Yugo Kanaya

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...

Correlations and emission ratios among bromoform, dibromochloromethane, and dibromomethane in the atmosphere

[1] Bromoform (CHBr 3 ), dibromochloromethane (CHBr 2 Cl), and dibromomethane (CH 2 Br 2 ) in the atmosphere were measured at various sites, including tropical islands, the Arctic, and the open Pacific Ocean. Up to 40 ppt of bromoform was observed along the coasts of tropical islands under a sea breeze. Polybromomethane concentrations were highly correlated among the coastal samples, and the ratios CH 2 Br 2 /CHBr 3 and CHBr 2 Cl/ CHBr 3 showed a clear tendency to decrease with increasing CHBr 3 concentration. These findings are consistent with the observations that polybromomethanes are emitted mostly from macroalgae whose growth is highly localized to coastal areas and that CHBr 3 has the shortest lifetime among these three compounds. The relationship between the concentration ratios CHBr 3 /CH 2 Br 2 and CHBr 2 Cl/CH 2 Br 2 suggested a large mixing/ dilution effect on bromomethane ratios in coastal regions and yielded a rough estimate of 9 for the molar emission ratio of CHBr 3 /CH 2 Br 2 and of 0.7 for that of CHBr 2 Cl/CH 2 Br 2 . Using these ratios and an global emission estimate for CH 2 Br 2 (61 Gg/yr (Br)) calculated from its background concentration, the global emission rates of CHBr 3 and CHBr 2 Cl were calculated to be approximately 820(±310) Gg/yr (Br) and 43(±16) Gg/yr (Br), respectively, assuming that the bromomethanes ratios measured in this study are global representative. The estimated CHBr 3 emission is consistent with that estimated in a very recent study by integrating the sea-to-air flux database. Thus the contribution of CHBr 3 and CHBr 2 Cl to inorganic Br in the atmosphere is likely to be more important than previously thought.

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.

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.

Behavior of OH and HO2 radicals during the Observations at a Remote Island of Okinawa (ORION99) field campaign: 1. Observation using a laser-induced fluorescence instrument

The hydroxyl (OH) and hydroperoxyl (HO2) radicals were measured by a laser-induced fluorescence instrument at Cape Hedo, Okinawa Island, Japan, in summer 1999 during the Observations at a Remote Island of Okinawa (ORION99) field campaign. The field deployment of the instrument and its calibrations are described in detail. From the frequent calibrations during the field campaign, it was shown that the instrument, utilizing an optical fiber to transmit the laser light to the detection cell located on a tower, had a sufficiently stable sensitivity to OH and HO2 in order to trace their diurnal and day-to-day variations. The detection limit of the instrument was typically around 4 × 106 radicals cm−3 with an integration time of 1 min. We could not examine fast OH variations. However, hourly averaged OH concentrations during daytime were statistically significant. The HO2 concentrations were higher and the detailed variations were detected. On average, OH and HO2 showed daytime maxima of around 4 × 106 radicals cm−3 and of around 17 pptv, respectively. The median, tenth, and ninetieth percentiles of the measured daytime HO2/OH concentration ratio were 76, 32, and 143, respectively. The power law dependence of HO2 on J(O1D) was about 0.5 when the NO concentration was lower than 300 pptv and was about 1 when the NO concentration was higher than 1 ppbv, which was consistent with the known radical chemistry in the lower troposphere.

Kinetics of Heterogeneous Reactions of HO2 Radical at Ambient Concentration Levels with (NH4)2SO4 and NaCl Aerosol Particles

The HO2 uptake coefficient (gamma) for inorganic submicrometer wet and dry aerosol particles ((NH4)2SO4 and NaCl) under ambient conditions (760 Torr and 296 +/- 2 K) was measured using an aerosol flow tube (AFT) coupled with a chemical conversion/laser-induced fluorescence (CC/LIF) technique. The CC/LIF technique enabled experiments to be performed at almost the same HO2 radical concentration as that in the atmosphere. HO2 radicals were injected into the AFT through a vertically movable Pyrex tube. Injector position-dependent profiles of LIF intensity were measured as a function of aerosol concentration. Measured gamma values for dry aerosols of (NH4)2SO4 were 0.04 +/- 0.02 and 0.05 +/- 0.02 at 20% and 45% relative humidity (RH), respectively, while those of NaCl were <0.01 and 0.02 +/- 0.01 at 20% and 53% RH, respectively. For wet (NH4)2SO4 aerosols, measured gamma values were 0.11 +/- 0.03, 0.15 +/- 0.03, 0.17 +/- 0.04, and 0.19 +/- 0.04, at 45%, 55%, 65%, and 75% RH, respectively, whereas for wet NaCl aerosols the values were 0.11 +/- 0.03, 0.09 +/- 0.02, and 0.10 +/- 0.02 for 53%, 63%, and 75% RH, respectively. Wet (NH4)2SO4 and NaCl aerosols doped with CuSO4 showed gamma values of 0.53 +/- 0.12 and 0.65 +/- 0.17, respectively. These results suggest that compositions, RH, and phase for aerosol particles are significant to HO2 uptake. Potential HO2 loss processes and their atmospheric contributions are discussed.

Comparison of Black Carbon Mass Concentrations Observed by Multi-Angle Absorption Photometer (MAAP) and Continuous Soot-Monitoring System (COSMOS) on Fukue Island and in Tokyo, Japan

Reducing uncertainties associated with measurements of black carbon (BC) particles is critical for improved quantification of their impacts on climate and health. We compared BC measurements using a continuous soot-monitoring system (COSMOS) and a multi-angle absorption photometer (MAAP) to assess their uncertainties. We found that measurements by COSMOS and MAAP instruments correlate strongly to each other, and their hourly ratio showed minimal temporal variations, but the MAAP values were systematically higher by a factor of 1.56 ± 0.19 (1σ), based on simultaneous observations on Fukue, a remote island in Japan, for about a year. This factor was almost independent of the air mass origins and seasons. Measurements in central Tokyo for about 2 months also yielded a similar relationship, with a systematic difference factor of ∼1.8. It is likely that the systematic differences are caused by differences in the conditions/protocols in the thermal/optical BC determinations used for calibration of each optical instrument. Based on results from the COSMOS instrument calibrated using an elemental carbon and organic carbon analyzer with thermal/optical transmittance correction, the MAAP absorption cross section (6.6 m2 g−1) needs to be systematically increased to 10.3 m2 g−1 at 639 nm for Fukue when b abs values derived from the built-in software are used. Small temporal fluctuations in the ratios of MAAP-derived BC to COSMOS-derived BC were possibly caused by humidity effects and temporal variations in the optical properties of the measured particles. For MAAP, we also found that low filter-transmittance (0.2–0.5) could either increase or decrease the BC reading. The current best recommendations with the MAAP instrument are to use an increased cross section, to use data with high filter-transmittance (>0.5) only, and to control humidity. Copyright 2012 American Association for Aerosol Research

Uptake of the HO2 radical by water: Molecular dynamics calculations and their implications for atmospheric modeling

[1] The mass accommodation coefficient α of the HO 2 radical in aqueous aerosols remains largely uncertain in atmospheric modeling. Therefore, in the present paper, a molecular dynamics computer simulation was performed to evaluate the HO 2 α in liquid water. The calculations yielded an α near unity, which defines a possible upper bound of the uptake coefficient γ. Implications for a large γ in the tropospheric atmosphere are discussed using model calculations for two typical cases: remote marine air and polluted urban air. It is suggested that the concentrations of HO 2 and other related species are quite sensitive to γ in the range of 0.2-1, particularly in the case of polluted urban air. In particular, the maximum diurnal HO 2 concentration is reduced by 73% in marine air and by 31% in urban air, when γ = 1 is incorporated.

Behavior of OH and HO2 radicals during the Observations at a Remote Island of Okinawa (ORION99) field campaign: 2. Comparison between observations and calculations

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 models 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.