Atmos. Chem. Phys. Discuss., 4, 121-140, 2004
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Growth of upper tropospheric aerosols due to uptake of HNO3
S. Romakkaniemi1, H. Kokkola1, A. Petzold2, and A. Laaksonen1
1University of Kuopio, Department of Applied Physics, Kuopio, Finland
2Deutsches Zentrum für Luft und Raumfahrt Oberpfaffenhofen, Institut für Physik der Atmosphäre, Wessling, Germany

Abstract. The effect of nitric acid on the equilibrium size distributions of upper tropospheric aerosols is calculated as a function of relative humidity. It is shown that HNO3 concentrations above a few tenths of a ppb can cause substantial increases in haze mode particle concentrations at relative humidities at about 60% and above. The effect can be strongly magnified when letovicite particles are present in addition to sulfuric acid aerosols. This is mainly due to the lowering of the deliquescence RH of letovicite in the presence of gaseous nitric acid at low temperatures. We have also compared equilibrium calculations of the HNO3 effect with observations of increased haze mode concentrations at relative humidities above 50% (Petzold et al., 2000). Nitric acid mixing ratios on the order of 0.5–2 ppb may explain the observed increase of haze mode particles at least partially.

Citation: Romakkaniemi, S., Kokkola, H., Petzold, A., and Laaksonen, A.: Growth of upper tropospheric aerosols due to uptake of HNO3, Atmos. Chem. Phys. Discuss., 4, 121-140, doi:10.5194/acpd-4-121-2004, 2004.
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