Air Pollution: A Slow, Silent Killer

Air pollution is a major threat to global health and prosperity, causing millions of premature deaths each year. It is a mix of hazardous substances from both human-made and natural sources, including vehicle emissions, fuel oils, natural gas, manufacturing by-products, and power generation. These pollutants can cause irritation, inflammation, and damage to the respiratory tract, increasing the risk of heart and respiratory diseases, lung cancer, and strokes. The effects of air pollution vary depending on factors such as the type of pollutant, length and level of exposure, individual health risks, and the cumulative impacts of multiple pollutants. While emissions are decreasing in some countries, air pollution remains a significant issue, particularly in low- and middle-income countries, where it contributes to a high number of premature deaths.

Particulate matter

PM is a portion of air pollution that is made up of extremely small particles and liquid droplets containing acids, organic chemicals, metals, and soil or dust particles. Natural sources of PM include volcanoes, fires, dust storms, and aerosolized sea salt. Manmade sources include combustion in mechanical and industrial processes, vehicle emissions, tobacco smoke, and household cleaning products.

PM has been linked to a variety of health problems, including respiratory and cardiovascular issues, and even cancer, strokes, and heart attacks. Short-term exposure to PM10 has been associated with worsening respiratory diseases, including asthma and chronic obstructive pulmonary disease (COPD). Long-term exposure to PM2.5 has been linked to premature death, particularly in people with chronic heart or lung diseases, and reduced lung function growth in children. The World Health Organization estimates that PM air pollution contributes to approximately 800,000 premature deaths each year, making it the 13th leading cause of mortality worldwide.

The effects of PM on health have been recognised since antiquity, but the lethality of air pollution was not fully understood until more recently. In 1930, a mixture of sulfur dioxide from factory emissions and dense fog in the Meuse Valley in Belgium led to acute pulmonary symptoms in several thousand people, and 60 deaths. In 1952, a similar event occurred in London, resulting in more than 3,000 excess deaths over 3 weeks.

It is important to limit exposure to PM, especially for those who are more susceptible, such as people with heart or lung diseases, children, older adults, and those from minority or low socioeconomic status populations. Monitoring air quality and taking measures to reduce emissions of pollutants that form PM can help protect public health and reduce the impact of PM on the population.

Nitrogen dioxide

NO2 is a highly reactive gas and is part of a group of gases known as nitrogen oxides (NOx). Other nitrogen oxides include nitrous acid and nitric acid. NO2 is used as an indicator for the presence of other nitrogen oxides. It is a major contributor to particle pollution and the chemical reactions that produce ozone.

The health effects of NO2 are particularly harmful to vulnerable subpopulations, including people with pre-existing medical conditions such as asthma, chronic obstructive pulmonary disease (COPD), cardiovascular disease, diabetes, and lung cancer. People of color are also identified as a vulnerable subpopulation. Those who live near emission sources are at higher risk of adverse health impacts.

While air quality has improved in recent years due to cleaner power plants, industrial sites, and vehicles, many people still breathe unhealthy levels of NO2. High concentrations of NO2 are found in large urban regions and near heavily traveled roadways. To protect public health, governments develop plans to reduce NO2 levels in areas where air quality does not meet national standards.

In summary, nitrogen dioxide is a harmful air pollutant that irritates the respiratory system and exacerbates respiratory conditions, particularly asthma. It is formed through the burning of fossil fuels and is present in high concentrations in urban areas. Vulnerable subpopulations are at higher risk of adverse health effects, and governments are working to reduce NO2 levels to improve air quality and protect public health.

Ozone

To protect public health and the environment, air quality regulators work to reduce ozone pollution. Efforts to lower emissions from power plants, industrial sites, and vehicles have led to improvements in air quality nationwide. However, ozone can be transported long distances by wind, affecting even rural areas. Therefore, it is essential to continue implementing measures to reduce air pollution and protect vulnerable populations from the harmful effects of ozone exposure.

Respiratory diseases

Air pollution is a major threat to global health and prosperity. It is a mix of hazardous substances from both human-made and natural sources. Outdoor and indoor air pollution cause respiratory and other diseases and are important sources of morbidity and mortality. According to the World Health Organization (WHO), air pollution kills 7 million people a year globally, a number that has increased over the past two decades.

Air pollution is a mix of hazardous substances from both human-made and natural sources. Vehicle emissions, fuel oils, natural gas to heat homes, by-products of manufacturing and power generation, particularly coal-fueled power plants, and fumes from chemical plants are some of the sources of air pollution.

Household air pollution is mainly caused by the use of solid fuels (such as wood, crop wastes, charcoal, coal, and dung) and kerosene in open fires and inefficient stoves. Most of the people exposed to this type of pollution are poor and live in low- and middle-income countries. Exposure to smoke from cooking fires causes 3.2 million premature deaths each year, mostly in low- and middle-income countries, where polluting fuels and technologies are used every day, particularly at home for cooking, heating, and lighting.

Particulate matter with a diameter of 10 microns or less can penetrate and lodge deep inside the lungs, causing irritation, inflammation, and damaging the lining of the respiratory tract. Smaller, more health-damaging particles with a diameter of 2.5 microns or less can penetrate the lung barrier and enter the bloodstream, affecting all major organs of the body. These pollutants increase the risk of heart and respiratory diseases, as well as lung cancer and strokes.

Ozone is a major factor in causing asthma (or making it worse), and nitrogen dioxide and sulfur dioxide can also cause asthma, bronchial symptoms, lung inflammation, and reduced lung function. In addition, nitrogen dioxide, along with other nitrogen oxides, can interact with the sun's ultraviolet light and a category of gases known as volatile organic compounds to produce secondary pollutants like ground-level ozone, which can pose health problems such as inflammation and damage to the airways.

Cancer

Air pollution is a major public health concern, threatening the progress made in reducing the global burden of cancer. It is a significant and far-reaching threat, with 99% of the world's population breathing unhealthy air, according to the World Health Organization (WHO). Outdoor air pollution, in particular, poses a serious challenge as it is ubiquitous and has severe adverse health effects, including cancer.

Outdoor air pollution has been classified as a Class I human carcinogen by the WHO, with strong evidence linking it to an increased risk of lung, head, and neck cancers. These cancers primarily affect the upper aerodigestive tract and have also been associated with smoking. Air pollution includes a mixture of outdoor and indoor pollutants, such as vehicle exhaust fumes, smoke from burning fuels, and natural sources like wind-blown dust and radon.

The link between air pollution and lung cancer has been well-established. Particulate matter (PM), especially PM2.5, has been implicated in lung cancer incidence and mortality. These tiny particles can build up in the lungs, damaging DNA and altering cell division, ultimately leading to cancer. Studies have found that air pollution is associated with an increased risk of lung cancer, even in non-smokers. In a multi-city study, air pollution was positively correlated with lung cancer mortality, similar to smoking. Another study in California showed that air pollution, including sulfur dioxide, ozone, and PM10, increased the risk of developing lung cancer over a 15-year period.

Additionally, air pollution has been associated with other types of cancer, although the evidence is more limited. A study in Hong Kong suggested that long-term exposure to ambient fine particulate matter (PM2.5) is linked to an increased risk of mortality from breast, liver, and pancreatic cancer. The same study also found higher incidences of these cancers in urban areas of China compared to rural regions, likely due to higher pollution levels. While pollution is a risk factor for cancer, other factors such as diet and exercise may have a more significant impact.

Indoor air pollution, caused by second-hand smoke, burning wood, and coal, can also increase the risk of lung cancer and other health conditions. However, the focus of cancer prevention and intervention strategies has primarily been on outdoor air pollution due to its widespread impact.

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