Suspended particulate matter is one of the most prevalent atmospheric pollutants. Natural sources of particulates, including windblown dusts and sea-spray, pollen, forest fires and volcanoes are estimated to exceed man-made emissions possibly by as much as twenty times. Man-made particulate emissions are emitted directly from fossil fuel combustion, industrial and agricultural sources or are a result of gas-particle conversions.
"Particulate matter" air pollution refers to microscopic airborne particles that can travel into the lungs and cause a variety of respiratory problems. These particulates are 10 microns or less in size (about half the width of a human hair) and are found both outdoors and in homes and work places. They are referred to as "PM10" (Particulate Matter 10 microns or less in diamater). Even smaller particles -- less than 2.5 microns in diameter -- which can penetrate even more deeply into the lungs, are called "PM2.5"< Any form of combustion will create small particulates, although the most harmful particulates are generated by combustion of organic materials. Tobacco is one obvious source of small particulates. There are other sources of combustion which can cause large quantities of small particulate to be released into the air. Woodsmoke is a major offender in many communities, whether it comes from a beehive burner, slash burning after land-clearing or logging, the burning of agricultural stubble, or a fireplace or woodstove. Building incinerators and furnaces can also contribute to airborne particulate levels.
Diesel-burning vehicles such as buses and trucks are another major source of this pollution, especially in the Asia-Pacific region, where diesel accounts for half of the fuel used for transport. Poor maintenance of diesel engines in low income countries is the norm, and can cause 10 to 15 times the emissions of a well-kept engine. High sulfur content fuels produce the most particulate pollution.
Small particle pollution from the combustion of organic materials is an extremely serious health threat -- it poses much more of a danger to human health than present levels of other common air pollutants such as ozone, sulphur dioxides and carbon monoxide. Persons with existing lung and heart problems are particularly at risk, especially if their local environment is strongly affected (i.e., from industrial sources or from a concentration of wood smoke during the winter months).
In 1995, higher rates of premature death from cardiopulmonary disease and lung cancer occurred in the American cities with higher levels of small particle pollution, where air pollution is thought to shorten lives by 1 to 2 years. Death rates rise by 1% per day when PM10 concentrations increase by 10 micrograms per cubic metre, affecting people with respiratory or cardiac disorders particularly.
Already in 1991, small particle pollution in 10 Asian cities was more than twice the maximum acceptable level. In Jakarta, air pollution causes 4000 deaths a year - 5 times more than car accidents.
Recent studies on particulate matter confirm the concern about the economic costs of the impact of this pollution on health. For the Paris region alone, they amount to around FF 12 000 million (EUR 1800 million), while for Wales and England estimates are up to 16 600 million pounds (EUR 24 000 million).
In terms of the absolute number of people affected, long-term exposure to suspended particulate matter was the most detrimental type of air pollution affecting health in Europe in the mid-1990s. Although the basis of quantitative estimates is still uncertain, it is likely that between 100 000 and 400 000 people each year die prematurely by more than 1 year as a result of exposure to ambient air pollution in Europe. Indoor exposure to environmental tobacco smoke and to radon is associated with several thousand cases of lung cancer and other severe illnesses per year.
In West Africa, the Harmattan winds often result in high atmospheric dust loading and poor visibility, and contribute to respiratory and other diseases. The continual build-up of mineral dust concentrations since the 1960s is likely to have a climatic impact through a land-atmosphere feedback mechanism (Ben Mohamed and Frangi 1986, Ben Mohamed 1985 and 1998).