Interdependence of the slopes and intercepts from log-log correlations of measured gas-particle paritioning and vapor pressure—I. theory and analysis of available data

Gas-particle partitioning is examined using a partitioning constant Kp = (F/TSP)/A, where F (ng m−3) and A (ng m−3) are the particulate-assiociated and and concentrations, respectively, and TSP is the total suspended particulate matter level (μg m−3). At a given temperature and for a given sample of particulate matter, compound-dependent values of Kp tend to be correlated with the sub-cooled liquid vapor pressure (pL0, toor according to log Kp = mr log pL0+bm. Theory predicts that br values should be somewhat similar, and that mr values should be near −1. This is supported by field and laboratory work. However, there is still noticeable variability in reported mr and br values, even when obtained by the same researchers sampling in the same location. Three possible thermodynamic sources of variability include variability in the compound-to-compound differences in the thermodynamics of adsorption, event-to-event variability in the specific surface area of the aerosol and event-to-event variability in the ambient temperature. Non-thermodynamic sources of variability include sorption of gaseous analytes to the filters used in differentiating between F and A, the presence of non-exchangeable component in the measured F values, within-event adsorption/desorption kinetics, within-event changes in contaminant levels, and within-event changes in temperature. Each of these sources of variability operate in their own way to cause variability in mr and br. In general, one can expect there to be a correlation in the obseved mr and br of the form br = msmr+bs. For the study of Yamasaki et al. (1982, Envir. Sci. Technol. 16, 189–194), one obtains ms = 5.77 and bs = −2.18, with r2 = 0.91. In the presence of such a correlation, one can expect that all log (F/TSP)/A vs log pL0 plot will tend to intersect at the same (x,y) poitn given by (−ms, bs. Exisiting field and laboratory data show this tendency.