Assessment of storage correction required for in situ 14CO production in air sample cylinders -: art. no. 1139

[1] We draw attention to an effect that has the potential to compromise measurements of atmospheric (CO)-C-14 by the in situ production of C-14 in air sample cylinders. We present first experimental determinations of the size of this effect using measurements made on cylinders containing an air sample and a CO/nitrogen calibration gas stored in laboratories in New Zealand from a few months to 11 years. These data are collated with measurements made on air samples stored at Scott Base, Antarctica to determine a mean in situ production rate for (CO)-C-14 of 4.7 +/- 0.5 molecules cm(-3) yr(-1) (STP) at sea level and in the latitude range 40-90degrees (geomagnetic) in a single floor laboratory. This rate is significant compared to observed annual cycles in (CO)-C-14 (typically 5-10 (CO)-C-14 molecules cm(-3)) caused by OH variations and clearly has to be corrected for when (CO)-C-14 data are used to determine atmospheric OH distributions.