Stanley A. Johnson

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.

The Influence of Humidity on Fine-Particle Aerosol Dynamics and Precipitation Scavenging

Precipitation chemistry and the chemical composition and mass loading of atmospheric fine-particle aerosols were examined for 25 individual precipitation events during a 12-month period. Aerosol and precipitation data were used (a) to determine the influence of the precipitation event on the mass loading and the chemical composition of the fine-particle aerosol, and (b) to calculate the apparent scavenging ratios for sulfate and ammonium ions. Two distinct types of aerosol behavior were observed. In one, the concentration of aerosol particles were observed to decrease during the rain but to recover quickly after the event. In the other, the aerosol particle concentration in the 0.3–1.0 μm size range was found to increase either during or just after the rain. The meteorology associated with each precipitation event was examined in detail to determine the factors responsible for the observed behavior of the aerosol particles. Particle mass concentration decrease in the first type of behavior was attributed ...

Composition and spectral characteristics of ambient aerosol at Mauna Loa observatory

Ambient aerosol particles were sampled continuously with a time resolution of {approximately}4 hours for a period of 8 days at the Mauna Loa Observatory, Hawaii, in August 1986. The samples were analyzed on-site for their chemical composition by attenuated total internal reflection infrared spectroscopy. The infrared absorption spectra of the samples also provided data on aerosol light absorbance characteristics at 9.1 and 10.6 {mu}m - wavelengths of interest in determining aerosol backscatter coefficients for CO{sub 2} lidars. The chemical species in the ambient aerosol varied considerably during this 8-day period. The aerosol was acidic ((NH{sub 4}){sub 3}H(SO{sub 4}){sub 2},NH{sub 4}HSO{sub 4}, or H{sub 2}SO{sub 4}) rather than neutral ((NH{sub 4}){sub 2}SO{sub 4}) for a major fraction of the sampling time. The samples generally showed much higher absorbance at 9.1 {mu}m than at 10.6 {mu}m. Changes in the chemical composition between (NH{sub 4}){sub 2}SO{sub 4} and the more acidic forms were accompanied by substantial changes in the samples absorbance at 9.1 {mu}m but lesser changes in the absorbance at 10.6 {mu}m. These variations could have a profound effect on backscatter coefficients of atmospheric aerosol particles at CO{sub 2} wavelengths.

Formation and characterization of sulfide clusters in molecular sieve zeolite materials

The incorporation of molybdenum into the faujasite pore system via reaction of molybdenum pentachloride with H-Y zeolite results in dealumination of the zeolite framework and formation of MoO{sub 3} species. These species are readily sulfided by H{sub 2}S, but MoS{sub 2} clusters are not produced. A sulfur-bridged dimeric molybdenum cluster, of proposed composition HO-Mo-(S){sub 3}-Mo-OH, is formed, which can strongly chemisorb CO. Sulfidation of niobium in this manner is not readily accomplished. 19 refs.