Fumikazu Taketani

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

Emissions of nonmethane volatile organic compounds from open crop residue burning in the Yangtze River Delta region, China

Open crop residue burning is one of the major sources of air pollutants including the precursors of photooxidants like ozone and secondary organic aerosol. We made measurements of trace gases including nonmethane volatile organic compounds (NMVOCs) in a rural area in central East China in June 2010. During the campaign, we identified six biomass burning events in total through the simultaneous enhancement of carbon monoxide and acetonitrile. Four cases represented fresh plumes ( 3 h after emission), as determined by photochemical age. While we were not able to quantify formic acid, we identified an enhancement of major oxygenated volatile organic compounds (OVOCs) as well as low molecular alkanes and alkenes, and aromatic hydrocarbons in these plumes. The observed normalized excess mixing ratios (NEMRs) of OVOCs and alkenes showed dependence on air mass age, even in fresh smoke plumes, supporting the view that these species are rapidly produced and destructed, respectively, during plume evolution. Based on the NEMR data in the fresh plumes, we calculated the emission factors (EFs) of individual NMVOC. The comparison to previous reports suggests that the EFs of formaldehyde and acetic acid have been overestimated, while those of alkenes have been underestimated. Finally, we suggest that open burning of wheat residue in China releases about 0.34 Tg NMVOCs annually. If we applied the same EFs to all crops, the annual NMVOC emissions would be 2.33 Tg. The EFs of speciated NMVOCs can be used to improve the existing inventories.

Trace detection of atmospheric NO2 by laser-induced fluorescence using a GaN diode laser and a diode-pumped YAG laser.

We report on the development of a highly sensitive detection system for measuring atmospheric NO(2) by means of a laser-induced fluorescence (LIF) technique at 473 nm using a diode-pumped Nd:YAG laser. A GaN-based laser diode emitting at 410 nm is also used as an alternative fluorescence-excitation source. For laboratory calibrations, standard NO(2) gas is diluted with synthetic air and is introduced into a fluorescence-detection cell. The NO(2) LIF signal is detected by a photomultiplier tube and processed by a photon-counting method. The minimum detectable limits of the NO(2) instrument developed have been estimated to be 0.14 ppbv and 0.39 ppbv (parts per billion, 10(-9), by volume) in 60 s integration time (signal-to-noise ratio of 2) for 473 and 410 nm excitation systems, respectively. Practical performance of the instrument has been demonstrated by the 24 hour continuous measurements of ambient NO(2) in a suburban area.

Laboratory measurements of emission factors of nonmethane volatile organic compounds from burning of Chinese crop residues

The emission factors (EFs) of nonmethane volatile organic compounds (NMVOCs) emitted during the burning of Chinese crop residue were investigated as a function of modified combustion efficiency in laboratory experiments. NMVOCs, including acetonitrile, aldehydes/ketones, furan, and aromatic hydrocarbons, were monitored by proton-transfer-reaction mass spectrometry. Rape plant was burned in dry conditions and wheat straw was burned in both wet and dry conditions to simulate the possible burning of damp crop residue in regions of high temperature and humidity. We compared the present data to field data reported by Kudo et al. (2014). Good agreement between field and laboratory data was obtained for aromatics under relatively more smoldering combustion of dry samples, but laboratory data were slightly overestimated compared to field data for oxygenated VOC (OVOC). When EFs from the burning of wet samples were investigated, the consistency between the field and laboratory data for OVOCs was stronger than for dry samples. This may be caused by residual moisture in crop residue that has been stockpiled in humid regions. Comparison of the wet laboratory data with field data suggests that Kudo et al. (2014) observed the biomass burning plumes under relatively more smoldering conditions in which approximately a few tens of percentages of burned fuel materials were wet.

Ground‐based measurement of fluorescent aerosol particles in Tokyo in the spring of 2013: Potential impacts of nonbiological materials on autofluorescence measurements of airborne particles

We present results from the observation of fluorescent (FL) aerosols in Tokyo in the spring of 2013. Ambient aerosol particles were analyzed using a single-particle laser-induced fluorescence instrument. The fluorescent emission from a single particle excited by a pulsed UV laser (excitation wavelength of 263 nm) was detected by three photomultiplier tubes with band-pass filters (fluorescence wavelength of 335–379, 420–500, and 500–600 nm). Fluorescence patterns from single particles were analyzed for investigating fluorophores and their sources using backward trajectory analysis, factor analysis, and a comparison with other tracer observations. The backward trajectory analysis suggested possible influences of long-range transport from northern China in some cases. Observed supermicron FL aerosols were classified into two types: combustion- and dust-type particles. The detection of combustion-type FL aerosols, which showed temporal variations similar to nitrogen oxides and elemental carbon, implied the presence of polyaromatic hydrocarbons (PAHs) and their derivatives. Dust-type FL aerosols, which were well correlated with the lidar-derived dust-aerosol optical depth near the surface (<1 km) and with mineral ions, were dominant in the supermicron size range. The number concentrations of coarse FL aerosols (≥2 µm), with which nonnegligible levels of fluorescence were recorded in all three channels, increased during Asian dust events (relative to a local dust event). It is suggested that PAHs and/or biological materials mixed with dust particles were transported from the North China Plain to the outflow region in East Asia during the observation period. Moreover, the autofluorescence measurement of airborne particles can be substantially affected by nonbiological materials in this region.

Shipborne observations of atmospheric black carbon aerosol particles over the Arctic Ocean, Bering Sea, and North Pacific Ocean during September 2014

Measurements of refractory black carbon (rBC) aerosol particles using a highly sensitive online single particle soot photometer were performed on board the R/V Mirai during a cruise across the Arctic Ocean, Bering Sea, and North Pacific Ocean (31 August to 9 October 2014). The measured rBC mass concentrations over the Arctic Ocean in the latitudinal region > 70°N were in the range 0–66 ng/m3 for 1 min averages, with an overall mean value of 1.0 ± 1.2 ng/m3. Single-particle-based observations enabled the measurement of such low rBC mass concentrations. The effects of long-range transport from continents to the Arctic Ocean were limited during the observed period, which suggests that the low rBC concentration levels would prevail over the Arctic Ocean. An analysis of rBC mixing states showed that particles with a nonshell/noncore structure made a significant contribution to the rBC particles detected over the Arctic Ocean.

Fluorescence detection of atmospheric nitrogen dioxide using a blue light-emitting diode as an excitation source

We report on the development of a low-cost and compact instrument for quantifying atmospheric NO(2) concentrations by detecting NO(2) fluorescence using a commercial light-emitting diode around 435 nm as a fluorescence excitation light source. The minimum detectable limit of the NO(2) instrument developed has been estimated to be 9.8 parts per billion of volume mixing ratio (ppbv) in a 60 s integration time and with a signal-to-noise ratio of 2.

Seasonal Response of North Western Pacific Marine Ecosystems to Deposition of Atmospheric Inorganic Nitrogen Compounds from East Asia

The contribution of the atmospheric deposition of inorganic nitrogen compounds produced in East Asia to the marine ecosystems of the North Western Pacific Ocean (NWPO) was investigated in this study using a 3-D lower trophic-marine ecosystem model (NEMURO) combined with an atmospheric regional chemical transport model (WRF-CMAQ). The monthly mean values for the wet and dry deposition of nitrogen compounds, including gases (HNO3 and NH3) and aerosol particles (NO3− and NH4+), were determined using the WRF-CMAQ for the NWPO from 2009–2016. These values were input into the NEMURO as an additional nitrogen source. The NEMURO indicated that the annual average chlorophyll mass concentration at the surface in the subtropical region (20°N–30°N; 125°E–150°E) of the NWPO increased from 0.04 to 0.10 mg/m3. Similarly, the gross primary productivity, integrated over sea depths of 0–200 m, increased from 85 to 147 mg C/m2/day because of this deposition. This study indicates that the supply of atmospheric inorganic nitrogen compounds from East Asia to the NWPO could have a high nutrient impact on the marine ecosystem in the subtropical region.