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Randolph D. Borys and Robert A. Duce

Abstract

Particulate lead, aluminum, sodium, vanadium, manganese and iodine, vapor phase iodine and ice nuclei were measured simultaneously in Providence, Rhode Island, over a period of one year. Interrelationships found were governed primarily by the physical properties of the aerosol. Weak positive correlations were observed between lead and ice nuclei. An argument is given using lead as an indicator of the aerosol surface area maximum, or that fraction of the aerosol which contains the greatest number of potential ice nucleating sites. Ice nucleus concentrations appeared to be controlled by large-scale air mass advection to the site studied.

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Alfred H. Woodcock, Robert A. Duce, and Jarvis L. Moyers

Abstract

Particles of sea salt of different size in the marine air of Hawaii exhibit different ratios of iodine to chlorine, whereas raindrops of various sizes in Hawaii warm orographic showers contain iodine and chlorine in a relatively constant ratio. The mean value of the I/Cl ratio for raindrops (∼2.0 × 10−3) corresponds to the mean found among the smaller of the salt particles of weight range ∼10−12–10−14 gm. On the other hand, the mean I/Cl value among the giant salt particles of weight range of ∼10−8–10−12 gm is shown to be ∼3 × 10−4. It appears that raindrop growth occurs through coalescence among cloud droplets formed on the 10−12–10−14 gm salt particles. This result is interpreted to mean that in warm oceanic tradewind clouds giant salt nuclei may not, after all, be essential to the formation of raindrops.

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Jarvis L. Moyers, William H. Zoller, and Robert A. Duce

Abstract

Gaseous iodine and particulate iodine and lead samples were collected simultaneously in a polluted atmosphere using activated charcoal and membrane filters. Concentrations of gaseous iodine varied from 10–18 ng m−3 and particulate iodine from 2–15 ng m−3 as determined by neutron activation analysis. The total iodine concentration found in this work is approximately twice that found in the unpolluted marine atmosphere. Lead concentrations varied from 0.4–3.7 µg m−3 as determined by atomic absorption spectrophotometry.

There is an apparent relationship between the concentration of total particulate matter in the air and the ratio of particulate iodine to gaseous iodine. This relationship is consistent with laboratory investigations of gaseous I 2 adsorption onto combustion aerosols reported by other investigators. Calculations indicate that the concentrations of gaseous iodine measured in this work should be sufficient to activate all lead containing particles to ice nuclei in a polluted atmosphere. It is suggested that large concentrations of ice nuclei are not generally observed in polluted air at ground level because the reaction of lead and iodine at the concentrations observed in this work proceeds slowly.

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