Indoor measurements of the sum of the nitrate radical, NO 3, and nitrogen pentoxide, N 2O 5 in Denmark

Abstract

There is a need for indoor measurements of nitrate radicals (NO 3) and nitrogen pentoxide (N 2O 5) to better understand removal and transformation of volatile organic compounds in indoor environments, and to evaluate the possible health effects from exposure to nitrated reaction products. NO 3 and NO 2 react to form N 2O 5 in the presence of a third molecule, and the fast equilibrium necessitates measurements of both NO 3 and N 2O 5 in the evaluation of indoor NO 3 chemistry. The sum of these two species, NO 3 ∗ , was quantified in an office building in Denmark by measuring an oxidation product of the cyclohexene/NO 3 reaction in a flow-tube set-up. NO 3 ∗ concentrations ranged from 1 to 58 ppt, where N 2O 5 was estimated to account for more than 68%. The concentrations of the precursors, NO 2 and O 3, and the photolysis of NO 3 were parameters, which clearly influenced NO 3 ∗ apparent from the different precursor concentrations, lighting and daylight versus dark samples in this study. Also indoor air pollutants, in particular alkenes such as limonene and α-pinene, can significantly reduce NO 3 ∗ . These first indoor measurements of NO 3 ∗ , warrant further high time resolution measurements of NO 3, N 2O 5, and organic nitrates indoors.