Xue, H., and G. Feingold, 2004:
A modeling study of the effect of nitric acid on cloud properties. J. Geophys. Res., 109, D18204, doi:10.1029/2004JD004750.
[1] The effect of nitric acid (HNO3) on cloud microphysical and radiative properties is
studied using an adiabatic cloud parcel model for a range of aerosol size distributions,
different water vapor mass accommodation coefficients, and HNO3 concentrations.
Results show that HNO3 not only increases cloud drop number concentration Nd, but also
leads to significantly broader droplet size spectra at both the small- and large-size ends.
The broader spectra are generally the result of competition for H2O and HNO3 among the
polydisperse droplets. The increase in the number of activated cloud droplets in the
presence of HNO3, and the deactivation of some of the small cloud droplets due to the
outgasing of HNO3, lead to spectral broadening at the small-size end. At the large-size end
the broadening is caused by an increase in the driving force for growth. For small
drops the driving force tends to be decreased by the presence of HNO3. Although Nd
increases with increasing HNO3 concentration, the increases in cloud optical depth and
albedo due to HNO3 cannot necessarily be predicted by the commonly used relationships
for cloud optical properties. The dependence of the cloud optical depth on Nd to the
one-third power is shown to be an overestimate because droplet spectra are significantly
broadened by HNO3. We show that broadening effects due to HNO3 and other chemical or
microphysical factors need to be considered when estimating cloud optical properties
and their effect on climate. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols
and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 1610
Global Change: Atmosphere (0315, 0325); KEYWORDS: cloud droplets, nitric acid, aerosol indirect effect
Citation: Xue, H., and G. Feingold (2004), A modeling study of the effect of nitric acid on cloud properties, J. Geophys. Res., 109,
D18204, doi:10.1029/2004JD004750.
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