Improved continuous measurement system for atmospheric total peroxy and total organic nitrate under the high NOx condition.

We improved the thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument to measure atmospheric total peroxy nitrates (PNs) and organic nitrates (ONs) continuously under the condition of high NOx. In TD-CAPS, PNs and ONs are dissociated in heated quartz tubes to form NO2, and the NO2 concentration is measured by cavity attenuated phase shift spectroscopy (CAPS). The original TD-CAPS system overestimates PN and ON concentrations in the presence of high NO concentrations. Our laboratory experiments and numerical simulations showed that the main cause of the overestimation was NO oxidation to NO2 by peroxy radicals generated in the heated quartz tubes. In the improved system, NO was converted to NO2 by adding excess O3 after the quartz tubes so that CAPS detected NOx (NO and NO2) instead of NO2. The uncertainty of the improved system was less than 20% with ∼15 parts per billion by volume (ppbv) NO and ∼80 ppbv NO2. The estimated detection limit (3σ) was 0.018 ppbv with an integration time of 2 min in the presence of 64 ppbv NO2. The improved system was tested for measurement of PNs and ONs in an urban area, and the results indicated that interference from NO was successfully suppressed.

Evaluation of Antibiotic Penicillin G Activities Based on Electrochemical Measurement of a Tetrazolium Salt.

This study focused on the electrochemical properties of tetrazolium salts to develop a simple method for evaluating viable bacterial counts, which are indicators of drug susceptibility. Considering that the oxidized form of tetrazolium, which has excellent cell membrane permeability, changes to the insoluble reduced form formazan inside the cell, the number of viable cells was estimated based on the reduction current of the tetrazolium remaining in the bacterial suspension. Dissolved oxygen is an important component of bacterial activity. However, it interferes with the electrochemical response of tetrazolium. We estimated the number of viable bacteria in the suspension based on potential-selective current responses that were not affected by dissolved oxygen. Based on solubility, cell membrane permeability, and characteristic electrochemical properties of the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium, we developed a method for rapidly measuring viable bacteria within one-fifth of the time required by conventional colorimetric methods for drug susceptibility testing.

Simultaneous Electrochemical Detection of Multiple Bacterial Species Using Metal-Organic Nanohybrids.

Organic metallic nanohybrids (NHs), in which many small metal nanoparticles are encapsulated within a conductive polymer matrix, are useful as sensitive electrochemical labels because the constituents produce characteristic oxidation current responses. Gold NHs, consisting of gold nanoparticles and poly(m-toluidine), and copper NHs, consisting of copper nanoparticles and polyaniline, did not interfere with each other in terms of the electrochemical signals obtained on the same electrode. Antibodies were introduced into these NHs to function as electrochemical labels for targeting specific bacteria. Electrochemical measurements using screen-printed electrodes dry-fixed with NH-labeled bacterial cells enabled the estimation of bacterial species and number within minutes, based on the distinct current response of the labels. Our proposed method achieved simultaneous detection of enterohemorrhagic Escherichia coli and Staphylococcus aureus in a real sample. These NHs will be powerful tools as electrochemical labels and are expected to be useful for rapid testing in food and drug-related manufacturing sites.

Evaluation of Bacterial Activity Based on the Electrochemical Properties of Tetrazolium Salts.

This study focused on the electrochemical properties of tetrazolium salts to develop a simple method for evaluating viable bacterial counts, which are indicators of hygiene control at food and pharmaceutical manufacturing sites. Given that the oxidized form of 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), which has excellent cell membrane permeability, changes to the insoluble reduced form of formazan inside the cell, the number of viable cells was estimated by focusing on the reduction current of MTT remaining in the suspension. Dissolved oxygen is an important substance for bacterial activity; however, it interferes with the electrochemical response of MTT. We investigated the electrochemical properties of MTT to obtain a potential-selective current response that was not affected by dissolved oxygen. Real-time observation of viable bacteria in suspension revealed that uptake of MTT into bacteria was completed within 10 min, including the lag period. In addition, we observed that the current response depends on viable cell density regardless of the bacterial species present. Our method enables a rapid estimation of the number of viable bacteria, making it possible to confirm the safety of food products before they are shipped from the factory and thereby prevent food poisoning.

Role of Dust and Iron Solubility in Sulfate Formation during the Long-Range Transport in East Asia Evidenced by 17O-Excess Signatures.

Numerical models have been developed to elucidate air pollution caused by sulfate aerosols (SO42-). However, typical models generally underestimate SO42-, and oxidation processes have not been validated. This study improves the modeling of SO42- formation processes using the mass-independent oxygen isotopic composition [17O-excess; Δ17O(SO42-)], which reflects pathways from sulfur dioxide (SO2) to SO42-, at the background site in Japan throughout 2015. The standard setting in the Community Multiscale Air Quality (CMAQ) model captured SO42- concentration, whereas Δ17O(SO42-) was underestimated, suggesting that oxidation processes were not correctly represented. The dust inline calculation improved Δ17O(SO42-) because dust-derived increases in cloud-water pH promoted acidity-driven SO42- production, but Δ17O(SO42-) was still overestimated during winter as a result. Increasing solubilities of the transition-metal ions, such as iron, which are a highly uncertain modeling parameter, decreased the overestimated Δ17O(SO42-) in winter. Thus, dust and high metal solubility are essential factors for SO42- formation in the region downstream of China. It was estimated that the remaining mismatch of Δ17O(SO42-) between the observation and model can be explained by the proposed SO42- formation mechanisms in Chinese pollution. These accurately modeled SO42- formation mechanisms validated by Δ17O(SO42-) will contribute to emission regulation strategies required for better air quality and precise climate change predictions over East Asia.

Simultaneous Optical Detection of Multiple Bacterial Species Using Nanometer-Scaled Metal-Organic Hybrids.

This paper describes a simple strategy to identify bacteria using the optical properties of the nanohybrid structures (NHs) of polymer-coated metal nanoparticles (NPs). NHs, in which many small NPs are encapsulated in polyaniline particles, are useful optical labels because they produce strong scattered light. The light-scattering characteristics of NHs are strongly dependent on the constituent metal elements of NPs. Gold NHs (AuNHs), silver NHs (AgNHs), and copper NHs (CuNHs) produce white, reddish, and bluish scattered light, respectively. Moreover, unlike NPs, the color of the scattered light does not change even when NHs are aggregated. Introducing an antibody into NHs induces antigen-specific binding to cells, enabling the identification of bacteria based on light scattering. Multiple bacterial species adsorbed on the slide can be identified within a single field of view under a dark field microscope based on the color of the scattered light. Therefore, it is a useful development for safety risk assessments at manufacturing sites, such as those for foods, beverages, and drugs, and environmental surveys that require rapid detection of multiple bacteria.

Development of highly sensitive optical nanoantenna for bacterial detection.

Gold nanoparticles (AuNPs) are chemically stable and serve as excellent labels because their characteristic red coloration based on the localized surface plasmon resonance (LSPR) does not fade. However, it is necessary to control the structure of AuNPs to use them as labels for various analyses, because their optical properties depend strongly on their size, shape, and state of aggregation. In this study, we developed gold nanostructures (AuNSs) by encapsulating many small AuNPs within a polymer for scattering light-based bacterial detection. The AuNSs consisting of many small nanoparticles provided stronger scattered light intensity than a single AuNP of the same particle size. We found that the aggregation of the AuNSs enhanced the scattering light intensity, depending strongly on their aggregation states, and did not affect the wavelength of the scattering light observed under a dark-field microscope. By specifically binding the antibody-introduced AuNSs to the antigen on the bacterial surface, it was possible to label the target bacteria and detect them based on their light scattering characteristics. In addition, to improve the accuracy of the selective identification of the cells of interest, labels based on scattered light should ideally have a fixed wavelength of scattered light with high intensity. From these perspectives, we developed a method of constructing an optical antenna on the surface of target bacterial cells using antibody-introduced NSs.

Quantification of Enterohemorrhagic Escherichia coli via Optical Nanoantenna and Temperature-responsive Artificial Antibodies.

Enterohemorrhagic Escherichia coli are a dangerous bacterium known to be harmful to the human body, with some infections even resulting in death. Given this danger, food factories are required to perform a quick bacterial test to confirm the absence of this pathogen prior to shipping. We have developed a novel molecular imprinting polymer (MIP) particle that has encapsulated gold nanoparticles (AuNPs) and which can function as both a receptor and an optical signal transmitter in biological systems. This MIP particle is artificially synthesized and can be engineered to specifically recognize and capture antigens on the bacterial cell membrane. In addition, MIP particles containing AuNPs generate strong scattered light signals, and binding of the MIP particles improves the optical intensity of the target bacterial cells. This enables clear visualization under a dark-field microscope and quantification of the target bacteria using the scattering light intensity. Here we describe the successful quantification of Escherichia coli O157 cells in real meat samples using this technology in conjunction with a simple labelling step.

Total hydroxyl radical reactivity measurements in a suburban area during AQUAS-Tsukuba campaign in 2017.

Missing hydroxyl radical (OH) reactivity from unknown/unmeasured trace species empirically accounts for 10%-30% of total OH reactivity and may cause significant uncertainty regarding estimation of photochemical ozone production. Thus, it is essential to unveil the missing OH reactivity for developing an effective ozone mitigation strategy. In this study, we conducted simultaneous observations of total OH reactivity and 54 reactive trace species in a suburban area as part of the Air QUAlity Study (AQUAS)-Tsukuba campaign for the summer of 2017 to gain in-depth insight into total OH reactivity in an area that experienced relatively high contributions of secondary pollutants. The campaign identified on average 35.3% of missing OH reactivity among total OH reactivity (12.9 s-1). In general, ozone-production potential estimation categorized ozone formation in this area as volatile organic compound (VOC)-limited conditions, and missing OH reactivity may increase ozone production potential 40% on average if considered. Our results suggest the importance of photochemical processes of both AVOCs and BVOCs for the production of missing OH reactivity and that we may underestimate the importance of reducing precursors in approach to suppressing ozone production if we ignore the contribution of their photochemical products.

Aerosol Liquid Water Promotes the Formation of Water-Soluble Organic Nitrogen in Submicrometer Aerosols in a Suburban Forest.

Water-soluble organic nitrogen (WSON) affects the formation, chemical transformations, hygroscopicity, and acidity of organic aerosols as well as biogeochemical cycles of nitrogen. However, large uncertainties exist in the origins and formation processes of WSON. Submicrometer aerosol particles were collected at a suburban forest site in Tokyo in summer 2015 to investigate the relative impacts of anthropogenic and biogenic sources on WSON formations and their linkages with aerosol liquid water (ALW). The concentrations of WSON (ave. 225 ± 100 ngN m-3) and ALW exhibited peaks during nighttime, which showed a significant positive correlation, suggesting that ALW significantly contributed to WSON formation. Further, the thermodynamic predictions by ISORROPIA-II suggest that ALW was primarily driven by anthropogenic sulfate. Our analysis, including positive matrix factorization, suggests that aqueous-phase reactions of ammonium and reactive nitrogen with biogenic volatile organic compounds (VOCs) play a key role in WSON formation in submicrometer particles, which is particularly significant in nighttime, at the suburban forest site. The formation of WSON associated with biogenic VOCs and ALW was partly supported by the molecular characterization of WSON. The overall result suggests that ALW is an important driver for the formation of aerosol WSON through a combination of anthropogenic and biogenic sources.

Relative and Absolute Sensitivity Analysis on Ozone Production in Tsukuba, a City in Japan.

The change in the ozone production rate on reducing its precursors, namely, ozone production sensitivity, is important information for developing a strategy to reduce ozone. We expanded a conventional sensitivity analysis theory by including peroxy radical loss by uptake onto particle surfaces in the aim of examining their potential impact. We also propose a new concept of absolute sensitivity that enables us to evaluate the quantitative effectiveness of precursor reduction toward mitigating ozone production over a given period and area. This study applies the theory to observations in Tsukuba, a city in Japan. The relative sensitivity analysis shows that ozone production was more sensitive to volatile organic compounds (VOCs) in the morning and evening, and it became more sensitive to NOx in the afternoon. NO depletion was a main trigger in this sensitivity regime transition. The absolute sensitivity analysis indicates that the VOC-sensitive period in the morning determines the total ozone production sensitivity in a day. While particles did not have significant impact on regime classification in Tsukuba, they have a potential to decrease the mitigating effect of VOC reduction on ozone production and to moderate the enhancement effect of NOx reduction depending upon uptake coefficients. A further study will benefit from a combination with an observation-constrained box model simulation or chemical transport modeling system, which may provide sensitivity analysis over a large spatial and temporal range.

Validation of in situ Measurements of Atmospheric Nitrous Acid Using Incoherent Broadband Cavity-enhanced Absorption Spectroscopy.

Incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS) is a useful technique for measuring trace gaseous species in the atmosphere. Recently, IBBCEAS was used to measure concentrations of nitrous acid (HONO) in the troposphere to resolve controversies related to its formation and loss. Here, measurements of HONO and a mixture of HONO and NO2 using IBBCEAS were validated by comparing them with those obtained with a NOx analyzer. Good agreement was found between these methods, given their respective experimental uncertainties. The detection limit of our IBBCEAS instrument was 0.2 ppbv, with a signal-to-noise ratio of 1, and a 5-min integration time.

Contributions of vehicular emissions and secondary formation to nitrous acid concentrations in ambient urban air in Tokyo in the winter.

Nitrous acid (HONO) plays an important role in the formation of OH radicals, which are involved in photochemical oxidation. HONO concentrations in ambient air at urban sites have previously been measured, but very few studies have been performed in central Tokyo. In this study, HONO concentrations in ambient air in southeast central Tokyo (near Tokyo Bay) in winter were determined by incoherent cavity enhanced absorption spectroscopy. The O3, NO, NO2, and SO2 concentrations were simultaneously determined. The NO concentrations were used to classify the parts of the study period into types I (high pollution), II (medium pollution), and III (low pollution). The maximum HONO concentrations in the type I, II, and III periods were 7.1, 4.5, and 3.0ppbv, respectively. These concentrations were comparable to concentrations previously found in other Asian megacities. The mean HONO concentration varied diurnally, and HONO was depleted between 00:00 and 03:00 each day. The sampling site is surrounded by roads with high traffic loads, but vehicular emissions were estimated to contribute <10% of the HONO concentrations. Two positive and negative relative humidity dependences of the HONO to NO2 ratio were confirmed, implying the existence of the two different secondary formation process of HONO. The NO2 to HONO conversion rates at night in the type I, II, and III periods were 6.3×10-3, 7.6×10-3, and 4.2×10-3h-1, respectively.

New System for Measuring the Photochemical Ozone Production Rate in the Atmosphere.

We have developed a new system for measuring photochemical ozone production rates in the atmosphere. Specifically, the system measures the net photochemical oxidant (Ox: the sum of ozone (O3) and nitrogen dioxide (NO2)) production rates (P-L(Ox)). Measuring Ox avoids issues from perturbations to the photostationary states between nitrogen oxides (NOx) and O3. This system has "reaction" and "reference" chambers. Ambient air is introduced into both chambers, and Ox is photochemically produced in the reaction chamber and not generated in the reference chamber. Air from the chambers is alternately introduced into an NO-reaction (NO: nitric oxide) tube to convert O3 to NO2, and then the Ox concentration is measured as NO2 using a laser-induced fluorescence technique. P-L(Ox) was obtained by dividing the difference in Ox concentrations between air samples from the two chambers by the mean residence time of the air in the reaction chamber. In this study, the P-L(Ox) measurement system was characterized, and the current detection limit of P-L(Ox) was determined to be 0.54 ppbv h-1 with an integration time of 60 s (S/N = 2), assuming an ambient Ox concentration of 100 ppbv. Field measurements of P-L(Ox) were conducted using the system at a remote forest location.

Thermal dissociation cavity attenuated phase shift spectroscopy for continuous measurement of total peroxy and organic nitrates in the clean atmosphere.

A thermal dissociation cavity attenuated phase shift spectroscopy (TD-CAPS) instrument was developed for measuring total peroxy nitrates (PNs) and organic nitrates (ONs) concentrations in the clean atmosphere. This instrument is easy to operate and can be applied to continuous measurement of PNs and ONs. A continuously measurable system is convenient to perform observations, especially in remote areas. Three lines (NO2, PNs, and ONs lines) were used for thermal dissociation. The NO2 line contains a quartz tube that is not heated, while the PN and ON lines contain quartz tubes that are heated at 433 K and 633 K, respectively. The concentrations of NO2, NO2 + PNs, and NO2 + PNs + ONs can be obtained from the NO2, PN, and ON lines, respectively. The lower limit values of the detection limit (3σ) for PNs and ONs were estimated to be 21 parts per trillion by volume with an integration time of 2 min. PNs were selectively thermally decomposed in the PNs line and formed NO2 quantitatively. In the ONs line, both PNs and ONs were thermally decomposed to produce NO2 quantitatively, but partial decomposition of HNO3 at 633 K interfered with the ONs measurement. Therefore, a HNO3 scrubber is required before the ONs line. Continuous observations were conducted with the TD-CAPS instrument in a remote area, and the instrument performed well for obtaining PNs and ONs concentrations.

Direct measurement system of nitrogen dioxide in the atmosphere using a blue light-emitting diode induced fluorescence technique.

An instrument for measuring atmospheric nitrogen dioxide has been developed by a light-emitting diode induced fluorescence (LED-IF) technique. Air was introduced into a fluorescence detection cell. A pulsed blue light LED with a peak wavelength of 430 nm was irradiated to excite NO2 molecules in this cell. Fluorescence emitted from excited NO2 molecules was detected by a dynode-gated photomultiplier tube. The current detection limit of the LED-IF instrument was estimated to be 7.0 and 0.91 ppbv (parts per billion by volume) at 1-min and 1-h integration times, respectively, with a signal to noise ratio of 2. This result indicates that this LED-IF instrument can measure sufficiently precise 1-h values of NO2 concentrations in the urban atmosphere. An NO2 test observation and an intercomparison of the LED-IF instrument with an NO2 measurement system based on a photolytic converter/NO-O3 chemiluminescence method were performed in the urban atmosphere. Concentration differences between the two methods were within ±25% for about 90% of the data. It has been demonstrated by these observations that NO2 concentrations can be observed in the urban areas using the LED-IF instrument.

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.

Prediction of rate constants for the gas phase reactions of triphenylene with OH and NO3 radicals using a relative rate method in CCl4 liquid phase-system.

The kinetics of CCl(4) liquid-phase reactions of ten kinds of polycyclic aromatic compounds (PACs) including triphenylene (TP) with NO(3) radicals have been investigated at 273K by a relative rate method using naphthalene (NA) as a reference compound. The obtained relative reaction rates of the tested PACs to NA in CCl(4) were as follows: 2.57±0.24 (acenaphthene), 2.11±0.30 (2,3-dimethylnaphthalene), 1.21±0.13 (fluoranthene), 0.56±0.07 (fluorene), 1.85±0.19 (1-methylnaphthalene), 1.77±0.12 (2-methylnaphthalene), 0.11±0.03 (1-nitronaphthalene), 1.59±0.23 (phenanthrene), 2.40±0.29 (pyrene), 0.22±0.04 (TP). TP is a semi-volatile PAC with four aromatic rings and it is chemically changed into mutagenic 2-nitrotriphenylene (2-NTP) via the gas-phase OH or NO(3) radical-initiated reactions. On the basis of the relative reactivity of the PACs in the CCl(4) liquid phase-system, the rate constants of the gas-phase reactions of TP with OH and NO(3) radicals at 298 K were predicted to be (8.6±1.2)×10(-12) cm(3) molecule(-1) s(-1) and (6.6±1.5)×10(-29)[NO(2)] cm(3) molecule(-1) s(-1), respectively. Based on the ambient concentrations of TP and 2-NTP and the obtained rate constant for the reaction of TP with OH radicals, the atmospheric loss rate of 2-NTP was also evaluated.

Acceleration of ammonium nitrite denitrification by freezing: determination of activation energy from the temperature of maximum reaction rate.

A reaction of ammonium nitrite in ice was investigated. Upon freezing, some nitrite is oxidized by dissolved oxygen and some nitrite reacts with ammonium to produce nitrogen and water in a denitrification reaction. The former reaction was accelerated only during freezing, and the latter one was accelerated even after the whole sample was frozen. The denitrification reaction proceeded at very low concentration in ice, which were conditions under which the reaction would not proceed in solution. The nitrogen production increased linearly with increasing initial concentration of ammonium nitrite. The concentration factor in the unfrozen solution in ice was estimated to be 50.6 when the initial concentration was 0.5 mmol dm(-3), as obtained from comparison of reaction rates in solution and in ice. A new method for determination of the activation energy is proposed that gives a value of 53 to 61 kJ mol(-1) for denitrification. The reaction order of the denitrification process is also determined using our method, and it is concluded to follow third-order kinetics.

Development of a selective light-emitting diode photolytic NO(2) converter for continuously measuring NO(2) in the atmosphere.

A photolytic converter of nitrogen dioxide (NO(2)) to nitric oxide (NO) using light-emitting diodes (LEDs) has been designed to measure NO(2) in the troposphere. The typical electrical power consumption of the photolytic converter (PLC) is only 44 W. The maximum conversion efficiency of NO(2) to NO of the photolytic converter is around 90%, which is higher than that of metal halides or high-pressure Xe arc lamps (up to ∼70%). The conversion efficiency of the PLC was almost constant for at least 2.5 months. The conversion efficiency of peroxyacetyl nitrate by the LED-PLC was measured to be 2.6 ± 0.1% (1σ). The interference of HONO using the PLC was experimentally estimated to be less than 3%, which is within the uncertainty of the instrument. An intercomparison of NO(2) measurements between the PLC-CLD and the laser-induced fluorescence (LIF) technique was conducted, and the NO(2) concentrations measured by the PLC-CLD method were in agreement with those obtained by the LIF technique, within the uncertainties of the instruments. Continuous observations were made on Fukue Island, a remote area. These results demonstrate the performance of the PLC for continuous ambient measurements.