A Universal Cloud and Aerosol Sounding System (UCASS) based on wide angle light scattering

Summary This presentation discusses a new optical particle counter design, developed at the Centre for Atmospheric and Instrumentation Research, University of Hertfordshire. The Universal Cloud and Aerosol Sounding System (UCASS) is an open geometry instrument, which uses wide-angle light scattering for the high precision sizing of particles from 0.3μm to 40μm. The instrument design and preliminary field results are discussed. Introduction Routine meteorological data are obtained in the atmosphere using disposable radiosondes, giving temperature, pressure, humidity and wind speed. Additional measurements are obtained from dropsondes, released from research aircraft. However, a crucial property not yet measured during these soundings is the size and concentration of atmospheric particulates, including dust. Instead, indirect measurements are employed, relying on remote sensing, to meet the demands from areas such as climate research, air quality monitoring, civil emergencies etc. In addition, research aircraft can be used in situ, but airborne measurements are expensive, and aircraft use is restricted to near-horizontal profiling, which can be a limitation, as phenomena such as long-range transport depend on the vertical distribution of aerosol. To take such measurements, the Centre for Atmospheric and Instrumentation Research has recently developed a low-cost, miniature particle counter for use with disposable radiosondes, dropsondes, UAVs or in dense ground-based sensor networks. Methods The UCASS sizes particles based on elastic light scattering. Particles passing through an optically defined sensing zone are counted, and the magnitude of the optical response is used to calculate the size. Modelled results using T-Matrix and Lorenz-Mie show that, for the optical set up utilized in the UCASS, the instrument response is largely independent of particle shape and optical absorption. Therefore, the system is suitable for the measurement of both spherical and none-spherical particles, and particles with unknown optical properties. In Situ Results Earlier versions of the UCASS have been used for the vertical profiling of mineral dust [1,2] and volcanic ash [3,4]. The more recent, open geometry system has been used for ground based air-quality monitoring [5],and most recently as a balloon borne sounding system during the Ice in Clouds Experiment –Dust (ICE-D) campaign, located in Cape Verde, August 2015. During ICE-D, the UCASS was launched coincident to a SAVEX flight, and comparisons between the UCASS and various aircraft instrumentation show good agreement for the sizing and counting of aerosol particles in the Saharan air layer. Conclusions Comparisons with aircraft mounted instrumentation show good agreement in the counting and sizing capabilities of the UCASS. These devices offer alternative sampling techniques to in-situ aircraft studies and can be used for deep vertical profiles with no restrictions on light levels. Therefore, these instruments can offer valuable information in addition to, or in lieu of aircraft measurements, thus aiding the measurement of the vertical distribution of cloud and aerosol particles. References [1] Nicoll K.A., Harrison, R. G., Ulanowski, Z. (2011) Observations of Saharan dust layer electrification. Env. Res. Lett., 6, 014001. [2] Ulanowski Z., et al. (2010) Radiosonde aerosol counter for vertical profiling of atmospheric dust layers. EGU 2010, EGU2010-13512. [3] Harrison R.G., et al. (2010) Self-charging of the Eyjafjallajökull volcanic ash plume. Env. Res. Lett. 5, 024004. [4] Ulanowski Z, Harrison, R. G., Nicoll K. A. (2010a) Measurements of atmospheric volcanic dust using an aerosol radiosonde. EGU 2010, GMPV7 (Volcanic ash: an agent in Earth systems). [5] Kaye, P. H., et al. (2014) A low-cost optical particle counter for networked deployment. Int. Conference on Atmospheric Dust, Castellaneta Marina.