Calculations of the ion-aerosol attachment coefficients are carried out for Fuchs' theory (as corrected in this paper) and for a theory which includes three body trapping. The resulting charge distributions agree quite well for particle? with radii greater than about 0.007 pm. For smaller particles three-body trapping becomes increasingly important. Comparison of theoretically predicted charge distributions with recently measured charge distributions at radii smaller than 0.02 pm show good agreement. Asymmetric charging due to differences in the physical properties of podtive and negative ions can result in large differences in the number of positively and negatively charged particles, particularly at larger radii. The asymmetric charge distribution is also shown to depend on the ionization rate. For the case when aerosol concentrations are comparable to the ion concentrations the effect of polydispersity on the charge distribution is difficult to predict. It is shown that a dominant size particle can establish a positive to negative ion ratio which, in turn, will determine a charge distribution at other sizes, different from that which would exist in the absence of the dominant species.

Measurements and analyses of the aerosol size distributions and optical properties found in the marine boundary layer (MBL) during the 1983 USNS Lynch cruise from Charleston, South Carolina, to Scotland via Canary Islands are presented. The data given are the most extensive and accurate measurements of the submicron marine aerosol size distribution to date and are supplemented by extensive meteorological observations. Eight detailed case studies of the evolution of the size distribution that occurred under different meteorological conditions are presented and discussed. The data indicate that repeated cycling of MBL air through nonprecipitating clouds at the top of the MBL is a major factor in shaping the size distribution and that new particle formation by heteromolecular, homogeneous nucleation is the most likely mechanism for sustaining the particle concentration below 0.04‐μm radius. Calculations of the scattering and extinction coefficients and optical depth of the MBL as a function of wavelength directly from the measured size distribution and MBL vertical structure are compared to measured values of the scattering coefficient and optical depth. These measured and calculated optical properties correlate well throughout the cruise and the results give a relatively consistent picture of the relationship between the aerosol size distribution and electromagnetic properties in the MBL.

The vertical evolution of microphysics in trade-wind cumuli (Cu) observed from the NCAR C-130 research aircraft during one flight of the RICO (Rain in Cumulus Over the Ocean) study is analyzed. Conditional sampling of > 200 Cu traversed on this flight is used to chose Cu for which the aircraft penetrated single and growing Cu turrets about 250-m below cloud top where maximum LWC is often found and where radar has often observed initial stages of precipitation. The vertical evolution of the sampled set of Cu was assumed to follow Lagrangian behavior. The entrainment rate, entrained parcel scales, mixing mechanisms, and effects on the droplet size distribution are measured and evaluated. A parcel model is applied over the 1100-m maximum Cu height of the traverses to determine the relationship between the observed large number of small droplets and the fewer ultra-giant sea-salt nuclei (UGN) in order to assess the role of these nuclei in evolving the size spectrum and in causing a growing "drizzle tail". New insight on these topics is obtained by using the PVM (Particle Volume Monitor) probe to measure incloud microphysics with 10-cm resolution.The results include the following: Entrainment causes primarily dilution of the drops without significant size changes, thus either extreme inhomogeneous mixing or more likely homogeneous mixing resulting from mixing with cool and humid entrained air take place. The entrained parcels are surprisingly small following lognormal behavior and decaying rapidly upon entering the Cu, as a result super-adiabatic drops are not evident. The entrained parcels are consistent with the Bragg-scattering "mantle echo" often observed by radar in small Cu. The FSSP (Forward Scattering Spectrometer Probe) droplet spectra are nearly constant with height. These "self-preserving" spectra are a result of an approximate balance between dilution by entrainment of droplets originating at cloud base, droplet activation on entrained CCN (cloud condensation nuclei), and detrainment and coalescence losses. Sea-salt nuclei follow Woodcock's wind dependence, and are shown with the parcel model to play an important role in forming the observed drizzle that increases with cloud height. Accretion is the dominant coalescence mechanism near cloud top in these Cu.

Measurements of aerosol size distributions (0.005 < r < 20 /am), cloud droplet spectra, SO2, 03, CN, and other supporting quantities were made in the cloudtopped and clear marine boundary layer (MBL) from an airship operating within about 50 km of the Oregon coast. Comparison of size distribution of interstitial aerosol within the cloud with the size distribution below the cloud clearly indicates that the processing of the aerosol through (nonprecipitating) stratus can lead to increased mass of the subset of particles which had served as cloud condensation nuclei (CCN). This increase in mass in the CCN results in a distinct "cloud residue" mode in the size distribution measured below the cloud. In all cases the aerosol mass in the cloud residue mode greatly exceeded the mass in the interstitial mode, even though the number concentration of interstitial particles sometimes exceeded the CCN concentration. Evidence of new particle formation in clear air was also found on numerous occasions. Analyses of the data indicate that the growth of newly formed particles into the observed size range is consistent with gas phase oxidation of SO2 to sulfate and subsequent condensation on the aerosol. However, the exact nucleation process, whether by homogeneous nucleation, ion-assisted nucleation, or heterogeneous nucleation on precursor embryos, is still an open question. can be classified into three types of experiments: (1) clear air profiling of the MBL, (2) profiling the MBL when marine stratus is present, and (3) measurements of ship plumes.Results of the profiling measurements showing the effects of cloud processing on the aerosol size distribution and evidence of new particle formation by heteromolecular nucleation are presented in this paper. Airship and InstrumentationThe slow airspeed of an airship immediately suggests its candidacy as a research platform for experiments which Paper number 94JD00797. 0148-0227/94/94 JD-00797505.00 require (1) a nearly stationary platform within an air mass, e.g., Lagrangian measurements; (2) vertical profiling measurements downwind of localized sources where high spatial resolution is required, e.g., plumes from stationary and slowly moving sources; or (3) measurements where lowspeed sampling decreases the difficulty of sampling and/or sampling errors, e.g., sampling cloud droplets and hydrometers. The slow airspeed of the airship can also be a significant disadvantage by limiting the meteorological conditions under which it can operate and the range to the order of 150 km from its base of operation.The airship used in the experiments reported here was the US-LTA model 138S airship and is shown in Figure 1. A gasoline-powered generator which can provide 55 amps of 115 V, 60 Hz power was mounted external to the gondola; 500 kg of scientific equipment was mounted in three instrument racks inside the gondola and particle-sampling equipment was mounted 1.8 m below the nose of the airship (see Figure 1). In addition to the scientific payload, a pilot plus two scientists could be accommoda...

The size distribution of particles smaller than 0.5 µm has been measured over the tropical Atlantic and Pacific oceans with a differential mobility analyzer. In regions remote from continental influences the size distribution generally has peaks at about .02‐.03 µm and at .08‐.15 µm with a minimum in the .05‐.08 µm radius range. The data provides strong evidence that nonprecipitating clouds play an important role in transferring material from the gas phase and from smaller particles into the 0.08 to .15 µm radius range, and that they are responsible for the doubly peaked size distributions frequently observed over the oceans.