Air Pollutants: What's Not Harming Our Air Quality?

Air pollutants are harmful substances in the atmosphere that damage human health, the environment, and cause property damage. These pollutants are often released during the burning of fossil fuels and can be categorized into gases, biological molecules, and particulates. The six common air pollutants, also known as criteria pollutants, include particulate matter, ground-level ozone, carbon monoxide, sulfur dioxide, nitrogen dioxide, and lead. However, there are other pollutants that are not included in this list of common pollutants, and understanding which ones are not can be important for specific contexts and applications.

Carbon monoxide is a pollutant

Carbon monoxide (CO) is a pollutant. It is a colourless, odourless, and poisonous gas that is harmful to human health. CO is formed by the incomplete combustion of carbon-containing compounds, such as fossil fuels, wood, and coal. This can occur through human activities, such as industrial emissions and the use of vehicles, or through natural sources like forest fires.

CO is dangerous because it blocks oxygen delivery to the body's organs and tissues. Exposure to high levels of CO can cause dizziness, confusion, unconsciousness, and even death. It is particularly harmful to individuals with heart disease, exacerbating existing cardiovascular issues and causing chest pain. Even healthy individuals can experience negative effects, such as vision problems and reduced cognitive abilities, when exposed to high concentrations of CO.

CO is considered a secondary air pollutant, which means it is not emitted directly into the atmosphere. Instead, it is formed as a result of the incomplete combustion of fossil fuels, particularly in vehicles and industrial processes. CO pollution is often associated with areas of heavy traffic congestion, as car, truck, and machinery engines that burn fossil fuels are significant contributors to outdoor CO levels.

Indoor sources of CO include unvented kerosene and gas space heaters, leaking chimneys and furnaces, gas stoves, and tobacco smoke. The highest levels of CO typically occur during colder months when inversion conditions trap air pollution near the ground. Large CO pollution events can even be observed from space over cities.

To mitigate the harmful effects of CO, organizations like the US Environmental Protection Agency (EPA) have established standards and data to help state, tribal, and local agencies maintain safe levels of CO in the atmosphere. These efforts aim to reduce CO pollution and protect public health.

Nitrogen dioxide is a pollutant

Nitrogen dioxide (NO2) is a pollutant. It is a highly reactive gas composed of nitrogen and oxygen. NO2 is one of a group of gases called nitrogen oxides (NOx), which also includes nitric oxide (NO) and nitrous oxide (N2O). Nitrogen dioxide is formed when fossil fuels such as coal, oil, methane gas, or diesel are burned at high temperatures. It is considered a primary pollutant as it is emitted directly into the atmosphere.

NO2 is a major air pollutant and is one of six widespread air pollutants for which there are national air quality standards to limit their levels in the outdoor air. It is a harmful substance that negatively affects the ecological system and human health. The health impacts of nitrogen dioxide pollution include irritation of the airways in the human respiratory system, aggravation of respiratory diseases, and an increased likelihood of hospital admissions. People with pre-existing medical conditions such as asthma, chronic obstructive pulmonary disease (COPD), and cardiovascular disease are at a higher risk of adverse health effects from nitrogen dioxide exposure.

Nitrogen dioxide is primarily released into the air through the burning of fuel. The largest sources of NO2 emissions are trucks, buses, and cars, followed by industrial processes such as oil and gas production, coal-fired power plants, and diesel-powered non-road equipment. NO2 emissions are also produced from burning natural gas (methane) both outdoors and indoors. Monitors have shown that the highest concentrations of outdoor NO2 are found in large urban regions.

Nitrogen dioxide contributes to particle pollution and the chemical reactions that form ozone. It also plays a role in the formation of photochemical smog, which occurs when primary pollutants interact with sunlight, oxygen, and sulfur dioxide. While nitrogen dioxide itself is a pollutant, it can also be formed through secondary reactions, such as the production of nitrous acid from nitrogen dioxide interacting with water.

Efforts to reduce NO2 emissions and improve air quality have been implemented. For example, the US EPA has established national and regional rules to reduce NO2 and NOx emissions, and the federal Clean Air Act has helped drive down nitrogen dioxide emissions from power plants, industrial sites, and on-road vehicles. These measures have led to a nationwide improvement in air quality, resulting in lower levels of nitrogen dioxide in the outdoor air compared to previous decades.

Sulphur dioxide is a pollutant

Sulphur dioxide, or sulfur dioxide in American English, is a major air pollutant. It is a colourless gas with a pungent odour, often described as the smell of burnt matches. Sulphur dioxide is released into the atmosphere through the burning of fossil fuels, particularly coal and other sulphur-containing fuels, by power plants and industrial facilities. It is also produced as a byproduct of metals refining. Natural sources of sulphur dioxide include volcanic activity.

Sulphur dioxide is considered harmful to both human health and the environment. In humans, it contributes to respiratory illness by making breathing more difficult, especially for children, the elderly, and those with pre-existing conditions. Longer exposures can aggravate existing heart and lung conditions. Sulphur dioxide is also associated with a higher mortality risk.

In the environment, sulphur dioxide can create secondary pollutants, such as sulfate aerosols, particulate matter, and acid rain, once released into the air. Acid rain can damage trees and plants, inhibit plant growth, and damage sensitive ecosystems and waterways. Sulphur dioxide also contributes to the formation of thick haze and smog, reducing visibility.

Due to the harmful effects of sulphur dioxide, governments and organisations have implemented measures to reduce emissions. For example, the US EPA's Acid Rain Program helped achieve a 33% decrease in emissions between 1983 and 2002. Additionally, federal regulations to reduce the sulphur content in diesel fuels have significantly lowered emissions from diesel vehicles and equipment.

Particulate matter is a pollutant

The sources of particulate matter vary. Some particles are emitted directly from sources such as construction sites, unpaved roads, fields, smokestacks, or fires. Others form in the atmosphere as a result of complex reactions of chemicals such as sulfur dioxide and nitrogen oxides. Outdoor sources of particle pollution include vehicle exhaust, burning wood, gas, and other fuels, while indoor sources include tobacco smoke, cooking, burning candles, and fuel-burning space heaters.

The health risks associated with particulate matter are particularly relevant to sensitive groups, including children, teenagers, older adults, pregnant women, and people with heart or respiratory problems. To protect public health, organizations like the New York State Departments of Health and Environmental Conservation (DEC) monitor particle pollution levels and issue alerts when levels are expected to be unhealthy. The Air Quality Index (AQI) is another tool used to inform the public about air quality and associated health risks, helping individuals take appropriate actions to protect their health.

In addition to health impacts, particulate matter can also affect climate, ecosystems, and materials. For example, black carbon, a constituent of particulate matter, contributes to climate warming, while nitrate and sulfate have a cooling influence. Particulate matter deposition can impact plants, soil, and water quality, and the metal and organic compounds in particulate matter can alter plant growth and yield.

To address the issue of particulate matter pollution, government agencies, such as the US EPA, have implemented rules and standards to reduce emissions of pollutants that form particulate matter. These efforts aim to improve air quality and protect public health, demonstrating the recognition of particulate matter as a significant pollutant that requires regulatory action.

Ozone is a pollutant

Ozone is a gas molecule composed of three oxygen atoms. While the ozone layer in the upper atmosphere shields us from the sun's ultraviolet radiation, ozone at ground level is a serious health risk. Ground-level ozone is formed by the reaction of sunlight on air containing hydrocarbons and nitrogen oxides. These react to form ozone at the source of the pollution or many kilometres downwind.

Ozone aggressively attacks lung tissue by reacting chemically with it. It is also a potent respiratory hazard, damaging mucous and respiratory tissues in animals. It can also damage plant tissues. Research has shown that high levels of ozone are associated with an increased risk of premature death, as well as respiratory illnesses, metabolic disorders, nervous system issues, and reproductive issues.

Ozone pollution is a particular problem in urban areas, especially during hot weather. This is because ozone is more likely to form in warmer temperatures, and because there are higher populations of vehicles, which emit pollutants that contribute to problematic ozone levels.

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