Balloon-borne optical counter for in situ aerosol measurements

A new balloon-borne optical particle counter has been developed to make in situ measurements of stratospheric aerosols. The intensity of light scatter ed at 60 degrees from the forward direction by individual particles is meas ured. Aerosol number concentrations in seven size channels can be inferred. The counter has been calibrated using polystyrene and polyvinyl toluene la tex spheres. There is good agreement between measured and calculated indivi dual pulse intensities for aerosol with radii from 0.16 to 2.6 mu m. The si ze resolution is limited by broadening of the pulse count/pulse height spec trum, arising mainly from the photoelectron statistics of photomultipliers. Stratospheric aerosol measurements have been made using this instrument at Kiruna (68 degrees N, 21 degrees E), Sweden, in February 1995, and at Aire sur I'Adour (44 degrees N, 0 degrees W), France, in 1992, 1993, and 1994. The uncertainties in the measurements are discussed. The retrieved aerosol concentrations and size distributions are presented, and shown to be broadl y consistent with measurements made by the University of Wyoming optical pa rticle counter.