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superimposed, on the long-term decreasing trend of CO concentration in the tro-
posphere, observed in the 1990s. It turned out that the instability of standard
samples used for calibration determined the systematic underestimation of the
observed CO concentration. Novelli et al. (2003) showed that the decrease of
tropospheric CO is con
ned mainly to the Northern Hemisphere, where emissions
to the atmosphere due to fossil fuel burning were substantially lower, constituting
1.8
0.2 ppb year
−
1
. In the Southern Hemisphere, between 1991 and 2001, this
trend was not observed.
The globally averaged CO concentration is characterized by a strong interannual
variability explained mainly by interannual changes of the scale of biomass burn-
ing. During the whole period of observations, the globally averaged CO concen-
tration was decreasing by about 0.5 ppb year
−
1
;
±
this decrease was mainly
concentrated north of 30
°
N. A strong increase of CO content in the troposphere
observed in 1997
1998 was connected with the impact of unusually widespread
and intensive forest
-
fires; more that 300 TgCO were emitted to the troposphere
because of
fires in boreal forests, such emissions can
cause changes of the dynamics of redox reactions in the troposphere on global
scales.
Wet tropical forests in the Amazon basin play a special role in the global eco-
dynamics due to huge sizes of their territory (about 5
fires. In the years of large-scale
10
6
km
2
) and high biotic
activity. Here all-the-year-round emissions to the atmosphere of natural biogenic
aerosol take place both of primary (micro-organisms, pollen, detritus of vegetative
origin) and secondary aerosol appearing due to gas-to-particles transformation of
organic, nitrogen- and sulphur-containing GHGs emitted to the atmosphere by
plants. In the dry season period, this background aerosol is
×
“
suppressed
”
by smoke
aerosol caused by deforestation and burning of biomass remains.
The processes of intensive convection and advection determine the long-range
transport of both types of aerosol to higher latitudes, with far-reaching conse-
quences from the viewpoint of affecting the chemical reactions in the atmosphere,
as well as the formation of climate and biogeochemical cycles of nutrients. On the
other hand, natural aerosol comes to the Amazon basin from distant regions,
including marine aerosol from the Atlantic Ocean and dust aerosol from Sahara,
which can serve as signi
cant nutrients for wet tropical forests. In July 2001, near
the city of Balbina, in the center of the Amazon region, Graham et al. (2003) carried
out measurements of aerosol which showed that the atmosphere contains both
coarse-scale and
fine-scale fractions, which consisted of organic compounds by 70
and 80 %, respectively. Coarse-scale aerosols also contained a small amount of soil
dust and sea-salt particles, while
fine-scale aerosols contained some amount of non-
marine sulphate. The concentration of coarse-scale aerosol particles averaged
3.9
gm
−
3
with the ratio of nocturnal to daytime values 1.9
±
ʼ
±
1.4
0.4, whereas the
concentration of
fine-scale aerosols increased in the daytime (an average of
gm
−
3
, with the ratio 0.7
±
ʼ
±
2.6
0.1).
Biomass burning during the last decades has increased with the growing pop-
ulation size. The geographical zones of intensive biomass burning have broadened.
Most considerable components of emissions in biomass burning include CO
2
, CO,
0.8
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