Simulating Indoor Atmospheres: Development Of An Explicit Chemical Mechanism
The focus of most air quality research until recently has been on the outdoor environment, and chemical mechanisms have been constructed and used to describe the key processes that occur there. However, in developed countries, we typically spend 90% of our time indoors, and so exposure to air pollutants is likely to occur in the indoor environment, whether at home, in the workplace or whilst commuting. There are some important differences between indoor and outdoor air chemistry. There is much less light indoors than outdoors, particularly in the UV, and so photolysis processes tend to be relatively unimportant indoors. There is also a much larger surface area available for reaction indoors compared with outdoors, owing to the presence of walls, floors, and furnishings. Consequently, chemical mechanisms with which to study indoor air have to account for these differences. They must also consider processes such as indoor-outdoor exchange, indoor emissions and the chemical degradation of species that are important indoors but do not feature in chemical mechanisms that describe atmospheric degradation outdoors. In this paper, a detailed chemical box model is described, that has been constructed based on a comprehensive chemical mechanism (the Master Chemical Mechanism) to investigate indoor air chemistry in a typical urban residence in the UK. Unlike previous modeling studies of indoor air chemistry, the mechanism adopted contains no simplifications such as lumping or the use of surrogate species, allowing more insight into indoor air chemistry than previously possible. The chemical mechanism contains around 16,000 reactions and 5,000 species. The results show a predicted indoor OH radical concentration up to 4.0 x 105 molecule cm-3, only a factor of 10–20 less than typically observed outdoors and sufficient for significant chemical cycling to take place. The reactions of ozone with alkenes and monoterpenes play a major role in producing new radicals. Concentrations of PAN-type species and organic nitrates reach concentrations of a few ppb indoors, with potential health implications. Sensitivity tests highlight that the most crucial parameters for modeling the concentration of OH are the light intensity levels, the air exchange rate and the outdoor concentrations of O3 and NOX.
KeywordsIndoor air chemistry master chemical mechanism ozone-terpene chemistry OH radicals
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