Full preventive conservation of Cultural Heritage items is connected to environmental evaluation or air quality control. Gaseous pollutants enhance most of degradation processes of materials due to its high acidity (low pH) (Grzywacz 2006). Although the pH electrodes technology is well developed for measuring this parameter in liquid phases and humid solids, no device can be found in the market able to measure quantitatively the whole concentration of acid-basic chemical species in the air. The TechnoHeritage groups C02 and IC2 have developed pH chemical sensors to measure both qualitative and quantitatively acidity/basicity of the air. Such sensors provide an optical response, i.e. absorption in the visible range, that varies the sensor colour depending on the whole acidity/basicity of the environment. These sensors have been proved in several Cultural Heritage sites (García-Heras et al. 2005, Peña-Poza et al. 2011). The optical response of the sensors was recorded with a conventional spectrophotometer and, hence, for long evaluation periods such as one year, the field work was not only time-consuming but subjected to the spectrophotometer moving and the electrical supply.