Measurements of Brown Carbon during ATom-2

A fraction of the ambient organic aerosol preferentially absorbs light at low wavelengths, hence the name brown carbon (BrC). Largely linked to wildfire emissions, BrC may be an increasingly important climate forcer due to anticipated future increases in wild fires. The global climate impacts of BrC have been assessed through model predictions, however, these results are highly uncertain. A major cause is poor understanding of how BrC changes following emissions. Lack of data over most of the globe limits insights on BrC processing and also assessment of model predictions. Direct measurement of chromophores in aerosol particles from filter samples collected during ATom 2 provided the first global-scale data set on BrC levels. ATom 2, From Atom 2, BrC levels were generally low, but higher levels were observed in certain regions, such as in the mid-Atlantic downwind of African wildfires. Other hot spots included the north Atlantic and portions of the Arctic. Further data analysis, including comparisons with predictions from the Community Atmosphere Model version 5 (CAM5) of the Community Earth System Model (CESM) are used to better understand the sources, atmospheric processes and radiative impacts of BrC on a global scale.