Yoshizumi Kajii

Influence of regional‐scale anthropogenic activity in northeast Asia on seasonal variations of surface ozone and carbon monoxide observed at Oki, Japan

Surface O3 and CO measurements were carried out at Oki, Japan during March 1994 to February 1996 in order to elucidate the processes determining temporal variations of O3 and CO in the northeast Asian Pacific rim region. The isentropic trajectory analysis was applied to sort out the influences of the air mass exchange under the Asian monsoon system and the regional-scale photochemical buildup of O3. The trajectories were categorized into five groups which cover background and regionally polluted air masses. The seasonal cycles of O3 and CO in the background continental air mass revealed spring maximum-summer minimum with averaged concentrations ranging from 32 and 120 ppb to 45 and 208 ppb, respectively. In contrast, O3 concentrations in the regionally polluted continental air mass ranged from 44 to 57 ppb and showed a winter minimum and a spring-summer-autumn broad maximum, which was characterized by photochemical O3 production due to anthropogenic activities in northeast Asia. CO concentrations in the same air mass showed a spring maximum of 271 ppb and a summer-autumn minimum of 180 ppb. The photochemical buildup of O3 resulting from anthropogenic activities in this region was estimated to be 21 ppb in summer, while its production was insignificant, an average 3 ppb, in winter. A comparison between data in northeast Asia and in Europe shows many similarities, supporting the contention that photochemical buildup of O3 from large-scale precursor emissions in both regions is very significant.

The atmospheric impact of boreal forest fires in far eastern Siberia on the seasonal variation of carbon monoxide: Observations at Rishiri, A northern remote island in Japan

Observations of carbon monoxide (CO) and ozone (O3) at the surface have been made at Rishiri, a northern remote island in Japan. O3 seasonal variation shows a spring maximum and summer minimum, which are typically observed at remote mid-latitude regions in the Northern Hemisphere. The seasonal cycle of CO shows a baseline enhancement and episodic high concentrations during the period from summer to early fall 1998, indicating a strong source of CO nearby. Both Advanced Very High Resolution Radiometer and Earth Probe Total Ozone Mapping Spectrometer satellite images during the same period produce clear pictures illustrating severe forest fire events and widespread smoke plumes in far eastern Siberia. Back trajectory analyses suggest that boreal forest fires in far eastern Siberia had a significant impact on CO observed at the site from summer to early fall 1998.

Regional background ozone and carbon monoxide variations in remote Siberia/East Asia

[1] Continuous measurements of O3 and CO were made during 1997–1999 at Mondy, a remote mountain site in East Siberia, in order to quantify their mixing ratios and their climatology in the ‘‘background’’ troposphere of continental Eurasia. The seasonal cycles of O3 and CO show the spring maximum-summer minimum similar to that previously reported in the remote Northern Hemisphere. The influences of Siberian forest fires on the variations of CO mixing ratios at Mondy were observed both on a local and a regional scale during spring 1997 and fall 1998, respectively. We further evaluate the possible impact of European pollution export to the remote atmosphere of Siberia using trajectory analysis. It was found that the O3 and CO mixing ratios in the air masses transported from Europe are higher than those from Siberia and high-latitude regions for most of the year. The medians of O3 and CO mixing ratios associated with the European air masses are 44.2 and 134 ppb, respectively, in comparison with 42.7 and 128 ppb in the Siberian air masses, and 41.0 and 110 ppb in the high-latitude air masses. The residence time analysis of air masses transported from the European continent indicates that CO mixing ratios significantly decrease with longer transport time of air masses from Europe, while rapid air motion retains higher CO mixing ratios in every season due to the admixture of polluted European air into the continental background air during air mass transport over Eurasia and photochemical loss by OH. Because of a shorter lifetime in summer, CO mixing ratios decrease at a rate of 6–7 ppb per day, while they decrease at a rate of 2–4 ppb per day in winter and spring. The similar trend is found for O3 but only in summer, at a rate of 2–3 ppb per day. From this analysis, we are able to identify that European pollution exerts an influence, though not very strong, on the background O3 and CO at Mondy in remote Siberia/East Asia. INDEX TERMS: 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry;

Transient absorption, lifetime and relaxation of C60 in the triplet state

Abstract Transient absorption and time-resolved thermal lensing techniques have been used to study the photophysical behavior of C 60 in benzene solution at room temperature. After the photoexcitation with a 308 nm XeCl excimer laser, the triplet state was the only transient species detectable with the 10 ns time-resolution. The triplet—triplet absorption spectrum with apparent band peaks at 330 and 745 nm covers the whole spectral range of 290–850 nm. The triplet lifetime in air-free benzene is 49±1 μs and essentially all the photon energy absorbed is released as heat, predominantly through the triplet state.

Development of a measurement system of OH reactivity in the atmosphere by using a laser-induced pump and probe technique

A novel instrument for measuring OH reactivity in the troposphere has been developed by using a laser-induced pump and probe technique. Air was introduced into a flow tube and OH was produced artificially using O3 photolysis by 266 nm laser. The OH decay rate in the flow tube was monitored by the time-resolved laser-induced fluorescence technique. In this article, the instrument, that is, the measurement principle, the flow tube and the fluorescence detection cell, is presented in detail. Interference by absorption of the 266 nm laser light by O3, and photolysis of NO2 and HCHO was found to be negligible. The influence of recycled OH from the HO2+NO reaction on the measured OH reactivity was estimated by a box model calculation. The systematic error of the measured decay rate was found to be less than 5% even in high NO condition ([NO]=20 ppbv). The dependence of the measured decay rate on the flow rate in the reaction tube was investigated. A slight change in the total flow rate does not influence the me...

Development of a ground-based LIF instrument for measuring HOx radicals : Instrumentation and calibrations

An instrument for measuringtropospheric OH/HO2 radicals by laser-inducedfluorescence developed in our laboratory is presentedin detail. It is based on FAGE (fluorescence assay bygas expansion) technique and OH is both excited anddetected at 308 nm corresponding to its A-X(0,0) band.The alignment of the laser beam, the design of thesample gas inlet, and the devices for the fluorescencedetection are optimized so as to reduce the backgroundsignal while keeping the OH sensitivity as high aspossible. A thermalized position of the expanding gasbeam is probed in our system and we did not observe asevere decrease of the HOx sensitivities under humidconditions. An optical fiber is used for deliveringthe laser light to the fluorescence detection cellmounted outside at a high position. Thus the laserbeam alignment is by far simplified and is made highlyreproducible, once settled properly. For thecalibration, two methods are employed: a system withlaser absorption measurements of OH and a system ofsimultaneous photolysis of H2O and O2. Thecalibration factors are compared well within thecombined uncertainty. Using the latter system, theconversion efficiency of HO2 to OH by NO additionis measured to be around 90%. The detection limitsfor OH and HO2 (S/N = 2) are estimated to be3.3 × 106 and 3.6 × 106cm−3 at noon,respectively, with an integration time of 1 min. Theresults of test observations at our institute are alsopresented.

Evidence for the seasonal variation of photochemical activity of tropospheric ozone: Continuous observation of ozone and CO at Happo, Japan

Ground based measurements of ozone as well as carbon monoxide have been carried out at Happo station. Annual cycles of ozone and CO concentration were obtained. Monthly means of ozone show maximum of ca. 65 ppbv in April or May and minimum of ca. 45 ppbv in December or January. The annual behaviour of CO is somewhat similar to that of ozone showing maximum of 225 ppbv in April and minimum of 151 ppbv in December. A positive correlation was obtained between ozone and CO during spring and summer. This fact indicates that photochemical ozone production in the troposphere is active in spring and summer. It should be noted that the highest correlation was obtained in April and May which corresponds to the month giving the ozone maximum concentration. The comparison between ozone and humidity in late spring revealed that although many events showing dry air parcels reaching the site were observed, simultaneous increase of ozone was not observed at all. This fact clearly indicates that the sporadic high concentration of ozone in spring is caused by the photochemical ozone formation in the troposphere rather than the intrusion of stratospheric air.

Daytime HO2 concentrations at Oki Island, Japan, in summer 1998: Comparison between measurement and theory

The daytime variation of hydroperoxy (HO 2 ) 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, HO 2 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, HO 2 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/NO 2 , HCHO/CH 3 CHO, SO 2 , HNO 3 and J(NO 2 ) were also observed. Unfortunately, the absolute value of J(O 1 D) was not measured. Model calculations for radical concentrations were performed and they were compared to the observed hourly HO 2 concentrations. On August 9 the calculated HO 2 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 HO 2 under certain conditions with plenty of isoprene. On other days, however, model usually overestimated HO 2 by a factor of 2, especially in the hours around noon. It is deduced that some important HO, 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 HO 2 would be more plausible than that with additional OH loss. The additional loss rate for HO 2 that can reduce the calculated HO 2 to the measured level was computed for each hour. Its variation correlated well with those of H 2 O and some photochemical products. The possibilities of HO 2 loss on aerosol surface, unknown acceleration of HO 2 reactions in the presence of high HO 2 and HO 2 reactions with carbonyl species are discussed.

Nighttime observation of the HO2 radical by an LIF instrument at Oki Island, Japan, and its possible origins

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 (∼10 ppt) via RO2 + NO reactions. Low NO2 (∼150 ppt) slowed NO3 production rate. Thus, the high observed HO2 suggests that the reactions of O3 with olefins are important HOx primary production mechanisms in the relatively clean atmosphere.

Photochemical reactions in the urban air : Recent understandings of radical chemistry

Abstract In this review article, recent understandings of the urban atmosphere are briefly presented, focusing on NOx (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.