###### Abstract  
In this work, a system consisting of two resistive sensors working in tandem to detect and quantify the acetic acid released during the degradation of cellulose acetate-based ancient cinematographic and photographic films is presented. Acetic acid must be constantly monitored to prevent reaching concentrations at which autocatalytic degradation processes begin. The sensors are constituted by a thin layer of metal oxide (tungsten oxide and tin oxide) deposited over an interdigitated electrode capable of being heated, chosen to maximize the array response towards acetic acid vapors. The signals obtained from the sensor array are mathematically processed to reduce the background signal due to interferent gases produced during degradation of ancient cinematographic films. The sensor array reported a LOD of 30 ppb for acetic acid, with a linearity range up to 30 ppm. Finally, the sensor array was tested with different cinematographic and photographic film samples made of cellulose acetate, whose degradation state and acetic acid production was validated using the conventional technique (A-D strips). The presented array is suitable for remote monitoring large number of films in collections since, compared to the official technique, it has a lower detection limit (30 ppb vs. 500 ppb) and is much quicker in providing accurate acetic acid concentration in the film boxes (15 min vs. 24 h). metal oxide semiconductor sensors; cultural heritage protection; cellulose acetate; cinematographic films; autocatalytic degradation; acetic acid; butanol  
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compounds released by the CH item are often mixed with numerous other released substances; thus, specific sensors must be used. Harmful compounds must be detected at the onset of the process, meaning low detection limits are required for the sensor. Environment condition monitoring is also critical to ensure that sensors and measuring devices can perform satisfactorily. The conditions to be monitored are temperature, pressure, humidity of measured gas representing the main parameters to monitor in museums in order to establish the conservation status of CH objects. A case of application is the preservation of historical photographical and movie films. CH movie films can go as back as early the beginning of the 20 th century while photographic films can date to even earlier. Both movies and photographic films used cellulose esters as support on which the photosensitive compounds were applied. The two main cellulose esters used (in order of time) were cellulose (di and tri) nitrate and cellulose (poly)acetate. Both polymers have good flexibility and mechanical resistance but over time they undergo various degradation processes that makes them rigid, brittle and, finally, unsuitable for reproduction and/or visualization. The two types of film polymer undergo different degradation pathways, meaning that sensors selective for different compounds are needed. Cellulose nitrate is a common semi-synthetic plastic film, formally known as \"celluloid\", and was widely used until 1940 when it started to be phased out in favor of cellulose (poly)acetate. Cellulose acetate is another very common semi-synthetic plastic film. Its use in both cinematographic and photographic films started around 1930 and completely supplanted celluloid between 1940 and 1950. Cellulose acetate consists of linear cellulose polymers in which each glucose monomer has two or three -OH groups functionalized as acetate ester [4; 5]. Triphenyl phosphate is the most common plasticizer used for acetate films in quantities from 5-25% by weight of the cellulose ester [6; 7; 8; 9]. The degradation of cellulose acetate is a two-stage process: in the first step, water from air humidity promotes the breakage of an ester bond between glucose and an acetate group. The product of this step is a (n-1) acetate glucose and an acetic acid molecule.