Individually, these particles and droplets are invisible to the naked eye. Collectively, however, they can appear as clouds or a fog-like haze. Fine particles can also be formed when combustion gases are chemically transformed into particles. Coarse particles have many sources, including wind-blown dust, vehicles traveling on unpaved roads, materials handling, and crushing and grinding operations. Both coarse and fine particles are of health concern because they can penetrate into the sensitive regions of the respiratory tract.
Fine particles are of greatest concern because they are linked to the most serious effects.
They can be deeply inhaled into the lungs where they can be absorbed into the bloodstream or remain embedded for long periods of time. They can cause persistent coughs, phlegm, wheezing, and physical discomfort. Several recently published community health studies indicate that significant respiratory and cardiovascular-related problems are associated with exposure to particle levels well below the existing particulate matter standards. These negative effects include premature death, hospital admissions from respiratory causes, and increased respiratory symptoms. Long-term exposure to particulate matter may increase the rate of respiratory and cardiovascular illness and reduce life span.