Unlike the famous ‘pea-souper’ smogs of a century ago, due to coal burning in cities, the problem is now mostly invisible. The main source of urban air pollution now is road transportation, predominantly from diesel vehicles. A key pollutant is Particulate Matter (PM).
PM consists of microscopic particles suspended in the air. The smaller the particles, the deeper they can penetrate into the respiratory system and bloodstream, making them more hazardous to our health.
Pollution concentrations are highest in densely congested urban environments and most specifically along the main roads themselves. PM varies in size and there is no safe level for health.