A recent survey of the Mars Global Surveyor (MGS) electron data for dayside photoelectron observations over regions of strong crustal fields revealed an unusual bimodal solar flux dependence. The elevated-flux population was associated with the timing of a large global dust storm in late 2001. The results of a systematic study parameterizing the photoelectron flux intensities against a solar flux proxy and MGS-observed atmospheric dust opacity are presented here. Instantaneous dust opacities were used as well as time-history averages and maximal values. The result is a functional form for the photoelectron fluxes against these parameters. The inclusion of instantaneous dust opacity values in the function do not improve the correlation, but a time-history window significantly enhances the correlation and explains the bimodal distribution in the electron fluxes. The best relationship was obtained with 7-Earth-month time-history dust opacity variables included in the function. The most likely explanation for this long-lived influence of dust storms is a composition and/or density change in the upper atmosphere.