Masazumi Koike

Observations of HO x and its relationship with NO x in the upper troposphere during SONEX

Simultaneous measurements of the oxides of hydrogen and nitrogen made during the NASA Subsonic Assessment, Ozone and Nitrogen Oxide Experiment (SONEX) afforded an opportunity to study the coupling between these two important families throughout the free troposphere and lowermost stratosphere. Moreover, the suite of measurements made during the campaign was unprecedented in its completeness, thus providing a uniquely detailed picture of the radical photochemistry that drives oxidation and ozone production in this part of the atmosphere. On average, observed hydrogen oxides (HOx = OH + HO2) agree well with both instantaneous and diel steady-state models; however, there is a persistent deviation of the observations that correlates with the abundance of nitrogen oxides (NOx = NO + NO2) in the sampled air mass. Specifically, the observed HOx tends to exceed the model predictions in the presence of high NOx concentrations, by as much as a factor of 5 (> 500 pptv NOx), and is sometimes as little as half that expected by steady state at lower NOx levels. While many possibilities for these discrepancies are discussed, it is argued that an instrumental artifact is not probable and that the discrepancy may bespeak a shortcoming of our understanding of HOx chemistry. The consistently elevated HOx in the presence of elevated NOx leads directly to greater ozone production than expected, thereby extending the NOx-limited regime of the upper troposphere. These results could thus have bearing on the predicted impacts of increasing NOx emissions into this region of the atmosphere from, for example, the growth of global air traffic.

Aging of black carbon in outflow from anthropogenic sources using a mixing state resolved model: Model development and evaluation

Received 29 June 2008; revised 26 November 2008; accepted 5 January 2009; published 27 March 2009. [1] The mixing state of black carbon (BC) aerosols, namely, the degree to which BC particles are coated with other aerosol components, has been recognized as important for evaluating aerosol radiative forcing. In order to resolve the BC mixing state explicitly in model simulations, a two-dimensional aerosol representation, in which aerosols are given for individual particle diameters and BC mass fractions, is introduced. This representation was incorporated into an aerosol module, the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (MADRID), and a new box model, MADRID-BC, was developed. MADRID-BC can accurately simulate changes in the entire BC mixing state resulting from condensation/evaporation processes. Aircraft observations conducted in March 2004 show that the mass fraction of thickly coated BC particles increased in air horizontally transported out from an urban area in Japan over the ocean. MADRID-BC generally reproduces this feature well when observed bulk aerosol concentrations are used as constraints. The model simulations in this particular case show that for particles with BC core diameters of 100–200 nm, the particle diameters, including both core and coating materials, had already increased by a factor of 1.6 on average when they left the source region and by as large as a factor of 1.9 of the BC core diameters after their transport over the ocean for a half day. The model simulations also show that 58% of the total condensed mass was partitioned onto BC-free particles during transport, indicating their importance for the BC mixing state. Although the model simulations are applied to a limited number of the observations in this study, they clearly show the time evolution of the coating thicknesses of BC-containing particles, which is necessary for calculating aerosol optical properties and cloud condensation nuclei activities.

Aging of black carbon in outflow from anthropogenic sources using a mixing state resolved model: 2. Aerosol optical properties and cloud condensation nuclei activities

Received 28 December 2008; revised 12 May 2009; accepted 24 June 2009; published 19 September 2009. [1] The Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution with resolution of a mixing state of black carbon (BC) (referred to as MADRID-BC hereinafter) has recently been developed to accurately simulate the time evolution of the entire BC mixing state. In this study, we apply MADRID-BC to evaluate the influence of changes in BC mixing state on aerosol optical properties and cloud condensation nuclei (CCN) activities in air parcels horizontally transported out from an urban area in Japan within the planetary boundary layer (PBL) over the ocean. The evaluation shows that the coatings on BC particles enhance light absorption at a wavelength of 550 nm by 38% in air leaving the source region and by 59% after transport over the ocean for half a day. When the model treats aerosols using the conventional size-resolved sectional representation that does not resolve BC mixing states, the simulated absorption coefficients and single scattering albedos are greater by 35–44% and smaller by 7–13%, respectively, than those from a simulation that resolves the BC mixing state. These results indicate that it is essential to take into account BC-free particles in atmospheric models for accurate prediction of aerosol optical properties, because the conventional representation cannot separately treat BC-containing and BC-free particles in each size section. The evaluation also shows that BC-containing particles having 55% and 83% of the BC mass can act as CCN at a supersaturation of 0.05% when they leave the source region and after transport for half a day, respectively. These results suggest the importance of the uplifting of BC particles from the PBL near source regions for their efficient long-range transport in the free troposphere. Results from comparisons with aerosol optical measurements conducted during various campaigns, such as the Asian Aerosol Characterization Experiment (ACE Asia) and the Indian Ocean Experiment (INDOEX), suggest that MADRID-BC simulations can capture general features of aerosol optical properties in outflow from anthropogenic sources.

Reactive Nitrogen and its Correlation with O3 and CO Over the Pacific in Winter and Early Spring

Measurements of NO, NOy, O3, and CO were made during NASAs Global Tropospheric Experiment/Pacific Exploratory Mission-West B (GTE/PEM-West B) carried out over the western Pacific in February and March 1994. NOx was calculated from NO using a photostationary state model ((NOx)mc). Correlations between these species are presented, and some insights into the sources of NOx and NOy are described. The boundaries between the lower, middle, and upper troposphere have been defined at potential temperatures of 311 K and 328 K, which correspond to the geometric altitudes of about 5 and 9 km at 30°N. Enhancements in the mixing ratios of NOy and CO were observed in the lower and middle troposphere. A positive correlation was found between these two species suggesting that the high NOy values were due to anthropogenic emissions over the continental surface. On the other hand, O3 increased little with increase in CO. As a result, NOy/O3 ratios were higher in air more influenced by pollution. NOy values in 55 and 28% of the air masses sampled in the lower and middle troposphere, respectively, were higher than the clean free tropospheric NOy-O3 range when O3 values simultaneously observed were used. High (NOx)mc/NOy ratios between 0.15 and 0.3 were found in the boundary layer with relatively low mixing ratios of CO and NOy during the three flights. These air masses were transported from a higher altitude (∼5 km) and a higher latitude (∼50°N) within a few days. The peroxyacetyl nitrate (PAN)/NOy ratios were generally high (∼0.4) in these air masses, and the thermal decomposition of PAN was a probable source of NOx. In the middle troposphere the (NOx)mc mixing ratio did not generally increase with NOy or CO, suggesting that the transport of air masses affected by anthropogenic emissions did not increase the NOx level significantly. In the upper troposphere, very minor effects from the continental surface sources were seen in the CO mixing ratio. By contrast, NOy values in 33% of the air masses were higher than those expected when stratospheric air intrusion is assumed to be a single source of NOy based on NOy-O3 correlation analyses. This result suggests significant free tropospheric NOy sources, namely exhaust from the aircraft and NO production by lightning activity. In fact, spikes in the (NOx)mc mixing ratios were observed near the aircraft corridor south of Tokyo at an altitude of 10 km. These two free tropospheric NOx sources were considered to be important in determining the levels of the upper tropospheric NOx and NOy during PEM-West B.

Ratios of reactive nitrogen species over the Pacific during PEM‐West A

Measurements of total reactive odd nitrogen (NOy) and known individual odd nitrogen species were made over the Pacific Ocean in September and October 1991 during the NASA Global Tropospheric Experiment, Pacific Exploratory Mission-West A (GTE/PEM-West A). The ratios between NOx (NO + NO2) calculated from observed NO assuming photochemical equilibrium ((NOx)mc), peroxyacetyl nitrate (PAN), and NOy have been investigated for these data. The mixing ratios of (NOx)mc, PAN, and NOy in the lower and middle troposphere generally decreased with the air mass age, which has been defined by the propane/ethane ratio (C3H8/C2H6). The (NOx)mc/NOy ratios in the continental air showed a C-shaped vertical profile and median values were 0.27, 0.11, and 0.20 in the lower, middle, and upper troposphere, respectively. In the maritime and tropical air the (NOx)mc/NOy ratios generally increased with altitude and were about 0.1 and 0.15 in the lower and upper troposphere, respectively. In the middle troposphere the (NOx)mc/NOy ratios were similar in continental, maritime, and tropical air. These results are consistent with the fact that the (NOx)mc/NOy ratio did not decrease with the air mass age in the middle troposphere, suggesting the existence of NOx sources in the free troposphere. The PAN/NOy ratios in the continental air were about 0.3 at all altitudes. In maritime and tropical air the PAN/NOy ratio increased sharply at altitudes between 3 and 5 km with values of about 0.03 below 3 km and between 0.1 and 0.2 in the middle and upper troposphere. The PAN/NOy ratio generally decreased with the air mass age in the middle troposphere. In spite of a longer photochemical lifetime of PAN than NOx the PAN/(NOx)mc ratio also generally decreased with air mass age. These observations indicate that the reactive nitrogen ratios in the continental air mass are influenced by anthropogenic emissions at all altitudes, although relative contributions from various NOx sources in the upper troposphere are still poorly understood. Some influence from the continental air can be seen in the anthropogenic origin species in the maritime air mass when compared with the tropical air mass (Kondo et al., this issue). Similar (NOx)mc/NOy ratios, however, were generally found between the maritime and tropical air masses and a difference was only seen in the slightly higher PAN/NOy ratios in the maritime middle tropospheric air. The high-latitude air is characterized by low (NOx)mc/NOy ratios and high PAN/(NOx)mc ratios, probably due to the low atmospheric temperatures.

Carbon monoxide column abundances and tropospheric concentrations retrieved from high resolution ground-based infrared solar spectra at 43.5°N over Japan

High spectral resolution (0.0024 cm−1), ground-based infrared (IR) solar spectra were recorded at Rikubetsu, Japan (43.5°N, 143.8°E), by a Fourier transform infrared (FTIR) spectrometer covering the 4.8-μm fundamental absorption band of carbon monoxide (CO). Total vertical CO columns and tropospheric concentrations, from May 1995 to May 1996, were retrieved from these spectra using an iterative inversion algorithm. Microwindows at 2111.00–2112.00 cm−1 and 2157.40–2159.20 cm−1 were used for the retrievals. Tropospheric CO concentrations above Rikubetsu retrieved from the IR solar spectra are in good agreement with aircraft measurements performed in the nearby area in recent years. The data exhibit seasonal variations in tropospheric CO concentrations. The averaged mixing ratios between 0 and 3 km are 219±26 parts per billion by volume (ppbv) in April and 115±7 ppbv in September. The data also show CO concentrations and seasonal variations decreasing with altitude. The vertical change in CO concentration is the greatest in spring and the smallest in fall. A maximum CO column of 3.31±0.34×1018 molecules cm−2 in April and a minimum of 2.04±0.10×1018 molecules cm−2 in September were observed. The CO column above Rikubetsu is consistent with observations at Kitt Peak, the International Scientific Station of the Jungfraujoch (ISSJ), and Zvenigorod, considering differences in altitude and latitude between the observatories.

Accumulation‐mode aerosol number concentrations in the Arctic during the ARCTAS aircraft campaign: Long‐range transport of polluted and clean air from the Asian continent

[1] We evaluate the impact of transport from midlatitudes on aerosol number concentrations in the accumulation mode (light‐scattering particles (LSP) with diameters >180 nm) in the Arctic during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. We focus on transport from the Asian continent. We find marked contrasts in the number concentration (NLSP), transport efficiency (TEN_LSP, the fraction transported from sources to the Arctic), size distribution, and the chemical composition of aerosols between air parcels from anthropogenic sources in East Asia (Asian AN) and biomass burning sources in Russia and Kazakhstan (Russian BB). Asian AN air had lower NLSP and TEN_LSP (25 cm �3 and 18% in spring and 6.2 cm �3 and 3.0% in summer) than Russian BB air (280 cm �3 and 97% in spring and 36 cm �3 and 7.6% in summer) due to more efficient wet scavenging during transport from East Asia. Russian BB in this spring is the most important source of accumulation‐mode aerosols over the Arctic, and BB emissions are found to be the primary source of aerosols within all the data in spring during ARCTAS. On the other hand, the contribution of Asian AN transport had a negligible effect on the accumulation‐mode aerosol number concentration in the Arctic during ARCTAS. Compared with background air, NLSP was 2.3–4.7 times greater for Russian BB air but 2.4–2.6 times less for Asian AN air in both spring and summer. This result shows that the transport of Asian AN air decreases aerosol number concentrations in the Arctic, despite the large emissions of aerosols in East Asia. The very low aerosol number concentrations in Asian AN air were caused by wet removal during vertical transport in association with warm conveyor belts (WCBs). Therefore, this cleansing effect will be prominent for air transported via WCBs from other midlatitude regions and seasons. The inflow of clean midlatitude air can potentially have an important impact on accumulation‐mode aerosol number concentrations in the Arctic. Citation: Matsui, H., et al. (2011), Accumulation‐mode aerosol number concentrations in the Arctic during the ARCTAS aircraft campaign: Long‐range transport of polluted and clean air from the Asian continent, J. Geophys. Res., 116, D20217, doi:10.1029/2011JD016189.