Air Pollutants: Five Common Toxins In Our Air

Air pollution is a pressing issue that poses significant risks to human health and the environment. Among the myriad of pollutants contaminating the air, six common air pollutants, known as criteria pollutants, are particularly pervasive and harmful. These insidious contaminants include particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. Each of these pollutants has its unique characteristics and sources, but they unite in their detrimental impact on the world we inhabit and our well-being. From respiratory ailments to environmental degradation, these pollutants serve as a stark reminder of the urgent need for action to safeguard our planet and its inhabitants.

Ground-level ozone: a pungent, pale blue gas, formed from other pollutants and sunlight/UV radiation

Ground-level ozone is a colourless, pungent, and highly irritating gas that forms just above the Earth's surface. It is considered a "bad" ozone and is harmful to human health and the environment. It is the main ingredient in "smog" and can cause a variety of health problems, particularly for children, the elderly, and people of all ages with lung diseases such as asthma. Exposure to ground-level ozone has also been linked to premature mortality and an increase in hospital admissions.

Ground-level ozone is a secondary pollutant, formed when two primary pollutants, nitrogen oxides (NOx) and volatile organic compounds (VOCs), react with sunlight and stagnant air. These primary pollutants are emitted from natural sources and human activities, with around 95% of NOx from human activity coming from burning coal, gasoline, and oil in motor vehicles, homes, industries, and power plants. VOCs from human activity are mainly from gasoline combustion, upstream oil and gas production, and residential wood combustion.

To address the harmful effects of ground-level ozone, the EPA in the United States has implemented regulations to help states reduce ozone levels in outdoor air. These regulations include developing limits based on human health and environmental criteria, as well as working with state and local governments to reduce air emissions of pollutants that contribute to ground-level ozone formation.

In Canada, the Ozone Annex was added to the Canada-United States Air Quality Agreement in December 2000 to address the transboundary air pollution leading to high levels of ground-level ozone. It is important for individuals to be mindful of ground-level ozone levels, especially when planning outdoor activities, as exposure can have significant health impacts.

Particle pollution: solid/liquid particles in the air, from dust to smoke, which can be harmful to health

Particle pollution, also known as particulate matter or soot, refers to a mix of tiny solid and liquid particles in the air. These particles are often so small that they are invisible, but when their levels are high, they make the air hazy and thick. Sources of particle pollution include dirty tailpipe exhaust, haze from wildfire smoke, dust from roads, farms, dry riverbeds, construction sites, and mines.

Particle pollution can be harmful to health. Larger particles, called PM10, irritate the eyes, nose, and throat. Smaller particles, called PM2.5, are more harmful as they can get into the deep parts of the lungs and even into the bloodstream. PM2.5 is also the main cause of reduced visibility (haze) in parts of the United States.

The health effects of particle pollution vary depending on the size of the particles and the length of exposure. Short-term exposure to high levels of PM2.5 has 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 to PM2.5 has been associated with an increased risk of strokes, coronary heart disease, reduced lung function growth in children, and premature death, particularly in people with chronic heart or lung diseases.

Some studies have found that different kinds of particles may carry greater health risks. Certain particles serve as carriers for other toxic chemicals, and this combination may worsen the impact on health. Overall, evidence suggests that reducing the levels of all types of particles in the air leads to better health and longer lives.

Carbon monoxide: a colourless, odourless, toxic gas, emitted from vehicles and combustion engines

Carbon monoxide (CO) is a colourless, odourless, and toxic gas that is emitted from vehicles and combustion engines. It is one of the six "criteria" air pollutants regulated by the EPA under the Clean Air Act. These criteria pollutants are so-called because they are regulated based on human health and environmental criteria.

Carbon monoxide is formed when carbon-containing fuels like natural gas, gasoline, or wood undergo incomplete combustion. This process occurs in the engines of cars, trucks, buses, and other vehicles, as well as in machinery that burns fossil fuels. It is also emitted by power plants, wildfires, and incinerators. The burning of fuel in internal combustion engines releases carbon monoxide, nitrogen oxides, and hydrocarbons. These emissions can escape from vehicle tailpipes and during refuelling, and they can damage lung tissue and aggravate respiratory diseases.

To combat this issue, regulatory bodies like the EPA and DEC work to control carbon monoxide pollution and maintain safe levels. They provide support for vehicle emission control programs and implement inspection and maintenance protocols for emissions testing. Additionally, catalytic converters are used in vehicles to reduce toxic gases and pollutants in exhaust gases by catalysing redox reactions.

Carbon monoxide is harmful to human health, particularly due to its ability to combine with blood and limit oxygen transport. When inhaled in large amounts, it reduces the amount of oxygen that can be transported in the bloodstream to critical organs like the heart and brain. Elevated levels of carbon monoxide outdoors can be concerning for individuals with heart disease. Indoors, high concentrations of carbon monoxide can lead to dizziness, confusion, unconsciousness, and even death.

Nitrogen oxides: includes nitrogen dioxide, a reddish-brown gas, soluble in water, from coal/petroleum combustion

Nitrogen oxides, including nitrogen dioxide, are among the six "criteria" air pollutants regulated by the EPA in the United States due to their harmful effects on human health, the environment, and property. Nitrogen dioxide (NO2) is a reddish-brown gas with a pungent, acrid odour and is one of the several oxides of nitrogen. It is produced from the reaction of nitrogen and oxygen gases during combustion, especially at high temperatures.

In ambient conditions, nitrogen dioxide is formed by various combinations of oxygen, nitrogen, ozone, and volatile organic compounds (VOCs) at high temperatures. Road traffic is the primary outdoor source of nitrogen dioxide, while indoor sources include tobacco smoke and the burning of fuels such as gas, wood, oil, kerosene, and coal in appliances like stoves, ovens, heaters, and fireplaces, particularly those that are unflued or poorly maintained.

Nitrogen dioxide is a strong oxidant, corrosive, and poorly soluble in water. It has a low partial pressure in the atmosphere, allowing it to exist as a volatile gas under normal ambient conditions. Its pungent odour becomes perceptible at concentrations of 188 μg/m3 (0.1 ppm). High concentrations of nitrogen dioxide can cause inflammation of the airways, and exposure to lower concentrations can deplete antioxidant defences in human bronchoalveolar lavage (BAL) fluid.

Nitrogen oxides react with ammonia, moisture, and other compounds to form nitric acid vapour and related particles, contributing to smog and acid rain. These reactions can have significant health impacts, including damage to lung tissue and respiratory problems. While nitric oxide (NO) is not considered hazardous at typical ambient levels, excess NO and its products may lead to respiratory issues, hematologic side effects, metabolic disorders, low blood pressure, nausea, vomiting, and diarrhoea.

Sulfur oxides: includes sulfur dioxide, a pungent, toxic gas, from coal, oil, and metal refining/emissions

Sulfur oxides, including sulfur dioxide, are common air pollutants. Sulfur dioxide (SO2) is a pungent, toxic gas composed of sulfur and oxygen. It is formed when sulfur-containing fuels such as coal, oil, and diesel are burned.

Coal-fired power plants are one of the biggest sources of sulfur dioxide emissions. Other major sources include commercial and institutional boilers, internal combustion engines, manufacturing, and industrial processes such as petroleum refining and metal processing. The burning of fossil fuels by power plants and other industrial facilities is the largest source of SO2 in the atmosphere. Ports, smelters, and other sources of sulfur dioxide can also cause high concentrations of emissions nearby, affecting people who live and work in these areas.

Sulfur dioxide contributes to air pollution and has harmful effects on human health, particularly the lungs. Exposure to SO2 can cause wheezing, shortness of breath, chest tightness, and other respiratory problems, especially during physical activity. Long-term exposure to high levels of SO2 increases respiratory symptoms and reduces lung function. Even short exposures to peak levels of SO2 can make it difficult for people with asthma to breathe during outdoor activities.

To address the issue of sulfur dioxide emissions, the Environmental Protection Agency (EPA) has implemented national and regional rules to reduce SO2 emissions and pollutants that form sulfur oxides (SOx). These regulations are designed to protect against exposure to SOx and help state and local governments meet the Agency's national air quality standards. Power plants use flue gas desulfurization equipment ("scrubbers") to clean sulfur from the smoke before it exits their smokestacks. Policies promoting the use of cleaner fuels and pollution controls on power plants have also helped reduce SO2 levels over time.

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