Controlling environmental factors, such as microclimatic conditions (temperature and relative humidity) and the levels of indoor pollutants within a museum, crucially affects the hosted exhibits and artworks. To evaluate the air quality of the library hosted by the Museum of Geoastrophysics of the National Observatory of Athens, a monitoring campaign was performed during the summer-time period (August 2016). The findings were compared against scientifically accepted standards and recommended conditions for repositories and paperwork exhibition areas. The temperature and the relative humidity proved to be the most crucial threat to the book collection, with the measured levels of temperature during the campaign being out of the recommended limit values. Both parameters presented also diurnal fluctuations which are not recommended. Synergistically, these inappropriate and uncontrolled conditions contribute to book deterioration on a long-term basis, leading to color and mechanical damage of the fibers and mold development. Furthermore, the library exhibited insufficient protection against pollutants. Despite the moderate infiltration, pollutants such as SO2, NO2 and O3 occurred in higher levels than the acceptable ones, which can also lead to embrittlement and discoloration of the paper and weakening or powdered surface to the leather covers of the books.