As an example, consider the NIPES spectra of HSO 4 -along with HSO 4 -(Sol) n shown in Figure7, where n=1,2 and Sol refers to succinic acid (SUA), water or sulfuric acid.( ) These spectra, obtained by irradiating the clusters at 157 nm, show that HSO 4 -has four bands of which X is the lowest energy feature. On comparing the HSO 4 -spectrum with spectra 5 and 7 in the figure, it is clear that binding with water shifts X to higher BE and the intensity pattern is somewhat retained. Bonding with SUA or H 2 SO 4 , however, substantially shifts the four bands and there are no similarities between three spectra and that of HSO 4 -. Thus, the two acids have a larger stabilization effect on HSO or Na x Cl x-1 being the most prominent fragmentation pathways. The carbon dioxide radical (CO •- 2 ) was also detected as a photolysis product, forming from the cleavage of a C-C bond in glyoxylate. The CO •- 2 photofragment was only detected in the 300-400 nm UV range and was likely stabilized by the salt, making it a transient species in the troposphere. The photochemical lifetime of the clusters was found to be approximately 10 hours, implying that glyoxylic acid/glyoxylate played a role in the photochemical aging of SSA. Hydration of sodium glyoxylate clusters resulted in increased photodissociation but did not result in the formation of the gem-diol form of aqueous glyoxylic acid, confirming that glyoxylate will remain photo-active in the actinic wavelength range.