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This paper presents an analysis of trace gases in the Asian summer monsoon(ASM) region on the basis of observations by the CRISTA infrared limb soundertaken in low-earth orbit in August 1997.The spatially highly resolved measurementsof peroxyacetyl nitrate (PAN) and O<sub>3</sub> allow a detailed analysis of aneddy-shedding event of the ASM anticyclone. We identify enhanced PAN volumemixing ratios (VMRs) within the main anticyclone and within the eddy, whichare suitable as a tracer for polluted air originating in Indiaand China.Plotting the retrieved PAN VMRs against potentialvorticity (PV) and potential temperature reveals that the PV value at which the PANVMRs exhibit the strongest decrease with respect to PV increases with potentialtemperature. These PV values might be used to identify the extent of the ASM.Using temperature values also derived from CRISTAmeasurements, we also computed the location of the thermal tropopauseaccording to the WMO criterion and find that it confines the PAN anomalyvertically within the main ASM anticyclone. In contrast, the shed eddy exhibitsenhanced PAN VMRs for 1 to 2 km above the thermal tropopause. Usingthe relationship between PAN as a tropospheric tracer and O<sub>3</sub> as astratospheric tracer to identify mixed air parcels, we further found theanticyclone to contain few such air parcels, whereas the region between theanticyclone and the eddy as well as the eddy itself contains many mixedair parcels. In combination, thisimplies that while the anticyclone confines polluted air masses well, eddyshedding provides a very rapid horizontal transport pathway of Asian pollutioninto the extratropical lowermost stratosphere with a timescale of only a fewdays

Observations of PAN and its confinement in the Asian summer monsoon anticyclone in high spatial resolution