Indoor air (photo)chemistry: A world-wide concern by Sasho Gligorovski
State Key Laboratory of Organic Geochemistry, Chinese Academy of Sciences
"The first field campaign performed in a high school in Marseille, France (2011) confirmed the existence of hydroxyl radicals (OH) that were more in line with typical outdoor concentrations than indoor concentrations (Gomez Alvarez et al., 2013). It was demonstrated that photolysis of nitrous acid (HONO) is the most important source of these highly reactive OH radicals in the indoor air. This set of innovatory first direct measurements of OH radicals indoors was followed with also avant-garde measurements of the solar actinic fluxes which can penetrate indoors and photolysis frequencies of key indoor species (Gandolfo et al., 2016). The results obtained are of enormous repercussions and need to be studied in the next few years much more profoundly due to their still unexplored implications. The facts just mentioned need to be taken in combination with the elevated concentrations of HONO present in the indoor air (Gligorovski, 2016). In addition, HONO is an important indoor air pollutant, which can react with amines leading to carcinogenic nitrosamines. While our understanding of photochemistry of the indoor surfaces is still in its infancy, the recent results (Gomez Alvarez et al., 2014, Gandolfo et al., 2015, 2017) based on the light induced heterogeneous NO2 reactions on domestic surfaces leading to HONO formation, suggest that it is an area that should be pursued further. Another campaign carried out in an office in Martigue, France (2016) was dedicated to evaluation of OH radical source strength. Again, the photochemical reactions play an important role to the oxidation capacity of indoor atmosphere. If we consider all these facts carefully, the concentration of OH radicals indoors, could reach levels that would be of serious concern from the standpoint of public health. For these reasons, it is very important to dedicate more efforts to determine the OH concentrations that can be attained in various indoor settings, in relation to factors such as light intensity, HONO concentrations, and humidity, among others."