Reactions of dinitrogen pentoxide (N2O5) with salty aqueous aerosol particles can produce several atmospherically relevant species including nitryl chloride (ClNO2) and nitric acid (HNO3). It has been postulated that the ratio of these products may depend on the temperature of the aerosol droplet, with cooler temperatures favoring higher relative production of ClNO2. If true, this effect would need to be included in chemical transport models to more accurately predict the concentration of reactive halogen species in the atmosphere. In this study we utilized chemical ionization mass spectrometry and a novel temperature controlled heterogeneous flow reactor to investigate the temperature dependence of ClNO2 production from 5°C to 25°C, temperatures relevant to the lower troposphere. Within the temperature range studied, we observed a negligible temperature dependence on the ClNO2 product yield. A lack of temperature dependence in the relative reaction rates poses intriguing questions regarding the mechanisms and rate limiting steps of the competitive hydrolysis and chlorination reactions. Additionally, the extensive characterization of the flow reactor and chemical ionization mass spectrometer required for this study will enable further investigations of atmospherically important heterogeneous reactions.

Measuring the temperature dependence of N2O5 branching into ClNO2 and HNO3 over salty water

ACS Spring 2022

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