Paul T. Cunningham

Oxygen-18 study of nonaqueous-phase oxidation of sulfur dioxide☆

Abstract In a study of the mechanisms of atmospheric sulfate formation, oxygen isotope ratios were measured in sulfates and in the SO 2 and water vapors from which they were formed, in the absence of liquid water. In a 3-l glass chamber, SO 2 and water vapor of various 18 O contents were isotopically equilibrated, and then air oxidation of the SO 2 to sulfate was performed by four different methods: high-voltage discharges, NO 2 addition, gamma irradiation and adsorption on activated charcoal. Isotopic equilibration between SO 2 and water vapor proceeded rapidly, resulting in a strong dependence of the δ 18 O of the sulfate on that of the water vapor. Oxidation of SO 2 on dry charcoal occurred through the apparent formation of 9-oxygen, 2-sulfur, chemisorbed molecules which decomposed to sulfate in leach water. The δ 18 O SO 2− 4 vs δ 18 O H 2 O relationships observed for these four nonaqueous-phase oxidations of SO 2 to sulfate, together with those in three previously reported aqueous-phase oxidations ( Fe 3+ -catalyzed air oxidation, charcoal-catalyzed air oxidation and H 2 O 2 oxidation), were compared to sulfate in rain and snow collected at Argonne, IL. The δ 18 O of sulfate in precipitation water was significantly higher than could be accounted for by any of the several oxidation reactions that were investigated as possible pathways in the formation of secondary sulfates in the atmosphere, either singly or in combination.

Primary Sulfates in Atmospheric Sulfates: Estimation by Oxygen Isotope Ratio Measurements

The relative amounts of primary and secondary sulfates in atmospheric aerosols and precipitation can be estimated from measurements of the stable oxygen isotope ratios. The oxygen-18 content of sulfates formed in power plant stack gases before emission into the atmosphere is significantly higher than that of sulfates formed from sulfur dioxide after emission. Results show that 20 to 30 percent of the sulfates in rain and snow at Argonne, Illinois, are of primary origin.

Airborne Detection of Acidic Sulfate Aerosol Using an ATR Impactor

As a first step in determining how aerosol acidity varies with altitude, studies were conducted using a new instrument called an ATR impactor installed aboard the Battelle Pacific Northwest Laboratorys DC-3 aircraft. This instrument combines collection of the aerosol by inertial impaction with infrared spectroscopic analysis by the highly sensitive ATR technique. Results from several series of flights have revealed the occurrence of acidic sulfate aloft, while simultaneously collected ground-level samples contained only neutral ammonium sulfate. Acidic sulfate was detected in aerosol samples collected on four of the five flights conducted in the Chicago area during the spring of 1981.

Laser-Raman Spectra of Gaseous BiBr3 and PbCl2

Raman spectra are reported for gaseous BiBr3 and PbCl2 at temperatures just above their boiling points. The strong resonance fluorescence due to subhalide species that is normally observed in these vapors (with 4880 Å excitation) was suppressed by addition of equimolar amounts of the corresponding mercuric halide. The observed Raman bands for the BiBr3-HgBr2 sample, which are attributable to BiBr3, confirm a pyramidal structure having C3V point symmetry. The spectrum attributable to PbCl2 in the case of the PbCl2-HgCl2 sample is consistent with a symmetric bent structure.

Seasonal Variations of Oxygen-18 in Atmospheric Sulfates

Abstract Oxygen-isotope analyses were made on samples of aerosol sulfates, SO2, water vapor, precipitation water, and precipitation sulfates collected over a two-year period near Chicago, Illinois, U.S.A. The purpose of this isotopic study was to help to elucidate the mechanisms of sulfate formation in the atmosphere. Oxygen-18 enrichments in precipitation sulfates varied seasonally and in phase with the corresponding enrichments in precipitation water. The ratio of the amplitudes of the enrichment-vs.-time curves indicated isotopic equilibration between SO, and atmospheric water prior to oxidation. Oxygen-18 enrichments in aerosol sulfates appeared to vary randomly with season, but averaged about the same as precipitation sulfates. If aerosol sulfates and precipitation sulfates were formed by the same hydrolysis-oxidation mechanism in clouds, relatively long residence times and transport distances of sulfate aerosols may have provided sufficient mixing to obscure seasonal effects such as were observed in...

Laser Raman Spectra of Solid and Molten NaNH2: Evidence for Hindered Rotation of the NH2−1 Ion

Results of a Raman study of solid and molten NaNH2 (mp≃ 211°C) from 25–220°C are reported. Three bands are observed in both the solid (3267, 3218, and 1531 cm−1) and the liquid (3267 dp, 3218 p, and 1550 p cm−1), which are assigned to the three expected fundamental modes of NH2−1 with C2v point symmetry. Additional bands were observed in the 300–700 cm−1 region for both the solid and the liquid. In the case of the liquid, the band envelope in this region was resolved into three Gaussian components, which are attributed to the hindered rotational modes of NH2−. There was no evidence of intermolecular hydrogen bonding between NH2− ions.

A Method for Eliminating Resonance Fluorescence Effects in Raman Studies of Some High Temperature Vapors: Raman Spectra of BiCl3 from 450 to 800°C

The applicability of laser-Raman spectroscopy to the study of structures of gaseous inorganic species at elevated temperatures (to 1000°C) has been demonstrated.1–6 Several studies have provided information on thermodynamic quantities,2 chemical equilibria,4, 6 and force constants2, 5 for both pure materials and mixtures. In a number of cases, however, strong resonance fluorescence has obscured the vibrational Raman spectra of the species present.3, 4 The source of this resonance fluorescence can be either the material under investigation4 or a species formed through disproportionation of the sample material. An example of the latter case is the resonance fluorescence of BiCl, which overlaps the gas phase Raman scattering of BiCl3.