Outdoor Air Pollution: The Major Culprit Unveiled

Outdoor air pollution is a pressing environmental health issue that affects people in low-, middle-, and high-income countries alike. It is estimated to cause 4.2 million premature deaths worldwide per year, with 68% of these being due to ischaemic heart disease and stroke. Fossil fuels are a major contributor to outdoor air pollution due to the pollutants they release when burned for energy, such as carbon monoxide, nitrogen oxides, and sulfur dioxide. Other factors include industrial activities, power plants, construction sites, waste burning, and traffic.

Fossil fuels

The burning of fossil fuels, particularly coal, petrol, and diesel, is a significant source of airborne particulate matter (PM) and ground-level ozone. These pollutants have been implicated as key contributors to the global burden of mortality and disease. Exposure to air pollution, even at low levels, has been associated with adverse health outcomes. The Global Burden of Diseases, Injuries, and Risk Factors Study 2015 identified ambient air pollution as a leading cause of disease burden, particularly in low- and middle-income countries.

Recent studies have estimated the global impact of fossil fuel pollution, with one study reporting that exposure to particulate matter from fossil fuels accounted for 21.5% of total deaths in 2012, decreasing to 18% in 2018 due to improved air quality measures in China. Another study, published in 2023, estimated that air pollution from fossil fuels caused 5.1 million deaths per year, contributing to 61% of the total estimated 8.3 million deaths linked to outdoor air pollution from all sources in 2019.

The health impacts of fossil fuel combustion are particularly detrimental to children under five, who are more susceptible to the adverse effects of air pollutants. Thousands of children under the age of five die annually from respiratory infections attributed to fossil fuel pollution.

Transitioning from fossil fuels to renewable energy sources is crucial to reducing air pollution and its associated health risks. Governments can play a key role in this transition by creating and enforcing regulations that limit fossil fuel burning by industries and investing in the development of clean, renewable energy sources.

Carbon monoxide

Breathing air with high concentrations of CO reduces the amount of oxygen transported in the bloodstream to critical organs like the heart and brain. While very high levels of CO are unlikely to occur outdoors, elevated levels outdoors can be dangerous for people with heart disease.

The burning of biomass fuels and tobacco smoke are significant sources of indoor carbon monoxide exposure in developing countries. Clogged chimneys, wood-burning fireplaces, and gas burners can also vent carbon monoxide into indoor spaces if they do not have properly working safety features. Incomplete oxidation during combustion can cause high concentrations of carbon monoxide in indoor air. Tobacco smoke and vehicle exhaust from attached garages can also be major sources of indoor carbon monoxide exposure.

In the United States, the Environmental Protection Agency (EPA) was created to enforce the Clean Air Act and reduce air pollution. The EPA sets and reviews standards for CO in outdoor air, helping state, tribal, and local agencies maintain safe levels of CO.

Radon

Outdoors, radon escapes from the ground and quickly dilutes to very low concentrations, typically ranging from 5 Bq/m3 to 15 Bq/m3. The level of outdoor radon is influenced by factors such as soil characteristics (including uranium and radium content), local topology, and meteorological conditions. For example, in areas with high radon fluxes from the soil, such as former uranium mining districts, short-term elevated outdoor radon levels have been observed. These high outdoor radon levels, while rare, can be of local health significance.

While outdoor radon is generally not a major health concern due to its low concentrations, it can still contribute to overall radiation exposure, especially in areas with elevated radon levels. The health effects of radon exposure are primarily associated with its radioactive decay products, which can damage DNA and increase the risk of lung cancer when inhaled.

To mitigate the potential risks of radon, organizations like the World Health Organization (WHO) and the International Atomic Energy Agency (IAEA) have established guidelines and safety standards for indoor radon levels in homes and workplaces. These standards aim to protect public health and reduce the risk of radiation exposure. Additionally, some countries have implemented regulations and building codes to prevent radon accumulation in newly constructed buildings, particularly in areas with high radon emissions.

Ultrafine particles

The burning of fossil fuels, such as coal, oil, and natural gas, releases UFPs and other pollutants into the atmosphere. Fossil fuels are a significant contributor to outdoor air pollution, and their use in vehicles and industries has led to increased UFP emissions. Regulations and international cooperation are crucial in mitigating UFP pollution. For instance, the United States established the Environmental Protection Agency (EPA) and modified the Clean Air Act to address air pollution.

While the EPA does not currently regulate UFP emissions, it requires notification of intentional nanoparticle manufacture and has drafted a Nanomaterial Research Strategy. The debate around UFP regulation extends to the European Union (EU) and Asia. China and South Korea, for example, have disputed the origins of ultrafine dust, with South Korea attributing about 80% of it to China. However, China claims its air quality has improved since 2013, and the two countries have since collaborated on environmental initiatives.

Urban areas are particularly susceptible to UFP pollution, with motor traffic being the primary source of outdoor UFP concentrations. The increasing trends of urbanisation and road traffic expansion will likely lead to greater population exposure to UFPs. Studies indicate that the average exposure to UFPs in Asian cities is approximately four times higher than in European cities, highlighting the varying levels of UFP pollution across different regions.

The health implications of UFPs are a significant concern. While the nose constantly filters out UFPs, preventing lung absorption, they can worsen respiratory conditions and lead to impaired breathing. The Clean Air Act aims to reduce the number of premature deaths related to UFP exposure and mitigate the negative health effects of air pollution.

Nitrogen dioxide

The Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument has been instrumental in measuring nitrogen dioxide air pollution over North America. TEMPO scans the continent every hour, measuring sunlight reflected and scattered off the Earth's surface, clouds, and the atmosphere. These measurements are used to determine the amount of nitrogen dioxide and other gases in the Earth's atmosphere. The data collected by TEMPO has revealed high levels of nitrogen dioxide over multiple urban areas across the United States, Canada, Mexico, and the Caribbean.

Visualizations of TEMPO data show that nitrogen dioxide pollution is typically higher in the morning and during rush hour in cities. As the day progresses, the morning pollution often dissipates, only to rise again during the second rush hour. TEMPO's continuous observations during daylight hours have provided valuable insights into the dynamics of nitrogen dioxide pollution, enabling a better understanding of pollution sources and population exposure.

To address the issue of nitrogen dioxide pollution, governments and industries must work together to implement regulations and policies that reduce the burning of fossil fuels. This may include transitioning to cleaner energy sources, improving fuel efficiency, and implementing emission control technologies. Additionally, public education and awareness about the impacts of nitrogen dioxide pollution can help individuals make informed choices and contribute to collective efforts to improve air quality.

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