Art works are affected by environmental factors as light, temperature, humidity. Air pollutants are also implicated in their degradation. The pollution in museums has two sources: the air from outside, which brings usually dust and inorganic particles, and the inside sources – the materials used for casings (sealants, textiles placed on the display cases, varnishes, wood) that emanate organic compounds. The dust is composed of particles with a diameter of approximately 2µm or higher, which come from soil (silica) or animal and vegetal residues (skin cells, pollen). They facilitate water condensation on objects surface and biologic attack. The inorganic compounds are a result of materials combustion (SO₂, NO₂, NO) and in presence of water they form acidic compounds which affect the museum objects. The organic compounds are usually peroxides, acids, phthalates, formaldehyde. The effects of these pollutants are: soiling, surface discolouration, embrittlement, corrosion. Therefore, conservators are interested in monitoring the pollution degree in the display cases or in the museum air and in analyzing the effects of pollutants on the exhibited objects. They use different methods for pollutants identification, like direct reading devices based on colorimetry, that can be read after few minutes and hours (they interact with the pollutants in atmosphere), or indirect reading samples that require a laboratory. The information gathered is used for the identification of pollution source and to analyze the concentration of pollutants needed to provoke damages on the surfaces of art objects. This paper is a review of pollutants that affect the art objects and of the monitoring systems used for their identification and measuring.