Development of a Bioaerosol single particle detector (BIO IN) for the Fast Ice Nucleus CHamber FINCH

In this work we present the setup and first tests of our new BIO IN detector. This detector was constructed to classify atmospheric ice nuclei (IN) for their biological content. It is designed to be coupled to the Fast Ice Nu- cleus CHamber FINCH. If one particle acts as an ice nu- cleus, it will be at least partly covered with ice at the end of the development section of the FINCH chamber. The de- vice combines an auto-fluorescence detector and a circular depolarization detector for simultaneous detection of biolog- ical material and discrimination between water droplets, ice crystals and non activated large aerosol particles. The exci- tation of biological material with UV light and analysis of auto-fluorescence is a common principle used for flow cy- tometry, fluorescence microscopy, spectroscopy and imag- ing. The detection of auto-fluorescence of airborne single particles demands some more experimental effort. However, expensive commercial sensors are available for special pur- poses, e.g. size distribution measurements. But these sen- sors will not fit the specifications needed for the FINCH IN counter (e.g. high sample flow of up 10 LPM). The newly developed -low cost- BIO IN sensor uses a sin- gle high-power UV LED for the electronic excitation instead of much more expensive UV lasers. Other key advantages of the new sensor are the low weight, compact size, and the lit- tle effect on the aerosol sample, which allows it to be coupled with other instruments for further analysis. The instrument will be flown on one of the first missions of the new German research aircraft "HALO" (High Altitude and LOng range).