Matthew E. Wise

Deliquescence behavior of organic/ammonium sulfate aerosol

Received 15 January 2002; revised 16 May 2002; accepted 23 May 2002; published 8 October 2002. [1] Recent studies have shown that tropospheric aerosols composed of internal mixtures of organics with sulfates are quite common with the organic composing up to 50% of the particle mass. The influences of the organics on the chemical and physical properties of the aerosol are not known. In this paper, we report the solubility of a series of dicarboxylic acids in saturated ammonium sulfate solution as a function of temperature. We also report the deliquescence relative humidity (DRH) of the pure dicarboxylic acids and of mixtures of dicarboxylic acids with ammonium sulfate. For the systems studied, we find that the presence of watersoluble dicarboxylic acids caused deliquescence to occur at a lower relative humidity (RH) than pure ammonium sulfate. In contrast, the less soluble dicarboxylic acids had no measurable effect on the deliquescence relative humidity of ammonium sulfate. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0320 Atmospheric Composition and Structure: Cloud physics and chemistry; 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry. Citation: Brooks, S. D., M. E. Wise, M. Cushing, and M. A. Tolbert, Deliquescence behavior of organic/ammonium sulfate aerosol, Geophys. Res. Lett., 29(19), 1917, doi:10.1029/2002GL014733, 2002.

Solubility and freezing effects of Fe2+ and Mg2+ in H2SO4 solutions representative of upper tropospheric and lower stratospheric sulfate particles

Chemical elements characteristic of earth minerals and meteorites are present withinbackground tropospheric and stratospheric sulfate aerosol particles. However, it isunknown if these elements are present predominantly as solids, including possiblesulfates, carbonates, and oxides, or rather as soluble aqueous metal ions or complexes.Further, it is unclear how these impurities could affect particle freezing. To addressthese questions, we have determined the total equilibrium metal solubility ([Fe

Phase changes in internally mixed organic/sulfate aerosols

Using a temperature controlled flow tube system equipped with FTIR detection of particle phase and relative humidity, we have measured the deliquescence (uptake of water) and efflorescence (loss of water) of internally mixed ammonium sulfate/maleic acid particles. Our results indicate that crystalline ammonium sulfate particles remain dry until reaching a deliquescence relative humidity of approximately 81%. In contrast, internally mixed particles deliquesce at significantly lower relative humidities. Results are presented for the deliquescence and efflorescence phase changes of mixed ammonium sulfate/maleic acid aerosols as a function of maleic acid wt%. The results suggest that the presence of water-soluble organics in tropospheric aerosol could alter the conditions under which phase changes occur in the atmosphere.

Laboratory studies of ice nucleation in sulfate particles: Implications for cirrus clouds

In the laboratory, we have used FTIR spectroscopy to monitor ice nucleation from atmospherically relevant compositions of sulfate particles. Measured freezing temperatures are presented as a function of aerosol composition. We find that sulfuric acid solution aerosol exhibits greater supercooling than ammonium sulfate solution aerosol of similar weight percent. Ice saturation ratios based on these measurements are also reported. We find that ammonium sulfate solution aerosol exhibits a relatively constant ice saturation of S∼1.48 for ice nucleation from 232 to 222 K, while sulfuric acid solution aerosol shows an increase in ice saturation from S∼1.53 to S∼1.6 as temperature decreases from 220 K to 200 K. These high saturation ratios imply that ice nucleation from sulfate aerosols will favor the formation of a small number of large ice particles, in agreement with many observations of cirrus clouds.