ONSITE COMPARISON OF CANISTER AND SOLID-SORBENT TRAP COLLECTION OF HIGHLY VOLATILE HYDROCARBONS IN AMBIENT ATMOSPHERES

A field experiment for the comparison of the efficiency of canisters a nd adsorption multibed tubes for sampling atmospheric highly volatile hydrocarbons at ppbv levels is described. The canister was passivated by the Summa process and the adsorption tubes were filled with Carbotr ap C, Carbotrap B and Carbosieve Sm. The sampling with the adsorption tubes was performed at ambient temperature and at -10 degrees C. The h ighest concentrations were generally obtained with canisters but these results are very similar to those obtained with refrigerated multibed adsorption tubes. Both methods appear to be equivalent for most of th e highly volatile hydrocarbons encountered in moderately polluted urba n areas. In contrast, sampling with ambient temperature tubes provides lower concentrations. This study has also shown that K2CO3 drying eff iciently removes humidity from air samples allowing the obtention of r eliable concentration data on highly volatile hydrocarbons at ppbv lev els. These drying tubs can easily be re-conditioned and tested for bla nks and memory effects, which greatly facilitates the control of exter nal contamination and sample cross-contamination.