Effect of humidity on nitric acid uptake to mineral dust aerosol particles A. Vlasenko1,3, S. Sjogren2, E. Weingartner2, K. Stemmler1, H. W. Gäggeler1,3, and M. Ammann1 1Laboratory of Radio- and Environmental chemistry, Paul Scherrer Institute, Villigen, Switzerland 2Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Villigen, Switzerland 3Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland
Abstract. This study presents the first laboratory observation of HNO3 uptake by
airborne mineral dust particles. The model aerosols were generated by dry
dispersion of Arizona Test Dust (ATD), SiO2, and by nebulizing a
saturated solution of calcium carbonate. The uptake of 13N-labeled
gaseous nitric acid was observed in a flow reactor on the 0.2–2 s reaction
time scale at room temperature and atmospheric pressure. The amount of
nitric acid appearing in the aerosol phase at the end of the flow tube was found to be a linear function of the aerosol surface
area. SiO2 particles did not show any significant uptake, while the
CaCO3 aerosol was found to be more reactive than ATD. Due to the
smaller uncertainty associated with the reactive surface area in the case of
suspended particles as compared to bulk powder samples, we believe that we
provide an improved estimate of the rate of uptake of HNO3 to mineral
dust. The fact that the rate of uptake was smaller at a concentration of 1012
than at 1011 was indicative of a complex uptake mechanism. The uptake coefficient averaged over the first 2 s of reaction time at
a concentration of 1012 molecules cm-3 was found to increase with
increasing relative humidity, from 0.022±0.007 at 12% RH to
0.113±0.017 at 73% RH , which was attributed to an increasing degree of solvation of the more basic minerals.
The extended processing of the dust by higher concentrations of HNO3 at 85% RH led to a water soluble coating on
the particles and enhanced their hygroscopicity.
Citation: Vlasenko, A., Sjogren, S., Weingartner, E., Stemmler, K., Gäggeler, H. W., and Ammann, M.: Effect of humidity on nitric acid uptake to mineral dust aerosol particles, Atmos. Chem. Phys., 6, 2147-2160, doi:10.5194/acp-6-2147-2006, 2006.