The effect of particulate pollutants are largely dependent on the particle size. Airborne particles such as dust, fumes, mist etc., are dangerous for human health. Particulate pollutants bigger than $5$ microns are likely to lodge in the nasal passage, whereas particles of about $1$ micron enter into lungs easily.

Lead used to be a major air pollutant emitted by vehicles. Leaded petrol is the primary source of air-borne lead emission. This problem has been overcome by using unleaded petrol. Lead interferes with the development and maturation of red blood cells.