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.

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.

Emissions of particles, gases, heat, and water vapor from ships are discussed with respect to their potential for changing the microstructure of marine stratiform clouds and producing the phenomenon known as ''ship tracks.'' Airborne measurements are used to derive emission factors of SO 2 and NO from diesel-powered and steam turbine-powered ships, burning low-grade marine fuel oil (MFO); they were 15-89 and 2-25 g kg 1 of fuel burned, respectively. By contrast a steam turbine-powered ship burning high-grade navy distillate fuel had an SO 2 emission factor of 6 g kg 1. Various types of ships, burning both MFO and navy distillate fuel, emitted from 4 10 15 to 2 10 16 total particles per kilogram of fuel burned (4 10 15-1.5 10 16 particles per second). However, diesel-powered ships burning MFO emitted particles with a larger mode radius (0.03-0.05 m) and larger maximum sizes than those powered by steam turbines burning navy distillate fuel (mode radius 0.02 m). Consequently, if the particles have similar chemical compositions, those emitted by diesel ships burning MFO will serve as cloud condensation nuclei (CCN) at lower supersaturations (and will therefore be more likely to produce ship tracks) than the particles emitted by steam turbine ships burning distillate fuel. Since steam turbine-powered ships fueled by MFO emit particles with a mode radius similar to that of diesel-powered ships fueled by MFO, it appears that, for given ambient conditions, the type of fuel burned by a ship is more important than the type of ship engine in determining whether or not a ship will produce a ship track. However, more measurements are needed to test this hypothesis. The particles emitted from ships appear to be primarily organics, possibly combined with sulfuric acid produced by gas-to-particle conversion of SO 2. Comparison of model results with measurements in ship tracks suggests that the particles from ships contain only about 10% water-soluble materials. Measurements of the total particles entering marine stratiform clouds from diesel-powered ships fueled by MFO, and increases in droplet concentrations produced by these particles, show that only about 12% of the particles serve as CCN. The fluxes of heat and water vapor from ships are estimated to be 2-22 MW and 0.5-1.5 kg s 1 , respectively. These emissions rarely produced measurable temperature perturbations, and never produced detectable perturbations in water vapor, in the plumes from ships. Nuclear-powered ships, which emit heat but negligible particles, do not produce ship tracks. Therefore, it is concluded that heat and water vapor emissions do not play a significant role in ship track formation and that particle emissions, particularly from those burning low-grade fuel oil, are responsible for ship track formation. Subsequent papers in this special issue discuss and test these hypotheses.