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

Reactive nitrogen species (N), defined here as all N-containing compounds except N and NO, have been shown to be important drivers for indoor air quality. Key N species include NO (NO + NO), HONO and NH, which are known to have detrimental health effects. In addition, other N species that are not traditionally measured may be important chemical actors for indoor transformations ( amines). Cooking and cleaning are significant sources of N, 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) budget and key species NO, HONO, and NH to demonstrate its suitability for indoor air quality applications. The tN levels were measured using a custom-built heated platinum (Pt) catalytic furnace to convert all N species to NO, called the tN oven. The measurement approach was validated through a series of control experiments, such that quantitative measurement and speciation of the total N budget are demonstrated. The optimum operating conditions of the tN 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 oven to convert reduced N species to NO was found to reach a maximum at 800 °C, with 103 ± 13% conversion for NH and 79-106% for selected relevant amines. The observed variability in the conversion efficiency of reduced N species demonstrates the importance of catalyst temperature characterization for the tN 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 budget during periods of longer-lived oscillations (>20 min), typical of indoor spaces. The measured NO, HONO and basic N (NH and amines) were unable to account for all the measured tN, pointing to a substantial missing fraction (on average 18%) in the kitchen. Overall, the tN instrument will allow for detailed survey(s) of the key gaseous N species across multiple locations and may also identify missing N fractions, making this platform capable of stimulating more in-depth analysis in indoor atmospheres.