Bromine and Chlorine budget in the Asian Monsoon outflow during PHILEAS

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In this proposal we apply for funding to participate in the PHILEAS (Probing High Latitude Export of air from the Asian Summer Monsoon) campaign with the HALO aircraft using the GhOST instrument. GhOST is a two-channel GC and GC/MS system, developed and build for operation on HALO at the University Frankfurt. The central question of the PHILEAS campaign is the investigation of the of the outflow of the Asian Monsoon Anticyclone (AMA) and its influence on the air masses mixed into the lower stratosphere. The scientific background and the costs of the campaign have been outlined in the co-ordination proposal to the PHILEAS campaign by the University Mainz (Prof. Dr. Peter Hoor). During PHILEAS, HALO will investigate the background UTLS (upper troposphere/lower stratosphere) and direct westward outflow from the Monsoon circulation over the Mediterranean in a first phase from Oberpfaffenhofen. In a second phase of the campaign HALO will be based in Alaska to probe eastward outflow of air from the monsoon region. Due to Rossby wave activity, the campaign base in Alaska offers a high probability to observe air masses shed of from the AMA in the lower stratosphere over the Pacific Ocean. The measurements with the GhOST instrument on HALO will provide information on a wide range of tracers, with different lifetimes and different source/sink characteristics. The emphasis of the measurements is on halogenated trace gases and in addition SF6 as mean age tracer. Depending on the set-up, the focus of the GhOST MS channel is either on the chlorine or on the bromine family. Within the proposal it is planned to perform the measurements and to use the observations for three distinct research questions related to PHILEAS: (i) What is the bromine budget in the AMA and how does this influence the lower stratosphere? (ii) What is the chlorine budget in the AMA and in air shed from the AMA? (iii) Is there an influence of anthropogenic pollution (use of e.g. CH2Cl2 or HCFC-22) or of biomass burning (CH3Cl), which could for example be related to boreal fires. In addition to these direct objectives, it is planned to further use the data for studies of global distributions of halocarbons in the tropopause region by combination with IAGOS-CARIBIC measurements funded in our group within the DFG CRC 301 (TPChange). Further, the data will be provided to and exploited in the DFG funded project QUANTITEE to investigate transit time distributions.