Atmospheric Chemistry, Sources, and Sinks of Carbon Suboxide, C₃O₂

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 is 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<br />and ozone were determined using relative rate techniques as k4 = (2.6 ± 0.5) ´ 10-12 cm3 molecule-1 s-1 at 295 K (independent 15 of pressure between ~25 and 1000 mbar) and k6 < 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 were also investigated, enabling photodissociation and hydrolysis rates 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<br />20 at the Earth´s surface, up to about 10 pptv in regions with relatively strong sources, e.g. 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.