Environmental and health risk associated with air pollution emitted by public transportation, and a new methodology for reducing the risk

Tiny smoke particles that are typically emitted today from a variety of vehicles are of major public concern, as they are known to cause major health and environmental problems. It is well recognized that those tiny particles are directly linked with lung cancer, and have harmful effect on the environment. As they are smaller than other types of particles (sub-micron size) it is more difficult to filter them and their residence time in the air, and hence exposure time, is much longer. It seems that at this stage, the worldwide extensive efforts to reduce their emission depend to a large extent on our scientific understanding of their formation and their dynamics before they are emitted. These involve a wide range of coupled phenomena related to combustion, fluid dynamics and chemistry which are taking place in the engine and in the exhaust system. Well-controlled oscillations of the flowfield in the exhaust system may cause the phenomenon of particle-grouping and eventually to coagulation/ aggregation. The knowledge of how to control the characteristics of the underlying flow may lead to a desirable behavior and, in the case of submicron and nano-metric smoke-particles it may lead to extensive particles' coagulation resulting in a dramatic decrease in their number and hence reduction in health/environmental risks. Hence, increase of smoke particles size by aggregation as they are in motion in the exhaust system will reduces their number, increase their size and enable us to capture them by conventional filters. Even if some of them are emitted, they impose lower risk. This target is the basis of the new methodology which we will elucidate, that is based on a mathematical model and lab experiments. The experiments show that the new design of exhaust systems leads to the desirable shift in the size distribution, and also show its potential for reducing the environmental problems associated with emission from transportation.