Highlights

Highlights from the Mini-campaign before BIBLE-A

1. The Gulfstream II jet aircraft JA8431 that can fly up to 13 km altitude was equipped with a set of instruments that enabled us to measure various atmospheric trace gases, aerosols and radiation: CO₂, CO, O₃, NO, NO_y, H₂O, aerosol size distribution and condensation nuclei with direct measurement in the aircraft; hydrocarbons, methyl halides, CFCs and HCFCs with whole air sampling and laboratory analysis; and PAN with cold trap and laboratory analysis. These chemical species are all important in the atmospheric radiation/climate system and in controlling the oxidative capacity of atmosphere and thereby air quality. The mini-campaign was carried out over/near Japan during 17 - 24 April 1998 for testing the instrument performance, along with investigating the distributions of trace gases and aerosols over/near Japan.

2. At 1:30 p.m. - 3:30 p.m. JST on 22 April 1998, at ~10 km altitude in latitudes 35⁰ N - 39⁰ N along a longitude of 144⁰ E, we observed many spike-like enhancements of NO and condensation nuclei concentrations. The horizontal size of the enhancement spikes was estimated to be 800 m in north-south direction. The peak NO concentration was 100 - 600 p Mol/Mol and once exceeded 1 n Mol/Mol, while the background NO level was as low as 50 p Mol/Mol that is considered as the typical background value in the Pacific troposphere. Note that the typical NO concentration level in the Japanese city air is ~20 n Mol/Mol.

Considering that the observation was carried out in the air traffic corridor for frequent flights between Japan and North America and in the downstream of the air traffic corridor for Japanese domestic flights and flights between Korea and North America, and in the time span of frequent air traffic, the observed spikes are ascribed to the plumes exhausted from aircraft engines. The observation frequency of the NO spikes seems to be less near Japan over the Pacific than over the Atlantic, as compared to the results obtained by similar observations during the NASA's SONEX campaign. It is not likely at the moment that the aircraft emission impacts the NO concentration seriously in the upper troposphere over/near Japan.

3. On 24 April 1998 over Japan Sea in latitudes 43⁰ N - 44⁰ N, we observed an air mass of elevated concentrations of CO, NO, NO_y, n-butane and condensation nuclei at altitudes 8 - 11 km.

According to the back trajectory analysis and the satellite cloud images, this air mass was located in the frontal convective region around Tenjin 2 days ago. This is an evidence that urban polluted air in a big Chinese city is blown up to the upper troposphere due to strong convection and transported aloft with the westerlies to over Japan or over the Pacific.

Highlights from BIBLE-A

1. In order to investigate the impact of biomass burning on tropospheric ozone chemistry in tropical Asia, BIBLE-A carried out the aircraft measurements of tropospheric ozone and related chemical species during 21 September - 10 October 1998. Following the local test flight in Nagoya, BIBLE-A took ferry flights among Nagoya, Saipan, Biak, Darwin, Bandung, Balikpapan, Biak, Saipan and Nagoya; one local flight based on Darwin; and 5 local flights based on Bandung. We obtained the horizontal distributions of trace gases and aerosols in the upper troposphere during ferry flights and the altitude distributions for 1 - 13 km altitudes during spiral flights and take-off/landing. Japanese and Indonesian scientists deployed ground-based observations on altitude profiles of pressure, temperature, winds and ozone concentration at several sites in Indonesia using balloon radiosondes.

2. The campaign was taken place in local dry season. However, there was a rainfall every day in Kalimantan, Sumatra and Java because of the year of La Nina. Convective clouds were commonly seen in the afternoon during the campaign period, and convection was active enough to yield lightning. On the other hand, hot spots due to biomass burning were observed with the NOAA/AVHRR satellite images.

Ozone (O₃) concentration above 3 km altitudes was less than 25 n Mol/Mol over the Indonesian region, confirming the ozone concentration to be identical to those observed so far in the tropics. NO, NO_y and CO concentrations were as low as the typical value over the western Pacific, being consistent to the low ozone concentration. In contrast to these background levels, air masses of elevated NO, CO, CO₂ and O₃ concentrations were frequently observed. They may be originated from biomass burning or urban air pollution. We were able to observe biomass burning plumes in the lower troposphere over Kalimantan and Sumatra. In addition we obtained the data implying that the air mass of urban pollution in a big city was transported up to 13 km altitude due to strong convection, along with the data implying that lightning affected the NO concentration at 13 km altitude.

3. Concentrations of O₃, CO, NO_y and some non-methane hydrocarbons in the upper troposphere over the Pacific were high in latitudes north of 22⁰ N or 26⁰ N, suggesting that polluted air masses of Asian continental origin were transported by the westerlies, while they were lower in lower latitudes ( 0⁰ to 20⁰ N) than in middle latitudes. Over Northern Australia, O₃, CO and NO_y concentrations were generally lower than those in middle latitudes. However, there was an air mass of concentration as high as those in middle latitudes. According to the back trajectory analysis, it is conceived to be originated from biomass burning in Africa.

Preliminary Results from BIBLE-B

1. In order to investigate the atmospheric environmental impact of bush fires in Northern Territory, Australia, BIBLE-B carried out an aircraft observation of altitude/horizontal distributions of atmospheric trace gases and aerosols near Darwin on 28 August to 13 September, 1999 in local dry season. The measurement was made by taking the ambient air into the instruments aboard a Gulfstream II jet aircraft with respect to CO, CO₂, O₃, NO, NO₂, NO_y, H₂O, aerosols, condensation nuclei and soot particles, or into the on-board canisters to analyze hydrocarbons and halocarbons in the laboratory, along with upward/downward ultraviolet radiation fluxes.

2. Tropospheric ozone concentration at latitudes 10⁰ S - 15⁰ S in Northern Australia (over Cape York Peninsula, Arafra Sea, Arnhem Land and Timor Sea) was 40 n Mol/Mol on the average, and was larger than the background average concentration of 20 n Mol/Mol in the equatorial Pacific, suggesting that photochemical ozone production was significant in this region due to the enhancement of ozone precursor gases such as nitrogen oxides and hydrocarbons released in bush fires.

On the other hand, CO and CO₂ in the middle and upper troposphere exhibited the average concentrations of 70 n Mol/Mol and 367 - 368μMol/Mol, respectively in Northern Australia. These values are equivalent to those in the equatorial Pacific. Since the atmospheric residence time of these species are longer than that of ozone, they are apt to be homogenized in the regional scale as a consequence of atmospheric mixing due to convection and diffusion.

3. Bush fires were observed every day and place in Northern Territory from the ground and space during the campaign period. The air mass measured over bush fires presented locally enhanced concentrations of CO, CO₂, NO, NO₂, NO_y, hydrocarbons, methyl halides and soot particles. Ozone concentration enhanced up to 80 n Mol/Mol in the plumes originated from bush fires. These enhancements were confined mostly in the planetary boundary layer below 3 km altitude. This is a consequence of less convective activity in local dry season.

We observed air massses originated from biomass burning sometimes above 5 km altitude. A further study is necessary to identify the source region of these air masses: whether they were of nearby Australian origin or brought by long-range transport from Africa.

4. The observation shows that the plume originated from bush fires was transported by the easterly to a horizontal distance of more than 1000 km over Timor Sea at 1.0 - 1.5 km altitude.