R. E. Larson

Marine boundary layer measurements of new particle formation and the effects nonprecipitating clouds have on aerosol size distribution

Measurements of aerosol size distributions (0.005 < r < 20 μm), cloud droplet spectra, SO2, O3, CN, and other supporting quantities were made in the cloud-topped 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.

CO, CCl4, CH4 and Rn-222 Concentrations at Low Altitude over the Arctic Ocean in January 1974

Abstract Samples of atmospheric Rn, CO, CH4, Freon-11 and CC1CCl4 were taken at various altitudes over the Arctic Ocean north of the Greenland Sea. The concentrations of these components were correlated and interpreted with respect to varying meteorological conditions related to air mass movements. Pronounced concentration gradients were seen in frontal zones, and evidence is found for low-level flow of continental air, both from North America and Europe, into the Arctic region. Comparisons show that Arctic air contains more Rn, CO and CH4 in winter than in summer. It is suggested that the Arctic Ocean could act as a sink (rather thin a source) for atmospheric CO during winter months. The rapid transport of Freon-11 from Europe to the Arctic is also in evidence, while the, observed behavior of CCl4 is difficult to interpret.

Aerosol size distributions at a site on the East Coast of the United States

Abstract Aerosol size distributions covering the range from 0.006 to 2.2 μm radius were measured with the NRL differential mobility analyzer and an optical particle counter during a 12-day period in June of 1979 at Wallops Island, VA. Changes in the size distribution were associated primarily with the history of the air mass as indicated by synoptic conditions. The coastal location made it possible to contrast continental and marine conditions. On one occasion a high pressure system moved from over the Great Lakes, across New England and out to sea. Circulation around this high first brought to the site air which had moved down the east coast of the U.S. and later air from the east with increasingly longer trajectories over water. As the length of the trajectory over water increased, a decrease in small particles was clearly evident.