Real-Time Size-Distributed Measurement of Aerosol Mass Concentration
MSP is introducing in this proposal a practical approach to a family of cascade impactors capable of real-time measurement of the size-distributed mass concentration of particles in the atmosphere. Further, because of the high sensitivity of the proposed mass transducers, these impactors will also provide nearly instantaneous information about the influence of water vapor on the size distribution of the particulate matter. The continuing need for energy development contributes to the potential of climate change, partly through carbon dioxide emissions, but also through the suspending of particulate matter from fossil fuel combustion or other industrial processes. The ability to measure the size and concentration of particles in the atmosphere is critical to a wide range of earth science needs. The warming expected for a doubling of atmospheric CO2 concentrations ranges from 2 C to 4.5 C; uncertainties concerning aerosol and cloud-aerosol interactions contribute significantly to this large range (Solomon, et al., 2007). The relationship between aerosol size distributions and relative humidity is important in understanding the direct effect and indirect effect of aerosol on climate. Relative humidity influences aerosol radiative forcing (Jeong, et al., 2007; Markowicz, et al., 2003) and complicates studies of aerosol optical thickness near clouds (Jeong and Li, 2010). Factors relating changes in aerosol size to changes in relative humidity are important in modeling the radiative impact of aerosol (Chin, et al., 2009). The instruments that we propose will enable researchers to make fast, accurate aerosol size distribution measurements with instruments that are small, light, and inexpensive, improving their ability to characterize aerosol properties in airborne measurements. The short response time of the proposed instruments will improve studies around clouds where aerosol properties change over short distances. These instruments may also be deployed in dropsondes or in ground-based networks covering currently under-sampled areas of the globe. We intend to develop a family of cascade impactors that report the size-distributed mass concentration of particles the atmosphere. These impactors will rely on highly sensitive micromechanical resonators, a derivative of microelectromechanical (MEM) sensors. The MEM sensors are tens of microns square and are able to quantify single digit picograms of material deposited on their surface. The family of instruments that will result from a successful three-phase SBIR development program will find application in airborne atmospheric studies, semiconductor cleanrooms, portable and personal aerosol exposure monitors, ambient samplers, industrial and academic research laboratories, and for the most part anywhere that cascade impactors are used today.
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