This article is meant to sensitise the public to the dangers of unprecedented levels of dust in the atmosphere. Dust is a generic term used to describe fine particles that are suspended in the atmosphere.
It is composed of tiny particles of many kinds of solid materials. The particles have diameters of less than 0.0025 millimetres (0.0001 inches); a million typical dust particles would have a total volume equal to about one grain of sand.
Dust is formed when such particles become entrained in the atmosphere by the turbulent action of wind or by the mechanical disturbance of fine materials. The potential for dust formation during construction activities is difficult to quantify and will be dependent on the type of activity to be undertaken, soil and substrata type, topographical features, precipitation, wind speed and direction as well as the shape, size, density and moisture content of the particles.
Dust is dispersed by wind. Smaller dust particles remain airborne for longer, dispersing widely and depositing more slowly over a wider area especially from unpaved roads around us. In relatively pure air, there are fewer than 500 particles of dust per cubic centimetre (1 cc = 0.06 cu inches), whereas dirty air may contain more than 50 000 particles per cc.
In Malawi, most dust emanates from unpaved roads especially those under construction. The fine suspended dust particles contribute significantly to the particulate loading in the atmosphere making road dust one major source of air pollution. For example, a vehicle travelling one kilometre each day down a dusty road will generate nearly a ton of dust over the course of a year.
If you multiply that by the number of vehicles that pass over the dirt road each day and you will get an idea of the tremendous amount of dust that enters the atmosphere. This dust will travel up to 160m before it finally settles down. The dust cloud formed when vehicles use these roads can impair the visibility and pose a hazard to motorists. Dust can also greatly increase the wear and tear on the moving parts of vehicles. It can also pollute nearby surface waters and stunt crop growth by shading and clogging the pores of the plants.
Dust particles from nearby roads can also creep into adjacent homes where it can cause breathing problems such as asthma, bronchitis, hay fever and coughing spells. Some types of lung diseases caused by the inhalation of dust are called by the general term ‘pneumoconiosis’. This simply means ‘dusty lung’. According to United Nations 1979 report, dust can also be a conveyor of other diseases.
What is the ultimate solution to the dust problem? Pave the dirt roads. As much as elected officials would like to do so, they also know that paving every dirt road would cost a fortune and likely bankrupt the government. But in cases where new roads are being constructed, there is a need to control the amount of dust generated. In other countries, dust is treated with suppressants such as calcium lignosulfate, calcium chloride, magnesium chloride and calcium chloride special.
These chemicals have the side benefit of stabilising the road surface resulting in reduced loss of gravel from the road surface and lower maintenance costs. Those who do not like chemicals have gone organic by applying soya soap stock, a by-product of soya bean oil extraction to dusty roads. One application of this extract does provide three to four months of dust control. This non-corrosive and environmentally friendly solution works by penetrating road surfaces and bonding the gravel together. The most popular dust control agent for dirt roads is water.
Water is environmentally friendly and relatively cheap if the source is nearby. For all its benefits, water is not the ideal dust control agent. Its regular use may be costly. Studies elsewhere have shown that labour and material costs of applying water once every day are six times higher than applying dust control agents.
Finally, I would like to appeal to those involved in road construction works and any other such activities which generate dust to control such emissions by regularly watering the surfaces for it has been proven that reducing air pollution can add five months to your life expectancy. The impact on health is substantial. —The author is a scientific officer for National Herbarium & Botanic Gardens of Malawi, writing in her personal capacity.
