Air Pollutants: Human-Caused Primary Pollutants And Their Harmful Effects

Primary air pollutants are those that are formed and emitted directly from particular sources. Two examples of anthropogenic primary air pollutants are carbon monoxide and nitrogen oxide, which are toxic gases that are emitted directly from vehicles and combustion engines. Carbon monoxide is colourless, odourless, and tasteless, and it inhibits the body's ability to carry oxygen to organs and tissues. Nitrogen oxide is formed through the combustion of coal and petroleum. These pollutants are of significant concern as they can cause serious health issues and even death.

Industrial processes, residential heating, and transportation

Industrial Processes

Industrial activities, particularly in the manufacturing and energy sectors, release a multitude of toxic pollutants into the atmosphere. The burning of fossil fuels, such as coal and oil, for electricity production, contributes to the emission of carbon dioxide, nitrogen oxides, sulfur dioxide, and particulate matter (e.g., fly ash and soot). These emissions are major precursors of acid rain and photochemical smog, which have detrimental effects on human health and the environment.

Residential Heating

Residential heating practices, especially the burning of solid fuels like wood or coal for space heating, are significant sources of indoor and outdoor air pollution. Inadequate ventilation in homes can lead to the accumulation of pollutants, including nitrogen dioxide (NO2), volatile organic compounds (VOCs), sulfur dioxide (SO2), carbon monoxide (CO), carbon dioxide (CO2), and particulate matter (PM). These pollutants can cause respiratory issues and have been linked to serious illnesses, including lung cancer.

Transportation

The transport sector, including road, air, rail, and water transport, is a major contributor to air pollution worldwide. Emissions from road traffic, particularly in urban areas, have raised concerns about their impact on human health and the environment. The combustion of fossil fuels in vehicles releases pollutants such as nitrogen oxides (NOx) and particulate matter, which contribute to urban smog and poor air quality. Aircraft emissions, including those from aviation fuel combustion and aircraft operations, are also a growing concern, especially with the projected increase in air traffic.

The mitigation of air pollution from these sources requires collective and individual efforts. Technological advancements, such as the introduction of three-way catalysts in vehicles, and policy interventions, such as emissions standards and traffic reduction measures, are crucial steps towards reducing air pollutant emissions and improving air quality.

Incomplete combustion of fossil fuels

Carbon Monoxide (CO)

A colourless, odourless, and toxic gas, carbon monoxide is a byproduct of incomplete combustion. When inhaled, it inhibits the blood's ability to carry oxygen by binding with haemoglobin, leading to symptoms such as headaches, dizziness, and even death in severe cases. Carbon monoxide is a common pollutant found in vehicle exhaust, industrial processes, and household appliances such as gas stoves and furnaces when they lack proper ventilation.

Particulate Matter (PM)

Particulate matter consists of tiny particles or droplets in the air, varying in size and composition. These particles can be a mixture of solid particles and liquid droplets, penetrating deep into the respiratory system. Fine particles, especially those with a diameter of 2.5 micrometres or smaller (PM2.5), are particularly harmful as they can reach the lungs and even enter the bloodstream. Health issues associated with exposure to particulate matter include respiratory conditions such as asthma and bronchitis.

Unburned Hydrocarbons (UHCs)

Unburned hydrocarbons contribute to the formation of ground-level ozone, which is a respiratory irritant and a contributor to climate change.

Sulfur Dioxide (SO2)

Sulfur dioxide is a harmful compound released during the combustion of fossil fuels containing sulfur impurities, such as coal and oil. It contributes to acid rain, which damages ecosystems, soil, and human-made structures. Additionally, sulfur dioxide can cause respiratory problems in humans.

Nitrogen Oxides (NOx)

Nitrogen oxides are another byproduct of incomplete combustion, and they also contribute to acid rain and respiratory issues.

Overall, the incomplete combustion of fossil fuels poses significant risks to both human health and the environment, leading to respiratory issues, heart problems, and environmental degradation.

Black carbon, a component of PM2.5

Black carbon is a major component of PM2.5, also known as particulate matter, and is sometimes referred to as soot. It is produced by the incomplete combustion of fossil fuels, biofuels, and biomass. Both anthropogenic and natural sources contribute to black carbon emissions. Examples of anthropogenic sources include diesel vehicles, biomass cookstoves, and brick manufacturing. Natural sources include wildfires.

Black carbon is a significant environmental health hazard and a leading cause of premature deaths worldwide. Due to their extremely small size, PM2.5 particles can penetrate deep into the lungs and facilitate the transport of toxic compounds into the bloodstream. They have been linked to various adverse health effects, including respiratory and cardiovascular issues, strokes, heart attacks, and aggravated asthma. These particles have even been detected in the lungs, livers, and brains of unborn babies, indicating potential impacts on early childhood development.

The health impacts of black carbon are not limited to humans but also extend to ecosystems. When black carbon particles settle on plant leaves, they increase the surface temperature, interfere with rainfall patterns, and affect plant growth and yield. Additionally, black carbon contributes to regional environmental disruption and accelerates glacier melting by reducing the ability of surfaces to reflect sunlight and absorbing light to generate heat.

Black carbon emissions have been declining due to improved practices in various sectors. For instance, there have been advancements in brick manufacturing, reduced open burning in agriculture, improved fuel and vehicle standards, and a transition to cleaner household energy sources. However, despite these positive changes, more efforts are needed to accelerate the reduction of black carbon emissions and mitigate their harmful effects on human health and the environment.

Nitrogen oxides and volatile organic compounds

Nitrogen oxides are also harmful as they can react with other atmospheric substances to create acid rain and contribute to ozone smog and particle pollution. People are primarily exposed to nitrogen oxides outdoors, and monitoring devices can help reduce their impact on health. VOCs, on the other hand, are a large group of compounds with carbon that easily becomes vapors or gases. They are emitted from liquids or solids and are prevalent in both indoor and outdoor environments. Common sources of VOCs include car fumes, repellents, air fresheners, aerosol sprays, paint, pesticides, and dry-cleaned clothing.

Formaldehyde, a colourless gas with a pungent smell, is one of the most common VOCs found indoors. It is emitted from building materials like particleboard, plywood, glue, and paints, as well as household and personal care products such as drapes, carpets, cleaning agents, and hair sprays. Short-term exposure to formaldehyde can cause eye, nose, and throat irritation, while long-term exposure has been linked to nasopharyngeal cancer. Other indoor sources of VOCs include combustion processes such as smoking, heating, cooking, and burning candles or incense.

To protect human health, it is crucial to identify the sources of these pollutants and reduce their impact. Smart indoor air quality monitors can help detect high levels of nitrogen oxides and VOCs, enabling people to take precautions and improve air quality. Additionally, understanding the units used to measure VOCs and their threshold values can aid in effectively managing indoor and outdoor pollution levels. Overall, addressing these two primary air pollutants, nitrogen oxides and VOCs, is essential for safeguarding the well-being of individuals and the environment.

Health impacts: cardiovascular issues and premature mortality

Cardiovascular issues and premature mortality are significant health impacts of air pollution. The risk of cardiovascular disease is increased by exposure to fine particulate matter (PM2.5), which has diameters of less than 2.5 µm. PM2.5 can be released into the atmosphere by the combustion of fuels in power generation, industrial processes, and vehicles.

The evidence for the impact of PM2.5 on cardiovascular health is strong, with exposure over a few hours to weeks potentially triggering cardiovascular disease-related heart attacks and death. Longer-term exposure can lead to an increased risk of cardiovascular mortality and decreased life expectancy. For example, a recent study found that air pollution could trigger acute coronary syndrome within an hour of exposure, resulting in a heart attack or unstable angina.

The effects of PM2.5 exposure are particularly acute in the first two days, with a 1 μg/m3 reduction in PM2.5 concentrations estimated to reduce the number of OHCA events by 8%, and a 3 μg/m3 reduction estimated to result in a 30% decrease in these events. The smallest ultrafine particles can cross the alveolar-capillary barrier and directly enter the bloodstream, interacting with the cardiovascular system and other organs.

In addition to the impact of PM2.5, other pollutants, such as carbon monoxide, ozone, nitrogen dioxide, and sulfur dioxide, can also have adverse health effects. These pollutants are included in the WHO Global Air Quality Guidelines due to their potential health impacts. Short- and long-term exposure to black carbon, a major component of PM2.5, has been associated with cardiovascular health effects and premature mortality.

Overall, air pollution has been linked to several million premature deaths globally every year, with ambient (outdoor) air pollution ranked as the fifth biggest risk factor for all-cause disease. Ischaemic heart disease and stroke account for approximately half of the early deaths attributed to air pollution.

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