Gas-To-Particle Conversion: Sulfur Dioxide in a Photochemically Reactive System

Citation

Roberts, Paul Thomas (1975) Gas-To-Particle Conversion: Sulfur Dioxide in a Photochemically Reactive System. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/c8qr-7m43. https://resolver.caltech.edu/CaltechTHESIS:10212022-160818228

Abstract

Particulate phase sulfur compounds are suspected to be major contributors to human health effects and visibility reduction. The formation of such aerosol sulfur compounds in a photochemically reactive system was studied, in both the laboratory and the field.

An aerosol vaporization technique was developed capable of measuring both total filter and cascade impactor aerosol samples for nanogram levels of sulfur compounds. This method measures the total aerosol sulfur species concentration.

Model calculations using measured aerosol and gas phase sulfur concentrations and air trajectory analysis provided estimated conversion rates for sulfur dioxide to aerosol sulfur compounds. For afternoon periods in Los Angeles, the pseudo-first order rate constant for SO₂ oxidation was from 1 to 15% hr^-1. The estimated rates were higher at higher levels of photochemical activity. In the atmosphere and in smog chamber studies, this rate is dependent upon the presence of O₃ and olefins, as well as SO₂. In smog chamber experiments with 1-heptene, NO_x and SO₂, the formation of the aerosol organic and sulfur compounds is consistent with the major aerosol producing step being a reaction between SO₂ and a reactive intermediate of the O₃-1-heptene reaction.

The size distribution of aerosol sulfur species was measured at various locations in the Los Angeles Basin. The sulfur was concentrated in the less than 0.5 μm size range during periods of high photochemical activity and in the 0.25-1.0 μm size range during other daylight hours. Measurements of the size distribution of aerosol sulfur species were taken during smog chamber experiments with 1-heptene, NO_x and SO₂ added to unfiltered ambient air, and irradiated with sunlight. A bimodal distribution developed with 2/3 of the sulfur in a mode below 0.1 μm and 1/3 in a mode above 0.2 μm in diameter.

The present and future effects of automobile emissions on aerosol sulfur compounds were estimated. The present contribution of motor vehicles to aerosol sulfur air quality at Pasadena is minimal. The introduction of the catalytic converter on new automobiles is estimated to produce a small increase in aerosol sulfur concentrations at receptor sites; however, the catalytic converter is estimated to produce dramatic increases in aerosol sulfur concentrations near roadways.

Thesis Files