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. Letovicite particles are less acidic than
the sulfuric acid particles and so more nitric acid can be absorbed.
This effect can be seen even at RH below 50% 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 0.5-2ppb may explain
the observed increase of haze mode particles at
Citation: Romakkaniemi, S., Kokkola, H., Petzold, A., and Laaksonen, A.: Growth of upper tropospheric aerosols due to uptake of HNO3, Atmos. Chem. Phys., 4, 549-556, doi:10.5194/acp-4-549-2004, 2004.