Emerging investigator series: an instrument to measure and speciate the total reactive nitrogen budget indoors: description and field measurements.

Reactive nitrogen species (N r ), defined here as all N-containing compounds except N 2 and N 2 O, have been shown to be important drivers for indoor air quality. Key N r species include NO x (NO + NO 2 ), HONO and NH 3 , which are known to have detrimental health effects. In addition, other N r species that are not traditionally measured may be important chemical actors for indoor transformations ( e.g. amines). Cooking and cleaning are significant sources of N r , whose emission will vary depending on the type of activity and materials used. Here we present a novel instrument that measures the total gas-phase reactive nitrogen (tN r ) budget and key species NO x , HONO, and NH 3 to demonstrate its suitability for indoor air quality applications. The tN r levels were measured using a custom-built heated platinum (Pt) catalytic furnace to convert all N r species to NO x , called the tN r oven. The measurement approach was validated through a series of control experiments, such that quantitative measurement and speciation of the total N r budget are demonstrated. The optimum operating conditions of the tN r oven were found to be 800 °C with a sampling flow rate of 630 cubic centimetres per minute (ccm). Oxidized nitrogen species are known to be quantitatively converted under these conditions. Here, the efficiency of the tN r oven to convert reduced N r species to NO x was found to reach a maximum at 800 °C, with 103 ± 13% conversion for NH 3 and 79-106% for selected relevant amines. The observed variability in the conversion efficiency of reduced N r species demonstrates the importance of catalyst temperature characterization for the tN r oven. The instrument was deployed successfully in a commercial kitchen, a complex indoor environment with periods of rapidly changing levels, and shown to be able to reliably measure the tN r budget during periods of longer-lived oscillations (>20 min), typical of indoor spaces. The measured NO x , HONO and basic N r (NH 3 and amines) were unable to account for all the measured tN r , pointing to a substantial missing fraction (on average 18%) in the kitchen. Overall, the tN r instrument will allow for detailed survey(s) of the key gaseous N r species across multiple locations and may also identify missing N r fractions, making this platform capable of stimulating more in-depth analysis in indoor atmospheres.