We report on the preparation of photoluminescent porous GaAs by the application of high voltage spark discharges at low repetition rates (20 Hz) in air and in argon atmospheres. The spark-processed porous (spp) samples were characterized by the observation of their visible photoluminescence (PL) when illuminated with UV monochromatic radiation. In contrast to previous work on spp-GaAs at high sparking frequencies we find that the PL of samples prepared at low sparking frequency is highly reproducible from sample to sample. Important differences are observed in the initial PL spectra of the spp-GaAs according to the atmosphere of preparation under similar conditions. After prolonged air exposure both the spp-GaAs prepared in air and in argon show two similar broad peaks at energy positions 2.5 and 3.1 eV. Raman results indicate that the PL might not be associated to any size dependent mechanism. We present evidence that oxygen compounds formed by the exposure to air of the samples play a role in the PL excited in the spp-GaAs. This is reinforced by x-ray photoelectronic spectroscopy measurements that indicate that the spp-GaAs is covered by an oxidized film.