Yukitomo Tsutsumi

Carbon monoxide in the upper troposphere over the western Pacific between 1993 and 1996

Air samples at 8.5–13 km were collected regularly using a commercial airliner between Australia and Japan, and they were measured for CO mixing ratios to obtain time series data from April 1993 to July 1996. When averaged over 12 latitudinal bands between 30°N and 30°S, two overall features emerge from these data. First, CO levels in the upper troposphere decreased in all latitudinal bands. Second, the seasonal cycle showed significant differences between the northern and southern hemispheres. In the southern hemisphere a strong maximum in the CO mixing ratio (up to around 90 ppb) was found in October-November. The most likely source for this enhanced CO is tropical biomass burning. Methane oxidation and transport of industrial CO from the northern hemisphere were estimated as relatively minor sources during the austral spring. Air mass trajectories indicate that an extremely high CO level of ∼130 ppb observed in November 1994 between 10° and 20°S was due to enhanced biomass burning in Southeast Asia and/or northern Australia. On the other hand, air mass trajectories for the 20°-30°S region indicate that CO-rich air from biomass burnings over southern Africa or South America was transported across the South Indian Ocean within ∼1 week by the strong westerly winds around the subtropical jet. Thus it is concluded that a rapid horizontal transport coupled with deep convection plays an important role in the appearance of the CO spring peak in the upper troposphere over the western South Pacific.

Tropospheric carbon monoxide and hydrogen measurements over Kalimantan in Indonesia and northern Australia during October, 1997

During the PACE-5 campaign over Australia and Indonesia in October 1997, we used an aircraft to measure carbon monoxide (CO) and hydrogen (H2). Latitudinal distributions of CO and H2 clearly showed a large increase from northern Australia to Kalimantan in Indonesia. Elevated CO levels over northern Australia were observed only in the smoke plumes of savanna fires. A thick smoke haze from forest fires over Kalimantan contained very high CO mixing ratios of 3 to 9 ppm. These enhanced CO mixing ratios correlated well with increased concentrations of H2, nitrogen oxides (NOx), and aerosols. Emission ratios from biomass burning in Kalimantan ranged 0.06 0.1 for H2/CO (ppb/ppb), 0.0002 to 0.0005 for NOx/CO (ppb/ppb), and 0.43 to 1.0 for number of aerosols/CO (cm−3/ppb). These values were much lower than emission ratios in northern Australia. This difference suggests that the biomass burning in Indonesia was intense and that, due to a strong El Nino event, an unique composition of trace gases was formed in the smoke haze.

Tropospheric ozone measurement at the top of Mt. Fuji

Since August of 1992, tropospheric ozone has been measured at the top of Mt. Fuji to investigate the background ozone feature of middle troposphere over Japan. During one year, the maximum concentration of monthly mean ozone at Mt. Fuji was 59.3 ppbv in May and minimum was 30.9 ppbv in August. The secondary minimum was recorded in January. The seasonal behavior showed a bi-modal trend. The diurnal amplitude of ozone in summer showed slight effect from the mountain and valley winds, but the amplitude around 2 ppbv is a lot smaller compared to other mountain data. The amplitude of other seasons did not show any significant variations. The effect of the mountain and valley winds were small at the top of Mt. Fuji because of the steep and windy summit. Day-to-day summertime variations varied wildly and often recorded low concentrations of ozone less than 20 ppbv. This low concentration of ozone sometimes continued for 3–5 days. This summer ozone minimum of the lower free troposphere was due to horizontal advection of the ozone poor air. In wintertime, the deviation of ozone concentration was very small. High peaks which lasted only a few hours were observed in spring. Analyzing the cross section chart on the 14th May 1993, the high peak of ozone on this day must have come from the stratosphere along the isentropic surface.

Aircraft measurements of ozone, NOx, CO, and aerosol concentrations in biomass burning smoke over Indonesia and Australia in October 1997: Depleted ozone layer at low altitude over Indonesia

The 1997 El Nino unfolded as one of the most sever El Nino Southern Oscillation (ENSO) events in this century and it coincided with massive biomass burning in the equatorial western Pacific region. To assess the influence on the atmosphere, aircraft observations of trace gases and aerosol were conducted over Kalimantan in Indonesia and Australia. Over Kalimantan in Indonesia, high concentrations of O3, NOx, CO, and aerosols were observed during the flight. Although the aerosol and NOx decreased with altitude, the O3 had the maximum concentration (80.5 ppbv) in the middle layer of the smoke haze and recorded very low concentrations (∼20 ppbv) in the lower smoke layer. This feature was not observed in the Australian smoke. We proposed several hypotheses for the low O3 concentration at low levels over Kalimantan. The most likely are lack of solar radiation and losses at the surface of aerosol particles.

Case studies of tropospheric ozone events observed at the summit of Mount Fuji

Tropospheric ozone events observed at the summit of Mount Fuji (3776 rn above sea level) were analyzed as case studies. The ozone, intruding from the lower stratosphere by the cutoff low or the tropopause fold over the Asian continent, is transported to the middle troposphere over Japan even in summer. The subtropical jet, which is intensified over Japan, also contributes to the summer intrusion from the stratosphere. A long stratospheric streamer, as described previously by Appenzeller et al. ( 1996), brings about a persistent ozone enhancement at the summit of Mount Fuji. The large variation of summer ozone over Japan is attributable to the alternate overspreading of these ozone-rich stratospheic air masses and the ozone-depleted subtropical maritime air mass. In contrast, winter ozone variation is relatively small at the summit of Mount Fuji. The steep potential temperature gradient between 500 hPa and 300 hPa in the winter cutoff low, which restrains vertical mixing in the upper troposphere, possibly causes less influence of the stratospheric air mass on the middle troposphere in winter, since mixing processes around a cutoff low play an important role in air mass exchange between the stratosphere and the troposphere.

Large injection of carbon monoxide into the upper troposphere due to intense biomass burning in 1997

AbstracL Air samples at 8-13 km were collected regularly using a commercial airliner to obtain long-term measurements of carbon monoxide (CO) mixing ratio in the upper troposphere over the western Pacific between Australia and Japan during April 1993 - December 1997. The measurements in 1997 clearly reveal an anomalous CO increase during September to November in the Southern Hemisphere, with a maximum of 320-380 ppb around 20°S in October. Tropical biomass burning, not urban/industrial emissions, was the main source for the enhanced CO in 1997. A similar southern-spring increase due to biomass burning was observed in previous years. The peaks showed a large interannual variation associated with the El Nino/Southern Oscillation (ENSO) events. The largest CO spring peak appeared during the strong El Nino event in 1997, while the weak La Nina year of 1996 was marked by a largely suppressed CO spring peak. The outgoing longwave radiation (OLR) anomaly is largest during the El Nino events indicating that the events cause a longer drought in the tropics and significantly influence the enlargement of biomass burning in tropical Southeast Asia. Thus the most likely cause for the ENSO-cycle CO variability is a year-to-year change of biomass-burning emissions mainly from Southeast Asia. The appearance of the CO spring peak in the southern subtropics is discussed on the basis of the possible long-range transport of biomass-burning CO from Southeast Asia to the upper troposphere over the western South Pacific.

Relationship of ozone and CO at the summit of Mt. Fuji (35.35°N, 138.73°E, 3776 m above sea level) in summer 1997

Ozone and CO were simultaneously measured for 17 days at the summit of Mt. Fuji (3776 m above sea level) in summer 1997. A classification of air mass origins based on backward trajectory analysis showed that both ozone and CO exhibit minimum concentrations in the air mass originating in southeast Asia, probably due to photochemical destruction during transport over the ocean. Both ozone and CO show maximum concentrations in the air mass originating in northeast Asia, reflecting background concentrations. Air mass groups transported long range from the Pacific, southeast Asia, and northeast Asia exhibit positive correlation between ozone and CO, while the air mass group staying around Japan that was thought to include fresh anthropogenic pollution negatively correlated. Diurnal variation of ozone in the air mass from the Pacific and southeast Asia (relatively clean and humid air) shows that ozone is likely to be photochemically destroyed in the air uplifted by valley winds at the summit in the daytime. Both diurnal variations of CO and ozone show evening enhancements in the case that the air at the summit passed over the Nagoya urban and industrial area before arriving at the summit. Thus, the polluted air is likely to be lifted up by convective plumes in the Nagoya area around noon, being transported with diffusion to Mt. Fuji in the evening.

Extremely high proportions of soot particles in the upper troposphere over Japan

Observation on tropospheric aerosol particles was carried out on 27 April 1991 over Tsukuba, Japan. Aerosol particles collected in the upper troposphere at 7.5 km altitude were studied by electron microscopy. Soot-containing particles were collected in a large number fraction (0.53) of the submicron particles. Such a high proportion of soot particles in the upper troposphere has not been reported in previous research. From the X-ray analysis, vanadium was also detected in some of the particles, indicating the origin of oil combustion. The oil-well fires in Kuwait are likely to be the origin of these soot particles. Calculated trajectories of the air suggested that these particles over Japan had circled the globe.

Aircraft Observation of CO2, CO, O3 and H2 over the North Pacific during the PACE‐7 Campaign

Aircraft observation under the Pacific Atmospheric Chemistry Experiment (PACE) program was performed from February 13 to 21, 2000 to examine in detail the distributions of CO2 in the free troposphere between 5 and 11 km. Continuous measurements of CO2mixing ratios were made using an on-board measuring system over the northern North Pacific between Nagoya, Japan and Anchorage, Alaska, and the western North Pacific between Nagoya and Saipan. Other trace gases, such as CO and O3, were also observed using continuous measuring systems at the same time. CO2 over the northern Pacific (35¼N and higher) showed highly variable mixing ratios, ranging from 374 ppm in the upper troposphere to 366 ppm in the lowermost stratosphere. This highly variable distribution of CO2 was quite similar to that of CO, but the relationship between CO2 and O3 showed a strong negative correlation. These results indicated that the exchange process between the stratosphere and the troposphere significantly influences the large CO2variation. On the other hand, the CO2 over the western North Pacific to the south of Japan showed no significant variation in the upper troposphere at 11 km but a relatively larger variability at 5 km. The CO2 enhancement at lower altitudes coincided with the CO elevation due to the intrusion of a polluted air mass. Trajectory analysis indicated that the Asian continental outflow perturbed the CO2 distributions over the western Pacific. Very low mixing ratios of O3 of less than 20 ppb were distributed in the latitude band of 15–30¼N at 11 km, reflecting the effects of transport from the equatorial region.

New technique to analyse global distributions of CO2 concentrations and fluxes from non-processed observational data

We have developed a new observational screening technique for inverse model. This technique was applied to our transport models with re-analysed meteorological data and the inverse model to estimate the global distribution of CO2 concentrations and fluxes. During the 1990s, we estimated a total CO2 uptake by the biosphere of 1.4–1.5 PgC yr-1 and a total CO2 uptake by the oceans of 1.7–1.8 PgC yr-1. The uncertainty of global CO2 flux estimation is about 0.3 PgC yr-1. We also obtained monthly surface CO2 concentrations in the marine boundary layer to precisions of 0.5–1.0 ppm. To utilize non-processed (statistical monthly mean) observational data in our analysis, we developed a quality control procedure for such observational data including a repetition of inversion. This technique is suitable for other inversion setups. Observational data by ships were placed into grids and used in our analysis to add to the available data from fixed stations. The estimated global distributions are updated and extended every year.