Air Pollutants: Six Major Hazards To Watch Out For

The Clean Air Act requires the US Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six commonly found and harmful air pollutants known as criteria air pollutants. These six criteria air pollutants are sulfur dioxide, nitrogen dioxide, particulate matter, carbon monoxide, ozone, and lead. These pollutants are found all over the US and can cause harm to human health, the environment, and property damage.

Carbon monoxide: a colourless, odourless, and toxic gas

Carbon monoxide (CO) is a colourless, odourless, and toxic gas that is formed by the incomplete combustion of carbon-containing fuels, such as natural gas, gasoline, or wood. It is emitted by a wide range of combustion sources, including motor vehicles, power plants, wildfires, and incinerators. The highest levels of carbon monoxide typically occur during the colder months of the year when air pollution becomes trapped near the ground beneath a layer of warm air.

Outdoor air pollution from carbon monoxide is primarily caused by cars, trucks, and other vehicles or machinery that burn fossil fuels. Indoor sources of carbon monoxide include unvented kerosene and gas space heaters, leaking chimneys and furnaces, gas stoves, wood stoves, and cigarette smoke. Higher levels of carbon monoxide generally occur in areas with heavy traffic congestion. Other sources of carbon monoxide emissions include industrial processes such as metal processing and chemical manufacturing, as well as residential wood burning and natural sources like forest fires.

Carbon monoxide is harmful when inhaled in large amounts as it reduces the amount of oxygen that can be transported in the bloodstream to critical organs like the heart and brain. Exposure to carbon monoxide can cause a range of health issues, including chest pain, reduced exercise capacity, and other cardiovascular effects, particularly in individuals with heart disease. Even healthy individuals can experience negative effects from high levels of carbon monoxide, including vision problems, reduced ability to work or learn, impaired manual dexterity, and difficulty performing complex tasks.

To protect public health and the environment, the U.S. Environmental Protection Agency (EPA) has established standards for carbon monoxide under the Clean Air Act. These standards aim to ensure that carbon monoxide levels are maintained below mandated ceilings, with substantial fines and penalties for non-compliance. The EPA works with state, tribal, and local air agencies to implement emission reduction strategies and monitor air quality to keep carbon monoxide levels within safe ranges.

Nitrogen dioxide: can cause coughing, wheezing, and difficulty breathing

Nitrogen dioxide (NO2) is one of the six major air pollutants that are regulated by the US Environmental Protection Agency (EPA). These six "criteria" air pollutants—which also include sulfur dioxide, particulate matter, carbon monoxide, ozone, and lead—are harmful to both public health and the environment. Nitrogen dioxide, in particular, has been shown to damage the human respiratory system and contribute to acid rain.

Nitrogen dioxide is a gas that can be released from nitrous or nitric acid as a byproduct of the reaction between nitric acid and organic materials, the burning of nitrocellulose, or the breakdown of rocket fuel. It is also produced during the combustion of propane in ice resurfacing machines, from electric arc welding, and from engine exhaust. Exposure to nitrogen dioxide can be harmful, with human-controlled exposure studies reporting associations between NO2 and respiratory symptoms such as coughing, wheezing, and difficulty breathing.

The respiratory health effects of nitrogen dioxide have been studied in children with asthma, with evidence suggesting that exposure to indoor NO2 emitted from unflued gas heating and cooking appliances can aggravate or trigger asthma symptoms. Higher indoor NO2 levels have been associated with more frequent coughing and wheezing, as well as increased reliever medication use during the day. In one study, a unit change in both outdoor and indoor NO2 levels, such as moving from a "low" NO2 area to a "high" NO2 area, resulted in a 1.16-fold increase in coughing at night symptoms.

Nitrogen dioxide toxicity can be described in three phases. The initial phase may include coughing, wheezing, difficulty breathing (dyspnea), chest pain, fever, sweating, and weakness. In the second phase, the patient may be relatively asymptomatic. The third phase, which develops 2 to 8 weeks later, is characterized by the development of bronchiolitis obliterans, with symptoms such as fever, chills, wheezing, coughing, difficulty breathing, and chest pain. Most patients exposed to acute nitrogen dioxide toxicity can make a full recovery if they receive adequate supportive care, including mechanical ventilation or extracorporeal membrane oxygenation (ECMO).

Particulate matter: includes dust, dirt, soot, and smoke

Particulate matter, also known as particle pollution, refers to a mix of solid particles and liquid droplets found in the air we breathe. These particles include dust, dirt, soot, and smoke, and can be seen with the naked eye or under a microscope. Particulate matter can be categorised based on size, with larger particles called PM10 and finer particles called PM2.5. These fine particles are the most harmful to human health as they can enter the lungs and travel to the air sacs, known as alveoli, where they irritate and damage the alveoli walls, leading to lung disease.

Sources of particulate matter include both human activities and natural processes. Human activities that contribute to particle pollution include cooking, combustion activities such as smoking tobacco or burning incense, household products like cleaning agents and air fresheners, hobbies such as woodworking or metalworking, and industrial processes in power plants and factories. Natural sources include wildfires, agricultural fires, and prescribed fires.

The Clean Air Act, established in 1970 and last amended in 1990, empowers the U.S. Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for six principal pollutants, including particulate matter. These standards aim to protect public health and the environment by limiting the levels of pollutants in outdoor air. As a result of these regulations, emissions of the six major air pollutants in the U.S. have dropped significantly, even as economic and demographic factors have increased.

To improve indoor air quality and reduce exposure to particulate matter, individuals can take several measures. Source control is the first step, which involves identifying and removing the source of the pollutant. Upgrading furnace filters to a higher MERV rating and improving ventilation by bringing in fresh air and filtering the indoor air can also help reduce particulate matter. By taking these steps, individuals can protect their respiratory health and reduce the spread of respiratory viruses, such as COVID-19.

Ozone: a pale blue pungent-smelling gas

Ozone, or ground-level ozone, is a pale blue pungent-smelling gas. It is one of the six major air pollutants, also known as criteria air pollutants, which are regulated by the US Environmental Protection Agency (EPA). These pollutants are harmful to human health and the environment.

Ozone is formed through the photochemical reactions of other pollutants such as nitrogen oxides, carbon monoxide, and volatile organic compounds. These reactions are triggered by strong sunlight and UV radiation. Indoor sources of ozone include electric motors in household appliances such as copiers and laser printers.

Ozone is suspected to have carcinogenic effects and has been linked to reduced lung function and respiratory diseases. Exposure to high concentrations of ozone has been associated with premature mortality. It is one of the main components of smog and contributes to air pollution, particularly at ground level.

In addition to its harmful effects on humans, ozone also damages vegetation and ecosystems. It accelerates the deterioration of certain materials, including rubbers, dyes, paints, coatings, and textiles. As a result, ozone is a significant concern for both human health and the environment, and efforts are made to regulate and reduce its presence in the atmosphere.

Lead: lead emissions come from ore and metals processing

The Clean Air Act, last amended in 1990, requires the US Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards for six principal pollutants ("criteria" air pollutants) that are harmful to human health and the environment. These six criteria air pollutants are sulfur dioxide, nitrogen dioxide, particulate matter, carbon monoxide, ozone, and lead.

Lead is a heavy metal that occurs naturally in the earth’s crust. It is mined for use in a variety of materials, including paint, ceramics glaze, batteries, and pipes. Lead is also commonly found in ore containing other frequently mined materials, such as iron, copper, silver, and zinc. This means that there are many different mining operations worldwide that could be responsible for releasing lead into the environment.

One of the major sources of lead emissions is ore and metals processing. Lead toxins from mining and ore processing can leach into the surrounding soil and water systems, impacting agriculture and water resources. This is particularly dangerous as lead can be absorbed through dermal and mouth contact, and can cause severe health issues, especially in children. Miners are also at risk of exposure, as they may inhale lead dust during the mining and crushing processes, or absorb lead through their skin if they do not have adequate protective equipment.

At a national level, the highest air concentrations of lead are usually found near lead smelters. Lead emissions also come from piston-engine aircraft operating on leaded aviation fuel, waste incinerators, utilities, and lead-acid battery manufacturers. Since lead has been removed from gasoline, air emissions of lead from the transportation sector, especially the automotive sector, have greatly declined. However, lead is still present in many soils and can be resuspended into the air.

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