Greta Jimenez
Air pollution is a pressing issue that affects billions of people worldwide, causing around 4.2 million premature deaths annually. There are several major air pollutants, including carbon monoxide (CO), ammonia (NH3), nitric oxide (NO), nitrogen dioxide (NO2), ozone (O3), particulate matter (PM), sulphur dioxide (SO2), and volatile organic compounds (VOC). These pollutants can be emitted from various sources, such as vehicles, combustion engines, industrial processes, and natural phenomena like wildfires. They have detrimental effects on human health, the environment, and property, leading to respiratory issues, ecosystem damage, and climate change. Understanding and mitigating these pollutants are crucial for safeguarding public health and the planet.
| Characteristics | Values |
|---|---|
| Carbon Monoxide (CO) | A colourless, odourless, and tasteless toxic gas. Produced by vehicles, combustion engines, boilers, fireplaces, ovens, tobacco smoke, etc. |
| Ammonia (NH3) | A colourless gas with a pungent odour. Produced by agricultural processes, fertilizer production, livestock waste management, cigarette smoke, and cleaning solutions. |
| Nitric Oxide (NO) | A colourless, toxic gas formed through the combustion of coal and petroleum. Sources include motor vehicles and thermal power plants. |
| Nitrogen Dioxide (NO2) | A harmful pollutant that can cause respiratory issues. |
| Ozone (O3) | Ground-level ozone is a pale blue gas with a pungent smell, formed through photochemical reactions of other pollutants. Sources include electric motors in household appliances. |
| Particulate Matter (PM) | Airborne liquid and solid particles of varying sizes, composed of sulphate, nitrates, ammonia, sodium chloride, black carbon, etc. Sources include power plants, vehicle traffic, construction sites, indoor stoves, etc. |
| Sulphur Dioxide (SO2) | A toxic gas with a pungent smell, arising from the combustion and refining processes of coal, oil, and metal-containing ores. |
| Volatile Organic Compounds (VOCs) | A large group of carbon-containing substances, including hydrocarbons, alcohols, aldehydes, and organic acids. Sources include emissions from incomplete combustion and volatile industry byproducts. |
| Black Carbon | A major component of PM2.5, it is produced by the incomplete combustion of fossil fuels, biofuels, and biomass. It is a warming agent and is linked to health issues and premature mortality. |
What You'll Learn
Carbon monoxide
CO is a significant air pollutant, and its presence in the air can have detrimental effects on human health. When inhaled, carbon monoxide inhibits the body's ability to carry oxygen in the bloodstream to vital organs and tissues, such as the heart and brain. This can lead to serious health issues, especially for individuals with pre-existing heart and respiratory conditions. Infants, the elderly, and those with cardiovascular and respiratory diseases are particularly vulnerable to carbon monoxide poisoning.
The concentration of CO is typically higher indoors than outdoors due to various indoor sources. Indoor sources of CO include gas stoves, malfunctioning or improperly vented gas appliances (such as water heaters, furnaces, and clothes dryers), space heaters, fireplaces, tobacco smoke, and car emissions. The highest levels of indoor CO usually occur during the colder months when indoor spaces are poorly ventilated, trapping air pollutants near the ground.
Outdoor air pollution from CO primarily comes from vehicles and machinery burning fossil fuels, such as cars, trucks, and construction equipment. Industrial processes, residential wood burning, and natural sources like forest fires also contribute to outdoor CO emissions. Higher levels of CO are often found in areas with heavy traffic congestion.
CO not only affects human health but also contributes to climate change. It participates in chemical reactions in the atmosphere, leading to the formation of ozone, a potent climate change gas. Additionally, CO is classified as a short-lived climate forcing agent, and reducing CO emissions is considered a potential strategy to mitigate the impacts of global warming.
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Ammonia
The five main groups of air pollutants are carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO2), sulphur dioxide (SO2), and particulate matter (PM). Particulate matter refers to inhalable particles composed of sulphate, nitrates, ammonia, sodium chloride, black carbon, mineral dust, or water. These particles can be further categorized as coarse particles (between 2.5 µm and 10 µm in diameter) and fine particles (less than 2.5 µm in diameter, also known as PM2.5).
While the focus on ammonia as a pollutant has not been a priority in some regions, there is growing recognition of its impact on air quality. Global emissions of ammonia have doubled in the past 70 years and are expected to continue rising due to the increasing demand for chemical fertilizers. Efforts to understand the precise chemical makeup and sources of ammonia pollution are ongoing, and researchers are working to determine the potential benefits of reducing ammonia emissions.
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Nitric oxide
In ambient conditions, nitric oxide rapidly oxidises in the air to form nitrogen dioxide. This oxidation process is influenced by available oxidants such as oxygen, ozone, and volatile organic compounds (VOCs). While nitric oxide itself is not considered the primary pollutant, its transformation into nitrogen dioxide contributes significantly to air pollution.
Nitrogen dioxide, a reddish-brown gas with a pungent odour, is a highly reactive gas and a strong oxidant. It can irritate the airways in the human respiratory system and aggravate respiratory diseases, particularly asthma. Prolonged exposure to elevated concentrations of nitrogen dioxide may also increase the risk of developing asthma and susceptibility to respiratory infections.
Overall, nitric oxide plays a crucial role in the formation of nitrogen dioxide, a significant air pollutant that poses risks to human health and the environment. Understanding the sources and transformation processes of nitric oxide is essential for developing strategies to reduce air pollution and protect public health.
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Nitrogen dioxide
NO2 primarily enters the air through the burning of fuel, with road traffic being the principal outdoor source. The outdoor concentration of NO2 can exceed 500 μg/m3 in dense urban areas, and it is higher on or near heavily travelled roadways. The main sources of NO2 emissions are trucks, buses, cars, and other diesel-powered vehicles and equipment. Industrial processes, such as oil and gas production, power plants, and boilers, also contribute significantly to NO2 emissions.
Indoor sources of NO2 include tobacco smoke and the burning of fuels like gas, wood, oil, kerosene, and coal in appliances such as stoves, ovens, heaters, and fireplaces, especially if they are unflued or poorly maintained. The average NO2 concentration can exceed 150 μg/m3 when unvented gas stoves are used. In developing countries, the burning of biomass, including wood, crop residues, and animal dung, also contributes to elevated indoor NO2 levels.
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Ground-level ozone
The formation of ground-level ozone is influenced by meteorological conditions, with higher levels typically observed during the summer months due to increased heat and sunlight. Regions with sunny skies, warm temperatures, and low humidity are more susceptible to elevated ground-level ozone concentrations. Additionally, winds can carry NOx gases over long distances, leading to ozone formation in less populated areas.
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