Measurement of atmospheric monocyclic aromatic hydrocarbons and chlorinated C-1- and C-2-hydrocarbons at ng.m(-3) concentration levels

An air sampling and analysis technique for thirteen monocyclic aromatic hydrocarbons (MAHs) and chlorinated C-1 and C-2-hydrocarbons (CHCs) at ng.m(-3) concentration levels is presented. Sampling was done on Carbopack B/Carbosieve SIII adsorbent tubes. The analysis on an automated on-line purge and trap (P&T) apparatus equipped with a thermal desorption unit proved to be not reproducible because of water interference and because of contamination from the apparatus itself. An off-line desorption unit, combined with thermal desorption by means of the on-line apparatus gave reproducible measurements with relative standard deviations (% SD, n = 4) from 0.9 to 8.3 at 2.2-4.1 mu g.m(-3) (+/-670 pptv). Limits of detection (LODs) at a signal/noise ratio equal to three were below 5.7 mu g.m(-3). For chloroform, benzene and toluene the LODs were 41.4, 96.0 and 48.7 ng.m(-3) respectively because of background levels of these compounds. Next to this analysis, a simple calibration method is presented which proved to be accurate and precise. A dynamic vapour pressure (DVP) calibration technique on the contrary, was tested and showed significant bias. The sampling and analysis method allowed to determine all mentioned volatile organic compounds (VOCs) in duplicate field measurements with 0.6-7.3% SD at 124-1374 ng.m(-3) concentrations and with 21.3 to 39.4% SD for 29 to 95 ng.m(-3) concentrations.