Radiative forcing of anthropogenic Brown Carbon in EC-Earth3

Brown carbon (BrC) influences atmospheric radiative forcing through its unique light-absorption characteristics. The role of  BrC as a significant absorbing component of organic aerosols (OA) has profound implications for understanding its impact on climate systems. However, the complex processes forming BrC, along with the chemical and optical properties that determine its behavior are not yet fully understood. These challenges are compounded by the fact that BrC's sources, formation processes, and interactions with other atmospheric components remain partially unknown. 

Existing approaches to represent BrC in climate models range from intermediate schemes that explicitly account for its emission and aging to simplified methods that assume constant weak absorbing properties in OA. Furthermore, studies indicate that BrC may impose a radiative burden comparable to black carbon (BC), potentially amplifying the overall forcing exerted by carbonaceous aerosols. 

However, it is not entirely clear how brown carbon contributes to atmospheric radiation and what role it plays in climate. Previous studies have offered varying estimates of BrC  direct radiative effect (DRE), underscoring the need for refined modeling and observational data to understand BrC's role in atmospheric dynamics and its contribution to global warming.  Here, we examined the global radiative impacts of anthropogenic BrC emissions using the EC-Earth3 Earth System Model. This study aims to address the significant uncertainties in climate modeling by enhancing the representation of BrC in models. This includes incorporating additional sources to provide more accurate estimations of its radiative effects.  Furthermore, the study will assess the role of BrC in driving regional climate variations and their potential contributions to global climate forcing. For the BrC emissions, we used the ECLIPSE (Evaluating the Climate and Air Quality Impacts of Short-lived Pollutants) dataset, developed by the Finnish Environment Institute. Also, we used the Organic Carbon (OC) and BC emissions from the ECLIPSE emission dataset. EC-Earth3 simulations were conducted across different years to represent both historical and future scenarios. Each simulation was run for six years, including a one-year spin-up period.  

Our preliminary results from historical simulations for the year 2010 indicate that the global mean direct radiative forcing of anthropogenic BrC emissions is negligible. However, regional effects are significantly more pronounced, which need to be studied further.