Dept. of Environmental Science
Oregon Graduate Center
Little is known about the scavenging of organic compounds, particularly the relative importance of gas and particle scavenging. A field study of organic compounds in rain and air was conducted in Portland, Oregon and at the Oregon coast in order to provide information on the scavenging process. The samplers collected organic compounds in the rain dissolved and particulate phases and in the atmospheric vapor and particulate phases. The rain sampling train consisted of a prefilter and filter, followed by two parallel sets of Tenax cartridges for the adsorption of dissolved organics. The air sampling train consisted of a glass fiber or Teflon membrane filter followed by parallel sets of adsorbents for the collection of vapors. Polyurethane foam and Tenax were both used in the air sampler. Analysis of the rain and air samples proceeded by either solvent extraction and on-column injection or direct thermal desorption onto a fused silica capillary column interfaced with a mass spectrometer and data system (GC/MS/DS). Concentration data were obtained for over 100 organic target compounds including PAHs, phenols, phthalate esters, alkanes, aromatics, and pesticides. Phenols were the dominant organic compounds found in rain samples, with concentrations in the ug/L range in Portland. PAHs and phthalates were also major constituents. Concentrations at the Oregon coast were generally a factor of 2 to 7 lower than in Portland. Gas and particle scavenging ratios were obtained from the air and rain concentration data. The gas scavenging ratios (Wg), obtained at ambient temperatures of 3-10Â°C, ranged from 3 to 10[superscript 5] at both sites. Wg values were generally a factor of 3 to 6 higher than the values predicted from the Henry's Law equilibrium, when 25Â°C literature values were used. However, Wg values for several PAHs agreed well with equilibrium when literature values obtained at the appropriate temperatures were used. Particle scavenging ratios (Wp) ranged from 10[superscript 3]to 10[superscript 5] and averaged -10[superscript 4]. These values were consistently lower than the 10[superscript 5] to 10[superscript 6] generally reported for inorganic species. Wp values were significantly lower for the least volatile PAHs than for the other organic compounds. Only alkanes and volatile PAHs exhibited Wp values larger than their Wg values. For the majority of compounds studied, gas scavenging was more important than particle scavenging.
Ligocki, Mary Peterson, "The scavenging of atmospheric trace organic compounds by rain" (1986). Scholar Archive. 97.