Fogwater collector design and characterization

Abstract

The detailed characterization of a rotating arm collector to sample ambient fog droplets for chemical analysis is presented. Because of the large volume of sample required, and because fog droplets are of supermicron size and are sensitive to local thermodynamic disturbances, conventional methods for atmospheric aerosol sampling are not suitable for fogwater sampling. Design criteria for fogwater samplers are outlined. Devices used in previous investigations are evaluated in light of these criteria. The design of a rotating arm collector is discussed, and it is shown that this instrument performs adequately in preserving the physical and chemical integrity of the sample at all stages of collection. Limitations in the design due to mechanical constraints are discussed. Results of an in situ calibration experiment using a chemically tagged monodisperse aerosol indicate a size cut of 20-pm diameter.