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Margaret A. Tolbert – One of the best experts on this subject based on the ideXlab platform.
Depositional ice nucleation on solid Ammonium Sulfate and glutaric acid particlesAtmospheric Chemistry and Physics, 2009Co-Authors: K. J. Baustian, Matthew E. Wise, Margaret A. TolbertAbstract:
Abstract. Heterogeneous ice nucleation on solid Ammonium Sulfate and glutaric acid particles was studied using optical microscopy and Raman spectroscopy. Optical microscopy was used to detect selective nucleation events as water vapor was slowly introduced into an environmental sample cell. Particles that nucleated ice were dried via sublimation and examined in detail using Raman spectroscopy. Depositional ice nucleation is highly selective and occurred preferentially on just a few Ammonium Sulfate and glutaric acid particles in each sample. For freezing temperatures between 214 K and 235 K an average ice saturation ratio of S = 1.10±0.07 for solid Ammonium Sulfate was observed. Over the same temperature range, S values observed for ice nucleation on glutaric acid particles increased from 1.2 at 235 K to 1.6 at 218 K. Experiments with externally mixed particles further show that Ammonium Sulfate is a more potent ice nucleus than glutaric acid. Our results suggest that heterogeneous nucleation on Ammonium Sulfate may be an important pathway for atmospheric ice nucleation and cirrus cloud formation when solid Ammonium Sulfate aerosol particles are available for ice formation. This pathway for ice formation may be particularly significant near the tropical tropopause region where Sulfates are abundant and other species known to be good ice nuclei are depleted.
Hygroscopic Growth of Ammonium Sulfate/Dicarboxylic AcidsJournal of Geophysical Research, 2003Co-Authors: Matthew E. Wise, Jason D. Surratt, Daniel B. Curtis, John E. Shilling, Margaret A. TolbertAbstract:
 Recent studies have shown that tropospheric Sulfate aerosols commonly contain 50% by mass organic species. The influence of these organics on the chemical and physical properties of Sulfate aerosols is not fully established. We have measured the water activity of pure dicarboxylic acids and eutonic mixtures of Ammonium Sulfate/dicarboxylic acids at 25°C and have calculated van’t Hoff factors for each individual system. We have also used the vapor pressure data to determine the hygroscopic growth curves for pure dicarboxylic acids and eutonic mixtures and provide power law fits to the data. For the systems studied we find that the presence of soluble dicarboxylic acids at the eutonic proportion depresses hygroscopic growth when compared to pure Ammonium Sulfate. In addition, we find that the presence of low-solubility dicarboxylic acids at the eutonic proportion has no effect on the hygroscopic growth when compared to pure Ammonium Sulfate. To model the hygroscopic growth curves of the eutonic solutions, we employed the Zdanovskii, Stokes, and Robinson method. It was found that this approximation was accurate to within 17% for all the systems studied.
Phase Changes in Internally Mixed Maleic Acid/Ammonium Sulfate AerosolsJournal of Geophysical Research, 2003Co-Authors: Sarah D. Brooks, Matthew E. Wise, Melinda C. Cushing, Rebecca M. Garland, Anthony J. Prenni, Erika Hewitt, Margaret A. TolbertAbstract:
 A temperature controlled flow tube system equipped with Fourier transform infrared (FTIR) detection of particle phase and relative humidity was used to measure the deliquescence and efflorescence of Ammonium Sulfate, maleic acid, and internally mixed maleic acid/Ammonium Sulfate particles. Our results indicate that maleic acid aerosols begin to take up water starting at a low relative humidity, ∼20%, and continue the constant uptake of water until the final deliquescence relative humidity (DRH), 89%, is reached. Internally mixed particles containing maleic acid and Ammonium Sulfate were found to deliquesce at a lower relative humidity (RH) than either of the pure species. Efflorescence studies indicated that while pure maleic acid particles crystallize at ∼18% RH, pure Ammonium Sulfate and all mixed aerosols effloresce at or just below 30% RH. Taken together, our results suggest that the presence of water-soluble organics internally mixed with Ammonium Sulfate aerosol could increase the range of conditions under which the aerosol is a solution.
Krishna N Reddy – One of the best experts on this subject based on the ideXlab platform.
Glufosinate and Ammonium Sulfate inhibit atrazine degradation in adapted soilsBiology and Fertility of Soils, 2008Co-Authors: Robert M Zablotowicz, L. Jason Krutz, Mark A Weaver, Cesare Accinelli, Krishna N ReddyAbstract:
The co-application of glufosinate with nitrogen fertilizers may alter atrazine cometabolism, thereby extending the herbicide’s residual weed control in adapted soils. The objective of this study was to assess the effects of glufosinate, Ammonium Sulfate, and the combination of glufosinate and Ammonium Sulfate on atrazine mineralization in a Dundee silt loam exhibiting enhanced atrazine degradation. Application of glufosinate at rates of 10 to 40 mg kg^−1 soil extended the lag phase 1 to 2 days and reduced the maximum degradation rate by 15% to 30%. However, cumulative atrazine mineralization averaged 85% 21 days after treatment and was independent of treatment. Maximum daily rates of atrazine mineralization were reduced from 41% to 55% by application of 1 to 8 g kg^−1 of Ammonium Sulfate. Similarly, cumulative atrazine mineralization was inversely correlated with Ammonium Sulfate rates ranging from 1.0 to 8 g kg^−1 soil. Under the conditions of this laboratory study, atrazine degradation was relatively insensitive to exogenous mineral nitrogen, in that 8 g (NH_4)_2SO_4 per kilogram soil repressed but did not completely inhibit atrazine mineralization. Moreover, an additive effect on reducing atrazine mineralization was observed when glufosinate was co-applied with Ammonium Sulfate. In addition, Ammonium fertilization alters the partitioning of ^14C-atrazine metabolite accumulation and nonextractable residues, indicating that Ammonium represses cleavage of the triazine ring. Consequently, results indicate that the co-application of glufosinate with N may increase atrazine persistence under field conditions thereby extending atrazine residual weed control in adapted soils.
Thomas J. Montville – One of the best experts on this subject based on the ideXlab platform.
mechanism by which Ammonium bicarbonate and Ammonium Sulfate inhibit mycotoxigenic fungiApplied and Environmental Microbiology, 1990Co-Authors: D A Depasquale, Thomas J. MontvilleAbstract:
In this study we examined the mechanism by which Ammonium bicarbonate inhibits mycotoxigenic fungi. Elevated extracellular pH, alone, was not responsible for the antifungal activity. Although conidia of Penicillium griseofulvum and Fusarium graminearum had internal pH (pHi) values as high as 8.0 in buffer at an external pH (pHo) of 9.5, their viability was not markedly affected. The pHi values from conidia equilibrated in glycine-NaOH-buffered treatments without Ammonium bicarbonate or Ammonium Sulfate were similar to values obtained from buffered treatments containing the Ammonium salts. Thus, inhibition did not appear to be directly related to increased pHi. Ammonium Sulfate in buffered media at pH greater than or equal to 8.7 was as inhibitory as Ammonium bicarbonate, but was completely ineffective at pH less than or equal to 7.8. The hypothesis that free ammonia caused the fungal inhibition was tested by using Ammonium Sulfate as a model for Ammonium bicarbonate. Viability, expressed as log CFU/ml, and percent germination of P. griseofulvum and F. graminearum decreased dramatically as the free ammonia concentration increased. Germination rate ratios (the germination rate in buffered Ammonium Sulfate divided by the germination rate in buffer alone) decreased linearly as the free ammonia concentration increased, further establishing NH3 as the toxic agent. Ammonium bicarbonate inhibits fungi because the bicarbonate anion supplies the alkalinity necessary to establish an antifungal concentration of free ammonia.