groups most likely to experience adverse health effects from PM exposure.

Frequently asked questions