EFFECTS OF TEMPERATURE, TSP AND PER CENT NONEXCHANGEABLE MATERIAL IN DETERMINING THE GAS PARTICLE PARTITIONING OF ORGANIC-COMPOUNDS

The temperature dependence of the measured, gas-particle partitioning ratio (F(T)/TSP)/A(T) has been examined for the case when a constant fraction x (%) of a compound is assumed to be bound within the particulate matter, and non-exchangeable with the gas phase. The parameter F(T) is the total (exchangeable + non-exchangeable) measured concentration in the atmosphere (ng m-3), A(T) is the gaseous concentration (ng m-3), and TSP is the level of suspended atmospheric particulate matter (mu-g m-3). It is assumed that the true thermodynamic constant K(p) depends upon 1/T according to log K(p) = m(p)/T + b(p) where m(p) depends on the enthalpy of desorption of the compound of interest, b(p) depends in part on other properties of the compound as well as the specific surface area of the particulate matter, and T is the temperature (Kelvin). When K(p) or TSP are low, the difference between the measured quantity (F(T)/TSP)/A(T) and K(p) can be significant even when the non-exchangeable fraction x is as low as a few per cent. This approach has been used to examine the PAH data set of Yamasaki et al. [(1982) Env. Sci. Technol. 16, 189-194]. It was found that the Yamasaki data set does not allow estimates of x that are consistent with the current understanding of the temperature dependence of log K(p) values. A likely reason for this result is some dependence of m(p) and b(p) on the exact nature of the particulate matter and atmospheric conditions such as relative humidity. It is concluded that estimates of x values for a given compound on actual particulate matter may only be possible by the direct examination of individual particulate matter samples.