Atmospheric Chemistry, Sources, and Sinks of Carbon Suboxide, C 3 O 2

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 C 3 O 2 . Rate coefficients for the reactions of C 3 O 2 with OH radicals and ozone were determined as k OH  =  (2.6 ± 0.5)  ×  10 −12 cm 3 molecule −1 s −1 at 295 K (independent of pressure between  ∼  25 and 1000 mbar) and k O 3 1.5  ×  10 −21 cm 3 molecule −1 s −1 at 295 K. A theoretical study on the mechanisms of these reactions indicates that the sole products are CO and CO 2 , as observed experimentally. The UV absorption spectrum and the interaction of C 3 O 2 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 C 3 O 2 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.