Satellite-based dry-wet seasonal changes of OCS surface budgets over the Amazon rainforests

Carbonyl sulfide (OCS) is the most dominant sulfur-containing species in the atmosphere and is an important tracer of the terrestrial gross primary productivity as it is involved only in photosynthesis. Biomass burning and terrestrial uptakes by plants and soil is the primary terrestrial source and sink of OCS, respectively.  The Amazon basin alone accounts for 10% of the global biomass burning emission and 33% of the global plant/soil uptake. However, both terms are sensitive to water stress, heat stress, and the associated wildfires in the dry seasons. Here, we estimate the dry-wet seasonal difference of the terrestrial OCS budget over the Amazon region by constraining the NCAR MOZART4 chemistry-transport model with the mid-tropospheric OCS abundances retrieved from NASA’s Thermal Emission Spectrometer (TES) measurements during 2004 and 2012.  Our perturbative calculations show that biomass-burning emissions that are predominant in the south rim of the Amazon have more influence on the mid-tropospheric OCS over the southeast subtropical Amazon. In comparison, the plant/soil uptakes that are predominant in the tropical Amazon have more influence over the northwest tropical Amazon.  This dipole spatial pattern helps distinguish the mid-tropospheric OCS seasonal variability due to biomass-burning emissions and plant/soil uptakes.