Articles | Volume 17, issue 14
Research article
20 Jul 2017
Research article |  | 20 Jul 2017

Atmospheric chemistry, sources and sinks of carbon suboxide, C3O2

Stephan Keßel, David Cabrera-Perez, Abraham Horowitz, Patrick R. Veres, Rolf Sander, Domenico Taraborrelli, Maria Tucceri, John N. Crowley, Andrea Pozzer, Christof Stönner, Luc Vereecken, Jos Lelieveld, and Jonathan Williams

Abstract. Carbon suboxide, O  =  C  =  C  =  C  =  O, has been detected in ambient air samples and has the potential to be a noxious pollutant and oxidant precursor; however, its lifetime and fate in the atmosphere are largely unknown. In this work, we collect an extensive set of studies on the atmospheric chemistry of C3O2. Rate coefficients for the reactions of C3O2 with OH radicals and ozone were determined as kOH =  (2.6 ± 0.5)  ×  10−12 cm3 molecule−1 s−1 at 295 K (independent of pressure between  ∼  25 and 1000 mbar) and kO3  <  1.5  ×  10−21 cm3 molecule−1 s−1 at 295 K. A theoretical study on the mechanisms of these reactions indicates that the sole products are CO and CO2, as observed experimentally. The UV absorption spectrum and the interaction of C3O2 with water (Henry's law solubility and hydrolysis rate constant) were also investigated, enabling its photodissociation lifetime and hydrolysis rates, respectively, to be assessed.

The role of C3O2 in the atmosphere was examined using in situ measurements, an analysis of the atmospheric sources and sinks and simulation with the EMAC atmospheric chemistry–general circulation model. The results indicate sub-pptv levels at the Earth's surface, up to about 10 pptv in regions with relatively strong sources, e.g. influenced by biomass burning, and a mean lifetime of  ∼  3.2 days. These predictions carry considerable uncertainty, as more measurement data are needed to determine ambient concentrations and constrain the source strengths.

Short summary
In this study we identify an often overlooked stable oxide of carbon, namely carbon suboxide (C3O2), in ambient air. We have made C3O2 and in the laboratory determined its absorption cross section data and the rate of reaction with two important atmospheric oxidants, OH and O3. By incorporating known sources and sinks in a global model we have generated a first global picture of the distribution of this species in the atmosphere.
Final-revised paper