Twomey

Twomey, S., "Atmospheric Aerosols." Elsevier, North-Holland, New York, 1977. 

The condensed phases also are important to the physical processes of the atmosphere however, their role in climate poses an almost entirely open set of scientific questions. The highest sensitivity of physical processes to atmospheric composition lies within the process of cloud nucleation. In turn, the albedo (or reflectivity for solar light) of clouds is sensitive to the number population and properties of CCN (Twomey, 1977). At this time, it appears impossible to predict how much the temperature of the Earth might be expected to increase (or decrease in some places) due to known changes in the concentrations of gases because aerosol and cloud effects cannot yet be predicted. In addition, since secular trends in the appropriate aerosol properties are not monitored very extensively there is no way to know... 

Cloud albedo is calculated to be sensitive to the droplet population. Twomey (1977) showed theoretically that albedo is enhanced by the addition of particles to the atmosphere. 

Pleith, W., W. Kozlowski, and T. Twomey, Reflectance spectroscopy and ellipsometry of organic monolayers, in Adsorption of Molecules at Metal Electrodes, 3. Lipkowski and P. N. Ross, Eds., VCH, New York, 1992, p. 285. 

Overcash, M., Twomey, J., and Kalla, D., 2009. Unit process life cycle inventory for product manufacturing operations, ASME International Manufacturing Science and Engineering Conference, West Lafayette, IN, USA. 

The calculation of diffusion coefficient spectra using modified Twomey method (1975) are based on these premises and assumptions ... 

The n-screen method (requiring n + 1 counters) to measure the ultrafine radon daughters distributions can be used to test Bricard-Raes theory. Most of the results reported here could be interpreted using this theory, however, more tests of the computational part will have to be done before calculating and analyzing the individual results. Also a new method, recently developed by Maher and Laird (1985), will be compared to Twomey s code. 

Twomey, S., Comparison of Constrained Linear Inversion and an Iterative Nonlinear Algorithm Applied to the Indirect Estimation of the Particle Size Distribution, J. Comp. Phys. 18 188-200 (1975). 

D. C. Hobbs, T. M. Twomey, Metabolism of Piroxicam by Laboratory Animals , Drug Metab. Dispos. 1981, 9, 114-118. 

Figure 5. Normalized S mass distribution, China Lake, CA—average of 8 samples. Aerosol segregated by LPl and analyzed by FVFPD. The solid histogram is the mass distribution with respect to the 50% aerodynamic cutoff diameter the dashed histogram is the inverted distribution obtained from LPl calibration data and Twomey (1975) inversion algorithm (a) July2-4, 1978 ("M = 0.765 fig/m ) (b) October 20-22, 1978 (M = 1.702 /ig/m ) (c) September 5-7, 1979 (M =...

Based on such correlations, it is reasonable to assume that the Twomey proposal is applicable, i.e., that anthropogenic emissions of S02 and other species that form particles in the atmosphere may contribute to CCN and hence have indirect effects on climate. 

This Kelvin equation says that the vapor pressure over a droplet depends exponentially on the inverse of the droplet radius. Thus, as the radius decreases, the vapor pressure over the droplet increases compared to that over the bulk liquid. This equation also holds for water coating an insoluble sphere (Twomey, 1977). 

The albedo (R) of a thick, boundary layer cloud that does not absorb solar radiation over a surface with zero albedo can be approximated (Twomey, 1991 Schwartz and Slingo, 1996 Baker, 1997) by... 

Platnick and Twomey (1994) have applied Eq. (KK) to marine clouds off the coast of California and southern Africa, to fogs in central California, and to ship tracks. Figure 14.42 shows a typical range of susceptibilities as a function of cloud droplet size. The measured susceptibilities in these studies covered three orders of magnitude, from 5 X 10-5 cm3 for fogs to 0.8 X 10-3 cm3 for marine clouds off south Africa and 2 X 10 2 cm3 for thin stratus clouds off the California coast. Similarly, Taylor and McHaffie (1994) report cloud susceptibilities in the range from 10-4 to >8 X 10-3 at various locations around the world. The highest susceptibilities were those with the smallest aerosol particle concentrations below the cloud base. As the particle concentration increased beyond 500 cm3, the susceptibility was relatively constant at 5 X 10"4 cm3. This means that the addition of new particles to a relatively clean air mass is far more effective than for a polluted one in terms of the effect on clouds. In short,... 

FIGURE 14-42 Cloud susceptibilities (logarithmic scale) and cloud droplet radii for stratus clouds off Africa and California and from fogs in California (adapted from Platnick and Twomey, 1994). 

Another piece of evidence for anthropogenic emissions leading to increased CCN and hence effects on cloud properties such as albedo and extent is found in ship tracks. These are lines of clouds that trace ship movements, either in initially cloud-free regions (Conover, 1966 Platnick and Twomey et al., 1994) or superimposed on preexisting clouds (Coakley et al., 1987). Emissions associated with the ship exhausts serve as CCN. This allows clouds to form where the background CCN concentration is too small for cloud formation. Alternatively, the CCN can modify existing cloud properties in the exhaust plume by changing the number and size distribution of the cloud droplets as well as the liquid water content (e.g., Ferek et al., 1998). 

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