Air Pollutants: Understanding The Main Culprits Harming Our Air

Air pollution is a pressing issue that poses significant risks to human health and the environment. The primary air pollutants of concern include carbon monoxide, ammonia, nitrogen dioxide, ozone, particulate matter, sulphur dioxide, and volatile organic compounds. These pollutants are known to have detrimental effects on human well-being, contributing to respiratory issues, heart disease, and even premature mortality. Among these, particulate matter, specifically PM2.5, stands out as the most pervasive health hazard, with efforts to reduce its presence leading to a notable decrease in associated deaths. While air quality has improved over the years, the challenge of reducing ammonia emissions persists, particularly in the agricultural sector. Understanding and addressing these main air pollutants are crucial steps towards safeguarding public health and mitigating the environmental impact of pollution.

Ground-level ozone

Nitrogen oxides and volatile organic compounds are emitted from both natural sources and human activities. The burning of coal, gasoline, and oil in motor vehicles, homes, industries, and power plants accounts for about 95% of NOx from human activity. VOCs, on the other hand, originate primarily from human activities such as gasoline combustion, upstream oil and gas production, and residential wood combustion.

Ozone is most likely to reach unhealthy levels on hot sunny days in urban environments, but it can also reach high levels during the colder months. It can trigger a variety of health problems and has been linked to premature mortality and an array of morbidity health endpoints, such as hospital admissions and asthma exacerbations. In addition to its effects on human health, ground-level ozone also negatively impacts vegetation and crop productivity, and can damage certain synthetic materials and textiles.

To address the issue of ground-level ozone, the EPA in the United States has implemented regulations to help states reduce ozone levels in outdoor air. They work with state, local, and tribal governments to reduce air emissions of harmful pollutants. In Canada, the Ozone Annex was added to the Canada-United States Air Quality Agreement in December 2000 to tackle transboundary air pollution contributing to high levels of ground-level ozone.

Particulate matter

The health effects of particulate matter have been widely studied, and exposure to PM2.5 in particular has been linked to a range of serious health problems. According to the CDC, inhaling particulate matter can cause asthma, lung cancer, respiratory diseases, cardiovascular disease, premature delivery, birth defects, low birth weight, developmental disorders, neurodegenerative disorders, mental disorders, and premature death. A 2014 meta-analysis also reported a link between long-term exposure to PM2.5 and coronary events, with an increased risk of heart attacks. Additionally, particulate matter may cause tissue damage by directly entering organs or indirectly through systemic inflammation.

The EPA has implemented rules to reduce emissions of pollutants that form particulate matter and is working with state, local, and tribal governments to improve air quality and protect public health. The Air Quality Index (AQI) is a useful tool that provides information on outdoor air quality and associated health risks, helping individuals take necessary precautions to protect their health.

Carbon monoxide

CO is a significant air pollutant that contributes to climate change. It participates in chemical reactions in the Earth's atmosphere that produce ozone, a known climate change gas. While CO has a weak direct impact on the climate, it is classified as a short-lived climate forcing agent. As a result, reducing CO emissions is considered a potential strategy to mitigate the effects of global warming.

In outdoor air, CO levels are regulated by organisations like the US Environmental Protection Agency (EPA), which sets and reviews standards for CO concentrations under the Clean Air Act. These standards help state, tribal, and local agencies ensure that CO is maintained at safe levels.

Indoors, 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 typically occur during colder months when inversion conditions trap air pollution near the ground. Even at relatively low levels, CO can be harmful to individuals with heart disease, causing chest pain and reduced exercise capacity. Repeated exposure may contribute to further cardiovascular issues. At very high levels, CO can cause dizziness, confusion, unconsciousness, and even death.

Nitrogen oxides

Nitric oxide (NO) and nitrogen dioxide (NO2) are the most common nitrogen oxides. NO is not considered hazardous under typical ambient conditions, but excess amounts and its by-products may cause respiratory issues, metabolic disorders, and other health problems. On the other hand, NO2 is a primary pollutant that can irritate and inflame the airways in the human respiratory system. Prolonged exposure to high levels of NO2 can cause permanent damage to the respiratory system, especially for individuals with asthma.

The primary sources of nitrogen oxides are road traffic and energy production. In large cities, the combustion of gasoline in automobiles, as well as coal-fired power plants and electric power plant boilers, contributes significantly to the emission of nitrogen oxides. Additionally, indoor sources of nitrogen oxides include tobacco smoke and the burning of fuels like gas, wood, oil, kerosene, and coal in appliances such as stoves, ovens, and heaters.

Sulphur dioxide

International shipping is a large source of sulphur, and activity levels have been increasing over time as other sources have been reduced. As a result, shipping is set to become one of the most important contributors to UK sulphur emissions in the coming years.

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