Removing CO2 from atmospheric samples for radiocarbon measurements of volatile organic compounds

Two methods employing LiOH to selectively remove CO2 from ambient whole air samples have been investigated. This is a necessary step in preparing an atmospheric sample for a measurement of the radiocarbon (C-14) 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 CO2 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 CO2 removal, while hydrocarbons were virtually unaffected. The following paper in this issue gives VOC radiocarbon results for samples characterized in this article.