Malcolm J. Campbell

Chemical characterization of plywood veneer dryer emissions

Abstract The chemical composition of the plywood veneer dryer emissions from eight steam- or gas-heated mills in the U.S. were analyzed by flame ionization detection gas chromatography and gas chromatography-mass spectrometry. The feed stocks examined consisted of three Pacific Northwestern species and three Southern yellow pines. The composition and the amount of emissions have changed since a 1972 study. The bulk of emissions was gaseous, and 40–95 % of total emissions consisted of ten terpenes. Of 28 components in the condensable portion of the emissions, 13 were identified by name and 4 by functional group. Isopimaric, dehydroabietic and oleic acids were most common. Some emissions were contaminants present in the air before entry into the dryers. Gaseous dryer emissions are similar to the foliage emissions and the cortical oleoresin content of living trees. Non-gaseous emissions are similar to biogenic components in rural aerosols and in wood extracts.

Radiocarbon tracer measurements of atmospheric hydroxyl radical concentrations

Radiochemical techiques have many untapped applications in atmospheric chemistry, especially when great sensitivity is required. We describe the application of these techniques to the measurement of hydroxyl radical concentrations in the troposphere.

Measurements of the diurnal OH cycle by a 14C-tracer method

The hydroxyl free radical, OH, is generally recognized as the primary oxidant for the removal of pollutants from the Earths atmosphere. Measurements of OH concentrations are needed to test models of atmospheric photochemistry. We have used the 14C-tracer technique to measure five ambient diurnal OH concentration cycles in relatively pure and in polluted air. The early-to mid-October maximum midday OH concentrations for pure and polluted air were found to be, respectively, 2.4 × 106 and 9.5 × 106 radicals cm–3 (10–13–4 × 10–13 relative to air). Night-time OH concentrations of less than 2 × 105 radicals cm–3 were measured. Estimates of OH concentrations from photochemical models and trace gas lifetimes are consistent with our observations.

Radiochemically ultrapure 14CO

Abstract Preparation of ultra high-purity 14CO tracers by the reduction of 14CO2 by Zn at 395°C are described. Purity levels of 10 −8 14 CO 2 14 CO have been obtained by successive freeze-outs of 12CO2 carrier gas at liquid-nitrogen temperature. Radiochemical purity of the 14CO is limited by radiolysis and surface catalysis. The radiolysis rate of 14CO corresponds to a G(CO2) of 2.5 ± 0.9. Techniques are discussed to reduce these problems.

Precision of the radiochemical OH measurement method

Abstract Twenty-eight radiochemical 14 C tracer measurement of tropospheric hydroxyl radical (OH) concentrations were obtained at a rural site near Washington State University, Pullman, WA (117°W, 47°N). Diurnal OH concentration variations were observed for the five days between 9 August and 14 August 1990. These data made it possible to estimate the midday precision and detection limit of the radiochemical OH measurement method. Experiments performed at a peak O 3 photolysis rate J (O( 1 D)) of (3.0±0.2) × 10 −5 s −1 yielded a mean midday OH concentration of (5.6±0.1 (1 σ )) × 10 6 cm −3 . Other data put an upper bound of 16% on fluctuations of instrument sensitivity. Low-light or nighttime background OH concentrations were less than (2.6±2) × 10 5 cm −3 . A lower detection limit of 10 5 cm −3 was obtained when extra care was taken with the low-level 14 C counting procedure.

The catalytic oxidation of 14CO in a flow reactor used to measure atmospheric hydroxyl radical concentrations

Measurements of ultra-low CO oxidation rates of materials suitable for construction of a hydroxyl radical monitor are described. The procedure consists of passing an ultrapure 14CO tracer over the test material and collecting the resultant 14CO2. Oxidation rates are measured for stainless steel, aluminum, alumina, titanium, and Teflon. Results show the oxidation rate with aluminum is at least an order of magnitude less than any other material (<104 cm−2s−1). These rates are three to four orders of magnitude lower than reported previously in the literature. Application to a ground-based hydroxyl monitor is discussed.