Aerosol Proteinaceous Matter in Coastal Okinawa, Japan: Influence of Long-Range Transport and Photochemical Degradation.

The characteristics, sources, and atmospheric oxidation processes of marine aerosol proteinaceous matter (APM), including total proteins and free amino acids (FAAs), were investigated using a set of 1 year total suspended particulate (TSP) samples collected in the coastal area of Okinawa Island in the western North Pacific rim. The concentrations of APM at this site (total proteins: 0.16 ± 0.10 µg m-3 and total FAAs: 9.7 ± 5.6 ng m-3, annual average) are comparable to those of marine APM. The major FAA species of APM are also similar to previously reported marine APM with glycine as the dominant species (31%). Based on the different seasonal trends and weak correlations of total proteins and FAAs, we found that they were contributed by different sources, especially with the influence of long-range transport from the Asian continent of northern China and Mongolia and the oceanic area of the Bohai Sea, Yellow Sea, and East China Sea. The photochemical oxidation processes of high-molecular-weight proteins releasing FAAs (especially glycine) were also considered as an important factor influencing the characteristics of APM at this site. In addition, we propose a degradation process based on the correlation with ozone and ultraviolet radiation, emphasizing their roles in the degradation of proteins. Our findings help to deepen the understanding of atmospheric photochemical reaction processes of organic aerosols.

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.

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.

Heterogeneity and potential aquatic toxicity of hydrogen peroxide concentrations in selected rivers across Japan.

Hydrogen peroxide (H2O2) is a reactive oxygen species formed in natural water. It is reportedly toxic to aquatic organisms with a predicted no-effect concentration (PNEC) of about 380 nM. In this study, a countrywide investigation of H2O2 concentrations in selected rivers across Japan was conducted to identify rivers that pose toxicity concerns. Twelve rivers with a total catchment area of 13,646 km2 were selected from different prefectures. Spatial and temporal variation studies showed that the H2O2 concentrations (avg. 320 nM, n = 111) varied by two orders of magnitude (range 21-2929 nM) across the rivers. The Yamato River in Osaka and Nara prefectures and the Kokubu River in Chiba Prefecture had the highest concentrations at 276-669 nM and 236-2929 nM, respectively. >75% of the data from the two rivers were either close to or exceeded the PNEC. Most of the results for the other rivers were less than the PNEC. There was a clear seasonal variation in the H2O2 concentrations, with the highest values obtained in summer because of high solar irradiation. The H2O2 concentration had the highest positive correlation (r = 0.61, p < 0.01, n = 111) with the product of dissolved organic carbon and solar radiation intensity, which suggests that these two factors in combination are important in determining the H2O2 concentrations in river water. It was also observed that bigger rivers had lower H2O2 concentration and vice-versa. This shows that the size of a river may influence its H2O2 concentration. This study is the first countrywide survey of H2O2 concentrations in different rivers and evaluation of their relationship with the PNEC. The data provide insight on the factors influencing the concentrations of H2O2 in river water.

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.

Harmful effects of radicals generated in polluted dew on the needles of Japanese Red Pine (Pinus densiflora).

• The effects of free radicals, ·OH and ·NO, generated in polluted dew water on needles of Pinus densiflora (Japanese Red pine) were investigated. • ·OH-generating solutions (HOOH with Fe(III) and oxalate ion; ·OH treatment) and ·OH- and ·NO-generating solutions (NO2 - ; ·OH/·NO treatment) were regulated at 25, 50 and 100 µmol and pH 4.4. HOOH only (HOOH treatment) was used as a control solution. Solutions were applied as a mist to the needle surface of P. densiflora seedlings before dawn twice a week for 3 months. • Within a month, net photosynthesis at near saturating irradiance (Pn) and stomatal conductance (gl) of ·OH-treated needles decreased with increasing solution concentration. The HOOH treatment had no effects on any of the measured parameters. Therefore, ·OH in the artificial dews caused the decreases in Pn and gl. In ·OH/·NO-treated needles, gl increased during the experiment, but Pn was unchanged. In all experiments, the characteristics of PSII were not significantly altered. • Free radicals in polluted dew water have harmful effects on the photosynthesis of P. densiflora and compound effects of ·OH and ·NO are different.

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.

Contribution of fulvic acid to the photochemical formation of Fe(II) in acidic Suwannee River fulvic acid solutions.

We investigated the contribution of fulvic acid to the photoformation of Fe(II) using aqueous Suwannee River fulvic acid (SRFA) as a surrogate for the humic-like substances (HULIS) found in atmospheric condensed phases. The effects of pH (3.2, 4.1, and 5.0) and wavelength (313, 334, 366, and 405nm) on Fe(II) photoformation were studied using monochromatic radiation at 20 degrees C. We calculated the wavelength-dependent Fe(II) photoformation efficiency values ("E-value"), defined here as a weighted sum of the product of the quantum yield and molar absorptivity of each Fe(II)-forming chemical species, and found that the E-values of acidic SRFA solutions were similar to those of Fe(OH)(2+). In addition, a comparison showed that the acidic SRFA solutions did not form Fe(II) fast enough to account for the observed Fe(II) formation efficiencies of the aqueous extracts of authentic aerosol samples. It was observed that 17-73% of Fe(III) had been reduced to Fe(II) in the dark in acidic SRFA solutions with added Fe(III) ranging from 0.5 to 10muM. The results of this study suggest that HULIS is unlikely to be the major reducing ligand in the process of photochemical formation of Fe(II) in acidic atmospheric drops. However, HULIS could reduce Fe(III) to Fe(II) in the dark, which in turn, could be important for night-time ()OH formation via the reaction between Fe(II) and H(2)O(2) (the Fenton reaction).

Wavelength dependence of Fe(ll) photoformation in the water-soluble fraction of aerosols collected in Okinawa, Japan.

We studied photoformation of Fe(II) in the water-soluble fractions (WSFs) of bulk aerosol particles collected in Okinawa, Japan, using radiation at wavelengths of 313, 334, 366, and 405 nm. Fe(II) photoformation quickly reached a steady state within 5 min of irradiation at all wavelengths. The steady-state Fe(II) concentrations were 85+/-13% (n = 39) of the total dissolved Fe (TDFe) concentrations in the WSF solutions. Apparent quantum yields of Fe(II) photoformation were determined based on total absorbance of the WSF solutions, and the means (+/-1 S.D.) were 0.019 (+/-0.034), 0.021 (+/-0.031), 0.014 (+/-0.023), and 0.010 (+/-0.025) at 313, 334, 366, and 405 nm, respectively. Comparison of the observed rates of Fe(II) photoformation for the WSF solutions and the calculated rates from the known Fe(II)-forming compounds suggested that Fe(oxalate)2- could account for the observed Fe(II) photoformation rates if the Fe(oxalate)2- concentration is sufficiently high (>20% of [Fe(III)]o). Furthermore, our study showed that the calculated wavelength dependence of Fe(ll) photoformation from Fe(oxalate)2- was consistent with that of Fe(II) photoformation observed in the WSF solutions. The results obtained here have implications to daytime Fe(III)/ Fe(II) cycles in the atmospheric water droplet.