Water uptake by sunlight and ozone exposed diesel exhaust particles

Two types of experiments were conducted to investigate the effect of aerosol aging on water uptake by diesel soot particles. First, in three experiments diluted diesel soot was exposed to sunlight for up to 10 hours in a 190 m3 Teflon film smog chamber and filter samples were collected at various time intervals. Second, diesel soot filter samples were exposed to 2 to 4 ppm ozone concentrations for 3 hours in a stainless steel chamber. Water uptake was measured by weighing the filter samples from each type of experiment by varying relative humidity in the weighing chamber of an electronic microbalance. When relative humidity was increased from 40% to 90% weights of fresh diesel soot samples from the smog chamber increased by less than 2% and sample weights of diesel soot aged in the chamber for 9 to 10 h increased by 7 to 8%. Sample weights for diesel soot filter samples aged in the stainless steel chamber in the presence of ozone in the dark increased by less than 2.5% over the same relative humidity range.