Combustion Processes as a Source of High Levels of Indoor Hydroxyl Radicals through the Photolysis of Nitrous Acid

Hydroxyl radicals (OH) are known to control the oxidative capacity of the atmosphere but then influence on reactivity within indoor environments is believed to be of little importance: Atmospheric direct sources of OH include the photolysis of ozone and nitrous acid (HONO) and the ozonolysis of alkenes. It has been argued that the ultraviolet light fraction of the solar spectrum is largely attenuated within indoor environments, thus, limiting the extent of photolytic OH sources. Conversely, the ozonolysis of alkenes has been suggested as the main pathway of OH formation within indoor settings. According to this hypothesis the indoor OH radical concentrations span in the range of only 104 to 108 cm(-3). However, recent direct OH radical measurements within a, school classroom yielded OH radical peak values at moderate light intensity measured at evenings of 1.8 x 106 cm(-3) that Were attributed to the photolysis of HONa In this 'work, we report results from chamber experiments irradiated with varying light intensities in order to mimic realistic indoor lighting conditions. The exhaust of a burning candle was introduced in the chamber as a typical indoor source causing a sharp peak of HONO, but also of nitrogen oxides (NOx). The photolysis of HONO yields peak OH concentration values, that for the range of indoors lightning conditions were estimated in the range 5:7 X 10(6) to 1.6 x 107 cm(-3). Excellent agreement exists between OH levels determined by a chemical clock and those calculated by a simple PSS model. These findings suggest that significant OH reactivity takes place at our dwellings and the consequences of this reactivity that is, formation of secondary oxidants ought to be studied hereafter.