Takemitsu Arakaki

Sources, sinks, and mechanisms of hydroxyl radical (•OH) photoproduction and consumption in authentic acidic continental cloud waters from Whiteface Mountain, New York: The role of the Fe(r) (r = II, III) photochemical cycle

Hydroxyl radical ( . OH) photoproduction in 25 authentic acidic (pH = 2.9 - 4.4) continental cloud waters from Whiteface Mountain, New York was quantified by phenol formed from the . OH-mediated oxidation of benzene (1.2 mM that was added as an . OH scavenger. Based on the effect of added bisulfite (HSO 3 - /HOSO 2 - ), an HOOH sink, the . OH photoproduction in these samples was apportioned into two categories: HOOH-dependent sources (dominant), and HOOH-independent sources (minor). On average only a small percentage (median = 9.4%, mean ± standard deviation = 16 ± 12%) of the HOOH-dependent . OH source is due to direct photolysis (313 nm) of HOOH. Nearly all of the HOOH-dependent . OH source is accounted for by an iron(II)-HOOH photo-Fenton reaction mechanism (Fe(II) + HOOH → Fe(III) +.OH + OH - ) that is initiated by photoreduction of Fe(III) to Fe(II) in the presence of HOOH. A photostationary state is established, involving rapid photolysis of Fe(III) to form Fe(II), and rapid reoxidation of Fe(II) to Fe(III). Consequently, a new term is introduced, Fe(r) (r = II, III), to represent the family of labile Fe(III) and Fe(II) species whose rapid photoredox cycling drives the Fenton production of . OH. The Fe(r) photochemical cycle, which drives the aqueous phase photoformation of . OH, is analogous to the classical NO x photochemical cycle, which drives the gas phase formation of O 3 and thus . OH. Based on the cloud waters studied here, the iron(II)-HOOH photo-Fenton reaction is a significant source of . OH to acidic continental cloud waters in comparison to gas-to-drop partitioning processes. Filtering (0.5 μm Teflon) cloud water samples had little effect on the . OH photoformation kinetics. Measured lifetimes of aqueous . OH ranged from 2.4 to 10.6 μs in these cloud waters, and decreased with increasing concentration of dissolved organic carbon. In acidic atmospheric water drops, the principal aqueous sinks for . OH will be reactions with dissolved organic compounds, bisulfite, and Cl - . Given such short chemical reaction lifetimes, little of the aqueous phase photoformed . OH is likely to escape to the gas phase.

A general scavenging rate constant for reaction of hydroxyl radical with organic carbon in atmospheric waters.

Hydroxyl radical (OH) is an important oxidant in atmospheric aqueous phases such as cloud and fog drops and water-containing aerosol particles. We find that numerical models nearly always overestimate aqueous hydroxyl radical concentrations because they overpredict its rate of formation and, more significantly, underpredict its sinks. To address this latter point, we examined OH sinks in atmospheric drops and aqueous particles using both new samples and an analysis of published data. Although the molecular composition of organic carbon, the dominant sink of OH, is extremely complex and poorly constrained, this sink behaves very similarly in different atmospheric waters and even in surface waters. Thus, the sink for aqueous OH can be estimated as the concentration of dissolved organic carbon multiplied by a general scavenging rate constant [kC,OH = (3.8 ± 1.9) × 10(8) L (mol C)(-1) s(-1)], a simple process that should significantly improve estimates of OH concentrations in atmospheric drops and aqueous particles.

Variation in CO2 assimilation rate induced by simulated dew waters with different sources of hydroxyl radical (·OH) on the needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc.)

The hydroxyl radical (*OH) is generated in polluted dew on the needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc.). This free radical, which is a potent oxidant, is assumed to be a cause of ecophysiological disorders of declining trees on the urban-facing side of Mt. Gokurakuji, western Japan. Mists of *OH-generating N(III) (HNO2 and NO2-) and HOOH + Fe + oxalate solutions (50 and 100 microM, pH 5.1-5.4) simulating the dew water were applied to the foliage of pine seedlings grown in open-top chambers in the early morning. Needles treated with 100 microM N(III) tended to have a greater maximum CO2 assimilation rate (Amax), a greater stomatal conductance (g(s)) and a greater needle nitrogen content (Nneedle), suggesting that N(III) mist acts as a fertilizer rather than as a phytotoxin. On the other hand, needles treated with 100 microM HOOH + Fe + oxalate solution showed the smallest Amax, g(s), and Nneedle, suggesting that the combination of HOOH + Fe + oxalate caused a decrease in needle productivity. The effects of HOOH + Fe + oxalate mist on pine needles were very similar to the symptoms of declining trees at Mt. Gokurakuji.

Aqueous-phase photoproduction of hydrogen peroxide in authentic cloud waters : wavelength dependence, and the effects of filtration and freeze-thaw cycles

Abstract Quantum yields (Φλ) of hydrogen peroxide (HOOH) photoproduction are reported at 313, 334, and 366 nm for authentic cloud waters collected over a three-year period (1991–1993) at Whiteface Mountain, New York. Quantum yields of HOOH production (based on the total sample absorbance) in these cloud waters ranged up to 0.014. For each sample the HOOH quantum yield decreased with increasing wavelength: Φ313 > Φ334 > Φ366. Action spectra for HOOH photoproduction in these cloud waters indicate that light between 290 and 380 nm is primarily responsible for the aqueous-phase HOOH photoproduction in tropospheric water drops. Quantum yields at 334 and 366 nm were each highly correlated with quantum yields at 313 nm. The cloud water absorbances per centimeter at 334 and 313 nm were also highly correlated. This suggests that similar classes; of chromophores were responsible for the aqueous-phase HOOH photoformation in the cloud waters from different events over a three-year period. The chromophores have not been identified, thus absolute quantum yields for HOOH formation from specific chromophores in an authentic sample could not be calculated. Comparisons of wavelength-dependent relative quantum yields in a given authentic cloud water sample (assuming Fe(oxalate)2− was the primary source of HOOH) with those for Fe(oxalate)2− in well-defined aqueous systems indicate that photolysis of Fe(oxalate)2− was not the primary source of HOOH photoproduction in any of the nine authentic cloud water samples studied. Filtration (0.5 μm Teflon) caused only small differences (⩽15% increase) in rates of HOOH photoformation versus unfiltered controls. Filtration through a 0.05 μm polycarbonate membrane filter did not cause distinguishable differences in the ultraviolet-visible absorption spectra of a cloud water sample previously filtered with a 0.5 μm Teflon filter. These observations suggest that particles were neither the dominant source nor the dominant sink of the photoproduced HOOH. Freezing (up to 403 d) caused only minor changes in HOOH photoproduction rates (−9 to + 12%), and in the ultraviolet-visible absorbance spectra and pH values of the cloud water studied. These observations indicate that freeze-thaw cycles in clouds will have only minor influences on the aqueous-phase photoformation of HOOH.

Photochemical formation of OH radicals in dew formed on the pine needles at Mt. Gokurakuji

Photochemical formation rates and sources of the hydroxyl (OH) radical were determined in dew water formed on the surface of Japanese red pine (Pinus densiflora) needles of declining (NO2 polluted area) and healthy pine stands at Mt. Gokurakuji located west of Hiroshima city in western Japan. The measured OH radical photoformation rates in dew water (n=10), which were normalized to the rate at midday on May 1 at 34°N, ranged from 0.67 to 5.18 µM h−1 (1M=1mol L−1). The mean value (2.69 µM h−1) was higher than that in dew water collected on a Teflon board and higher than the mean value in rain water published previously. Of the total OH radical formation rate observed in dew water on the pine needles, 16.4 % was estimated to originate from N (III) (NO2− and HNO2) and 24.6 % was estimated to originate from NO3−. There were other sources of OH radical photochemical formation in dew water on the pine needles besides photolysis of NO2− and NO3−.

Photochemical Formation of Hydroxyl Radicals in Tissue Extracts of the Coral Galaxea fascicularis

Various stresses induce the formation of reactive oxygen species (ROS) in biological cells. In addition to stress‐induced ROS, we studied the photochemical formation of hydroxyl radicals (˙OH), the most potent ROS, in coral tissues using phosphate buffer‐extracted solutions and a simulated sunlight irradiation system. ˙OH formation was seen in extracts of both coral host and endosymbiont zooxanthellae. This study is the first to report quantitative measurements of ˙OH photoformation in coral tissue extracts. Our results indicated that whether or not coral bleaching occurred, coral tissues and symbiotic zooxanthellae have the potential to photochemically produce ˙OH under sunlight. However, no significant difference was found in the protein content‐normalized formation rates of ˙OH between corals incubated under different temperatures and irradiance conditions. ˙OH formation rates were reduced by 40% by reducing the UV radiation in the illumination. It was indicated that UV radiation strongly affected ˙OH formation in coral tissue and zooxanthellae, in addition to its formation through photoinhibition processes.

Transboundary secondary organic aerosol in western Japan indicated by the δ13C of water-soluble organic carbon and the m/z 44 signal in organic aerosol mass spectra.

The stable carbon isotope ratio (δ13C) of low-volatile water-soluble organic carbon (LV-WSOC) was measured in filter samples of total suspended particulate matter, collected every 24 h in the winter of 2010 at an urban site and two rural sites in western Japan. Concentrations of the major chemical species in fine aerosol (<1.0 μm) were also measured in real time by aerosol mass spectrometers. The oxidation state of organic aerosol was evaluated using f44; i.e., the proportion of the signal at m/z 44 (CO2+ ions from the carboxyl group) to the sum of all m/z signals in the organic mass spectra. A strong correlation between LV-WSOC and m/z 44 concentrations was observed, which suggested that LV-WSOC was likely to be associated with carboxylic acids in fine aerosol. Plots of δ13C of LV-WSOC versus f44 showed random variation at the urban site and systematic trends at the rural sites. The systematic trends qualitatively agreed with a simple binary mixture model of secondary organic aerosol with background LV-WSOC with an f44 of ∼0.08 and δ13C of -17‰ or higher. Comparison with reference values suggested that the source of background LV-WSOC was likely to be primary emissions associated with C4 plants.

Continuous-flow complete-mixing system for assessing the effects of environmental factors on colony-level coral metabolism

A small-scale chamber experimental system was designed to study the effects of temperature on colony-level coral metabolism. The system continuously supplies fresh seawater to the chamber, where it is mixed immediately and completely with the seawater already present. This continuous-flow complete-mixing system (CFCM system), in conjunction with theoretical equations, allows quantitative determination of chemical uptake and release rates by coral under controlled environmental conditions. We used the massive hermatypic coral Goniastrea aspera to examine variations in pH, total alkalinity, and total inorganic carbon for 16 days at 27 degrees C under controlled light intensities (300 and 0 micromol m(-2) s(-1)). We confirmed the stability of the CFCM system with respect to coral photosynthetic and calcification fluxes. In addition, we obtained daily photosynthetic and calcification rates at different temperatures (27 degrees C, 29 degrees C, 31 degrees C, and 33 degrees C). When seawater temperature was raised from 31 degrees C to 33 degrees C, the gross primary production rate (Pgross) decreased 29.5%, and the calcification rate (G) decreased 85.7% within 2 days. The CFCM system allows quantitative evaluation of coral colony chemical release and uptake rates, and metabolism.