GAS-SOLID PARTITIONING OF SEMIVOLATILE ORGANIC-COMPOUNDS TO MODEL ATMOSPHERIC SOLID-SURFACES AS A FUNCTION OF RELATIVE-HUMIDITY .1. CLEAN QUARTZ

Evaluating the relative importance of adsorption to particle surfaces vs absorption into organic material in particles for gas/particle partitioning in the atmosphere requires a comparison of relevant gas/solid partitioning constants with field-determined values. Gas/quartz partitioning constants K-p (m(3)/mu g) were measured at 20 degrees C for clean quartz as a function of relative humidity (RH) for 11 semivolatile polycyclic aromatic hydrocarbons (PAHs) and n-alkanes. Increasing RH from similar to 30 to similar to 70% caused the K-p values to decrease by a factor of 10. With adsorption to the quartz surface as the only possible sorption mechanism, surface-area-normalized partition constants (K-p,K-s, m(3)/m(2)) were calculated. For quartz, correlations of log K-p,K-s with the fog of the vapor pressure were found to lie significantly below the corresponding lines for urban particulate matter. We conclude that adsorption to mineral/oxide surfaces like clean quartz is not important in determining K-p values in urban air; such sorption may be important in rural/remote environments.