HR: 14:40h
AN: A33C-03    [Abstracts]
TI: Variability of CCN Sizes
AU: * Hudson, J G
EM: hudson@dri.edu
AF: Desert Research Institute, 2215 Raggio Pkwy, Reno, NV 89512-1095, United States
AU: Mishra, S
EM: subhashree.mishra@dri.edu
AF: Desert Research Institute, 2215 Raggio Pkwy, Reno, NV 89512-1095, United States
AB: Cloud condensation nuclei (CCN) are characterized by their critical supersaturation (S_c), which is a function of particle size and chemistry. The relationship between particle size and S_c represents CCN solubility. Small variability of size-S_c measurements has been cited as evidence that CCN can be deduced from particle size measurements alone. Since particle size is easier to measure than particle chemistry or CCN this would have advantages for indirect aerosol effect investigations; e.g., remote sensing of CCN. However, we present size-S_c measurements with a greater range of variability, which appears to limit or cast doubt on the practicality of deducing CCN from particle size measurements. CCN size is determined by passing an aerosol through a differential mobility analyzer (DMA) and then to a CCN spectrometer (i.e., Hudson, 1989), which provides a mean value of S_c. Several different sizes provide a size-S_c relationship (Hudson and Da, 1996). Airborne measurements in three different environments have confirmed Hudson and Da (1996) that CCN are significantly smaller in cleaner air masses where they behave like NaCl or ammonium sulfate. CCN are two to four times larger in polluted air masses. Associated volatility measurements suggest that they are probably sulfate internally mixed with less soluble material. Dusek et al. (2006) found only very large CCN and a small size-S_c range. This led them to conclude that CCN can be determined solely based on particle size. The much larger range of CCN sizes that we measured in a greater variety of air masses indicates that this conclusion might only be valid in polluted air masses such as those that they measured. Dusek et al. (2006) also said that, although there might be different size-S_c ranges in different air masses, if there were limited variability in size-S_c within each air mass, then it still might be possible to deduce CCN from size measurements, as long as the size-S_c relationship is determined for each air mass. However, this would require not only measurements of such, but also an analysis similar to Dusek et al. (2006) for each air mass. Mixed air masses would present a problem. Dusek et al., (2006), Science, 312, 1375-1378. Hudson, (1989), J. Atmos. & Ocean. Techn., 6, 1055-1065. Hudson and Da, (1996), J. Geophys. Res., 101, 4435-4442.
DE: 0305 Aerosols and particles (0345, 4801, 4906)
DE: 0320 Cloud physics and chemistry
DE: 0321 Cloud/radiation interaction
DE: 0345 Pollution: urban and regional (0305, 0478, 4251)
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly