Road dust consists of airborne solid particles that are generated by the crushing and abrasion of asphalt, gravel, other road pavement materials, road markings, tires and brake pads as well as of dirt and other materials found on road and parking lot surfaces. Particles larger than ten microns in size (PM10) can remain suspended in the air for hours, while those under 2.5 microns (PM2.5) can stay in the air for more than ten days and will sometimes travel hundreds of miles.
Road dust is a largely overlooked environmental and health hazard because it is usually invisible and because it is overshadowed by pollution from other, more obvious sources, especially automobile exhaust. It is also because of its complex composition and that fact that its health risks can likewise be complicated and difficult to understand. However, road dust can, in fact, be a serious medical concern that is linked not only to asthma and other breathing problems but also to heart disease and even to cancer. Although inhaled large particles are likely to be trapped in the nose and mouth, causing sneezing and coughing that helps expel them from the airways, smaller particles, usually invisible to the human eye, can penetrate deep into the lungs and from there can be transferred into the bloodstream and thus, ultimately, into the heart and other organs.
Road dust is also harmful in another way. That is, it eventually exits the air and enters the soil and water bodies, including ground water. It can also enter the soil and water in the form of toxic runoff, which is created by the washing away of the particles from pavement surfaces by rain before they can become airborne. In addition to harming aquatic organisms, it can also affect humans both through the consumption of such organisms and by drinking the contaminated water.
Ways in which road dust could be reduced include lowering road traffic speeds, reducing the volume of road traffic, reducing the amount of land that is paved over for roads and parking lots, and developing more durable materials for road surfaces, road markings, tires and brakes.