Upgrading photolysis in the p-TOMCAT CTM: model evaluation and assessment of the role of clouds

A new version of the p-TOMCAT Chemical Transport Model (CTM) which includes an improved photolysis code, Fast-JX, is validated. Through offline testing we show that Fast-JX captures well the observed J(NO(2)) and J(O(1)D) values obtained at Weybourne and during a flight above the Atlantic, though with some overestimation of J(O(1)D) when comparing to the aircraft data. By comparing p-TOMCAT output of CO and ozone with measurements, we find that the inclusion of Fast-JX in the CTM strongly improves the latter's ability to capture the seasonality and levels of tracers' concentrations. A probability distribution analysis demonstrates that photolysis rates and oxidant (OH, ozone) concentrations cover a broader range of values when using Fast-JX instead of the standard photolysis scheme. This is not only driven by improvements in the seasonality of cloudiness but also even more by the better representation of cloud spatial variability. We use three different cloud treatments to study the radiative effect of clouds on the abundances of a range of tracers and find only modest effects on a global scale. This is consistent with the most relevant recent study. The new version of the validated CTM will be used for a variety of future studies examining the variability of tropospheric composition and its drivers

Chemistry of the Antarctic boundary layer and the interface with snow: an overview of the CHABLIS campaign

CHABLIS (Chemistry of the Antarctic Boundary Layer and the Interface with Snow) was a collaborative UK research project aimed at probing the detailed chemistry of the Antarctic boundary layer and the exchange of trace gases at the snow surface. The centre-piece to CHABLIS was the measurement campaign, conducted at the British Antarctic Survey station, Halley, in coastal Antarctica, from January 2004 through to February 2005. The campaign measurements covered an extremely wide range of species allowing investigations to be carried out within the broad context of boundary layer chemistry. Here we present an overview of the CHABLIS campaign. We provide details of the measurement location and introduce the Clean Air Sector Laboratory (CASLab) where the majority of the instruments were housed. We describe the meteorological conditions experienced during the campaign and present supporting chemical data, both of which provide a context within which to view the campaign results. Finally we provide a brief summary of highlights from the measurement campaign. Unexpectedly high halogen concentrations profoundly affect the chemistry of many species at Halley throughout the sunlit months, with a secondary role played by emissions from the snowpack. This overarching role for halogens in coastal Antarctic boundary layer chemistry was completely unanticipated, and the results have led to a step-change in our thinking and understanding

Peroxy Radical Inter Comparison Exercise A formal comparison of methods for ambient measurements of peroxy radicals. Final report

Available from TIB Hannover: RA 831(3597) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman