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Context. Icy dust grains play an important role in the formation of complexinter- and circumstellar molecules. Observational studies show that polycyclicaromatic hydrocarbons (PAHs) are abundantly present in the ISM in the gasphase. It is likely that these non-volatile species freeze out onto dust grainsas well and participate in the astrochemical solid-state network, butexperimental PAH ice studies are largely lacking. Methods. Near UV/VISspectroscopy is used to track the in situ VUV driven photochemistry of pyrenecontaining ices at temperatures ranging from 10 to 125 K. Results. The mainphotoproducts of VUV photolyzed pyrene ices are spectroscopically identifiedand their band positions are listed for two host ices, \water and CO. Pyreneionisation is found to be most efficient in \water ices at low temperatures.The reaction products, triplet pyrene and the 1-hydro-1-pyrenyl radical aremost efficiently formed in higher temperature water ices and in low temperatureCO ice. Formation routes and band strength information of the identifiedspecies are discussed. Additionally, the oscillator strengths of Py, Py^+ andPyH are derived and a quantitative kinetic analysis is performed by fitting achemical reaction network to the experimental data. Conclusions. Pyrene isefficiently ionised in water ice at temperatures below 50 K. Hydrogenationreactions dominate the chemistry in low temperature CO ice with trace amountsof water. The results are put in an astrophysical context by determining theimportance of PAH ionisation in a molecular cloud. The photoprocessing of asample PAH in ice described in this manuscript indicates that PAHphotoprocessing in the solid state should also be taken into account inastrochemical models.

Photochemistry of the PAH pyrene in water ice: the case for ion-mediated solid-state astrochemistry