Within the scope of the ALTZOMONI campaign in March 2006 it was possible to sample various times the urban plume of Mexico City at a site located at about 4000 m a.s.l. and approximately 60 km to the southeast of the city. Continuous GC-ECD measurements of peroxiacetic nitric anhydride (PAN) and peroxipropionic nitric anhydride (PPN) were used to determine the pollution plume events. High PAN and PPN levels usually coincided with higher CO levels and slightly enhanced O3 values as determined by FTIR. Aerosol Mass Spectrometer results show that, overall, organic aerosols correlate well with PANs. However, some individual PAN peaks are also accompanied by higher aerosol fractions of NO3 and SO4. The results indicate that polluted air masses are present at high altitudes over the Mexico City basin and may likely have a long-range effect. This is in particular true for PAN and PPN. Maximum values up to 2.84 ppbv for PAN and 570 pptv for PPN were observed, which are remarkably high values for almost mid-tropospheric conditions. Together with considerable long lifetimes in the range of weeks at this altitude PAN may serve efficiently as a reservoir species for NO2.