Biomass Burning Emitting Large Amounts of Trace Gases and Aerosols

In recent years, there have been an increasing concerns raised about changes in the global climate that are closely intertwined with chemical variations of the atmosphere. The greenhouse effect and the depletion of the ozone layer are the examples of such changes. It is essential to predict future changes as well as to understand the current situation in order to deal with environmental changes. Science communities around the world have focused on creating chemical transport models with the use of data on chemical processes occurring in the atmosphere to do so.

Since data input into these models plays an extremely important role in their reliability for predicting climate changes, it is important to understand the amount of trace gases and aerosols emitted by industrial activities, forest fires and volcanic eruptions etc. However, there is not sufficient data assure reliability of the models at present.

Of particular urgency is data of trace gases emitted by forest fires. The data of these gases not only have seasonal and geographical variations, but also lacking the background information to estimate the amount released.

Biomass burning occurs almost every year in the tropical regions of Africa, Latin America and Southeast Asia during the dry season (see Fig. 1). Biomass burning is a source of trace gases (CO2, CO, CH4, NMCHs, NOx) and aerosols in the atmosphere. These atmospheric trace constituents and tropospheric ozone (O3), which is produced by photochemical process as a second pollutant, substantially influence chemical processes in the troposphere and the greenhouse effect.

Biomass Burning and Lightning Experiment (BIBLE)

Photo 1 shows a savanna burning in northern Australia. Previously, savanna-burning observation has been focused mainly on Africa and Brazil despite the fact that the burning is frequent in Indonesia and Australia. The National Space Development Agency of Japan (NASDA) conducted the Biomass Burning and Lightning Experiment (BIBLE) between 1998 and 2000. The mission investigated the effects of forest fires and lightning on atmospheric contents variation using an aircraft. In cooperation with researchers from the University of Tokyo, Nagoya University and California University, BIBLE mission took measurements of O3, CO, CO2, NO, reactive nitrogen (NOy), aerosols, condensation nuclei and ultraviolet radiation from the instruments abord Gulfstream-II. Atmospheric species were also sampled in the stainless steel container (see Photo 2).

Fig. 2 shows concentrations of O3, CO, NO, NOy, C2H6 and C2H4 in the upper troposphere (an altitude of 8–13.5 km) measured during BIBLE-A (September – October 1998). The data reveals low concentrations of CO, NO, NOy, C2H6 and C2H4 over the tropical Pacific, and high concentrations over Indonesia. Combining some meteorological analyses and the high concentration of short-lived C2H4, we confirmed that gases were emitted around Indonesia based on the data characteristics specific to such activities.

These emissions also produce O3 through photochemical reactions. Fig. 2 shows high concentrations of O3 over northern Australia to the south of Indonesia, a different distribution from other trace gases.

A backward trajectory analysis revealed that the O3 air mass passed over western Indonesia to northern Australia between four and nine days earlier. Therefore, we concluded that the ozone we observed during the BIBLE-A mission was produced as the emission released near the ground was transported into the troposphere by a strong upwelling over Indonesia.

Based on the BIBLE-A observation data, it was estimated that ozone would be produced during this transportation at an average rate of 1.8 ppbv/day, which well agrees with the calculations based on the photochemical models. The finding was reported as a rare and precious case of quantitative studies on ozone production in the tropical troposphere.

Total Emissions Derived from Satellite Data

The BIBLE-B mission was conducted from August to September 1999 to investigate the effects of trace gases emitted by savanna burning in northern Australia.

A substantial increase in the concentrations of the burning byproduct such as CO2 and CO was observed in the boundary layer near a burning area (at an altitude below 3 kilometers). Since the concentration ratio of these emission was constant and well correlated, it is thought to be derived from a single release source.

Such release ratio is used to find the emission factor – the correlation between the amount of emitted trace gases and biomass burning. By combining the emission factor and forest burning losses estimated from satellite data, we calculated the individual amount of emitted trace gases observed during the BIBLE-B mission.

With the help from Northern Territory Bushfire Council, a local research institute, we have made detailed study of NOAA-AVHRR and LANDSAT-TM data and Australia-specific vegetation parameters accumulated in past field research. As a result, we were able to significantly reduce the error in the emission amount estimate than the estimate that has previously been reported.

Such a detailed information of the savanna burning in Australia, where the observation had been limited is expected to improve the quality of the database incorporated into atmospheric chemical models.

Also, in the BIBLE-B mission, changes in trace gas concentrations were observed at upwind, downwind, and directly above the burning areas, and analyzed with concentration change of the byproduct and photochemical transport models. This has enabled us to quantitatively describe photochemical process that the gases emitted from the savanna burning go through, and the effect it provide on climate change.

Airborne Observations in Japan

The BIBLE-C mission was conducted from November to December 2000. Its objective was to conduct the quantitative estimation and effect evaluation of atmospheric nitrogen oxides generated by the lightning. Which are frequent during the period from the end of the dry season through much of the rain season in northern Australia.

Researchers observed the lightning involved air mass along their path and extracted the rates and amounts nitrogen oxides production from the increase in their concentration. The acquired information will be very useful to the international science community.

The researcher’s findings from these three BIBLE missions spanned over three years have been presented in research papers, and they will be compiled and published in the BIBLE Special Section in the Journal of Geophysical Research.

By the way, evaluating the effects of the recent revitalization of Asian industrial activities on rapid changes in the compositions and amounts of trace gases have increasingly become an important issue. NASDA has launched a new airborne observation project called the Pacific Exploration of Asian Continental Emission (PEACE), and performed its first mission in Japan between December 2001 and January 2002.

Collaborative Observations Contributing to Future Plans

PEACE mission observed the polluted air flowed from the Asian continent to Japan and examined its specific sources by comparing obtained data with the distributions of pollutants predicted from atmospheric chemical transport models. Also, the mission obtained data on SO2 while testing an air pollution observation sensor slated to be mounted onboard a satellite. This data is expected to provide us useful information.

Satellite observations are effective tools in monitoring the progress of large-scale phenomena in extensive areas over a long period of time. However, collaboration with airborne and ground-based observations is required to observe shorter and smaller scale phenomenons, including those occurs under the cloud. The atmospheric observation data accumulated by the PEACE mission does not only have the scientific importance in itself but also provide the important data set that would contribute to the things such as evaluation of the satellite data and formulation of international environment policy.


* Please access to the below website for details of the BILBE missions.

http://www.eorc.jaxa.jp/AtmChem/GLACE/bible/BIBLE.html