Abstract
We use an inverse model analysis to compare the top-down constraints on Asian sources of carbon monoxide (CO) in spring 2001
from (1) daily MOPITT satellite observations of CO columns over Asia and the neighboring oceans and (2) aircraft observations
of CO concentrations in Asian outflow from the TRACE-P aircraft mission over the northwest Pacific. The inversion uses the
maximum a posteriori method (MAP) and the GEOS-CHEM chemical transport model (CTM) as the forward model. Detailed error characterization
is presented, including spatial correlation of the model transport error. Nighttime MOPITT observations appear to be biased
and are excluded from the inverse analysis. We find that MOPITT and TRACE-P observations are independently consistent in the
constraints that they provide on Asian CO sources, with the exception of southeast Asia for which the MOPITT observations
support a more modest decrease in emissions than suggested by the aircraft observations. Our analysis indicates that the observations
do not allow us to differentiate source types (i.e., anthropogenic versus biomass burning) within a region. MOPITT provides
ten pieces of information to constrain the geographical distribution of CO sources, while TRACE-P provides only four. The
greater information from MOPITT reflects its ability to observe all outflow and source regions. We conducted a number of sensitivity
studies for the inverse model analysis using the MOPITT data. Temporal averaging of the MOPITT data (weekly and beyond) degrades
the ability to constrain regional sources. Merging source regions beyond what is appropriate after careful selection of the
state vector leads to significant aggregation errors. Calculations for an ensemble of realistic assumptions lead to a range
of inverse model solutions that has greater uncertainty than the a posteriori errors for the MAP solution. Our best estimate
of total Asian CO sources is 361 Tg yr−1, over half of which is attributed to east Asia.
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