SCAVENGING OF AIRBORNE POLYCYCLIC AROMATIC HYDROCARBONS BY RAIN.

The variation of the concentrations of some polycyclic aromatic hydrocarbons in rain with time during three precipitation events was determined. On all occasions these concentrations were found to decrease during the precipitation events. The apparent removal rate constants on a precipitation amount base for two of the three events were calculated to be 1. 46 and ca. 3 mm** minus //1. For the third event the concentration decrease did not allow the calculation of the apparent removal rate constant. Furthermore, concentrations of polycyclic aromatic hydrocarbons in rain sampled simultaneously at ground level and at an altitude of 200 m were determined. It is concluded on the basis of these findings that at least on the event with sampling at two altitudes the main process responsible for the presence of phenanthrene in rain is below-cloud gas-phase scavenging and that for the other compounds except fluoranthene and benz left bracket a right bracket anthracene it holds that in-cloud scavenging is the main process; for fluoranthene and benz left bracket a right bracket anthracene below-cloud gas-phase scavenging and in-cloud scavenging are about equally important.