Studies on the Occurrence and Distribution of Wood Smoke Marker Compounds in Foggy Atmospheres

Fog water and interstitial air samples were collected simultaneously and analyzed for methoxylated phenols, which have been previously reported as incomplete combustion products from wood lignin. The purpose of the study was to ascertain if methoxylated phenols could be detected in fog sampled in residential areas, and how these compounds distributed between the fog droplets and the interstitial air. The fog water was collected with a Teflon ^circler filament fog collector and filtered through a 0.2 μm filter before extraction and GC analysis. Vapor samples were collected using a dichotomous sampler to separate the fog droplets from the interstitial air; the organic vapors were collected on polyurethane foam. Guaiacol, 4-methylguaiacol, and syringol were the most commonly found of sixteen confirmed methoxylated phenols in fog samples. In order to assess air/water distribution, accurate measures of Henry's law constant (H) are need; measurements of H by headspace gas chromatography and gas-stripping are presented. Field measured air/water distributions approximately followed H, suggesting that previously reported enrichment factors (EF = H/field distribution) into fog water are related to analyte hydrophobicity, described either by the octanol -water partition coefficient (K_{rm ow}) or water solubility (S). A theoretical model is presented that assumes that there is a third phase in the fog-air system that acts like a separate organic phase and partitions chemicals into it. Making no further assumptions as to the nature of this unknown phase, the enrichment can be described as either EF = 1 + AK _{rm ow} or EF = 1 + Z/S, where A and Z are derived from the plots of EF vs. K _{rm ow} and EF vs. S, respectively.