LBNL Report Number
Many environmentally-persistent chemical pollutants are semi-volatile organic compounds (SVOC) (such as polycyclic aromatic hydrocarbons and pesticides) that enter the base of the food chain through pathways that depend initially on their phase distributions in the atmosphere. Many of these SVOC have been shown to have potential for reproductive and endocrine disrupting effects.
The environmental fates of semi-volatile organic species are phase dependent because atmospheric reactions and transport and deposition processes differ for gaseous and particulate semi-volatile species. For example, for many SVOC, the nature and extent of contaminant transport from air to surface water or from air to vegetation and into food chains are very strongly dependent on partitioning between the gas and particle phases in the atmosphere. Whether intermedia transport takes place in the gas or particulate phase can have a strong impact on the estimated extent of human and ecosystem exposures. In addition, health effects due to exposure to toxic air pollutants are phase dependent since lung deposition patterns differ between the gas and particulate phases. Furthermore, strategies to control semi-volatile organic environmental pollutants require information on phase distributions.
Efforts to move from the existing qualitative characterization of the importance of partitioning of SVOC to more quantitative characterization have been hindered by a number of scientific obstacles. One major problem is the quality of many of the measurements of the partitioning of these chemicals between the gas phase and airborne particulate matter, between the gas phase and soils, and between the gas phase and vegetation. For example, most existing measurements of vapor-particle partitioning are suspected to show large artifacts (biases) due to the sampling methods used. An additional problem is the lack of a modeling framework that includes coupled mass exchange at multiple media boundaries (soil, air, vegetation, etc.), and that appropriately links the space and time scales involved in long-range transport when multiple media are integrated.