Air Pollutants That Trigger Bronchial Asthma

Air pollution is a contamination of the air with substances that harm human health or the environment. It can cause and worsen lung diseases, including bronchial asthma. Outdoor air pollution includes primary pollutants emitted directly into the atmosphere and secondary pollutants formed in the air from chemical transformations of the primary. These chemical reactions depend on temperature and can be influenced by global climate change. Several studies have found a positive association between air pollution and asthma incidence, with vulnerable groups including children, pregnant people, and older people.

Ground-level ozone

Ozone (O3) is a gas molecule composed of three oxygen atoms. While the ozone layer in the upper atmosphere shields us from much of the sun's ultraviolet radiation, ozone at ground level is a dangerous air pollutant. Ground-level ozone is formed from gases emitted from sources such as car tailpipes, smokestacks, and factories. It is also created by chemical reactions between emissions of burning fuel and volatile organic compounds (VOCs), heat, and sunlight.

Several studies have found a correlation between high ozone levels and increased asthma symptoms, medication use, and hospital admissions for asthma, particularly during the warm season. For example, a study of lifeguards in Galveston showed greater obstruction of their airways at the end of the day when ozone levels were high. Additionally, children with asthma used their inhalers more frequently on days with higher ozone concentrations. Long-term exposure to ozone is also linked to the aggravation of asthma and is likely one of the many causes of asthma development. It causes inflammation and damage to the airway lining, similar to how sunburn damages the skin.

People with asthma are especially susceptible to the effects of ozone exposure. Children, in particular, may be disproportionately affected due to their higher risk of exposure through outdoor activities and exercise. Furthermore, ozone exposure can increase the responsiveness of people with allergic asthma to other allergens, such as house dust mite antigens. Overall, ground-level ozone is a significant contributor to air pollution and poses a serious health risk, especially for individuals with asthma.

Nitrogen dioxide

High levels of NO2 exposure can increase the severity of asthma exacerbations, especially in children with colds and those who have bronchial hyper-responsiveness. In addition, NO2 exposure has been associated with respiratory symptoms in both children and adults. The risk is more significant in children, as they are more susceptible to the effects of air pollution.

NO2 exposure can also enhance the asthmatic response to allergens through eosinophilic activation in the airways. This activation increases eosinophilic inflammation in response to inhaled allergens in the distal lower airways. This inflammation can be measured in bronchial washes, bronchoalveolar lavage, and sputum.

Furthermore, short-term exposure to high concentrations of NO2, even for as little as 30 minutes, can affect bronchial responsiveness in individuals with mild asthma. This effect was observed at NO2 concentrations of 500 micrograms.m3, with a tendency for increased bronchial responsiveness at 260 and 1,000 micrograms.m3.

Overall, nitrogen dioxide (NO2) is a significant air pollutant that can cause bronchial asthma and worsen symptoms in those already suffering from the condition. Reducing NO2 pollution is crucial to improving human health, especially in urban areas with higher pollution levels.

Sulphur dioxide

Air pollution can cause asthma and other respiratory issues. It can also worsen asthma symptoms, leading to more hospital visits and, in some cases, early death. Outdoor air pollution includes primary pollutants, emitted directly into the atmosphere, and secondary pollutants formed through chemical transformations of the primary.

One such pollutant is sulphur dioxide (SO2). SO2 is a by-product of burning fossil fuels, transportation, volcanic activity, and industrial processes. It is also present in smog and haze. SO2 can cause a range of harmful effects on the lungs, including wheezing, shortness of breath, and chest tightness, particularly during physical activity. Long-term exposure to high levels of SO2 increases respiratory symptoms and impairs lung function. Even short-term exposure to peak levels of SO2 can cause breathing difficulties for people with asthma when they are outdoors. This is especially true for children and older adults, who are at an increased risk of hospitalisation or emergency room visits due to SO2 exposure.

The impact of SO2 on asthma has been the subject of various studies. One study, focusing on urban children, linked specific outdoor air pollutants, including fine particulate matter and ozone, to non-viral asthma attacks. Another study examined the mechanisms of sulphur dioxide-induced bronchoconstriction in both normal and asthmatic individuals. It found that atropine and SCG inhibited the SO2 response, suggesting that vagal efferent mechanisms are involved in the bronchial response to SO2. However, the lack of inhibition caused by atropine in hyperreactive subjects indicates that vagal mechanisms may not be solely responsible for hyperreactivity to SO2.

While SO2 emissions have decreased over time due to policies promoting cleaner fuels and pollution controls on power plants, it remains a significant health concern. High levels of SO2 can still occur during the start-up or shutdown of polluting sources or when their equipment malfunctions. As a result, individuals living or working near these sources, such as ports and smelters, are at the highest risk of exposure.

Carbon monoxide

The elderly, young children, and individuals with respiratory conditions like asthma or emphysema are at greater risk of carbon monoxide poisoning. Additionally, those with cardiovascular disease, anaemia, or sickle cell anaemia are more susceptible. Certain jobs or activities that require strenuous exertion can also increase the risk of CO poisoning.

To protect against carbon monoxide poisoning, it is essential to have working CO detectors installed in homes, especially in spaces with fuel-burning appliances or attached garages. Maintaining and properly using fuel-burning devices can also help prevent carbon monoxide leaks and reduce the risk of exposure.

In summary, carbon monoxide is a hazardous and potentially deadly gas that can cause serious health issues, including bronchial asthma. Taking precautionary measures, such as using CO detectors and proper ventilation, is crucial to minimise the risk of carbon monoxide poisoning.

Particulate matter

Asthma is a chronic respiratory disease characterised by variable airflow obstruction, bronchial hyperresponsiveness, and airway inflammation. People with asthma are at greater risk from breathing in small particles and irritating gases, which can irritate the airways and make asthma worse. These small particles are called "particulate matter" or "PM". The smallest particles (PM2.5) are the most dangerous as they can get deep into the lungs or even the bloodstream. Particulate matter frequently contains various immunogenic substances, such as fungal spores and pollen, which have been independently associated with the exacerbation of asthma symptoms.

Several studies have found a link between exposure to particulate matter and the development of asthma. A study of 184,604 children in Taiwan, for example, found that both prenatal and postnatal exposure to air pollutants, particularly PM2.5, were associated with the later development of asthma. Similarly, a study of urban children in the United States found that asthma attacks were associated with locally elevated levels of fine particulate matter and ozone in outdoor air.

The UK Daily Air Quality Index is based on concentrations of nitrogen dioxide, sulphur dioxide, ozone, PM2.5, and PM10. People with asthma should ideally live at least 300 metres from major roadways, especially those with heavy truck traffic, as concentrations of motor vehicle emissions such as ultrafine PM and black carbon particles decrease substantially at this distance. On days when air pollution levels are high, people with asthma should avoid unnecessary outdoor activity, especially if it entails vigorous exercise that increases minute ventilation and thus the total inhaled dose.

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