Sol-gel coatings technology has been used to synthesize glassy chemical sensors with optical response. Sensitive phase consisting on an organic dye was immobilized into a silica sol-gel matrix with controlled densification degree, which provides an adequate porous thin layer able to exchange gaseous species with acid-basic properties. This system works as a pH sensor sensitive enough to detect in the air the whole contribution of different compounds from pollution (whatever their provenance or chemical nature). The sensors were patented by some of the present authors and applied for monitoring several kinds of spaces in museums located at different sites and conserving different cultural heritage goods.

The measurement of the equivalent air pH during all the four year seasons in a museum provides an image on the dynamic evolution of the air quality connected both to the atmospheric changes and the events occurring inside the museum: visitors, cleaning works, management, temporarily exhibitions, vandalism, social events, etc. Comparison of the environmental pH in different museum spaces informs on the indoor air regime, ventilation system efficiency and the proper quality of the air for each one of the museum spaces according to their use, for instance in exhibition halls, archives, storerooms, offices, laboratory or restoration rooms.

During 2020-2022 sol-gel pH sensors have been used for monitoring environmental conditions in the following museums: National Natural Sciences Museum in Madrid, Navy Museum in Madrid, Navy Museum in Cartagena and Glass and Crystal Museum in Málaga. In all cases the evaluations were carried out four times, each one during each meteorological season. Sensors are autonomous, they don’t need neither wires nor connections and were installed in critical positions according to the museum staff for monitoring the environment in exhibition halls, showcases, archives, storerooms and outdoor façades. Data from outdoor positions were needed to check the urban pollution impact into the ventilation systems and the indoor air quality, which affect the cultural goods materials and their proper conservation. The pH data recorded in situ with portable measurement units during 3-4 days were analyzed and compared throughout the evaluation year to offer some preventive conservation recommendations adapted to the own museum characteristic such as its geographical location, kind and nature of cultural goods exhibited or stored, ventilation systems, managements strategies, visitors regime, etc.