chapter - Atmospheric and Oceanic Science

Background on other regional aspects: Land use change, aerosols and trace gases
of tropospheric ozone concentrations correspond to the seasonal cycle and extent of
biomass burning in tropical South America (Kaufman, 1998).
Tropospheric ozone associated with biomass burning is an important greenhouse
gas and modifies atmospheric chemistry though its impact on the radical OH
that affects the atmospheric cleansing capacity and it has an indirect effect on the
greenhouse gas concentration. Photochemical production of ozone is tied to the
abundance of pollutants from sources such as biomass burning, and urban pollution.
Ecosystems have a significant interaction with the tropospheric ozone. Some
vegetation emissions play an important role in cleansing the atmosphere of tropospheric
ozone but may also increase the concentration through photochemical reactions
associated the VOC's emitted by vegetation Tropospheric measurement of
ozone concentration in S. America have been showing significant concentration in
rural areas, away from main urban centers and have been attributed to biomass
burning (Andreae et al. 1988; Kirschhoff et al. 1988).
During the peak of the burning season in central South America the number
of particles in the air goes up an order of magnitude from the values during the rest
of the year (Martins et al 1998). Solar radiation and in particular the
Photosynthetically Active Radiation (PAR) reaching the surface is reduced by about
10-30% reducing surface temperature and light available for plant growth (Schafer
et al. 2002) . The effect of this on vegetation is not well established (Gu et al. 2004).
A dynamical vegetation model was successfully coupled to the mesoscale atmospheric
model with the biomass burning aerosols emission module. It has been
shown that the non-linear effects associated to the interaction between the aerosols,
radiation and vegetation are responsible for significant changes in the vegetation
properties and the precipitation regime in the transition season between the dry and
wet periods in southwestern Amazonia. A preliminary report was presented by
Moreira et al. (2004).
However particulate matter containing black carbon and greenhouse gases
absorb radiation causing warming. The combination of a cooler surface (by a couple
of degrees) for lack of solar radiation and a warmer boundary layer due to
absorption increases the thermal stability and reduces the chances of cloud formation,
thus reducing the possibility of rainfall. Freitas et al. (2004) have indicated the
possibility of rainfall decrease in the La Plata Basin as a response to the radiative
effect of the aerosol load transported from biomass burning the Cerrado and
Amazon regions. An individual case studied by Freitas et al. (2004) during the transition
period from the dry to the wet season in central South America (September)
suggests a reduction of precipitation of the order of 10-15% in Southern
Brazil/Uruguay in a particular event.
The beginning of the South American Monsoon System is characterized by
the transition of a very polluted to a clear atmosphere, due to biomass burning.
Biogenic aerosol and aerosol produced by biomass burning have a direct role on the
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