The sources of outdoor or ambient air pollution are varied and may be either natural or produced by human activities. Air pollutants have been linked to a range of adverse health effects, including respiratory infections, cardiovascular diseases and lung cancer. Reducing air pollution will decrease the global burden of disease from these illnesses.
Human beings need good-quality air for their health and well-being. Air is a mixture of nitrogen (78 percent), oxygen (21 percent), carbon dioxide and some inert gases (1 percent). It also contains varying quantities of water vapour as well as numerous harmful substances: natural pollutants such as dust and volcanic ash, and pollutants that are produced by human activities.
Air quality is simply the state of the air around us. Clean, unpolluted air would be considered good air quality. The presence of pollutants in the air, whether due to natural or human causes, in sufficiently high concentrations, results in poor air quality. Air quality thus describes the healthiness and safety of the atmosphere.
The sources of outdoor or ambient air pollution are varied and may be either natural or human-made. Natural outdoor air pollution includes oxides of sulphur and nitrogen from volcanoes, inorganic biological decay, lightning strikes and forest fires, and pollen from plants, grasses and trees, and particulate matter from dust storms. Natural pollution is all around us all the time. However, concentrations can sometimes increase dramatically, for example after a volcanic eruption or at the beginning of the growing season.
Perhaps of more concern, given our ability to have greater control over its release into the atmosphere, is anthropogenic pollution, which can also have a detrimental impact on ambient air quality. The most common source of anthropogenic air pollution outdoors is the burning of fossil fuels such as coal, oil and gas, in power stations, industrial facilities, homes and vehicles. Depending on the nature of the fuel and the type of combustion process, pollutants released into the atmosphere from the burning of fossil fuels include nitrogen oxides, sulphur dioxide, carbon monoxide, particulate matter, lead and volatile organic compounds (VOCs). Other sources of these pollutants include forest fires, the manufacturing of chemicals, fertilisers and paper, and waste incineration. These pollutants are all referred to as primary pollutants, as they have direct sources.
Unlike the ozone layer in the stratosphere, which makes our planet habitable by absorbing harmful solar ultraviolet radiation, ground-level or tropospheric ozone is a pollutant that is formed indirectly by the action of sunlight on VOCs in the presence of nitrogen dioxide. Ozone is referred to as a secondary ambient air pollutant.
Both primary and secondary pollutants are, to a greater or lesser extent, detrimental to human health, depending on their concentration in the air and the sensitivity of the individual. As a consequence, national and international legislation exists to regulate and control the amount of pollution emitted into the atmosphere, and to ensure that objectives for improving ambient air quality are achieved.
Generally, pollution is unseen or invisible. However, at times the pollutants in a particular airshed can reach such high concentrations that the air actually appears polluted. In larger urban centres, particularly in the summer, pollution may form smog — a brownish yellow or greyish white haze hovering over the skyline. Smog consists of particulate matter and ground-level ozone.
Particulate matter (PM) is defined as either PM10 (1/8 the thickeness of a human hair) or PM2.5 (1/20 the thickness of a human hair). These minute particles are released into the air in liquid or solid form and can include dust, dirt, soot and smoke. The sources of PM are vehicles, factories, construction activities, fires, naturally occurring windblown dust and vegetation.
Other hazardous air pollutants may adhere to PM and increase its toxicity. Particulate matter can also be formed in the air as a result of chemical reactions between gases such as nitrogen oxides, sulphur dioxide and carbon monoxide. Particulate matter, and PM2.5 in particular, can penetrate deep into the lungs, damaging lung tissue and reducing lung function.
Ground-level ozone (O3) is the main component of photochemical smog or summer smog. Ground-level ozone is a compound that forms in the lower atmosphere as the result of a reaction between nitrogen dioxide (NO2) and other airborne substances in the presence of ultraviolet light. Ground-level ozone is the same as the ozone in the upper atmosphere: the only difference is elevation. Ground-level ozone in low concentrations can irritate the eyes, nose and throat and can decrease lung function and affect physical performance.
Your lungs take in the air around you. As PM2.5 comprises a mixture of microscopic solids, combustion products, metals and other toxins, it is a cause of serious health concern. The small particles that we breathe deep into our lungs become lodged in the alveoli, eventually damaging lung function. Even low concentrations of PM2.5 can cause an array of both short- and long-term health effects. Individuals who are sensitive to high levels of pollution may experience a variety of symptoms that range from uncomfortable to life threatening. People with a pre-existing illness such as diabetes, lung disease (e.g. asthma, chronic bronchitis, emphysema and lung cancer) or heart disease will be more sensitive to air pollution than the average population.
Other high-risk groups include the elderly, children and athletes. With age, the heart, lungs and immune system are weakened, and health problems such as cardiovascular diseases or respiratory illnesses increase.
Indoor air pollution from solid fuel use, along with urban outdoor air pollution, are estimated to be responsible for 3.1 million premature deaths worldwide every year and 3.2 percent of the global burden of disease. More than half of the health burden from air pollution is borne by people in developing countries.
Air pollutants have been linked to a range of adverse health effects, including respiratory infections, cardiovascular diseases and lung cancer. Reducing air pollution levels will decrease the global burden of disease from these illnesses.
Pollution prevention requires policies on air quality and transport, air pollution control regulations in cities, emission controls in industry, and the promotion of clean, renewable energy sources. Interventions to reduce indoor air pollution include switching from the domestic use of solid fuel to cleaner fuels; introducing efficient technology and ventilation in homes, schools and the working environment; and stopping smoking. Efforts to significantly reduce air pollutants will also help to reduce greenhouse gas emissions and mitigate the effects of global warming.
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