Water uptake by combustion aerosol particles from common anthropogenic
combustion sources was estimated by weighing filter samples while var
ying the relative humidity in the weighing chamber of an electronic mi
crobalance. This technique was suitable for samples which weighed more
than 3 mg. Significant water uptake was observed for diesel soot, gas
oline exhaust, and wood smoke particles. Weights for typical diesel so
ot samples increased by slightly less than 2% as relative humidity was
increased from 40% to 90%. Automobile exhaust sample weights increase
d by at least three to four times and wood smoke by at least three to
more than five times as much as diesel soot sample weights. No effect
of temperature was observed. It was concluded that atmospheric mass lo
adings of particulate matter from these sources increase by a small bu
t significant amount as atmospheric relative humidity increases.