Abstract: The present invention relates to a process and apparatus for quantifying solid residue on a sample. The process includes using a solid substrate and an aerosolizing device, adding a solid material to the aerosolizing device, forming a particle cloud of solid particles, wherein at least 1% of the mass concentration of solid particles have a mass median aerodynamic particle diameter up to about 10 ?m, thus applying the solid particles to the solid substrate(s) to form treated substrate(s), maintaining at a temperature of from about 30 to about 120° C. for at least a portion of the process, and removing a portion of solid particles from the treated substrate(s), and analyzing said at least one sample. The present invention further comprises an apparatus for applying solid particles to a substrate. The process can be used, for example, to analyze the dirt pickup resistance of a solid sample.