|
Biomass burning is the burning of
living and dead vegetation. It includes the human-initiated burning
of vegetation for land clearing and land-use change as well as
natural, lightning-induced fires. Scientists estimate that humans
are responsible for about 90% of biomass burning with only a small
percentage of natural fires contributing to the total amount of
vegetation burned.
 Burning vegetation
releases large amounts of particulates (solid carbon combustion
particles) and gases, including greenhouse gases that help warm the
Earth. Greenhouse gases may lead to an increased warming of the
Earth or human-initiated global climate change. Studies suggest
that biomass burning has increased on a global scale over the last
100 years, and computer calculations indicate that a hotter Earth
resulting from global warming will lead to more frequent and larger
fires. Biomass burning particulates impact climate and can also
affect human health when they are inhaled, causing respiratory
problems (Fig. 1).
Since fires produce carbon
dioxide, a major greenhouse gas, biomass burning emissions
significantly influence the Earth's atmosphere and climate. Biomass
burning has both short- and long-term impacts on the environment.
Vegetation acts as a sink -- a natural storage area -- for carbon
dioxide by storing it over time through the process of
photosynthesis. As burning occurs, it can release hundreds of years
worth of stored carbon dioxide into the atmosphere in a matter of
hours. Burning also will permanently destroy an important sink for
carbon dioxide if the vegetation is not replaced.
What is the annual, global amount
of greenhouse gases that are released into the atmosphere due to
biomass burning? How does biomass burning impact the Earth's
atmosphere and climate? Researchers involved in the Biomass Burning
Program at NASA Langley Research Center (LaRC) are currently
working to answer these questions. The major goal of this research
is to quantify the effects of global fires on the composition and
chemistry of the atmosphere and the Earth's climate.
Field experiments
From 1986-1993, LaRC scientists
conducted 12 field experiments from aircraft to measure the amount
of gases and particulates from fires in six different ecosystems.
Measurements were taken during chaparral fires in California (1986,
87), wetland fires in Florida (1987, 88), boreal forest fires in
Canada (1987, 88, 89, 90), tropical rainforest fires in Mexico
(1990, 91), savanna grassland fires in South Africa (1992), and
boreal forest fires in Siberia (1993).
Scientists also studied the
southeast Asia fires in 1997. These fires were unique since they
involved both the burning of above-ground vegetation and
below-ground peat -- a form of coal. Smoldering peat produces more
gases and particulates than burning vegetation per unit area. These
fires covered an area of more than 45,000 square kilometers -- an
area comparable to the combined area of Rhode Island, Delaware,
Connecticut, and New Jersey. The fire's thick smog cloud covered
almost all of southeastern Asia, resulting in more than 20 million
cases of smog-related health problems. Gases and particulates
produced during the 1997 fires were measured as far away as
Hawaii.
From these field experiments,
scientists measured greenhouse gases (carbon dioxide, methane, and
nitrous oxide), chemically active gases (carbon monoxide and nitric
oxide), and particulates from diverse ecosystems. This research
showed how the production of gases and particulates from fires
varies with the type of ecosystem burned, the fire's
characteristics, and the vegetation's moisture content. As a result
of these measurements, LaRC researchers developed a fire combustion
model to determine emissions from each ecosystem based on fire
temperature. Knowing the amount of emissions is important for
accurate estimates of the environmental impacts of these greenhouse
gases. In addition, this model is useful for determining the
contribution of biomass burning to the total production of
greenhouse gases, a requirement for the Kyoto Treaty. This
international treaty limits the amount of greenhouse gas emissions
of certain industrialized nations.
 Researchers also discovered
that bacteria in soil enhance production of the greenhouse gas
nitrous oxide. Nitrification is a biological process where bacteria
convert ammonium, found naturally in soil and also in fire ash, to
nitric oxide and nitrous oxide. They believe that the increased
concentrations of ammonium in the ash lead to more nitrification
after a fire, thereby releasing additional nitric oxide and nitrous
oxide. The amount of these gases produced by bacteria after a fire
may surpass the amount released during biomass burning.
Space measurements
The only way to accurately
determine the exact location and extent of fires is to have a
global perspective from space, making space-based measurements
extremely important. Since no satellite has ever been dedicated to
fire monitoring and measuring, most observations of fires from
space are obtained from existing satellites developed for other
purposes. Astronauts also photograph fires from the Space Shuttle
(Fig. 2). Fire measurements come from the Defense Meteorological
Satellite Program (DMSP) satellites and the Advanced Very High
Resolution Radiometer (AVHRR) on the National Oceanic and
Atmospheric Administration (NOAA) satellites. DMSP nighttime images
provide information about the location and frequency of active
fires, while AVHRR satellites can help determine the size of the
area burned. Remote sensing of global fires indicates that Africa
is the "fire center" of the planet with more biomass consumed by
fire in Africa than anywhere else on Earth (Fig. 3).
 Future research
The year 2000 was one of the worst
fire years ever recorded in the United States. As of November 14,
2000, a total of 90,674 wildfires burned 7.26 million acres across
the United States as compared to the previous ten-year average
(1990-1999) of 3.79 million acres burned. On one day, August 29,
2000, 84 large fires (100 acres or more) were burning
simultaneously. Total fire suppression cost in 2000 was about $1.6
billion, making fire monitoring an important social, health,
economic, and national security concern.
Scientists are continuing to
develop new instruments for measuring and monitoring fire from
aircraft and spacecraft. This research will help assess the impact
of fire-produced gases and particulates on atmospheric composition
and chemistry and on climate. In August 2000 and January 2001,
researchers set controlled fires at the Impact Dynamics Research
Facility at LaRC to test new fire monitoring and measurement
instrumentation that will eventually help researchers study global
fires (Fig. 4 and Fig. 5). Tests like these will support the
Interagency Agreement signed in November 2000 between LaRC and the
United States Department of Agriculture Forest Service.
In this partnership, LaRC will
develop instruments for the remote sensing of fires to be flown on
aircraft by the Forest Service. Instruments will monitor active
fires, measure fire temperature and the area burned, and provide an
exact geographical location of a fire. Information from these
instruments will also help fire fighters more efficiently and
economically plan how to control and fight fires. The fire
monitoring instrumentation will provide information about the fire
to the ground in real time, giving fire fighters an unique and
comprehensive perspective to help meet the growing demands of fire
control in the United States.
|
