Modeling of the production of secondary gaseous products in confined atmospheres

Confined environments are indoor spaces in which the air is not renewed or very poorly renewed by fresh outdoor air (spacecraft, submarines, etc.). In these environments, indoor air quality (IAQ) is expected to be highly influenced by homogeneous and heterogeneous chemistry. This paper presents a representative example of the contribution of these two phenomena to the production of secondary gaseous pollutants indoors by analyzing the chemical degradation of isoprene. An indoor air quality model was developed in the Matlab environment to compute the concentrations of both organic and nonorganic gaseous species involved in this mechanism. Two kinds of initial conditions (concentrations of nitrogen oxides, ozone and isoprene) were considered for the simulations. The results show strong interactions between homogeneous and heterogeneous reactions. Especially, the integrated reaction rate (IRR) of the heterogeneous hydrolysis of nitrogen dioxide emerges very high. Demonstration of strong interactions between inorganic and organic chemistries is also made, the conversion between NO and NO2 being of central importance in the degradation cycle of isoprene. The type and amount of secondary products obtained are assessed. The results emphasize the strong influence of ozone and nitric oxide concentration levels indoors.