Using a New Top-Down Constrained Emissions Inventory to Attribute the
Previously Unknown Source of Extreme Aerosol Loadings Observed Annually
in the Monsoon Asian Free Troposphere
Abstract
The contribution of biomass burning to the total aerosol loading over
Monsoon Asia is both significant while also continuing to increase in
recent decades. To better match the spatio-temporal distribution of
aerosols and trace gasses observed in the free troposphere, this work
applied a 3-D constrained emission inventory based on top-down remotely
sensed NO2 measurement to investigate the most extreme
of the annually occurring biomass burning seasons in Monsoon Asia. In
2016 this constituted an extreme event observed over a 6-day period
covering millions of square kilometers, including over regions which are
typically in the rainy phase of the Monsoon at this time. The results
are shown to be consistent with respect to TRMM precipitation, AERONET
measurements, MODIS AOD, MOPITT CO, and reanalysis meteorology, over
both the biomass burning source as well as the millions of square
kilometers downwind both to the East and to the Southwest. Reproducing
the observed long-range transport pattern requires the time of biomass
burning to be increased, regions not previously identified as burning to
be actual source regions, and the emissions of BC to be 6.6 to 11.9 time
larger than current inventories. The underlying mechanism for this
long-range transport involves a new 3-D pathway that can occur during
the transition from the North to the South Monsoon. The results are also
consistent with the new idea that large loadings of BC in the lower free
troposphere may significantly affect the meteorological field and the
overall vertical distribution of aerosols in the tropical troposphere.