Removing CO2 from Atmospheric Samples for Radiocarbon Measurements of Volatile Organic Compounds

Two methods employing LiOH to selectively remove CO 2 from ambient whole air samples have been investigated. This is a necessary step in preparing an atmospheric sample for a measurement of the radiocarbon ( 14 C) content of its non-methane volatile organic compounds (VOC) fraction, which in turn gives the fraction of VOC that is biogenic. A reliable estimate of the biogenic contribution to VOC is fundamental in deciding on a national tropospheric ozone abatement strategy. Both methods, using a LiOH-coated annular denuder or a LiOH-packed tube, were shown capable of decreasing CO 2 in ambient air samples (nominal 360 ppm) by 4 orders of magnitude, while having only a modest effect on their VOC content (20% loss, on average). The samples were from a variety of urban and rural locations. Detailed VOC speciation showed that aldehydes generally experienced the greatest loss during CO 2 removal, while hydrocarbons were virtually unaffected. The following paper in this issue gives VOC radiocarbon results for samples characterized in this article.