Microscale atmospheric dispersion models have been employed recently to predict the possible effect of photocatalytically active surfaces on the air pollution in urban areas. These simulations use the photocatalytic deposition velocity as an input value. However, no generally accepted experimental method for the determination of the photocatalytic deposition velocity is available. Here a method to determine the photocatalytic deposition velocity is proposed which is based on ISO 22179-1 et seqq. specifying test methods for the determination of the air-purification performance of materials that contain a photocatalyst or have photocatalytic films on the surface. It is assumed that the rate of the photocatalytic surface reaction of a species i, R-A(i), is given by an expression having the mathematical form R-A(i) = (A)k(i)K(i)c(i)/(1 + KiCi) where the kinetic parameters (A)k(i) and K-i are variables depending on the photon flux, the temperature, the humidity and the concentration of other pollutants. Under steady state conditions the mole balance of a differential volume of a fluid element inside the plug flow reactor described in the cited ISO standards reads Y=(A)k(i)K(i)X - const(i). This equation is a linear equation of the two variables Y=ln(C-in,C-i/C-out,C-i)/(C-in,C-i - C-out,C-i) and X = A(r)/q(V)(c(in,i)-c(out,i)) where c(in,i), c(out,i), A(r), and q(v) are the inlet and outlet concentration of the pollutant i under consideration, the irradiated photocatalytically active surface, and the volumetric flow rate through the photocatalytic reactor, respectively. It is argued that the slope (A)k(i)K(i) of this equation is the demanded' photocatalytic deposition velocity V-pc,V-i. Thus, the measurement of C-out,C-i at varying C-in,C-i makes the photocatalytic deposition velocity accessible. (C) 2014 Elsevier B.V. All rights reserved.