Disclosed is an in-vitro method to determine efficacy of a cosmetic composition or of one or more ingredients comprised therein to inhibit a particulate pollutant from contacting skin, said method comprising the steps of: (i) contacting a human skin equivalent with a cosmetic composition to form, upon drying, a layer thereof extending along mutually perpendicular X and Y and Z axis where along said Z axis said layer is 1 to 100 μm, where said Z axis indicates thickness of said layer; (ii) depositing, on said layer, a known amount of a model fine particulate matter comprising a first substance responsive to depth profile analysis where said cosmetic composition comprises a second substance, not comprised in said model fine particulate matter but also responsive to said depth profile analysis where the response of said first and second substances are distinguishable; (iii) for a pre-determined period after depositing said model fine particulate matter, periodically measuring response of said first and said second substance by said depth profile analysis, to thereby determine the amount of said model fine particulate matter at defined intervals along said Z axis; and, (iv) ascertaining said efficacy based on the amount of said model fine particulate matter at said defined intervals along said Z axis throughout said pre-determined period.