COSMOGENIC14CO FOR ASSESSING THE OH-BASED SELF-CLEANING CAPACITY OF THE TROPOSPHERE

Carl A M Brenninkmeijer,Patrick Jöckel,Sergey S Gromov

doi:10.1017/rdc.2021.101

Carl A M Brenninkmeijer, Patrick Jöckel + Show 1 more

Open Access

https://doi.org/10.1017/rdc.2021.101

Copy DOI

Abstract

ABSTRACTAn application of radiocarbon (14C) in atmospheric chemistry is reviewed.14C produced by cosmic neutrons immediately forms14CO, which reacts with hydroxyl radicals (OH) to14CO2. By this the distribution and seasonality (the lifetime of14CO is ∼1 month) of the pivotal atmospheric oxidant OH can be established.14CO measurement is a complex but unique application which benefitted enormously from the realization of AMS, bearing in mind that14CO abundance is of the order of merely 10 molecules per cm3not only provides14CO an independent measure for the OH based self-cleansing capacity of the troposphere, but also enabled detection of14C production due to high energy solar protons in 1989. Although its production takes place throughout the atmosphere and does not have the character of a point source, transport processes in the atmosphere affect the distribution of14CO. Vertical mixing in the troposphere renders gradients in its production rate less critical, but considerable meridional gradients exist. One question has remained open, namely confirmation of calculated14C production by direct measurement. A new sampling method is proposed. The conclusions are a guide to future work on14CO in relation to OH and atmospheric transport.

Highlights

Before a fresh cosmogenic 14C atom (produced by 14N(n,p)14C) enters the main carbon cycle, it almost instantaneously forms 14CO and a such partakes in atmospheric chemistry for a period of a month or so
An application of radiocarbon (14C) in atmospheric chemistry is reviewed. 14C produced by cosmic neutrons immediately forms 14CO, which reacts with hydroxyl radicals (OH) to 14CO2
The distribution and possible changes of OH in the troposphere have been a bone of contention for years. It was not known if OH does change over large parts of the troposphere or even globally on a scale of several years and if OH remained stable at all over the current decades of the Anthropocene

Summary

Introduction

Before a fresh cosmogenic 14C atom (produced by 14N(n,p)14C) enters the main carbon cycle, it almost instantaneously forms 14CO and a such partakes in atmospheric chemistry for a period of a month or so. High production combined with the longer lifetime of 14CO in much of the stratosphere (by mass) implies that its rate of transport into the troposphere (overall variable with season and stronger in the NH) is a key factor.

Results

Conclusion