Deadly Gas: Air Pollution's Main Culprit

Air pollution is caused by the release of gases, liquids, or solids into the atmosphere, and it can have detrimental effects on human health, the economy, and the environment. While there are natural sources of air pollution, such as volcanic activity, wildfires, and biological decay, most air pollution is a result of human activity. The burning of fossil fuels for transportation, electricity, and industrial processes is a major contributor to air pollution. Gases such as carbon monoxide, sulfur dioxide, nitrogen oxides, and volatile organic compounds (VOCs) are common pollutants produced by engines and industrial combustion processes. Additionally, human activities like open burning of garbage, vehicle emissions, and the use of chemicals in various industries further exacerbate air pollution. Among these various pollutants, sulfur dioxide is considered the gas that causes the maximum air pollution.

Carbon monoxide

CO is a harmful pollutant when inhaled in large amounts. It reduces the amount of oxygen that can be transported in the blood to vital organs, such as the heart and brain. Exposure to high levels of CO can cause dizziness, confusion, unconsciousness, and even death. People with heart disease are particularly vulnerable to the effects of CO, even at lower levels, which can cause chest pain and reduced exercise capacity. Healthy individuals can also be affected by high levels of CO, potentially developing vision problems and experiencing reduced manual dexterity and difficulty performing complex tasks.

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 exhaust from attached garages. The highest levels of CO typically occur during colder months when inversion conditions trap air pollution near the ground.

Outdoor sources of CO include cars, trucks, and other vehicles or machinery that burn fossil fuels. Higher levels of CO are generally found in areas with heavy traffic congestion. While very high levels of CO are unlikely to occur outdoors, elevated CO levels can be concerning for individuals with heart disease.

CO contributes to climate change by participating in chemical reactions in the atmosphere that produce ozone, a potent climate change gas. CO is classified as a short-lived climate forcing agent, and reducing CO emissions is considered a potential strategy to mitigate the effects of global warming.

Nitrogen dioxide

NO2 is a significant air pollutant in urban settings, along with sulfur dioxide and carbon monoxide. It is released directly into the atmosphere from the burning of fossil fuels such as fuel oil, gasoline, and natural gas. The dominant sources of nitrogen dioxide are thermal power plants and automobiles.

In North America, nitrogen dioxide is primarily produced from burning fossil fuels for transportation, power generation, and industrial activity, as well as from wildfires. The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument has been used to measure nitrogen dioxide pollution over North America, providing valuable data on the concentrations of this gas in the atmosphere. TEMPO has revealed high levels of nitrogen dioxide over multiple urban areas across the continent, with enhanced levels observed over major highways during rush hour.

Efforts to reduce NOx emissions from power plants and automobiles have led to significant decreases in nitrogen dioxide levels in some regions. However, increases have been noted in areas of oil and natural gas extraction. Overall, nitrogen dioxide is a significant contributor to air pollution, particularly in urban and industrial areas, and its presence has detrimental effects on human and environmental health.

Sulphur dioxide

The burning of these sulphur-containing materials during industrial processing or electricity generation releases toxic sulphur dioxide and sulphur trioxide, together called sulphur oxides, into the atmosphere. Sulphur dioxide forms secondary particulate matter (PM2.5) when it oxidises to sulphuric acid (H2SO4) by combining with water vapour. It also reacts with ammonia (NH3) to create another dangerous compound called ammonium sulphate ((NH4)2SO4). Sulphur dioxide also contributes to smog, which results from high concentrations of sulphur oxides in the atmosphere, exacerbated by dampness and particulate matter.

International shipping is a large and growing source of sulphur emissions, and shipping is set to become one of the most important contributors to UK sulphur emissions in the future. India is the largest emitter of SO2 in the world, contributing more than 21% of global emissions, mainly from coal-based electricity generation. Russia is the second-largest emitter, causing approximately 12% of global emissions, with most emissions stemming from smelters.

In recent decades, sulphur dioxide emissions from energy production in the UK have been vastly reduced due to restrictions on the sulphur content of fuels and the closure of coal-fired power plants. Between 1990 and 2023, emissions of sulphur dioxide in the UK decreased by 97%, from 312 thousand tonnes to 95 thousand tonnes. This reduction was driven by a decline in coal use in energy industries, with emissions from coal combustion decreasing by almost 100% from 2005 levels to 2023.

Volatile organic compounds (VOCs)

Volatile organic compounds, or VOCs, are gases that are emitted from solids or liquids. They include a variety of chemicals, some of which have adverse health effects. VOCs are emitted from thousands of everyday products, including paints, varnishes, waxes, cleaning products, disinfectants, cosmetics, degreasers, and hobby products. They are also found in building materials, such as foam insulation, carpets, and furniture glues, as well as in home cleaning products, personal care products, and tobacco smoke.

VOCs can be found in both indoor and outdoor air, with concentrations typically higher indoors—up to ten times higher than outdoors. This is due to the widespread use of products containing VOCs in enclosed spaces. Some VOCs have short- and long-term health effects, including eye, nose, and throat irritation, headaches, nausea, dizziness, and difficulty breathing. Long-term exposure can damage the liver, kidneys, and central nervous system, and some VOCs are linked to cancer. They may also worsen symptoms for people with asthma and COPD.

To reduce exposure to VOCs, it is recommended to read product labels, avoid or limit the use of products with harmful ingredients, safely dispose of unwanted products, and increase ventilation when using products containing VOCs. It is also advised to let new carpets or building products air outside before installing them and to avoid storing products with VOCs indoors. Ensuring effective ventilation systems in offices and schools can help reduce VOC levels produced by printers and copiers.

In terms of regulations, VOCs are regulated in pollutant discharges to surface waters and as hazardous waste during transportation. The VOC Solvents Emissions Directive in the European Union aims to reduce industrial emissions of VOCs, covering activities such as printing, surface cleaning, vehicle coating, and dry cleaning. The Paints Directive also limits the use of organic solvents in decorative paints, varnishes, and vehicle finishing products. However, there are currently no federally enforceable standards for VOCs in non-industrial settings.

It is important to note that the definition of VOCs can vary, and some VOCs are exempt from outdoor air pollution regulations due to their non-reactive nature in smog formation. Despite this, VOCs play a significant role in air pollution and can have detrimental effects on human health, making their regulation and control crucial.

Smoke and soot

Smoke contains particulate matter, which is a mixture of solid and liquid droplets suspended in the air. These particles can be hazardous to human health, especially when inhaled. Fine particulate matter (PM2.5) is of particular concern as it can penetrate deep into the lungs and potentially enter the bloodstream. Individuals with cardiovascular or respiratory diseases, older adults, children, pregnant women, outdoor workers, and those of lower socioeconomic status are at greater risk from the health effects of smoke inhalation.

Soot is a type of particulate matter that is composed largely of carbon-based particles resulting from the incomplete combustion of hydrocarbons or organic fuel, such as wood. It can also include non-carbon elements like sulfur and trace metals. Soot is considered a hazardous substance with carcinogenic properties and has been linked to various types of cancer and lung disease. Soot is a common byproduct of coal burning, internal combustion engines, power plant boilers, waste incineration, and house fires, among other sources.

The Environmental Protection Agency (EPA) in the United States has implemented programs and standards to reduce emissions from transportation sources, including the Diesel Emissions Reduction Act program, which provides funding to projects that reduce harmful emissions from diesel engines. These efforts have resulted in significant improvements in air quality and public health, with reductions in smog and soot. Similar initiatives are being undertaken internationally, such as the North American Emission Control Area (ECA) for large ocean-going vessels, which has led to significant reductions in air pollution.

Overall, smoke and soot are significant contributors to air pollution, with harmful effects on human health and the environment. Efforts to reduce emissions and improve air quality are ongoing, with a focus on regulating transportation sources and implementing clean technologies.

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