Showing papers by "Michael R. Hoffmann published in 1990"
TL;DR: Inorganic and organic peroxides have become the focus of increased attention by atmospheric chemists during the last decade as discussed by the authors, and they serve as an important link between gas phase radicals and aqueous phase chemistry in the atmosphere.
209 citations
TL;DR: Under anaerobic conditions, Shewanella putrefaciens is capable of respiratory-chain-linked, high-rate dissimilatory iron reduction via both a constitutive and inducible Fe(III)-reducing system, but in the presence of low levels of dissolved oxygen, this microorganism is extremely slow.
Abstract: Under anaerobic conditions, Shewanella putrefaciens is capable of respiratory-chain-linked, high-rate dissimilatory iron reduction via both a constitutive and inducible Fe(III)-reducing system. In the presence of low levels of dissolved oxygen, however, iron reduction by this microorganism is extremely slow. Fe(II)-trapping experiments in which Fe(III) and O_2 were presented simultaneously to batch cultures of S. putrefaciens indicated that autoxidation of Fe(II) was not responsible for the absence of Fe(III) reduction. Inhibition of cytochrome oxidase with CN– resulted in a high rate of Fe(III) reduction in the presence of dissolved O_2, which suggested that respiratory control mechanisms did not involve inhibition of Fe(III) reductase activities or Fe(III) transport by molecular oxygen. Decreasing the intracellular ATP concentrations by using an uncoupler, 2,4-dinitrophenol, did not increase Fe(III) reduction, indicating that the reduction rate was not controlled by the energy status of the cell. Control of electron transport at branch points could account for the observed pattern of respiration in the presence of the competing electron acceptors Fe(III) and O_2.
117 citations
TL;DR: In this paper, a two-term rate law for the pH range of 2.0-6.3 was established for the Peroxymonosulfate (PMS) reaction.
Abstract: The stoichiometry and mechanism of the oxidation of
aqueous S(-II) by HSO_5^-, is similar to the oxidation of
S(-II) by H_2O_2, but the rate of oxidation by HSO_5^-; is 3-4 orders of magnitude faster than the corresponding reaction with H_2O_2. A two-term rate law of the following form is found to be valid for the pH range of 2.0-6.3: -d[S(-II)]/dt = k_1[H_2S][HSO_5^-] + k_2K_(a1)[H_2S][HSO_5^-]/[H^+], where k_1 = 1.98 X 10^1 M^(-1) s^(-1),k2 = 1.22 X 10^4 M^(-1) s^(-1), and K_(al) = [H^+][HS^-]/[H_2S] = 2.84 X 10^(-8) M at 4.9 °C, µ = 0.2 M, and [S(-II)] = [H_2S] + [HS^-] + [S^(2-). At high pH and high [HSO_5^-]/[S(-II)] ratios SO_4^(2-) and H^+ formation are favored, whereas at low pH and low [HSO_5^-]/[S(-II)] ratios
elemental sulfur (S_8) is favored as the principal reaction
product. Peroxymonosulfate is a monosubstituted derivative
of hydrogen peroxide that is thermodynamically more
powerful as an oxidant than H_2O_2 and kinetically more
reactive. These properties make HSO_5^- a potentially important oxidant in natural systems such as remote tropospheric clouds and also a viable alternative to H_2O_2 for the control of malodorous sulfur compounds and for the
control of sulfide-induced corrosion in concrete sewers.
94 citations
TL;DR: In this paper, the chemistry at Riverside is controlled by the balance between HNO_3 production from NO_x emitted throughout the Los Angeles basin and NH3 emitted from dairy cattle feedlots just west of Riverside, California.
89 citations
TL;DR: The chemical composition of cloudwater in the Sierra Nevada is dominated by NO−, SO−, and NH−4−, although inputs of formic and acetic acid also are important, particularly when anthropogenic inputs are small.
57 citations
TL;DR: In this article, measurements of inorganic aerosol and gas phase species are presented for three sites in central California during a 4-day period in April 1988, where the measurement sites were located along an east-west transect at Visalia, Ash Mountain, and Lower Kaweah.
55 citations
TL;DR: A side-by-side comparison of the Rotating Arm Collector (RAC) and the Caltech Active Strand Cloudwater Collector (CASCC) was conducted at an elevated coastal site near the eastern end of the Santa Barbara Channel in southern California as discussed by the authors.
30 citations
TL;DR: In this article, measurements of various inorganic species in snow collected in central and southern California during the winter of 1987-1988 indicate a combined influence of anthropogenic and maritime sources, depending on the meteorological conditions and wind patterns.
27 citations
TL;DR: In this paper, the authors analyzed snow samples from central and southern California during the winter of 1987-1988 from there storms and analyzed for carbonyl compounds and carboxylic acids.
22 citations
TL;DR: Aldehydes react with bisulfite to form HASA, which are the conjugate bases of strong acids as discussed by the authors, and can be selectively transported through an ion-exchange membrane if they are specifically converted to electrolytes in the membrane.
Abstract: Organic nonelectrolytes can be selectively transported through an ion-exchange membrane if they
are specifically converted to electrolytes in the membrane. Aldehydes react with bisulfite to form
hydroxyalkanesulfonates (HASA), which are the conjugate bases of strong acids. Aldehydes are shown
to be transported efficiently across an anion-exchange membrane via the coupled counter-transport
of HMSA ion with hydroxide ion and the relay of an aldehyde from one membrane-bound bisulfite
ion to another. Permeation rates are in the order of formaldehyde > acetaldehyde > acetone; this
relationship parallels the relative order of the stability constants for formation of the respective
adducts with bisulfite ion. Aldehydes can be separated readily from other organic solutes by this
method.
18 citations