1. Understanding The Effect Of Anthropogenic Aerosol Weekly Cycles Upon The Climate Using A Global Model Of Aerosol Processes (GLOMAP) Introduction GLOMAP David A. Ridley, Dominick Spracklen, Kirsty Pringle, Ken Carslaw, Martyn Chipperfield School of Earth and Environment, University of Leeds, UK The Global Model of Aerosol Processes (GLOMAP) is a detailed microphysical model simulating the transport and evolution of aerosol species on a 3D global scale. Its purpose is to study the importance of different aerosol processes in the atmosphere so that parameterisation within General Circulation Models (GCMs) can be improved. Sensitivity studies of aerosol concentrations have been undertaken and comparisons of model results with in-situ observations from different campaigns are found to be positive. We intend to simulate aerosol weekly cycles within GLOMAP to determine the effects upon aerosol burden and cloud formation, and hence elucidate a connection between observed changes in the radiation budget of the Earth and anthropogenic aerosol emissions. The Global Model of Aerosol Processes (GLOMAP) is an extension of the chemical transport model TOMCAT and includes processes such as aerosol nucleation, growth, coagulation and deposition. TOMCAT 3D Offline CTM Forced by ECMWF Winds Convective transport Convective and resolved rain Emissions Anthrop + volcanic SO 2 emissions DMS emissions from wind stress and DMS sea surface concentration Sea salt aerosol generation function Nucleation and Condensation Binary H 2 SO4/H 2 O nucleation Condensational growth Coagulation Semi-implicit fast numerical solution Dry Deposition Dry deposition of aerosol Hygroscopic Growth Equilibrium size given by solution of Kohler equation Sulfur Chemistry 8 sulfur species 8 sulfur reactions Aqueous phase chemistry Oxidants from full chemistry run SourcesMicrophysicsRemoval GLOMAP Aerosol size spectrum ( ~ 1nm – 24µm) Clouds Convective and frontal rain In-cloud nucleation scavenging Below cloud scavenging By simulating weekly cycles in emissions we can determine if this has any noticeable effect upon aerosol size distribution and consequent cloud formation. Weekly variations in cloud cover are a possible cause for the so-called weekend effect. Weekly cycles in other pollutants, such as NOx from transport emissions, may have stronger weekly cycles and hence contribute significantly to enhanced CCN formation on weekdays. Including a primary aerosol component in the emissions could act to simulate the nucleation that occurs in the dense emission plumes. An offline cloud microphysics model can be used to examine possible cloud responses to modelled changes aerosol burden. The ultimate aim is to quantify how this aerosol indirect effect changes the radiation budget and hence whether it can account for the observed DTR weekend effect. Research SO 2 CCN @ 0.3% DTR ‘Weekend Effect’ Model Design As well as total aerosol number, size distributions can be obtained from the model allowing calculation of condensation nuclei (CN) and cloud condensation nuclei (CCN) concentrations. December 1995 (Monthly Average) Comparisons of CN concentration measurements from aircraft observations (during the Intercontinental Transportation of Ozone Precursors [ITOP] campaign) and GLOMAP show favourable results. The diurnal temperature range (DTR) is an important climatic indicator. A recent study has shown variations between weekday and weekend DTR comparable in magnitude to long term temperature trends 2. This must be an anthropogenic effect, however the mechanism is still unclear. Emissions Weekly cycles are useful in characterising anthropogenic effects. If significant climatic changes are detected on this scale then we can begin to understand how emissions will affect the climate in the long term. GLOMAP Comparison With Observations Weekly Cycles Fig. 3 Comparison of P3 aircraft CN concentration measurements (blue) with concurrent GLOMAP CN concentration (orange). Aircraft pressure is also shown (black) Fig. 1 Schematic of GLOMAP Fig 2. Global maps of surface layer SO 2 concentration and CCN concentration at 0.3% supersaturation 1 Fig. 4 DTR difference between Saturday-Monday average and Wednesday-Friday average over the USA 2 Fig 5. Daily SO 2 levels from Manchester, UK averaged over 4 years. Values are displayed as a fraction of the mean 1 Spracklen DV, Pringle KJ, A global off-line model of size-resolved aerosol microphysics: Model development and prediction of aerosol properties, submitted Atmos. Phys. Chem. 2004 2Forster PMD, Solomon S, Observations of a "weekend effect" in diurnal temperature range, PNAT 11225-11230 SEP 30 2003 Contact email: ridley@env.leeds.ac.uk When urban SO 2 measurements are averaged over several years a clear weekly trend can be seen. This is used to weight the SO 2 emissions in GLOMAP. Future Plans School of Earth & Environment Environment