We present direct indoor measurements of the nitrate radical (NO3) and dinitrogen pentoxide (N2O5) produced from combustion cooking emissions in a residential kitchen. When the indoor ozone (O3) concentration was low (â¼4 ppbv), nitric oxide (NO) emitted from gas stove combustion suppressed NO3 formation. However, at moderate O3 levels (â¼40 ppbv), measured NO3 concentrations reached 3â4 pptv, and the indoor NO3 reactivity loss rate coefficient reached 0.8 sâ1. A box model of known chemistry agrees with the reactivity estimate and shows that moderate O3 levels led to a nitrate radical production rate of 7 ppbv hâ1. These indoor NO3 production rates and reactivities are much higher than those typically found outdoors. We conclude that at low O3 levels indoor combustion suppresses nitrate radical chemistry, but when sufficient O3 enters residences from outdoors or is emitted directly from indoor sources, gas stove combustion emissions promote indoor NO3 chemistry.