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Abstract:
Multiannual satellite measurements of tropospheric
NO2 columns are used for evaluation of CO2 emission
changes in China in the period from 1996 to 2008. Indirect
top-down annual estimates of CO2 emissions are derived
from the satellite NO2 column measurements by means
of a simple inverse modeling procedure involving simulations
performed with the CHIMERE mesoscale chemistry–
transport model and the CO2-to-NOx emission ratios from
the Emission Database for Global Atmospheric Research
(EDGAR) global anthropogenic emission inventory and Regional
Emission Inventory in Asia (REAS). Exponential
trends in the normalized time series of annual emissions
are evaluated separately for the periods from 1996 to 2001
and from 2001 to 2008. The results indicate that the both
periods manifest strong positive trends in the CO2 emissions,
and that the trend in the second period was significantly
larger than the trend in the first period. Specifically,
the trends in the first and second periods are best estimated
to be in the range from 3.7 to 8.3 and from 11.0 to 13.2%
per year, respectively, taking into account statistical uncertainties
and differences between the CO2-to-NOx emission
ratios from the EDGAR and REAS inventories. Comparison
of our indirect top-down estimates of the CO2 emission
changes with the corresponding bottom-up estimates
provided by the EDGAR (version 4.2) and Global Carbon
Project (GCP) glomal emission inventories reveals that while
acceleration of the CO2 emission growth in the considered
period is a common feature of both kinds of estimates, nonlinearity
in the CO2 emission changes may be strongly exaggerated
in the global emission inventories. Specifically,
the atmospheric NO2 observations do not confirm the existence
of a sharp bend in the emission inventory data time
series in the period from 2000 to 2002. A significant quantitative
difference is revealed between the bottom-up and
indirect top-down estimates of the CO2 emission trend in
the period from 1996 to 2001 (specifically, the trend was
not positive according to the global emission inventories,
but is strongly positive in our estimates). These results confirm
the findings of earlier studies that indicated probable
large uncertainties in the energy production and other activity
data for China from international energy statistics used as
the input information in the global emission inventories. For
the period from 2001 to 2008, some quantitative differences
between the different kinds of estimates are found to be in the range of possible systematic uncertainties associated with
our estimation method. In general, satellite measurements of
tropospheric NO2 are shown to be a useful source of information
on CO2 sources collocated with sources of nitrogen oxides; the corresponding potential of these measurements should be exploited further in future studies
