Measurements of VOCs from the TAMS Network

Abstract

Target volatile organic compounds (VOCs) were measured at a network of urban air monitoring locations in Boston, Chicago, Houston, and the Seattle/Tacoma area. Following a pilot-scale field evaluation of available techniques for determining concentrations of VOCs in ambient air, a technique based on evacuated stainless steel canisters was selected to collect whole air samples. Twenty-four-hour integrated samples were collected every twelfth day at ten sites over a 2-year study period. Battelle Columbus Laboratory (BCL) analyzed the samples for 25 target VOCs using cryogenic focusing, gas chromatographic separation and mass selective detection with flame ionization detection as backup. Duplicate canister samplers were operated each sampling period at one of the ten sites in the Toxic Air Monitoring System (TAMS) network to estimate overall method precision. In addition, every 10th analysis was repeated by BCL to obtain a measure of analytical precision. Finally, each sampling period a clean evacuated canister was sent to Research Triangle Park to be filled with an audit gas mixture of known concentrations. The audit canisters were analyzed along with the routine field samples to estimate method accuracy. The target compounds found most ubiquitously were benzene, toluene, xylene and ethylbenzene. These aromatic compounds were highly correlated and proportionally related in a manner suggesting that the primary contributors were mobile sources in all the urban locations studied. Annual median concentrations for target compounds ranged from 0.1 to 4.0 part per billion volume (ppbv) range, while individual 24-h concentrations occasionally reached as high as 20 ppbv.