If we assume a constant ratio between reactive surface area and particle mass, such a relationship could represent the following processes: 1) heterogeneous GEM oxidation without significant consumption of reactants (other than GEM), 2) GEM nonreactive uptake (physisorption) without significant desorption or 3) GEM reactive uptake (chemisorption) without significant desorption, and if reactive adsorption sites are abundant relative to the adsorbate so that their progressive occupation is not a rate-limiting factor.