Natural formation of chloro- and bromoacetone in salt lakes of Western Australia

Western Australia is a semi-/arid region known for saline lakes with a wide range of geochemical parameters (pH 2.5-7.1, Cl- 10-200 g L-1. This study reports on the haloacetones chloro- and bromoacetone in air over 6 salt lake shorelines. Significant emissions of chloroacetone (up to 0.2 µmol m-2 h-1) and bromoacetone (up to 1. 5 µmol m-2 h-1) were detected, and a photochemical box model was employed to evaluate the contribution of their atmospheric formation from the olefinic hydrocarbons propene and methacrolein in the gas phase. The measured concentrations could not explain the photochemical halogenation reaction, indicating a strong hitherto unknown source of haloacetones. Aqueous-phase reactions of haloacetones, investigated in the laboratory using humic acid in concentrated salt solutions, were identified as alternative formation pathway by liquid-phase reactions, acid catalyzed enolization of ketones, and subsequent halogenation. In order to verify this mechanism, we made measurements of the Henry's law constants, rate constants for hydrolysis and nucleophilic exchange with chloride, UV-spectra and quantum yields for the photolysis of bromoacetone and 1,1-dibromoacetone in the aqueous phase. We suggest that heterogeneous processes induced by humic substances in the quasi-liquid layer of the salt crust, particle surfaces and the lake water are the predominating pathways for the formation of the observed haloacetones

The geochemical cycling of reactive chlorine through the marine troposphere

Heterogeneous reactions involving sea‐salt aerosol in the marine troposphere are the major global source for volatile inorganic chlorine. We measured reactant and product species hypothesized to be associated with these chemical transformations as a function of phase, particle size, and altitude over the North Atlantic Ocean during the summer of 1988. Concentrations of HCl were typically less than 1.0 ppbv near the sea surface and decreased with altitude and with distance from the U.S. east coast. Concentrations of Cl volatilized from aerosols were generally equivalent to the corresponding concentrations of HCl and ranged from less than detection limits to 125 nmol m−3 STP. Highest absolute and percentage losses of particulate Cl were typically associated with elevated concentrations of anthropogenic combustion products. Concentrations of product nss SO42− and N03− in coarse aerosol fractions indicate that on average only 38% of measured Cl− deficits could be accounted for by the combined effects of acid‐base desorption and reactions involving nonacidic N gases. We hypothesize a mechanism for the Cl loss initiated by reaction of O3 at sea‐salt aerosol surfaces, generating Cl2 followed by rapid photochemical conversion of Cl2 to HCl via Cl atoms (Cl˙) and eventual recapture of HCl by the aerosol. Simulations with a zero‐dimension (0‐D) photochemical model suggest that oxidation by Cl˙ may be an important tropospheric sink for dimethyl sulfide and hydrocarbons. Under low‐NOx conditions, the rapid cycling of reactive Cl would provide a catalytic loss mechanism for O3, which would possibly explain the low O3 concentrations often observed above the world\u27s oceans

Kinetics and mechanism of the reaction of OH with the trimethlbenzenes - experimental evidence for the formation of adduct isomers

The reversible gas-phase addition of OH radicals to the trimethylbenzenes was investigated in pulsed experiments utilizing VUV flash-photolysis resonance-fluorescence of H(2)O in the temperature range of 275-340 K. Triexponential OH decays were observed in the presence of the trimethylbenzenes, indicating the participation of more than one adduct species. Analytical solutions for the system of differential equations with two adduct isomers were derived, and the OH decay curves were evaluated based on this reaction model. This led to significant improvements of fit qualities and notable changes in OH rate constants compared to a previous model with a single adduct species. The detailed analysis was confined to 1,3,5-trimethylbenzene where reversible formation of two OH-aromatic ortho- and ipso-adduct isomers is feasible in accordance with the extended reaction model. Only after inclusion of additional isomerization reactions, consistent thermochemical data were obtained from the fitted rate constants. Reaction enthalpies of -83 ± 7 kJ mol(-1) and -35 ± 22 kJ mol(-1) were derived for the formation of one adduct isomer and the isomerization into the other, respectively. Based on literature data, the more and less stable adducts were assigned to ipso- and ortho-adduct isomers, respectively. The potential isomerization precluded the determination of primary yields of adduct isomers but formation of the ipso-adduct in any case is a minor process. For the rate constants of the OH + 1,3,5-trimethylbenzene reaction an Arrhenius expression k(OH) = 1.32 × 10(-11) cm(3) s(-1) exp(450 ± 50 K/T) was obtained. Based on the same approach, the rate constants of the OH reactions with 1,2,3-trimethylbenzene and 1,2,4-trimethylbenzene were derived as k(OH) = 3.61 × 10(-12) cm(3) s(-1) exp(620 ± 80 K/T) and k(OH) = 2.73 × 10(-12) cm(3) s(-1) exp(730 ± 70 K/T), respectively

Einfluß von heterogenen Reaktionen auf die Bildung und Verteilung von Photooxidantien

Quellstärken, Konzentrationen, physikalische und chemische Eigenschaften von Aerosolen lassen einen Beitrag zur Chemie der Troposphäre erwarten, der je nach der Adsorptionsneigung atmosphärischer Spurenstoffe zu deren Abbau beitragen kann. Der Aufbau einer Aerosol-Smogkammer ermöglicht die Simulation dieser chemischen und physikalischen Prozesse, die zur Umwandlung von Spurengasen unter dem Einfluß von Aerosolen und zur Bildung von aktiven Spezies der Atmosphäre und Ozon und anderen Photooxidantien führen. Eine Photoaktivierung, die OH-Radikale bildet und einen heterogenen Photoabbau induziert, wurde bei TiO2 und Fe sub 2 O sub 3-Aerosol nachgewiesen, eine Cl-Atombildung bei Kochsalz, einem in Form von Seesalz weitverbreiteten Aerosol

Photochemical activation of chlorine by iron-oxide aerosol

The photochemical activation of chlorine by dissolved iron in artificial sea-salt aerosol droplets and by highly dispersed iron oxide (Fe2O3) aerosol particles (mainly hematite, specific surface ~150 m2 g−1) exposed to gaseous HCl, was investigated in humidified air in a Teflon simulation chamber. Employing the radical-clock technique, we quantified the production of gaseous atomic chlorine (Cl) from the irradiated aerosol. When the salt aerosol contained Fe2O3 at pH 6, no significant Cl production was observed, even if the dissolution of iron was forced by “weathering” (repeatedly freezing and thawing for five times). Adjusting the pH in the stock suspension to 2.6, 2.2, and 1.9 and equilibrating for one week resulted in a quantifiable amount of dissolved iron (0.03, 0.2, and 0.6 mmol L−1, respectively) and in gaseous Cl production rates of ~1.6, 6, and 8 × 1021 atoms cm−2 h−1, respectively. In a further series of experiments, the pure Fe2O3 aerosol was exposed to various levels of gaseous hydrogen chloride (HCl). The resulting Cl production rates ranged from 8 × 1020 Cl atoms cm−2 h−1 (at ~4 ppb HCl) to 5 × 1022 Cl atoms cm−2 h−1 (at ~350 ppb HCl) and confirmed the uptake and conversion of HCl to atomic Cl (at HCl to Cl conversion yields of 2–5 %, depending on the relative humidity). The Fe2O3 experiments indicate that iron-induced Cl formation may be important for highly soluble combustion-aerosol particles in marine environments in the presence of gaseous HCl

Detection of NH (X3 [Sigma]-) by resonance fluorescence in the pulsed vacuum UV photolysis of NH3 and its application to reactions of NH radicals

Hansen I, Kohse-Höinghaus K, Zetzsch C, Stuhl F. Detection of NH (X3 [Sigma]-) by resonance fluorescence in the pulsed vacuum UV photolysis of NH3 and its application to reactions of NH radicals. Chemical Physics Letters. 1976;42(2):370-372.Using resonance fluorescence the kinetics of NH (X3 [Sigma]-) was studied in the pulsed vacuum UV photolysis of mixtures of NH3 and NO. The rate constant of the reaction NH + NO was determined to be (4.7 = 1.2) x lO - 11 cm 3 molecule - 1 s -

Gas-phase reaction of the OH-benzene adduct with O2 : reversibility and secondary formation of HO2

The reaction of OH radicals with benzene and consecutive reactions of benzene-OH adducts with O2 were studied in the gas phase in N2-O2 mixtures at atmospheric pressure and room temperature. OH was produced by pulsed 248 nm photolysis of H2O2. Time-resolved detection of both OH and benzene-OH adducts was performed by continuous-wave (cw) UV-laser long-path absorption at around 308 nm. The reaction: OH + benzene -> products [reaction (1)] was not affected by the presence of O2. Rate constants k1= (1.10 +/- 0.07) x 10-12 cm3 s-1 and (1.06 +/-0.07) x 10-12 cm3 s-1 were obtained in N2 and O2, respectively. In N2 addition of NO2 did not change k1, from which an upper limit of 5% is derived for formation of H atoms in reaction