Regensburg 1998 – wissenschaftliches Programm

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SYA: Symposium Physik für die Umwelt

SYA 2: Sondersymposium “Physik für die Umwelt” – Wissenschaftliche Poster

SYA 2.46: Poster

Dienstag, 24. März 1998, 16:45–19:00, C

Heterogeneous Conversion of Nitrogen Oxides on Sodium Salt Aerosols — •Andreas Wahner, Thomas Mentel, and Martin Sohn — FZ-J"ulich, Institut f"ur Atmosph"arische Chemie, ICG-3, D-52425 J"ulich

Heterogeneous conversion of N2O5 to HNO3 is an important step in the removal of nitrogen oxides from the troposphere in the absence of sun-light. Sodium nitrate and -sulfate are fractions in marine aerosol. The heterogeneous hydrolysis of N2O5 on aqueous sodium nitrate and sulfate aerosols is studied in a large aerosol chamber. The aerosol size distribution is measured by electromobility classification and by light scattering. N2O5 is formed in situ by reaction of O3 with NO2. Trace gases are measured by in-chamber FTIR spectroscopy. In the presence of aqueous aerosol fast conversion of N2O5 to HNO3 is observed. The effective uptake coefficient for N2O5 on aqueous NaNO3 aerosol is determined to about 0.002, an order of magnitude smaller than expected for aqueous surfaces. The uptake coefficients on sodium bisulfate and -sulfate aerosol are about 0.02 and 0.03, comparable to those on other aqueous systems. This observation of a ’nitrate effect’ supports the ionic reaction mechanism which assumes dissociation of N2O5 in NO2+ and NO3- as the first step in hydrolysis. The role of water- and substrate activity in the aerosol for the rate of the conversion will be discussed.