Production and use of 13N labeled N2O5 to determine gas-aerosol interaction kinetics

摘要

Dinitrogen pentoxide has aroused significant interest in atmospheric chemistry because of its importance in the night time chemistry of nitrogen oxides to influence the tropospheric oxidation capacity. We have used an established method of 13N production to synthesize 13N labeled N2O5 for the first time in order to study N2O5 uptake kinetics on aerosol particles. 13N is produced via the 16O(p, α)13N reaction in a gas target attached to the IP2 endstation of the Injector 2 cyclotron at PSI. The 13NO produced in the gas target is transported to a laboratory where it is mixed, under dry conditions, with non-labeled NO and O3 in a gas reactor, giving 13NNO5. The N2O5 thus produced is fed into an aerosol flow tube together with a humidified aerosol gas flow. The gaseous species present in the resulting gas flow are selectively separated via a narrow parallel plate diffusion denuder system, while aerosol particles can be trapped on a particle filter placed at the end of the denuder system. The activity of the 13N labeled species trapped on the denuder plates and in the particle filter can be monitored via scintillation counters. A system for the routine online production of 13N labeled N2O5 has been assembled and used to assess the conformity of the results by kinetic modeling of gas phase N2O5 chemistry, showing good agreement. A few exemplary experiments of uptake of labelled N2O5 to ammonium sulfate and citric acid particles are presented that are in good agreement with results obtained with other methods reported in the literature