Air — Water Partitioning of Volatile Organic Compounds and Greenhouse Gases in the Presence of Salts
Falabella, James Benjamin
MetadataShow full item record
The determination of accurate volatile organic compound (VOC) and greenhouse gas (GHG) partitioning coefficients for air-water interfaces is essential for pollution and global climate modeling. In the atmosphere, oceans, and groundwater the concentration of dissolved salts is high enough to significantly alter the air-water partitioning behavior of the VOC or GHG, prohibiting the use of literature data or predictive models that omit the salt effect. Despite the great need for air-water partitioning data of the VOCs and GHGs threatening the environment, there is a lack of air-water partitioning data in the presence of dissolved salt. Furthermore, there are large disagreements between reported data from different research groups, which hamper model development. Henry s constants of several VOCs with salts were measured with a new high-throughput headspace gas chromatography (HTHSGC) method to create a library of internally consistent air-water partition coefficients for modeling. The VOCs studied included a homologous series of 1-alkanols, 2-ketones, organic sulfides, and the principle components of gasoline including: toluene, ethylbenzene, o-xylene, methyl tertbutyl ether, and ethyl tertbutyl ether. A model with temperature-independent parameters based on dilute solution theory was developed using the library of data to resolve the disagreements between literature sources and perform a priori prediction of salt effects. The model correlated air-water partitioning data in the form of Henry s constants over temperature ranges as wide as 300 Kelvin, salt concentrations up to 4 molal, and pressures up to 1000 bar. Extrapolations of up to 50 K, and 1 molal salt and 100 bar pressure can also safely be performed to eliminate the need for additional experiments. The temperature-independent salt effect parameter was found to be directly proportional to the critical volume of the VOC and all homologous VOCs explored followed the same linear trend allowing a priori prediction of the salt effect for unexplored compounds.