Redox chemistry of iron in fog and stratus clouds

The redox chemistry of Fe in fog and cloudwater has been investigated at coastal and inland locations in the Los Angeles basin, in Bakersfield California, and in Delaware Bay. Samples were collected and analyzed for Fe (Fe(II)), Fe(III), total(Fe), sulfur (S(IV), S(VI)), organic ligands (formate, acetate, oxalate), total organic carbon (TOC), pH, major cations (sodium, calcium, magnesium, potassium, ammonium), chloride, sulfate, nitrate, peroxides, and aldehydes (HCHO); the amount of sunlight was also measured. The ratio Fe(II)/Fe(total) varied between 0.02 and 0.55. The concentration of Fe(II) varied between 0.1 and 5 micromole, and the concentration of total Fe varied between 2 and 27 micromole. The atmospheric redox cycle of Fe involves both dissolved and aerosol surface species and appears to be related to the presence of organic compounds which act as electron donors for the reduction of Fe(III). Fe(III) reduction is enhanced by light but significant Fe(II) levels were observed in the dark. We suggest that reduction of Fe(III) species by organic electron donors may be an important pathway that affects the speciation of Fe in both urban and rural atmospheres. It is possible that reactions involving Fe and organic compounds might be an important source of carboxylic acids in the troposphere

Tio2 mediated photocatalytic inactivation of gram-positive and gram-negative bacteria using fluorescent light

Photocatalytic inactivation of six different species of bacteria using fluorescent light and TiO2 was conducted. Up to five surface loadings of TiO2 varying from 234-8662 mg/m2, impregnated on membrane filters were used with fluorescent light of constant illuminance of 3900 Lux for the inactivation of four ATCC bacteria (E. coli K-12, Pseudomonas fluorescens, Bacillus subtilis and Microbacterium sp.) and two other species of bacteria (Microbacteriaceae str. W7 and Paenibacillus sp. SAFN-007) collected from outdoor air in Singapore. A Gram-negative bacterium E. coli K-12 was the most effectively inactivated, while Gram-positive Bacillus subtilis exhibited the least response to the photocatalytic treatment. The inactivation rate increased with an increase in the TiO2 loading, the maximum inactivation of most bacteria was achieved at an optimum TiO2 loading of 1116-1666 mg/m2. 100% of the E. coli K-12 was inactivated after 30 minutes of treatment at a TiO2 loading of 1666 mg/m2, while inactivation of one log10 was obtained for Microbacterium sp., Paenibacillus sp. SAFN-007 and Microbacteriaceae str. W7 after two hours. Preliminary experiments indicate that the photocatalytic inactivation using Degussa P25 is 1.83-5.41 times higher than that of Hombikat UV-100

Peracids in water treatment:a critical review

Abstract Peracids have gained interest in the water treatment over the last few decades. Peracetic acid (CH₃CO₃H) has already become an accepted alternative disinfectant in wastewater disinfection whereas performic acid (CHO₃H) has been studied much less, although it is also already commercially available. Additionally, peracids have been studied for drinking water disinfection, oxidation of aqueous (micro)pollutants, sludge treatment, and ballast water treatment, to name just a few examples. The purpose of this review paper is to represent comprehensive up-to-date information about the water treatment applications, aqueous reaction mechanisms, and disinfection by-product formation of peracids, namely performic, peracetic, and perpropionic acids

Simultaneous spectrophotometric measurement of iron(II) and iron(III) in atmospheric water

A new analytical method employing di-pyridyl ketone benzoylhydrazone (DPKBH) as a colorimetric chelating agent for the simultaneous determination of iron(II) and iron (III) in cloudwater has been developed. A spectrophotometric detection limit of 4 nM for both Fe(III) and Fe(II) with a linear response from 4 nM to 0.1 µM was established for samples extracted with CHCl_3-H_2O. DPKBH chelation without CHCl_3 extraction showed a linear response from 0.1 to 30 µM. The molar extinction coefficients of the Fe(II)-bis(DPKBH) (є_2) and Fe(III)-bis(DPKBH) (є_1) complexes are є_l and є_2 = 3.6 X 10^4 L mol^(-1) cm^(-1) at 370 nm and є_2 = 1.1 X 10^4 L mol^(-1) cm^(-1) at 660 nm. Analytical interference studies on the possible changes in the oxidation state of iron with S(IV), oxalate, and other potential electron donors have also been carried out. This analytical method has been used to determine iron(II) and iron(III) simultaneously in cloudwater samples collected within the Los Angeles basin airshed. The concentration of Fe(II) varied from 0.3 to 5 µM, and the concentration of Fe(III) varied from 0.6 to 1.4 µM during several stratus cloud events

Multiphasic Redox Chemistry of Iron in Urban Atmosphere

A knowledge of the exact speciation of all oxidation states of transition metals in atmospheric water droplets as a function of variables such as pH, organic ligand content and ionic strength is critical to the computational assessment of in situ reaction pathways involving S(IV), O_2, RHCO, NO_x, ROOH, and H_2O_2. Likewise, a knowledge of the speciation of metals such as Fe and Mn in wet and dry atmospheric deposition and the subsequent speciation changes upon introduction to marine waters is important to the assessment of the ability of marine biota to utilize these elements for nutritional needs. Iron is emitted to the troposphere from both natural (e.g., windblown dust) and anthropogenic (e.g., coal combustion) sources. It has been proposed that atmospheric Fe participates in a variety of reactions such as the oxidation of S(IV) and organic compounds by Fe(III) via direct electron transfer, and the catalytic auto-oxidation of SO_2 to SO_4^(2-) in the droplet phase

Photoreduction of Iron Oxyhydroxides and the Photooxidation of Halogenated Acetic Acids

The photolytic reduction of ferrihydrite (am-Fe_2O_3*3H_2O), lepidocrocite (γ-FeOOH), goethite (a-FeOOH), hematite (α-Fe_2O_3), maghemite (γ-Fe_2O_3) and iron-containing aerosol particles (Fe_(aerosol)) in the presence of a series of halogenated acetic acids has been investigated. The fastest rates of photoreduction of Fe(lll) to Fe(ll) were achieved with ferrihydrite as an electron acceptor and fluoroacetic acid as an electron donor. The relative rates of photooxidation of the monohalogenated acetic acids with ferrihydrite in order of decreasing reactivity were as follows: FCH_2CO_2H > CICH_2CO_2H > BrCH_2CO_2H > ICH_2CO_2H; for multiple substituents the relative order of reactivity was as follows: FCH_2CO_2H > F_2CHCO_2H > F_3CCO_2H. With respect to the iron oxide electron acceptors, the relative order of reactivity toward monohaloacetate oxidation was am-Fe_2O_3-3H_2O > γ-Fe_2O_3 > γ-FeOOH ≥ α-Fe_2O_3 ≥ Fe_(aerosol) > α-FeOOH. Strong kinetic isotope effects observed for the photooxidation of CICD_2CO_2H suggest that the oxidation of the mono- and disubstituted haloacetic acids proceeds via hydrogen-atom abstraction by surface-bound hydroxyl radicals to produce haloacetate radicals, which in turn yield the corresponding halide and glycolic acid. Fully halogenated haloacetic acids appear to be oxidized via a photo-Kolbe mechanism to yield the corresponding halo acids and CO_2