Increasing the accuracy of climate prediction
SVOCs play a critical role in the formation of secondary organic aerosols (SOAs), aerosols that arise from oxidation of gas-phase organic species. Although SOAs account for a large portion of the submicron atmospheric aerosol mass, there is considerable uncertainty about their sources, evolution and properties – leading to uncertainties in climate models. With EU support of the ERSGVSOAF (Exploring the role of semivolatile gas-phase vapors in secondary organic aerosol formation) project, scientists developed and field-tested a significantly improved method for quantification of SVOCs in the gas phase. SVOCs are multiphasic. Building on recent work successfully determining relative gas- and particle-phase partitioning of SVOCs but without quantification, the team developed a system to quantify SVOCs in an ambient aerosol mixture. The automated ERSGVSOAF instrument consists of three denuders in series to separate gas-phase analytes from the aerosol. The denuder series is interfaced with a modified version of an existing thermal desorption proton transfer reaction mass spectrometer to measure SVOCs in the gas and the particle phases. Unattended indoor measurements demonstrated the very high mass resolution capabilities and low detection limits for both gas and aerosol species. Excellent physical and chemical characterisation enabled identification of hundreds of aerosol species and SVOCs. Researchers then deployed the instrument at the ground-based SEARCH tower site in Centreville, Alabama, United States. The flux tower has been established in an area influenced strongly by biogenic VOCs and somewhat by anthropogenic emissions. Results of the deployment have provided valuable insight that reduces current uncertainties regarding SOAs. The improved sensitivity and enhanced detection limit of the ERSGVSOAF instrument enable quantification of the degree of oxidation of SVOCs. Greater understanding of the sources and evolution of SOAs will improve predictive capabilities of regional and global climate models with important impact on policymaking and effectiveness.
Keywords
Climate, semivolatile, semivolatile organic compounds, oxidation, secondary organic aerosols, gas-phase
