title: Unexpectedly high indoor hydroxyl radical concentrations associated with nitrous acid.
abstract: The hydroxyl (OH) radical is the most important oxidant in the atmosphere since it controls its self-oxidizing capacity. The main sources of OH radicals are the photolysis of ozone and the photolysis of nitrous acid (HONO). Due to the attenuation of solar radiation in the indoor environment, the possibility of OH formation through photolytic pathways indoors has been ignored up to now. In the indoor air, the ozonolysis of alkenes has been suggested as an alternative route of OH formation. Models and indirect measurements performed up to now according to this hypothesis suggest concentrations of OH radicals on the order of 10(4)-10(5) molecules per cubic centimeter. Here, we present direct measurements of significant amounts of OH radicals of up to 1.8⋅10(6) molecules per cubic centimeter during an experimental campaign carried out in a school classroom in Marseille. This concentration is on the same order of magnitude of outdoor OH levels in the urban scenario. We also show that photolysis of HONO is an important source of OH radicals indoors under certain conditions (i.e., direct solar irradiation inside the room). Additionally, the OH concentrations were found to follow a linear dependence with the product J(HONO)⋅[HONO]. This was also supported by using a simple quasiphotostationary state model on the OH radical budget. These findings force a change in our understanding of indoor air quality because the reactivity linked to OH would involve formation of secondary species through chemical reactions that are potentially more hazardous than the primary pollutants in the indoor air.
authors.affiliation: Aix Marseille University, Centre National de la Recherche Scientifique, Formation de Recherche en Evolution 3416, 13331 Marseille, France.
authors.forename: Elena
authors.initials: E
authors.lastname: Gómez Alvarez
authors.forename: Damien
authors.initials: D
authors.lastname: Amedro
authors.forename: Charbel
authors.initials: C
authors.lastname: Afif
authors.forename: Sasho
authors.initials: S
authors.lastname: Gligorovski
authors.forename: Coralie
authors.initials: C
authors.lastname: Schoemaecker
authors.forename: Coralie
authors.initials: C
authors.lastname: Schoemacker
authors.forename: Christa
authors.initials: C
authors.lastname: Fittschen
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Doussin
authors.forename: Henri
authors.initials: H
authors.lastname: Wortham
mesh_terms: D016902:Air Pollution, Indoor / Q000032:analysis*; D004784:Environmental Monitoring / Q000706:statistics & numerical data*; D005602:France; D017665:Hydroxyl Radical / Q000032:analysis*; D008956:Models, Chemical; D009608:Nitrous Acid / Q000737:chemistry*; D010084:Oxidation-Reduction; D010782:Photolysis; D012574:Schools
chemical_list: D017665:Hydroxyl Radical; D009608:Nitrous Acid
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