Automated trace analysis of airborne C₁- and C₂-halocarbons

Summary

Representative concentrations of volatile halocarbons in ambient air are determined by automated, repetitive sampling with sorbent-packed traps, followed by on-line thermodesorption, stationary-phase focussing, capillary gas chromatography, and electron-capture detection. Cryogenic enrichment and the associated problem of water-collection are avoided by ambient trapping using micro-traps packed with organic polymer- and carbon molecular-sieve sorbents. Under optimization of flow conditions and by use of thick-film capillaries, components with boiling points even below ambient temperature can be analyzed on-line by capillary gas chromatography, without the need for cryogenic peak focussing during injection. Data storage, quantification, statistical evaluation, and graphics generation are performed with commercial software programs. The instrumentation can be adapted for monitoring chemically stable volatile trace components with low and medium polarity. The results obtained with the instrumentation show that atmospheric levels of the major C₁/C₂-halocarbons may fluctuate over short time intervals; therefore, several hundred values must be accumulated for comparison of air pollutant burdens at different locations.