Date of Award

1983

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Oceanography

Department

Oceanography

First Advisor

Robert Duce

Abstract

Atmospheric boron has been separated into gaseous and particulate components for the first time by passing air through a simple impregnated filter sampling system. A Nuclepore filter for particulate boron collection preceded KOH impregnated Whatman 41 filters for gaseous boron collection. The filters were contained in a single 47 mm filter holder. Boron was determined by visible spectrophotometry with 2,4-dinitro-1,8-naphthalene dial (DNNDO) and brilliant green. This method was employed to allow short time scale variations of atmospheric boron to be measured. The goal of this work was to investigate the role of the oceans on atmospheric boron. Gaseous and particulate boron and rain water were collected at urban, rural, mid-continental, and remote island sites. Sea surface microlayer samples were collected in the Pacific and Atlantic oceans.

Boron exists in the atmosphere primarily in the gas phase. Gaseous boron concentrations ranged from 1-233 ng/m3 while particulate boron ranged from 0.02-8 ng/m3. Mean gaseous boron collected at Oahu (97 ± 21 ng/m3) was a factor of 6 higher than the gaseous boron observed in Colorado (16 ± 9 ng/m3). Gaseous boron concentrations in urban Ohio were also relatively high (77 ± 51 ng/m3), supporting reports of boron volatilization during coal combustion. A four month series of daily samples collected at Narragansett, R.I. revealed gaseous boron variations to exist on a time scale of several days.

Total boron concentrations in rain are similar from remote marine areas of Samoa and Enewetak, and from coastal Narragansett R.I., ranging from 0.4-15 ug/l. Total boron in rain from inland Colorado ranged from 3-9 ug/1. Mean concentrations of particulate boron was quite similar at all locations (~2 ng/m3), except Hawaii (~0.6 ng/m3). Scavenging ratios for boron average ~1000, similar to values for other elements removed from the atmosphere by rain. This, along with the covariance of boron and Na observed in rain shower sub-samples, suggests that scavenging of aseosol boron may control the concentration of boron in rain, even though a significant gas phase of boron apparently exists.

Analyses of the ocean surface microlayer showed slight positive (0.05 ± 0.04) enrichments relative to bulk seawater. Theoretical considerations suggest that fractionation occurring during bubble bursting processes at the sea surface could account for enrichments of boron observed in aerosols.

Laboratory studies and a literature survey suggest that B(OH)3 is the species of gaseous boron that exists in the atmosphere. If this is indeed the case, then thermodynamic calculations suggest that particulate boron produced by the ocean is a major source of B(OH)3 in the atmosphere, due to sea salt aerosol degassing. The calculations also suggest that the ocean acts as a net gaseous B(OH)3 sink.

Estimates of inputs of boron to the troposphere reveal that the ocean and vulcanism are the major sources, and that natural sources dominate anthropogenic sources by a factor of 10. Comparison of the source strengths of atmospheric boron with the tropospheric burden, calculated using data presented in this dissertation, predict a residence time for gaseous and particulate boron of 20-40 days and 2-6 days, respectively. Sinks of atmospheric boron are difficult to estimate, primarily because of the uncertainty associated with wet and dry deposition estimates.

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