A Simple Procedure for Evaluating Global Cosmogenic 14C Production in the Atmosphere Using Neutron Monitor Data

Abstract

Radiocarbon (14C) produced by cosmogenic processes in the atmosphere reacts rapidly with atomic oxygen to form 14CO. The primary sink for this species is oxidation by the OH radical, the single most important oxidation mechanism for pollutants in the atmosphere. Hence, knowledge of the spatial and temporal distribution of 14CO allows important inferences to be made about atmospheric transport processes and the distribution of OH. Because the chemical lifetime of 14CO against OH attack is relatively short, 1–3 months, its distribution in the atmosphere should show modulations due to changes in 14C production caused by variations in the solar cycle. In this work we present a simple methodology to provide a time series of global 14C production to help interpret time series of atmospheric 14CO measurements covering the whole of solar cycle 23. We use data from neutron monitors, a readily available proxy for global 14C production, and show that an existing 6-year time series of 14CO data from Baring Head, New Zealand, tracks changes in global 14C production at the onset of solar cycle 23.