A sampler for radiocarbon in surface air

Abstract

Compact, automatic equipment for the collection of carbon dioxide from surface air at ambient temperature is described. An oil-free, diaphragm-type compressor pumps air through a silica gel bed, which removes water vapor, and then through a bed of Linde 5A molecular sieve, which adsorbs carbon dioxide quantitatively. The sample is collected over periods of 24 to 28 hours to minimize the influence of transient conditions. In this period, approximately 10 liters of carbon dioxide, equivalent to 5 grams of carbon, are collected. The carbon dioxide is desorbed from the molecular sieve by heating to 500°C and is transferred in vacuo to a purification train. The C14 content of biweekly samples is measured in 7.5-liter gas proportional counters. The specific activity of the carbon increased over the period January 1964 to December 1964, showing that C14 from a stratospheric reservoir was continuously entering the troposphere. However, the values from the first half of 1965 were lower and varied slightly.