John W. Spence

Infrared Measurement of Fluorocarbons, Carbon Tetrachloride, Carbonyl Sulfide, And Other Atmospheric Trace Gases

A cryogenic procedure for concentrating trace gases in the atmosphere has been developed and applied to the ambient air at Research Triangle Park, NC, Atlantic Beach, NC, and New York City. The concentrated gases have been analyzed by long path infrared absorption spectroscopy, with a detectability down to partial pressures of 10−11 atmospheres. Carbonyl sulfide has been detected at partial pressures in the range 1 × 10−10 atm. to 3 × 10−10 atm. Carbon tetrachloride was always detected with a rather narrow partial pressure range of 0.7 × 10−10 atm. to 1.1 × 10−10 atm. Fluorocarbon-11 values ranged from about 1.3 × 10−10 atm. at Research Triangle Park to 8 × 10−10 atm. at New York City. Fluo-rocarbon-12 covered the range 1.8 × 10−10 atm. to 1.0 × 10−9 atm. Hydrocarbon pollutants varied widely in concentration, but were always detected, even in the clean rural air.

Carbon monoxide production in photooxidation of organic molecules in the air

Sources and sinks of atmospheric carbon monoxide have not been in balance. The estimated rates of CO removal have been as much as a factor of two higher than estimated rates of emission. These discrepancies are much reduced when one considers the atmospheric photooxidation of the non-methane organic material released by vegetation. From known oxidation mechanisms it has been inferred that these photo-oxidations might be the largest single source of atmospheric carbon monoxide. A laboratory confirmation of this expected high CO yield is reported in this paper. Recognizing this large CO source allows the source-sink budgets to be balanced in both hemispheres, with due regard to isotope measurements, lifetime estimates and the inter-hemispheric CO concentration gradient. If the average OH radical concentration is 4 × 105 radicals cm−3, the source-sink balance indicates that the non-methane organic matter is producing in the Northern hemisphere 5.1 × 1014gy−1 CO (46% of the total), and in the Southern hemisphere, 2.5 × 1014gy−1 (50% of the total).

Laboratory investigations of the impact of dry deposition of SO2 and wet deposition of acidic species on the atmospheric corrosion of galvanized steel

Abstract A series of short-term laboratory experiments were conducted in which galvanized steel samples were exposed to sub-ppm levels of SO2. Dew was produced periodically on the test panels, and, at the end of some experiments, panels were sprayed with solutions of various pH levels. Both dew and rain rinse samples were analyzed for SO32−, SO42− and Zn. The laboratory results suggest that as a first approximation the damage to galvanized steel induced by the dry deposition of SO2 can be calculated by equating the dry SO2 flux to the Zn corrosion flux. SO2 will deposit onto a fresh dry surface until an amount similar to that of a monolayer has formed. Under wet conditions, the dry deposition flux is controlled by the gas-phase resistance of the atmosphere. Wet deposition of ammonium bisulphate induces corrosion which depends not only on the pH of the incident rain, but also on the exposure history of the samples.

Synthesis and Thermal Stability of Peroxy Alkyl Nitrates

Because of their thermal instability at ambient atmospheric conditions, peroxyalkyl nitrates are not likely to act as sinks for nitrogen dioxide in the lower atmosphere and will not have a significant role in smog modeling studies. PAkNs may, however, be of importance in the understanding of stratospheric nitrate chemistry.

Effects of acid deposition on paints and metals: Results of a controlled field study

A controlled field study was conducted in Research Triangle Park, NC to determine the impact of acid deposition on paints and metals. A computer-controlled system was designed so that test panels of galvanized steel, five exterior paints and Teflon could be exposed under the following conditions: (1) dry deposition only; (2) dry plus ambient wet deposition; and (3) dry deposition plus deionized water. A 78-day, 11-rain-event exposure experiment was conducted in which ambient and DI run-off samples were collected from each material on a rain-event basis and chemically analyzed. The run-off results show that the dry and wet deposition of acidic species accelerates the dissolution rates of galvanized-steel corrosion products and alkaline compounds in exterior paints. CaCO3 and ZnO in latex paints and Al in aluminum flake paint react with acids either directly deposited or produced in thin films of moisture covering the surfaces. The results indicate that the uptake of SO2 into moisture is strongly influenced by the reactivity of the material towards H+. Galvanized steel was found to have the highest SO2 deposition velocity, whereas an oil-based paint, containing no known alkaline compounds, had the smallest value. Run-off results also suggest that Zn corrosion products were dissolved in ambient precipitation by acids produced by dissolved CO2.

Atmospheric Oxidation of Methyl Chloride Methylene Chloride, and Chloroform

Chlorinated atmospheric pollutants are presently receiving much attention because of expected chlorine-ozone interactions in the stratosphere.1,2 The fully halogenated pollutants,such as CCI3F, CCl2F2, and CCl4, have no known removal processes that operate in the troposphere. These compounds are accumulating on a global scale, their atmospheric mixing ratios having reached about 2 X 10-10 for CCl2F2,1.2 X 10-10 for CCl3F, and 9 X 10-11 for CCl4.3-5

Acid rain effects on the exterior durability of architectural coatings on wood

Abstract Acid rain is an important consequence of pollutants generated by modern industrial societies and is known to cause damage to ecological systems, construction materials and cultural artifacts. The assessment of the damage caused to paint films has included laboratory, exposure chamber, and exterior weathering experiments. This study uses visual assessment of paints applied directly to southern yellow pine and exposed at 30° south to either natural acid rain or deionized water spray sites in North Carolina and Ohio to determine damage by acid rain. An acrylic latex paint with a pigment volume concentration (PVC) of 52 and a volume solids (VS) of 35% was formulated with calcium carbonate or sodium potassium alumino-silicate extenders. This high PVC paint formulation is one known to stress the binding capacity of the latex and thus produce early grain cracking failures over bare wood. Major effects observed include severe yellowing and increased mildewing of the carbonate containing paints exposed to acid rain. While acid rain can damage exterior paints, much of the damage can be minimized by careful selection of the polymers and pigments used in the formulation.

Atmospheric weathering caused by dry deposition of acidic compounds

The study was conducted to investigate the effects of deposition on galvanized steel and painted panels using mobile covering/deionized spray devices at exposure sites located at Steubenville, OH and Research Triangle Park (RTP), NC. Ambient rain and deionized spray runoff samples from the panels were collected on an event basis for seven months and underwent detailed chemical analysis. The analysis indicated that the dry deposition of acid gases at the sites increased the dissolution rate of galvanized steel corrosion products. Although the average SO2 level in Steubenville was ten times the RTP value, the rate of Zn dissolution was only 1.9. This result in conjunction with the presence of large amounts of Ca in the Steubenville runoff samples suggest that neutralization of acidic gases by dry deposited basic particulates may be important at the Steubenville site. At the RTP site low levels of anions were found in the runoff from the painted panel with H(1+) as the most abundant cation. This result is consistent with the lack of reactivity towards acidic gases due to the absence of alkaline paint components.

The effect of specimen size, shape, and orientation on dry deposition to galvanized steel surfaces

Abstract Galvanized steel specimens varying in size, shape, orientation angle and previous exposure history (weathered specimens) were exposed at Research Triangle Park, NC, in the absence of natural precipitation. The soluble corrosion products were assumed to represent the effects of dry deposition of airborne substances. The statistical analysis of their variability in relation to atmospheric conditions suggested that these substances included sulfur dioxide, nitric acid, hydrochloric acid, and calcium (presumably from coarse particles). The specimen characteristic most influencing inferred dry deposition was previous exposure history. Deposition of gases depended on surface condition (wetness), wind speed, temperature, and to a lesser extent, orientation angle. Deposition of particles depended on orientation angle. Loss of soluble zinc from specimens varied with specimen size to the −0.2 power, even though Reynolds numbers based on average wind speeds and specimen length were well below those classically expected to produce turbulent flow.

Fading of Selected Drapery Fabrics by Air Pollutants

A statistically designed laboratory study to assess both direct and synergistic effects of air pollutants and other environmental factors on six different classes of materials was recently completed.1 One of the material classes was dyed textile fabrics. Drapery fabrics were specifically selected because they are economically important, are designed to have a fairly long life, and are subject to atmospheric fading. In fact, fading, whether caused by sunlight, pollution or both, frequently limits the useful life of draperies.