A SIMPLE, INEXPENSIVE, LIGHT WEIGHT, ROBUST AEROSOL OPTICAL SCATTER CELL.

The Intergovernmental Panel on Climate Change, in its fourth assessment report in 2007, states that anthropogenic aerosols 'remain the dominant uncertainty in radiative forcing'. More aerosols should reflect more sunlight out to space and tend to cool the climate, or alternatively, if the aerosols contain black carbon they may heat the air and cause clouds to evaporate, and less cloud would reflect less sunlight to space. More aerosols could lead to clouds having more but smaller water cloud droplets so they would appear 'whiter' and reflect more sunshine back to space, in addition, if the smaller droplets are less likely to coalesce and form rain and dissipate, so the cloud lifetime may increase. For ice clouds the situation is even more complex and uncertain. When the temperature falls below freezing most of the water drops remain as liquid and are 'supercooled'; only a very few aerosol particles have the property of being an 'ice nuclei' and promoting freezing. The effect of anthropogenic aerosols on the number of ice nuclei is essentially unknown. In addition aerosols themselves can be composed of pollutants which are deleterious to health, and so we need to know more about their sources, how they are transported around the atmosphere and how they are removed from the air, if we are to understand and consequently improve models forecasting pollution levels. To improve our knowledge of aerosols in the atmosphere we need better measurements of their distribution and how this changes as a function of the different weather patterns and how the aerosols influence the cloud properties. In particular we need to be able to make measurements form a wide range of platforms and in extreme conditions: for example close to sea surface in high wind conditions. Although the range of instrumentation available is wide those with a temporal response suitable for the investigation of particle fluxes (~10Hz) are too large and expensive, while those with a smaller foot print are again expensive and have too slow a temporal response. To address these problems researchers at the University of Leeds developed a small, light weight, fast response optical spectrometer, CLASP, and its participation in a wide variety of projects is tantamount to it success and popularity. Use had to be made, however, of a commercially available scatter cell that has proven overly complex with components used in its fabrication that are now obsolete; in addition the punitive licence agreement required form the manufacturer means that no further cell development can occur and the increasing number of requests to purchase a CLASP unit refused. The team that originally developed CLASP have been working on a new and vastly improved scatter cell from which a new generation of fast response, small, light weight aerosol spectrometers can be developed to address the need for instrumentation that can be used in extreme deployment scenarios, in personal samplers, or on platforms where size and weight is an issue. This new cell is currently at Technology Readiness Level (TRL) 3 and funding is requested to progress this cell to TRL 4 and beyond.