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.

Accurate measurements of the size distribution of atmospheric aerosols in the size (radius) range from 0.006 to 2.5 #m made from a ship within 300 km of the east coast of the United States are presented. As air advects from land to sea, there is a rather rapid decay of particles smaller than 0.05 #m during the first day or so. After this initial decay of small particles the size distribution was often found to remain remarkably stable for hours. Significant changes in the size distribution were often associated with changes in air masses and meteorological conditions. Some of the changes can be explained qualitatively. Others, such as a pronounced double l•ak which occurred occasionally in the fine-particle range, are more difficult to understand. Possible physical mechanisms which might produce a double-l•aked distribution are discussed, including the increase in the mass of cloud condensation nuclei as a result of the chemical formation of new material from gases absorbed in cloud droplets during a cloud formationevaporation cycle. Using the measured size distributions, volume extinction coefficients were calculated for the wavelength range 0.3-10 #m. The calculations compare favorably to the measured scattering coefficients at 0.55-#m wavelength. Particles in the radius range 0.1-0.3 #m made the largest contribution to the total extinction at optical wavelengths on nearly all occasions. 1980; Zhulanov et al., 1982].The very low concentration of small particles often encountered in the marine environment requires more sensitive instrumentation than that employed in urban studies. Because of the increased sensitivity and accuracy achievable with the differential mobility size analyzer, its recent development is especially important for marine aerosol measurements. The differential mobility size analyzer was used in the studies by Hoppel [1979] and Haaf and Jaenicke [1980] in the marine environment and is also used in this study to obtain size distributions at radii below 0.5 #m.The total concentration of particles in continental air is of the order of 10,000 particles/cm 3. Over the remote oceans the This paper is not subject to U.S. copyright. Published in 1985 by the American Geophysical Union. Paper number 4D 1281. total concentrations are often of the order of 100 particles/cm 3. This implies that there are processes which remove particles from an air mass as it moves from continental to marine regions. In 1980, the USNS Hayes made a research cruise off the east coast of the United States which was sponsored jointly by the Environmental Biology Branch and Atmospheric Physics Branch of the Naval Research Laboratory (NRL). The purpose of our participation in the cruise was to investigate the evolution of the size distribution in air masses advecting off the east coast of the United States with special emphasis on submicron particles. The cruise track is shown in Figure 1, where the boxes indicate stations on which the ship stopped from 4 to 10 hours for biological sampling. INSTRUMENTATIONAerosol size distri...

Sodium and manganese in barnacle shells, collected from habitats with salinities varying from l-