Disclosed is a method of determining efficacy of a cosmetic composition to inhibit an atmospheric pollutant from contacting skin, comprising the steps of: (i) filling a sample holder of known dimensions with known amount of said composition to form a layer of defined thickness therein, where said sample holder is amenable to fluorescence-based assay； (ii) depositing, on said layer, a known amount of a model fine particulate matter which resembles an atmospheric pollutant at least in size and which comprises a material responsive to fluorescence microscopy which is excitable by a wavelength (ʎex) and which emits radiation (ʎem) where (ʎex) ≠ (ʎem)； (iii) irradiating said composition and said model fine particulate matter by said ʎex and recording intensity of fluorescence at ʎem a plurality of times for a defined period during which said model fine particulate matter interacts with said layer； and, (iv) determining, corrected intensity of fluorescence at ʎem by the following equation； corrected Intensity = recorded intensity / average transmittance where said average transmittance is the average of the transmittance of the composition measured at ʎex and ʎem determined by Beer-Lambert law by measuring the absorbance at ʎex and ʎem, where the corrected intensity is inversely proportional to said efficacy of said composition.L'invention concerne un procédé de détermination de l'efficacité d'une composition cosmétique pour empêcher un polluant atmosphérique de venir en contact avec la peau, comprenant les étapes suivantes : (i) remplissage d'un porte-échantillon de dimensions connues avec une quantité connue de ladite composition pour former une couche d'une épaisseur définie à l'intérieur de celui-ci, ledit porte-échantillon pouvant être soumis à un dosage à base de fluorescence ； (ii) le dépôt, sur ladite couche, d'une quantité connue d'un modèle de matière particulaire fine qui ressemble à un polluant atmosphérique au moins en ce qui concerne la taille et qui compren
