To determine the reaction rate coefficient of volatile organic compounds (VOCs) with ozone, the reduction of ozone through a flow-tube reactor was measured by a sensitive chemiluminescent detector. In this study, temperature dependence of the rate constant of ozone with linalool, k(T) = A exp(-B/T), was explored (T = 299-322 K). Consequently, temperature-dependent parameters A and B were experimentally determined as (1.6 +/- 0.4) x 10(-15) cm(3) molecule(-1) s(-1) and 396 +/- 26 K, respectively, for the first time. The rate constant of linalool + O-3 reaction varied by 10% with changes in temperatures from 299 to 322 K.

<p>To determine the reaction rate coefficient of volatile organic compounds (VOCs) with ozone, the reduction of ozone through a flow-tube reactor was measured by a sensitive chemiluminescent detector. In this study, temperature dependence of the rate constant of ozone with linalool, k(T) = A exp(−B/T), was explored (T = 299–322 K). Consequently, temperature-dependent parameters A and B were experimentally determined as (1.6 ± 0.4) × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹ and 396 ± 26 K, respectively, for the first time. The rate constant of linalool + O₃ reaction varied by 10% with changes in temperatures from 299 to 322 K.</p>

© 2016 The Chemical Society of Japan.To determine the reaction rate coefficient of volatile organic compounds (VOCs) with ozone, the reduction of ozone through a flow-tube reactor was measured by a sensitive chemiluminescent detector. In this study, temperature dependence of the rate constant of ozone with linalool, k(T) = A exp(?B/T), was explored (T = 299-322 K). Consequently, temperature-dependent parameters A and B were experimentally determined as (1.6 ± 0.4) × 10-15 cm3 molecule-1 s-1 and 396 ± 26 K, respectively, for the first time. The rate constant of linalool + O3 reaction varied by 10% with changes in temperatures from 299 to 322 K.

A new system that uses the total reactivity with ozone (R-O3) was developed for measuring biogenic volatile organic compounds (BVOCs) emitted from vegetation into the atmosphere. The decrease in ozone caused by the reaction with VOCs was monitored at the ppbv level by dual chemiluminescence detectors (CLDs) based on the NO-O-3 reaction. Ozone was monitored by the dual CLDs before and after the reactor to correct for fluctuations in the ozone concentration. Such dual detectors can remove the interference caused by water vapor. A glass double-tube was adopted as the reactor. The loss rate of ozone to the wall was typically (6 +/- 3) x 10(-4) s(-1). Gaseous cyclohexane was also added to the sample before it was introduced into the reactor to scavenge secondary OH radicals. From the characterization of the R-O3 analyzer using the standard VOC sample, the dependence of ozone reduction on the reaction time and reactivity were shown to agree with theoretical predictions. A calibration procedure for determining the reaction time was also established. Consequently, the detection limit for R-O3 in a 57-s reaction was determined to be 1.4 x 10(-4) s(-1) (S/N = 3), which corresponded to 27 ppbv of limonene. It was confirmed that the R-O3 analyzer was capable of measuring BVOC levels. Finally, a practical trial was conducted in which BVOCs emitted from a real needle-leaf tree were monitored. BVOC emissions from the tree were detected and a significant increase in R-O3 was observed when the tree was irradiated with light.

A new system that uses the total reactivity with ozone (RO3) was developed for measuring biogenic volatile organic compounds (BVOCs) emitted from vegetation into the atmosphere. The decrease in ozone caused by the reaction with VOCs was monitored at the ppbv level by dual chemiluminescence detectors (CLDs) based on the NO-O3 reaction. Ozone was monitored by the dual CLDs before and after the reactor to correct for fluctuations in the ozone concentration. Such dual detectors can remove the interference caused by water vapor. A glass double-tube was adopted as the reactor. The loss rate of ozone to the wall was typically (6 ± 3) × 10-4 s-1. Gaseous cyclohexane was also added to the sample before it was introduced into the reactor to scavenge secondary OH radicals. From the characterization of the RO3 analyzer using the standard VOC sample the dependence of ozone reduction on the reaction time and reactivity were shown to agree with theoretical predictions. A calibration procedure for determining the reaction time was also established. Consequently the detection limit for RO3 in a 57-s reaction was determined to be 1.4 × 10-4 s-1 (S/N = 3) which corresponded to 27 ppbv of limonene. It was confirmed that the RO3 analyzer was capable of measuring BVOC levels. Finally a practical trial was conducted in which BVOCs emitted from a real needle-leaf tree were monitored. BVOC emissions from the tree were detected and a significant increase in RO3 was observed when the tree was irradiated with light. © Taiwan Association for Aerosol Research.

Volatile organic compounds, VOCs, are emitted from various sources into the atmosphere. Through the reactions of VOCs with atmospheric radicals (eg. daytime OH and nighttime NO3) and all-day O3, the formation of secondary organic aerosols, SOA, is common and therefore an important subject of study. To investigate the mechanisms of reactions in the atmosphere and to control SOAs effectively, it is essential to capture the behavior of emitted VOCs with consideration of their radical reactivity.Meanwhile, organic nitrates (ONs) like alkyl nitrates (ANs) and peroxyalkyl nitrates (PNs) have been focused upon as important intermediates for SOA. To investigate the mechanisms of SOA formation from VOCs, it is essential to capture the behavior of intermediates such as ONs. In this manuscript, tools for measuring (1) total radical reactivity of VOCs and (2) total particulate organic nitrates were developed as applications for present NO2 analyzers.

N2O5 detection in the atmosphere has been accomplished using techniques which have been developed during the last decade. Most techniques use a heated inlet to thermally decompose N2O5 to NO3, which can be detected by either cavity based absorption at 662 nm or by laser-induced fluorescence. In summer 2007, a large set of instruments, which were capable of measuring NO3 mixing ratios, were simultaneously deployed in the atmosphere simulation chamber SAPHIR in Julich, Germany. Some of these instruments measured N2O5 mixing ratios either simultaneously or alternatively. Experiments focused on the investigation of potential interferences from, e. g., water vapour or aerosol and on the investigation of the oxidation of biogenic volatile organic compounds by NO3. The comparison of N2O5 mixing ratios shows an excellent agreement between measurements of instruments applying different techniques (3 cavity ring-down (CRDS) instruments, 2 laser-induced fluorescence (LIF) instruments). Datasets are highly correlated as indicated by the square of the linear correlation coefficients, R-2, which values were larger than 0.96 for the entire datasets. N2O5 mixing ratios well agree within the combined accuracy of measurements. Slopes of the linear regression range between 0.87 and 1.26 and intercepts are negligible. The most critical aspect of N2O5 measurements by cavity ring-down instruments is the determination of the inlet and filter transmission efficiency. Measurements here show that the N2O5 inlet transmission efficiency can decrease in the presence of high aerosol loads, and that frequent filter/inlet changing is necessary to quantitatively sample N2O5 in some environments. The analysis of data also demonstrates that a general correction for degrading filter transmission is not applicable for all conditions encountered during this campaign. Besides the effect of a gradual degradation of the inlet transmission efficiency aerosol exposure, no other interference for N2O5 measurements is found.

To determine the reaction rate coefficient of volatile organic compounds with ozone, the reduction of ozone through a flow-tube reactor was measured by a chemiluminescent detector. The validity of the method was confirmed by examination on isoprene. Consequently, the reaction rate coefficient of 2,5-dimethylfuran, DMF, with ozone was determined as (4.2 +/- 0.9) x 10(-16) cm(3) molecule(-1) s(-1) the first time. It was suggested that ozonolysis can be important for the fate of DMF in the atmosphere.

Exhaust emissions from a diesel vehicle were studied using FTIR, SMCA-REMPI, and SMPS. With these techniques, quantitative emission properties of NO, NO2, N2O, NH3, CO, CH4, C2H4, C3H6, HCHO, toluene, toluene + CH2, toluene + 2CH(2), beta-methylstyrene, naphthalene, 2-methylnaphthalene, phenanthrene, and o-cresol, as well as particle size distributions, were obtained in constant-speed operation at 0-80 km/h, which corresponds to a brake mean effective pressure (BMEP) of 0-293 kPa. NO emission increased as the in-cylinder temperature increased, corresponding to increased engine load. NO2 and N2O had a strong correlation to equivalence ratio. The emission characteristics of non-aromatic hydrocarbons depended on engine load. At low load, the emissions were high because low in-cylinder temperature and Exhaust Gas Recycling (EGR) prevented complete fuel oxidation. Equivalence ratio had a slight influence on the non-aromatic hydrocarbon emissions. The profiles of aromatic hydrocarbon exhibited two shapes. One was a toluene group and another was a styrene and naphthalene group. The shapes of the toluene group were similar to those of non-aromatic hydrocarbons. On the other hand, the styrene and naphthalene group emissions at idling were low, suggesting that they were not formed at low load. These features concerning the two groups of aromatic hydrocarbons were also observed in a transient driving cycle. Emission of accumulation mode particles was correlated with equivalence ratio. Higher emissions were observed when the equivalence ratio was higher, and the particle diameters also increased. Emission of nucleation mode particles increased as the engine load increased, because the amount of injected fuel per cycle increased. (C) 2010 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

A simultaneous multi-composition analyzing (SMCA) resonance enhanced multi-photon ionization (REMPI) system was used to investigate gasoline engine exhaust. Observed peaks for exhaust were smaller mass numbers than those from diesel exhaust. However, large species up to three ring aromatics were observed suggesting that soot precursor forms even in the gasoline engine. At low catalyst temperature condition, the reduction efficiencies of a three-way catalyst were higher for higher mass numbers. This result indicates that the larger species accumulate in the catalyst or elsewhere due to their lower vapor pressures. To evaluate the emission of low volatility species, the accumulation should be taken into account. In the hot mode, reduction efficiencies for aromatic species of three-way catalyst were almost 99.5% however, they fall to 70% in the cold start condition. © 2009 SAE International.

Time-resolved measurements of the concentration of volatile organic compounds (VOCs) and polycyclic aromatic hydrocarbons (PAHs) in exhaust from a diesel vehicle fitted with an oxidation catalyst and operated in JE05 mode are performed at a sensitivity of 10ppb using a supersonic jet/resonance enhanced multi-photon ionization (jet-REMPI) method. The concentrations of benzene, naphthalene, and phenol in exhaust from the test vehicle are measured before entering and after exiting from the oxidation catalyst. The total hydrocarbon (THC) is measured simultaneously using a constant volume sample (CVS) instrument fitted with a flame ionization detector (FID). Concentration changes of benzene, naphthalene and phenol are recorded at 1 s intervals and quantified using standard samples. Comparison of these signals with the real-time THC data shows that the time dependence of the individual species is almost the same as that of the THC before the oxidation catalyst but substantially different after.

A simple real-time measurement system for the components of volatile organic compounds (VOCs) and polyaromatic hydrocarbons (PAHs) in automobile exhaust gas using a laser ionization method was developed. This method was used to detect VOCs and PAHs in the exhaust gas of a diesel truck while idling, at 60 km/h, and in the Japanese driving mode JE05. As a result, various VOCs and PAHs, such as xylene and naphthalene, were simultaneously detected, and real-time changes in their concentration were obtained at 1 s intervals. Copyright © 2009 SAE International.

Real-time analysis of benzene in automobile exhaust gas was performed using the Jet-REMPI (supersonic jet / resonance enhanced multi-photon ionization) method. Real-time benzene concentration of two diesel trucks and one gasoline vehicle driving in Japanese driving modes were observed under ppm level at 1 s intervals. As a result, it became obvious that there were many differences in their emission tendencies, because of their car types, driving conditions, and catalyst conditions. In two diesel vehicle, benzene emission tendencies were opposite. And, in a gasoline vehicle, emission pattern were different between hot and cold conditions due to the catalyst conditions. Copyright © 2009 SAE International.

Internally mixed states of submicron particles during transport from the Asian continent to the Pacific Ocean were analyzed using a single-particle time-offlight mass spectrometer. The observation was conducted at Tsukuba in Japan in the spring of 2005 in order to investigate springtime transport of particles from the continent. The sum of ion intensities of sulfate (HSO4 -) detected in particles originating from the continental air masses counted for 75% of that in all particles during the observation. By analyzing correlations among compounds, origins and internally mixed states of compounds were estimated. It was found that nitrate was mixed with sulfate-rich particles as the air mass approached Japan. It was confirmed that Asian mineral dust particles played significant roles for transport of continental sulfate to Japan. As a result of analysis on internal mixing of chlorine and nitrate, it was implied that the chlorine loss in fine sea salt particles had already proceeded at Tsukuba. It was characteristic that fluoride ions were significantly detected, coal combustion in the Asian Continent can be an important source of fluorides detected in Japan through the westward transportation of fine particles including fluorides.

A sensitive, real-time, and molecular-selective analyzer using a resonance-enhanced multiphoton ionization/time-of-flight mass spectrometer (REMPI-TOFMS) was combined with the chamber method to measure emission factors of VOCs during painting. Temporal variation of VOC emission was successfully captured on site on a second time scale. Exact and detailed assessment of emission is realized with molecular-dependent characteristics considered.

The electronic spectrum of benzo[e]pyrene (BeP) was recorded using resonance-enhanced multi-photon ionization (REMPI) spectroscopy. A number of bands were observed and assigned to the origin band and vibronic bands of the S-1-S-0 transition. Ab initio calculations were performed to assign the vibrational structures in S-1. The origin band of BeP is well separated in energy from the origin band of benzo[a]pyrene (BaP), an isomer of BeP, and so BeP and BaP can be readily distinguished by the REMPI method, despite having the same mass.

In this study, we propose a new principle for measuring atmospheric NO using a laser-induced fluorescence (LIF) NO2 detector. NO is chemically converted into NO2; then, NO2 is detected by the LIF technique. To convert NO into NO2, ozone is added to sample air. Since there exists tin-reacted NO and loss of NO2 due to further reaction of NO2 with ozone depending on both the concentration of ozone and reaction time, the enhanced NO-concentration is less than the initial NO concentration. Using chemical kinetic analysis, we successfully derive the relationship between NO concentration and LIF signals. We also Propose a unique calibration method for an LIF NO2 detector without using a chemiluminescent NOx analyzer; this method is based on the gas phase titration technique. The limits of the detection of the developed instrument for NO2 and NO measurements are 14 ppt and 22 ppt, respectively. We perform ambient air measurements in a suburb of Tokyo using the developed LIF NO analyzer and a commercial chemiluminescent NO analyzer. A comparison of the measurement results reveals that they are in excellent agreement, with slope of 0.99 and a Correlation coefficient of 0.99. (C) 2008 Elsevier Ltd. All rights reserved

Real-time analysis of secondary organic aerosol (SOA) particles formed from 1,4-cyclohexadiene (CHD) ozonolysis in a smog chamber was performed using a laser-ionization single-particle aerosol mass spectrometer (LISPA-MS). The instrument can be used to obtain both the size and chemical compositions of individual aerosol particles with a high time-resolution (approximate to 2 s at the maximum). Both positive- and negative-ion mass spectra can be obtained by changing the voltage polarity of the instrument. The negative-ion spectra of the SOA particles provided important information about the chemical compositions of the SOA particles. In the negative-ion spectra, intense mass peaks were determined to correspond to ions with carboxyl and aldehyde groups. The signal intensities of the intense mass peaks from compounds with carboxyl groups were higher than those from compounds with aldehyde groups as a function of the particle size. The peaks suggest that the SOA particles contain more oxygenated organic compounds as the particle size increases, namely, the chemical compositions of the SOA particles vary as a function of the particle size. We demonstrated that the real-time single-particle analysis of SOA particles by using the LISPA-MS technique can be used to clarify the formation and transformation processes of SOA particles in smog chambers.

Supersonic jet/resonance enhanced multi-photon ionization (Jet-REMPI) technique was focused on the analyzing method for gas mixture like exhaust gas from automobiles. In this method, when the mass number and wavelength of excitation laser are determined adequately, the target compound can be monitored selectively. We developed a new analyzer utilizing REMPI method. Using this analyzer, real-time monitoring of exhaust gas from a motorcycle and diesel vehicles was conducted. As a result of real-time monitoring test of the vehicles, concentrations of aromatic compounds like benzene toluene etc. were quantified and real-time changes of their concentrations were observed. © 2007 SAE International.

A real-time analysis of secondary organic aerosol (SOA) particles formed from cyclohexene ozonolysis in a smog chamber was performed using a laser-ionization single-particle aerosol mass spectrometer (LISPA-MS). The instrument obtains both size and chemical compositions of individual aerosol particles with a high time-resolution (similar to 2 s at the maximum). Both positive and negative-ion mass spectra are obtained. Standard particles generated from dicarboxylic acid solutions using an atomizer were also analyzed. For both standard and SOA particles, the negative-ion mass spectra provided information about the molecular weights of the organic compounds in the particles, since the intense ions in the negative-ion mass spectra are mainly attributable to the molecular-related ions [M-H](-). It was demonstrated that the realtime single-particle analysis of SOA particles by the LISPA-MS technique can reveal the formation and transformation processes of SOA particle in smog chambers.

The presence of iodine chemistry, hypothesized due to the overprediction of HO2 levels by a photochemical box model at Rishiri Island in June 2000, was quantitatively tested against the observed NO/NO2 ratios and the net production rates of ozone. The observed NO/NO2 ratios were reproduced reasonably well by considering the conversion of NO to NO2 by IO, whose amount was calculated so as to reproduce the observed HO2 levels. However, the net production rates of ozone were calculated to be negative when such high mixing ratios of IO were considered, which was inconsistent with the observed buildup of ozone during daytime. These results suggest that iodine chemistry may not be the sole mechanism for the reduced mixing ratios Of HO2, or that "hot spots" for iodine chemistry were present. Diurnal variations in the mixing ratios of HCHO, CH3CHO, peroxy acetyl nitrate (PAN) and HNO3 observed during the study are presented along with the simulated ones. The box model simulations suggest that the effect of iodine chemistry on these concentrations is small and that important sources of CH3CHO and sinks of PAN are probably missing from our current understanding of the tropospheric chemistry mechanism. (c) 2007 Elsevier B.V. All rights reserved.

Total OH reactivity was observed by use of the laser-induced pump and probe technique, and the urban air quality in Tokyo was diagnosed comprehensively. The concentrations of NO,, CO, 03, non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) were observed simultaneously. The observations were conducted in July and August 2003, and in January, February, May, and November 2004. Generally, the observed OH reactivity was higher than the calculated values derived using the observed concentrations of the trace species. The differences between the observed and calculated values in summer, spring, and autumn were approximately 30%. However, the difference in winter was smaller than those in the other seasons. In addition, while the differences observed in summer, spring, and autumn correlated with the total reactivity of the OVOCs (Sigma(i) k(OVOCi)[OVOCi](s(-1)), k(i) is rate constant of its compounds with OH), the correlations were not confirmed in the case of winter because atmospheric oxidation was less active and OVOCs levels were low in winter. These results suggest that the secondary products of the photochemical reactions in the atmosphere would be a missing sink for the OH loss process in the urban area. (c) 2006 Elsevier Ltd. All rights reserved.

To understand the nocturnal sink of NOx in the outflow from the Asian source area, simultaneous observations of NO3, N2O5, and related compounds were conducted utilizing an instrument based on laser-induced fluorescence at Izu-Oshima Island, Japan, during June 2004. Consequently, significant levels of NO3 and N2O5 were successfully observed, particularly in the polluted air mass originating from Tokyo. This observation concurred with the equilibrium among NO3, NO2, and N2O5 gases. As a result of steady-state analysis, nocturnal NO, losses were evaluated as 1.8 and 0.2 ppbv night(-1) for polluted and maritime air, respectively. It was confirmed that the nocturnal NOx sink during the observation was promoted by the NO3 loss by VOC. DMS is significant for nocturnal loss of NOx over the sea. (c) 2006 Elsevier Ltd. All rights reserved.

To investigate the photostationary state (PSS) of nitrogen oxides (NO,), fast and precise measurements of related compounds were simultaneously carried out in the urban atmosphere. A PSS parameter phi including the observed peroxy radical (ROx) was examined. Consequently, phi was not significantly different from unity in many cases. Observed NOx, O-3, J(NO2) and ROx could reasonably elucidate the PSS of NO,. Meanwhile, in some cases with large ROx/O-3, phi was significantly less than unity. It was suggested that the reaction rate coefficients of ROx with NO could be critical for the PSS in the urban atmosphere. It was confirmed that the LIF instrument is promising to observationally approach the PSS of NOx. (c) 2006 Elsevier Ltd. All rights reserved.

Uptakes of sulfate and nitrate onto Asian dust particles during transport from the Asian continent to the Pacific Ocean were analyzed by using a single-particle time-of-flight mass spectrometer. Observation was conducted at Tsukuba in Japan in the springtime of 2004. Sulfate-rich dust particles made their largest contribution during the 'dust event' in the middle of April 2004. As a result of detailed analysis including backward trajectory calculations, it was confirmed that sulfate components originating from coal combustion in the continent were internally mixed with dust particles. Even in the downstream of the outflow far from the continental coastline, significant contribution of Asian dust to sulfate was observed. Asian dust plays critical roles as the carrier of sulfate over the Pacific Ocean.

The laser-induced fluorescence (LIF) detector with a thermal converter has been developed for measuring atmospheric N2O5. The detection limit for N2O5 was 11 pptv for 10-min averaging (S/N = 2, [NO2] = 0). The field measurements of N2O5 were conducted in the urban atmosphere in winter. N2O5 was successfully monitored during four nights. Typically, observed N2O5 level was in the range of 0-200 pptv. Note that N2O5 reached 800 pptv at one night, when NOx level was extremely high and the temperature was low. After the data were selected by the stability of NOx, N2O5 chemistry was discussed for a representative case of the urban night. Observed trend of N2O5 was compared with the theoretically predicted one. The heterogeneous loss rate of N2O5 on the aerosol surfaces was estimated as 5.2 x 10(-4) s(-1). Consequently, it was confirmed that N2O5 loss was critical for NO., budget in the urban atmosphere in winter, in comparison with NOx loss via NO3. The LIF instrument proved to be useful for studying nocturnal chemistry of N2O5 in the source region. (c) 2005 Elsevier Ltd. All rights reserved.

Preparation of standard NO3 gas is explored at the level of ppbv for atmospheric measurements utilizing an LIF instrument. The sequence of thermal decomposition of N2O5 and gas phase titration of NO3 by adding NO is useful. To reduce NO2 contamination in N2O5, N2O5 trapping after mixing NOx and O-3 was adopted. As a convenient method in the field studies, dynamic mixing NOx and O-3 was explored.

An instrument for measuring atmospheric nitrate radical (NO3) and dinitrogen pentoxide (N2O5) has been developed by a thermal conversion/laser-induced fluorescence (TC/LIF) technique. N2O5 is thermally decomposed and converted to NO3, which is measured by laser-induced fluorescence. In situ, fast-response, sensitive measurement of NO3/N2O5 is expected by use of LIF. In detecting NO3, dual-wavelength excitation at 622.96 and 618.81 nm was adopted to remove potential interference and to guarantee high selectivity. A high-power dye laser system was used as the source of excitation light. To measure ambient air directly, the NO3 detection cell was placed on the rooftop. The laser beam was guided by an optical fiber into the excitation cell. Transmittance of the laser beam was 80% for a 10 m long fiber. To calibrate the instrument, the series of thermal decomposition of N2O5 and the gas phase titration of NO3 by NO were conducted. NO3 reduction by adding NO was also applied to determine accurately the zero points of the detector. After optimization of conditions such as gate timing in photon counting and the settings of the N2O5 converter, the present detection limits of NO3 and N2O5 were determined to be 4 and 6 pptv, respectively, for the integration time of 10 min (signal-to-noise ratio=1). It was confirmed that the interference of NO2 on N2O5 detection is negligible, but can be significant for NO3 measurement when NO2 concentration is extremely high (&gt; 100 ppbv). Measurement of N2O5 in ambient air was made in the urban area of Tokyo, Japan. Observed data demonstrated the capacity of the TC/LIF instrument with a powerful dye laser and a single-path excitation cell for ambient measurements. In this article, we focus on the instrumentation and characterization. (c) 2005 American Institute of Physics.

Total OH reactivity was measured in the suburban area, Tokyo, in July and August 2003, by use of a laser-induced pump and probe technique. More than 90% of the measured data of the OH loss rates were higher than the calculated values with simultaneously measured concentrations of various trace species. The maximum difference between the measured and calculated values is 34.3%. However, this difference was reduced to be 24.6% when using the rate coefficient of the OH + NO2 reaction recommended by IUPAC 1997, which is 40% larger than the most recently recommended value (JPL 2002). We concluded that this disagreement is due to the uncertainty of the OH + NO2 rate coefficient as well as existence of unmeasured VOCs. VOCs were quantitatively important as contribution to the OH loss processes.

An instrument for measuring atmospheric peroxy radicals has been developed by chemical amplification/laser-induced fluorescence (PERCA/LIF) technique. The small concentration of peroxy radicals is converted to the large amount of NO2, which is measured by laser-induced fluorescence instead of luminol chemiluminescence. Several advantages, that is, high sensitivity, high selectively, and fast time response, are expected by use of LIF for the NO2 measurement, in comparison with luminol chemiluminescence. When using this system, simultaneous measurements of NO2 and peroxy radicals are available. The present optimum condition for the reaction tube (1/4 in. Teflon) was determined to be the reaction tube length of 3 m, the NO and CO concentrations of 3 ppmv and 10%, respectively. The calibration, including humidity dependence of the detection sensitivity of peroxy radicals, was conducted and the present detection limit of peroxy radicals was determined to be 2.7 and 3.6 pptv at the ambient relative humidity of 50 and 80%, respectively, for the integration time of 1 min (S/N=2). This detection limit was calculated assuming the ambient O-3 and NO2 mixing ratios of 30 and 20 ppbv, respectively. The influence of the NO2 detection sensitivity by adding high concentrations of CO was investigated and the quenching of excited NO2 by CO can affect the ambient measurement significantly under the high NO2 and low peroxy radical concentrations. Exploratory ambient air measurements were made in suburban area of Osaka, Japan. These results demonstrated the performance of PERCA/LIF for ambient measurements. (C) 2004 American Institute of Physics.

An airborne instrument for in situ measurements of tropospheric nitrogen dioxide (NO2) was developed using the photolytic conversion technique followed by chemiluminescence detection of NO. This instrument was used for the measurements of NO2 on board the NASA P-3B aircraft during the Transport and Chemical Evolution Over the Pacific (TRACE-P) campaign. Comparison in the laboratory indicated less than 10% difference between our NO2 instrument and two independent laser-induced fluorescence instruments in the NO2 range of 30 parts per trillion by volume (pptv) to 50 ppbv. The magnitudes of potential errors in airborne tropospheric NO2 measurements were further assessed using the TRACE-P data set. The systematic errors estimated for the median NO2 mixing ratios, 70 pptv at 0-2 km (30 pptv at 2-8 km), were 19% (39%). The random errors for a 10 s integration time were estimated to be 5-10%, depending on altitude. The observed NO2 mixing ratios were compared to those calculated by a photochemical box model. Overall, the calculated NO2 values correlated very well with those observed (r(2)=0.97), although the calculations were systematically higher than the observations by about 30%, except for the highest flight levels. The calculated/observed NO2 ratio remained nearly constant, having values close to 1.3 at 0-4 km, and decreased with altitude. The difference between the observed and model-calculated values, however, was within the combined uncertainty in the measurement and model calculation. The underlying causes for this difference are to be determined in future studies.

A compact, fast-response instrument for measuring atmospheric NO2 by single-wavelength excitation laser-induced fluorescence (LIF) technique was improved. A single-pass alignment of a more powerful, pulsed laser was utilized to realize the pptv (= 10(-12) by volume) of the limit of detection (LOD). As a result, the LOD reached 1.8 pptv for 1-min averaging (SIN = 1). To determine the instrumental zero accurately, interference by particles was cancelled out utilizing an NO2 scrubber tube coated with a mixture of titanium dioxide (TiO2) and hydroxyapatite. Consequently, it was confirmed that the combination of the improved single-wavelength LIF instrument with the scrubber was reasonable for measuring atmospheric NO2. (C) 2003 Elsevier Ltd. All rights reserved.

In this review article, recent understandings of the urban atmosphere are briefly presented, focusing on NO, (NO and NO2), NO3 and HOx (OH and HO2), which are the key species for photochemical ozone production in the urban air. For NOx chemistry, relationship between NOx and HOx, and photostationary state (PSS) of the conversion between NO and NO2 are introduced with examples of recent research. Chemistry of nitrate radicals in the nighttime is also introduced. In addition, recent and representative techniques for the measurements of reactive nitrogen species in the troposphere are presented. As for HOx radicals, important formation and loss processes and measurement methods developed recently are introduced. Recent campaign-based observations of HOx radicals in the troposphere are also presented. (C) 2003 Japanese Photochemistry Association. Published by Elsevier Science B.V. All rights reserved.

Measurements of oxidized nitrogen species, including peroxyacetyl nitrate (PAN), nitrogen oxides (NOx), nitric acid (HNO3), and nonmethane hydrocarbons (NMHCs), were made along with ozone (O-3) and carbon monoxide (CO) at Rishiri Island, a remote island in northern Japan, as part of the Rishiri Island Study of Oxidants and Transport for Tropospheric Ozone (RISOTTO). Full seasonal observations of O-3, CO, NMHCs, and PAN, together with data sets of NOx, and HNO3 for 6 months reveal short-term and seasonal characteristics of chemistry of the air masses in northeast Asia. Temporal variations of O-3, PAN, and HNO3 typically show day-to-day variations in winter and diurnal variations in summer, dominated by long-range transport and local photochemistry, respectively. Seasonal variations of O-3 and PAN show a spring maximum and a summer minimum, which are consistent with previous field observations made in Europe and North America. Air mass segregation based on back trajectory calculation suggests that PAN, which is photochemically produced in continental source regions, is most effectively transported to remote sites in spring owing to low temperatures in this season, while HNO3 is not effectively transported due to its high deposition velocity. It is concluded that transport of polluted air masses from continental source regions considerably enhances the April maximum in O-3 and PAN observed at remote sites in northeast Asia. Back trajectory analysis also indicates that the seasonal cycles of PAN in the Eurasian continental background air masses are maximum in spring, minimum in summer, and show a secondary maximum in fall in contrast to NOx and HNO3 which have a summer maximum and a winter minimum.

HO2 radical concentrations were measured by a laser-induced fluorescence instrument for three nighttime periods during the intensive field campaign at Rishiri Island, Japan, in June 2000. The HO2 mixing ratio had temporal variations around its average of 4.2 +/- 1.2 (1 sigma) pptv and showed a positive correlation with the summed mixing ratio of four monoterpene species, alpha-pinene, beta-pinene, camphene, and limonene, that sometimes reached 1 ppbv. Our model calculations suggested that ozonolysis reactions of monoterpenes were the main source of nighttime radicals and they explained 58% of measured HO2 concentration levels. The model roughly reproduced the dependence of the HO2 mixing ratio on the square root of the radical production rate due to the ozonolysis reactions of the monoterpenes. However, the absolute HO2 mixing ratio was significantly underpredicted by the model. We discuss possible reasons in terms of misunderstood RO2 chemistry, RO2 interference with HO2 observations, unknown radical production process associated by high NO2 mixing ratio, and the contribution of unmeasured olefinic species to radical production via their reactions with ozone. (C) 2002 Elsevier Science Ltd. All rights reserved.

[1] During the Observations at a Remote Island of Okinawa (ORION99) field campaign, HO2 radical and NOx concentrations were simultaneously measured with other important parameters relevant to photochemistry. The observed HO2 concentration levels, the relationship between HO2 and NOx, and the balance between NO and NO2 were well reproduced by model calculations based on the current photochemistry theory, indicating that the photochemistry taking place at the island was understandable within known chemistry. Thus the photochemical ozone production rate estimated from the calculated peroxy radical concentrations would be reliable. The isoprene peroxy radical + NO reaction contributed to ozone production by the similar degree to the HO2 + NO reaction because of high isoprene concentrations at ground level. The net ozone production rate during daytime was calculated to be +0.2-3.4 ppbv h(-1) due to moderate NO concentrations (36-244 parts per trillion by volume (pptv)) there which were higher than the NO compensation point of 30 pptv. Sensitivity studies showed that the ozone production rate was calculated within NOx-limited regime. Thus the ozone production rate would be relatively uniform throughout the boundary layer even if isoprene concentration had a steep vertical gradient. Up to 20 ppbv of ozone would be photochemically produced in a day, suggesting that clear diurnal variations of ozone with daytime buildup of 16 ppbv observed for the air mass traveled over the island in 1996 could be explained by photochemistry.

[1] The observed midday maximum in the mixing ratio of HO2 at Rishiri Island in June 2000 was similar to10 pptv, but photochemical box model simulations overpredicted HO2 at this location by an average of 70%. This overestimation was significant only when the mixing ratio of NO was lower than 300 pptv, and was coincident with overprediction of the NO/NO2 ratio. We detected several organoiodines, presumably emitted from seaweeds, and propose the presence of the IO radical. IO could reduce HO2 mixing ratios via the formation of HOI that may subsequently be scavenged by aerosols or lost by photolysis and may also convert NO to NO2 directly. Model calculations with known iodine chemistry could reproduce the observed HO2 with 12-25 pptv of IO. Although iodine chemistry is unlikely to explain the entire discrepancy in HO2, several pptv of IO could significantly reduce HO2 mixing ratios and NO/NO2 ratios.

The OH and HO2 concentrations observed during the Observations at a Remote Island of Okinawa intensive field campaign (ORION99) were compared with those calculated by using the ancillary observations as input parameters. Detailed comparisons were performed for HO2 with the time resolution of 10 min. During daytime, the observed HO2 concentration levels and variations were basically well reproduced by the model calculations without including heterogeneous processes. On average, the model underestimated daytime HO2 by only 20%. The squared correlation coefficient between observed and calculated HO2 was 0.79. The model underestimated HO2 significantly during a morning period with high NO, concentrations by up to a factor of 3 and for sudden surges observed during noontime on two days by a factor of 1.5. The basically good agreement between measured and calculated HO2 at Okinawa Island was in contrast with the significant model's overestimation of midday HO2 by a factor of 2 at Oki Island. The causes for the difference are discussed. For OH, detailed comparisons were not possible owing to the large uncertainties of measurements and calculations. However, diurnal patterns of OH on several days calculated by a simple steady state model were similar to those observed, indicating the observed OH data were statistically significant when they were averaged hourly. During, one night, HO2 concentrations were observed to be 2-5 pptv, positively correlating with NO2. The model significantly underestimated HO2 by up to a factor of 4 and did not reproduce the positive correlation. Currently, no explanations can be given for the nocturnal behaviors.

A simple and compact instrument for NO2 measurement by laser-induced fluorescence (LIF) technique with a pulsed solid state laser and a multi-pass excitation system was developed and optimized for several conditions. As a result of laboratory experiment, the limit of detection (LOD) reached 94 pptv for 60 s integration. It was thought that an LIF instrument with this LOD value would be capable of quantifying sub-ppbv NO2 in unpolluted marine atmosphere. As the second step, a field test of the instrument was conducted in the marine atmosphere at Cape Hedo, Okinawa Island, Japan, in summer 1999, Intercomparison between the LIF instrument and a chemiluminescence detector with a photolytic converter (PLC-CL) was also made in this test. Consequently, the LIF instrument was shown to be of practical use for measuring NO2 in clean maritime air. (C) 2001 Elsevier Science Ltd. All rights reserved.

The daytime variation of hydroperoxy (HO2) radical concentration was observed by an instrument based on laser-induced fluorescence with NO addition at Oki Island, Japan, in July/August 1998. Although OH was not detected due to the high detection limit of the instrument, HO2 was determined with the detection limit of 0.8 parts per trillion by volume (pptv) (S/N=2, integration time of 1 min). On average, HO2 showed a maximum concentration of around 9 pptv in the early afternoon hours. During the field campaign, chemical species and meteorological parameters such as O-3, CO, nonmethane hydrocarbons(C-2-C-6), NO/NO2, HCHO/CH3CHO, SO2 HNO3 and J(NO2) were also observed. Unfortunately, the absolute value of J((OD)-D-1) was not measured. Model calculations for radical concentrations were performed and they were compared to the observed hourly HO2 concentrations. On August 9 the calculated HO2 matched the observation very well within the uncertainties of observations (+/-26%, 1 sigma) and the model (+/-24%, 1 sigma). This indicates a good performance of model calculations in estimating HO2 under certain conditions with plenty of isoprene. On other days, however, model usually overestimated HO2 by a factor of 2, especially in the hours around noon. It is deduced that some important HOx loss chemistry is missing in the model, Although the cause of the discrepancy is not fully understood, possible mechanisms to explain the overestimation are studied. A hypothesis with additional loss of HO2 would be more plausible than that with additional OH loss. The additional loss rate for HO2 that can reduce the calculated HO2 to the measured level was computed for each hour. Its variation correlated well with those of H2O and some photochemical products. The possibilities of HO2 loss on aerosol surface, unknown acceleration of HO2 reactions in the presence of high H2O and HO2 reactions with carbonyl species are discussed.

HO2 (hydroperoxy) radical of unexpectedly high concentration around 3 ppt was measured by an instrument based on laser-induced fluorescence with NO addition at Oki island, Japan, on the night of August 9/10, 1998. We confirmed that the interference by atmospheric organic peroxy (RO2) radicals was insignificant and concluded that the measured signal originated from nighttime HO2. Model calculations constrained to ancillary measurements indicated that HO2 and RO2 were produced primarily via the reactions of ozone with olefins, especially those with internal olefins, and that NO3 chemistry was relatively unimportant. HO2 concentration was kept high by nighttime NO (similar to 10 ppt) via RO2 + NO reactions. Low NO2 (similar to 150 ppt) slowed NO3 production rate. Thus, the high observed HO2 suggests that the reactions of O-3 With olefins are important HOx primary production mechanisms in the relatively clean atmosphere.

Continuous measurement of CO has been carried out at remote sites in Japan, Oki (36°N), Happo (36°N) and Benoki (27°N). Seasonal variation at each site exhibited a clear cycle with a maximum in spring and a minimum in summer. It has been revealed that the concentrations of CO at Oki are substantially higher than at Mace Head throughout a year. Comparison of trajectory-categorized data between Oki and Mace Head has been made to elucidate that the concentration at Oki is higher than Mace Head both in the clean "background" and in the regionally polluted air mass. The spring maximum at Oki occurs in April that is one month later than the reported data at other remote sites in the northern hemisphere. © 1999 Elsevier Science Ltd. All rights reserved.

Optical absorption spectra of cobalt cluster ions, Co-n(+), and vanadium cluster ions, V-n(+), were analyzed by a theoretical calculation based on the spin-polarized DV-X alpha method, and their electronic and geometric structures were obtained, Relative absorption cross section associated with each electronic transition was calculated; the calculation enables a qualitative comparison of calculated spectrum with a measured one not only in its transition energy but also in Irs intensity profile. This analysis shows that Co-4(+), Co-3(+), and V-4(+) have, respectively, a tetrahedral structure with a bond distance of 2.00 Angstrom, an equilateral triangle with a bond distance of 2.30 Angstrom, and a distorted tetrahedral structure with five bonds having a distance of 2.34 Angstrom and one of 2.89 Angstrom. The differences in the population between majority and minority spins (spin-difference) evaluated from the electronic structure thus obtained were 2.0, 1.7, and zero per atom in Co-3(+), Co-4(+) and V-4(+), respectively. These spin differences indicate care a ferromagnetic and an antiferromagnetic spin-coupling in the cobalt and vanadium cluster ions, respectively.

The OH and HO2 concentrations observed during the Observations at a Remote Island of Okinawa intensive field campaign (ORION99) were compared with those calculated by using the ancillary observations as input parameters. Detailed comparisons were performed for HO2 with the time resolution of 10 min. During daytime, the observed HO2 concentration levels and variations were basically well reproduced by the model calculations without including heterogeneous processes. On average, the model underestimated daytime HO2 by only 20%. The squared correlation coefficient between observed and calculated HO2 was 0.79. The model underestimated HO2 significantly during a morning period with high NOx concentrations by up to a factor of 3 and for sudden surges observed during noontime on two days by a factor of 1.5. The basically good agreement between measured and calculated HO2 at Okinawa Island was in contrast with the significant model's overestimation of midday HO2 by a factor of 2 at Oki Island. The causes for the difference are discussed. For OH, detailed comparisons were not possible owing to the large uncertainties of measurements and calculations. However, diurnal patterns of OH on several days calculated by a simple steady state model were similar to those observed, indicating the observed OH data were statistically significant when they were averaged hourly. During one night, HO2 concentrations were observed to be 2-5 pptv, positively correlating with NO2. The model significantly underestimated HO2 by up to a factor of 4 and did not reproduce the positive correlation. Currently, no explanations can be given for the nocturnal behaviors. Copyright 2001 by the American Geophysical Union.

The daytime variation of hydroperoxy (HO2) radical concentration was observed by an instrument based on laser-induced fluorescence with NO addition at Oki Island, Japan, in July/August 1998. Although OH was not detected due to the high detection limit of the instrument, HO2 was determined with the detection limit of 0.8 parts per trillion by volume (pptv) (S/N=2, integration time of 1 min). On average, HO2 showed a maximum concentration of around 9 pptv in the early afternoon hours. During the field campaign, chemical species and meteorological parameters such as O3, CO, nonmethane hydrocarbons(C2-C6), NO/NO2, HCHO/CH3CHO, SO2, HNO3 and J(NO2) were also observed. Unfortunately, the absolute value of J(O1D) was not measured. Model calculations for radical concentrations were performed and they were compared to the observed hourly HO2 concentrations. On August 9 the calculated HO2 matched the observation very well within the uncertainties of observations (± 26%, 1σ) and the model (± 24%, 1σ). This indicates a good performance of model calculations in estimating HO2 under certain conditions with plenty of isoprene. On other days, however, model usually overestimated HO2 by a factor of 2, especially in the hours around noon. It is deduced that some important HOx loss chemistry is missing in the model. Although the cause of the discrepancy is not fully understood, possible mechanisms to explain the overestimation are studied. A hypothesis with additional loss of HO2 would be more plausible than that with additional OH loss. The additional loss rate for HO2 that can reduce the calculated HO2 to the measured level was computed for each hour. Its variation correlated well with those of H2O and some photochemical products. The possibilities of HO2 loss on aerosol surface, unknown acceleration of HO2 reactions in the presence of high H2O, and HO2 reactions with carbonyl species are discussed. Copyright 2000 by the American Geophysical Union.

大気汚染物質の環境影響を知るには、発生源周辺での多地点同時実時間分析や多成分同時実時間分析が重要となる。本研究では、1台のレーザー誘起蛍光法LIF-NO_2計を最大限に活用し、多地点または多成分(NO_2, NO, O_3,オゾン反応性等)の同時実時間分析を実現した。特に、発生源試料や都市大気試料について多成分同時分析を試みた結果、「ポテンシャルオゾン」に対する発生源の寄与を短時間で調べる新手法の確立に成功した

多様な揮発性有機化合物VOCを前駆体とする大気中での二次粒子生成を把握するには、VOCのラジカル反応性評価が有効である、本研究では、LIF-NO2計やCLD-NO計を活用したOH,O3反応性計測法を新たに実現する。前年度に、LIF-NO2計およびCLD-NO計を活用したOH,O3各反応性の測定試験を試み、シクロヘキサン標準ガスのOH反応性の定性分析と、スチレン標準ガスのO3反応性計測に成功した。本年度は以下の研究を実施した1)LIF-NO2計を活用したOH反応性計測での定量分析を目指した。上述の競争反応-LIF法によるOH反応性測定では、定量性に難があったため、VOCの有/無に対するNO2の相対的変化と反応性の関係をトルエン標準試料にて校正する手順に変更した結果、発生源レベルでのOH反応性の定量に成功した。さらに、実試料への応用として、塗料蒸気のOH反応性測定に成功し、本手法の実用性を確認した。2)CLD-NO計を活用し、VOC干渉を受けないCLD-O3計を新たに構築し、VOC有/無によるO3変化を直接実時間測定した。反応時間可変のガラス二重管フローチューブを新たに構築し、反応時間および反応性に対するO3の応答を調べた。その結果、二次ラジカルを生成する成分も含め、O3反応性の定量に初めて成功した。装置最適化の結果、ppbvレベルのVOC試料の秒単位での実時間分析を実現した。実試料への応用として、植物放出BVOCのO3反応性実時間測定に初めて成功し、植物への物理的刺激によるVOC放出の短時間変動をO3反応性として包括的に捕捉した。また、2,5-ジメチルフランの反応速度定数を初めて決定した。以上のように、比較的簡便・汎用的なVOCのラジカル反応性計測法を確立した

人間活動に伴い放出される有害微量成分のうち芳香族炭化水素について、共鳴多光子イオン化法にて高速・選択的・高感度に直接分析し、発生源放出特性の詳細な把握と大気環境への影響評価を試みた。自動車排気では、揮発由来成分と燃焼由来成分で排出挙動が大きく異なることを秒単位で捕捉した。塗装からの放出では、ベンゼンなど高揮発性成分の影響が、塗布直後に重大であることを実験的に確認した。1秒値相関解析の短時間現象への有効性を示した

A unique system that uses the totalreactivity with ozone (RO3) has been developed for measuring biogenic volatileorganic compounds (BVOCs) emitted from vegetation into the atmosphere. However,the sensitivity of the RO3 analyzer was insufficient for measuring the atmospherein the forests. Recently, the sensitivity of the ozone monitor in the analyzerhas been improved. In this study, further improvement of the analyzer wasexplored. As a result of reduction of noises in the detector, the detectionlimit of RO3 analyzer reached 0.2 x 10-4 s-1 (S/N = 3, 60-s average). After theimprovement, a practical test for measuring RO3 in the forest was conducted atTokorozawa in summer. Consequently, it was experimentally confirmed that coexistingNO can be critical as interference of measurement. This issue remains to besolved. Additionally, in order to realize a versatile procedure for measuring RO3in the forests, combination of sampling and RO3 analysis was challenged. Atpresent, the signal of BVOCs as RO3 was preliminarily captured. It wasindicated that the sampling procedure be promising.

A unique system that uses the total reactivity withozone (RO3) has been developed for measuring biogenic volatile organic compounds(BVOCs) emitted from vegetation into the atmosphere. However, the sensitivity ofthe RO3 analyzer was insufficient for measuring the atmosphere in the forests.Recently, the sensitivity of the ozone monitor in the analyzer has beenimproved. In this study, further improvement of the analyzer was explored. As aresult of reduction of noises in the detector, the detection limit of RO3analyzer reached 0.2 x 10-4 s-1 (S/N = 3, 60-s average). After the improvement,a practical test for measuring RO3 in the forest was conducted at Tokorozawa insummer. Consequently, it was experimentally confirmed that coexisting NO can becritical as interference of measurement. This issue remains to be solved. Meanwhile,as another application of improved RO3 analyzer, temperature dependence of ratecoefficients of the reaction linalool+O3 was experimentally determinedsuccessfully. The RO3 analyzer is promising for kinetic studies of BVOCs+O3reactions.

Photochemical oxidant (tropospheric ozone, O3) isstill important. Total oxidants (called as ‘potential ozone’ in Japan, PO=NO2+O3)are convenient to simply recognize the behavior of ozone. In this study, utilizingaccurate and versatile NO2 analyzers, CAPS-NO2, (1) construction of a portableNO2 analyzer and a test of moving observation of exhaust gas nearby emissionsources were conducted. Moving observation of NO2 was successful for 25minutes. In a parking area, exhaust gases emitted from automobiles intoatmosphere were directly monitored. (2) Simultaneous observation of PO, NOx, and/orNO2 at two sites was explored. The first site (a ‘laboratory’ in the university)was 100 m away from another site (an ‘office’ room). The laboratory is closerto a parking area than the office. Consequently, it was confirmed that theambient air outside the laboratory be representative in the university.Additionally, it was also confirmed that observation at the laboratory bedesirable to capture exhaust gases from the parking area. The portable analyzerand procedures for simultaneous observation at two sites are expected as newtools for capturing the atmospheric impact of exhaust gases. In order toexplore the actual situations of exhaust gases, observation of real atmosphereis essential.

A unique system that uses the total reactivity withozone (RO3) has been developed for measuring biogenic volatile organiccompounds (BVOCs) emitted from vegetation into the atmosphere. However, thesensitivity of the prototype of RO3 analyzer was insufficient for measuringambient atmosphere in the forests. In this study, the improvement of RO3analyzer was explored, especially focused on the improvement of thefast-response chemiluminescent ozone analyzer, CLD-O3. Consequently, thesensitivity of CLD-O3 was achieved. However, the noises were still large atpresent. The upper limit of quantifiable ozone ratio ([O3(VOC)]/[O3(VOC=0)] wasnot improved drastically. As a next step, continuing improvement of analyzers,including reduction of noises by cooling the photomultiplier of CLD-O3, isessential.

光化学オキシダント（対流圏オゾンO3）は依然重要な大気汚染問題である。ポテンシャルオゾンPO(= O3 + NO2) を考えるとO3の複雑な反応挙動を単純化できる。本研究では、高確度な汎用 NO2 計に基づく秒単位での PO, NOx 直接同時測定法を確立した。さらに、都市郊外における実大気観測も試みた。その結果、延べ34日にわたって実大気観測を実施し、実大気PO, NOx の同時高速測定に基づく排ガスNO2/NOx 比の評価にも成功した。今回実現した実大気観測に基づく排ガスNO2/NOx 比の実状把握は、今後の光化学オキシダント現象の解明に向けた足掛かりとなる、と期待される。

大気光化学反応での有機硝酸 ANs（RONO2）生成経路への分岐は光化学オキシダント Ox の生成を抑制するので、Ox 挙動の正しい把握のためにはANs 挙動も重要である。そこで本研究では、高確度 NO2 計 CAPS-NO2を活用し、汎用的かつ高確度な ANs 全量計を構築した。性能評価の結果、ANs 検出下限 0.3 ppbv を得た。さらに、所沢キャンパスにて実大気中ANs 全量の連続測定を試みた結果、ANs の日変化の捕捉に成功し、装置の実用性を確認した。さらに観測結果を解析したところ、日ごとのANs 生成分岐比 11 – 32 % を得た。今後の国内での観測例の蓄積が期待される。

①研究の背景と目的：　国内では大気中の光化学オキシダント（主にオゾン）の濃度上昇傾向が報告され、その挙動把握と対策が急務であり、オゾンとその前駆体（窒素酸化物や揮発性有機化合物）の挙動把握が重要である。最近特に、植生など自然発生源からの放出成分が、自動車排ガスなど人為放出成分と共存する際の挙動が注目されている。代表者はこれまでに、オゾン・窒素酸化物・揮発性有機化合物の高度観測法を研究・開発してきた。代表者が着任後に大気環境研究を始めるにあたり、本拠となる所沢におけるオゾンと関連成分の動態把握がまず必要となる。そこで本研究では、これまでの経験や機器を活用し、所沢の大気中オゾンやその前駆体の観測を実施し、大気微量成分の基本的な特性の把握を目指す。特にオゾンについて、可能な範囲で連続的に観測を続け、各季節ごとに典型的な日変化を把握する。本研究は、所沢という地理的条件を最大限に活用し、都市と自然が共存する郊外地域にて大気観測を実施して、光化学オキシダントの挙動を解明を進めつつ、今後の大気環境研究を進めるうえでの基盤を確立する点が、特に有意義である。②研究の方法：（２－１）大気観測の実施・・・所有する計測装置を活用し、大気中のオゾンを自動連続観測した。測定器は研究室内に設置して安定に運転しつつ、大気試料をテフロン配管と継手を経由して屋外から測定器まで導入した。データは、ロガーや既存ＰＣを活用して取得・記録した。（２－２）観測結果の解析・・・本研究で得られた観測データに関して、（ａ）オゾン日変化パターン、（ｂ）オゾンの季節変動、（ｃ）近隣の公開データとの比較、（ｄ）大気光化学反応の検証、について解析した。以上を通して、所沢キャンパスでのオゾンを中心とする大気化学的状況の初期的な把握を目指した。③研究の結果と考察：（３－１）大気観測概況・・・２０１２年６月２０日から３月１８日まで、所沢キャンパス１００号館実験室の外気について、オゾン濃度の自動連続測定を実施した。観測では１分間隔でデータを記録しつづけた。得られた「生」の１分値データは約３８．７万点であったが、いくつかの欠測期間や不具合（夏期の停電１日間、年度末の実験棟屋外補修工事に伴う試料採取不可、等）を考慮して異常値等を除外して解析した結果、６０分平均値としての正味の測定データ数は６０７０点であった。工事等に左右されない安定的な連続観測の実現は、今後改善すべき課題である。（３－２）観測結果概況・・・観測期間を通して、日中（午後２時頃）にピークを持ち、夜間（特に冬季）に低濃度になる、都市郊外大気に典型的なオゾン濃度の日変化パターンを実験的に確認した。日射が強く光化学活性の高い「夏季」には、「秋季」「冬季」と比較して、日中オゾン濃度の最大値が高かった。なお、本研究では、一般的にオゾン濃度が高い「春季」は、観測していないためデータを得られなかった。所沢キャンパスが、東京近郊の都市郊外大気でのオゾン研究に十分適用可能であることを示唆した。近隣の公開データ（環境省「そらまめ君」、１時間値）と所沢キャンパスのオゾン観測結果を比較したところ、最寄の「所沢北野」観測局と本観測結果は、全体的によく一致した（６０分値での相関係数０．９０、回帰直線・・・公開データ＝０．９５ｘ早大観測値＋１．５ｐｐｂｖ）。また、周辺の観測局（「東大和」「狭山」「入間」「中富」）などとも比較的良い相関・一致を示し、所沢キャンパス周辺１０ｋｍ程度までの範囲ではオゾンは似た挙動を示すことも確認された。これら観測局の中で中心に位置する所沢キャンパスは、近隣のオゾン現象を調べるのに適していることが示された。なお、本研究では、窒素酸化物ＮＯｘの観測は準備が間に合わなかったため、オゾンとＮＯｘの同時観測と相関解析などは、今後の課題である。