Commercial kitchen operations produce a diverse range of gas-phase reactive nitrogen species

Abstract

Gas-phase reactive nitrogen species (N_r) are important drivers of indoor air quality. Cooking and cleaning are significant direct sources indoors, whose emissions will vary depending on activity and materials used. Commercial kitchens experience regular high volumes of both cooking and cleaning, making them ideal study locations for exploring emission factors from these sources. Here, we present a total N_r (tN_r) budget and contributions of key species NO, NO₂, acidic N_r (primarily HONO) and basic N_r (primarily NH₃) using novel instrumentation in a commercial kitchen over a two-week period. In general, highest tN_r was observed in the morning and driven compositionally by NO, indicative of cooking events in the kitchen. The observed HONO and basic N_r levels were unexpectedly stable throughout the day, despite the dynamic and high air change rate in the kitchen. After summing the measured NO_x, HONO and N_r,base fractions, there was on average 5 ppbv of N_r unaccounted for, expected to be dominated by neutral N_r species. Using co-located measurements from a proton transfer reaction mass spectrometer (PTR-MS), we propose the identities for these major N_r species from cooking and cleaning that contributed to N_r,base and the neutral fraction of tN_r. When focused specifically on cooking events in the kitchen, a vast array of N-containing species was observed by the PTR-MS. Reproducibly, oxygenated N-containing class ions (C_1–12H_3–24O_1–4N_1–3), consistent with the known formulae of amides, were observed during meat cooking and may be good cooking tracers. During cleaning, an unexpectedly high level of chloramines was observed, with monochloramine dominating the profile, as emitted directly from HOCl based cleaners or through surface reactions with reduced-N species. For many species within the tN_r budget, including HONO, acetonitrile and basic N_r species, we observed stable levels day and night despite the high air change rate during the day (>27 h⁻¹). The stable levels for these species point to large surface reservoirs which act as a significant indoor source, that will be transported outdoors with ventilation.