Interactive versus inventory-based BVOC emissions reshape regional cloud-radiative and ozone feedbacks in EC-Earth3-AerChem-BVOC

Biogenic Volatile Organic Compounds (BVOCs) influence aerosol-cloud interactions and climate radiative impacts by changing the formation of Secondary Organic Aerosols (SOA) and atmospheric oxidation capacity. Current Earth System Models (ESMs) typically employ two approaches to BVOC emissions: prescribed offline emission inventories (e.g., MEGAN) or online calculated emissions that do not link to plant physiological processes or vegetation dynamics. To date, most ESMs generally lack a fully interactive coupling of plant BVOC emissions with photosynthesis-based ecosystem processes, vegetation dynamics, meteorology, and atmospheric chemistry, thus the quantified impacts on global/regional radiative forcing and climate patterns remain insufficiently understood.
In this study, we integrated a process-based vegetation BVOC emission scheme that is fully coupled with the TM5 atmospheric chemistry component within EC-Earth3-AerChem. Leveraging this interactive capability, we evaluate the impact by contrasting a simulation driven by prescribed offline inventories against this online experiment. Results for the boreal summer (JJA) indicate that while the online-coupled BVOC scheme captures the general global distribution of BVOCs, it significantly reshapes regional emission hotspots. Specifically, tropical forest source regions exhibit distinct spatial heterogeneity, characterized by an east-west dipole in the Amazon and a core-periphery contrast in the Congo Basin. This emission redistribution caused by online coupling further induces significant changes in SOA optical depth (diagnosed at 550 nm) and Cloud Condensation Nuclei (CCN) concentrations, accompanied by a widespread increase in mid-tropospheric (500 hPa) ozone across the tropics and subtropics.
With an online coupled BVOC scheme, the Shortwave Cloud Radiative Effect (SWCRE) becomes more negative (enhanced cloud cooling) over large areas, consistent with the spatial patterns of net Top-of-Atmosphere (TOA) radiation differences. The surface temperature response presents significant regional divergence, consistent with competing contributions in the radiative budget. Over the Congo Basin, warming signals are linked to widespread reductions in SOA and CCN, which weaken the aerosol cooling effect. In contrast, over parts of the Eastern Amazon, warming occurs despite increased SOA loading, suggesting that the greenhouse effect from enhanced tropospheric ozone overrides the local aerosol cooling potential. Meanwhile, cooling signals appear over ocean regions such as the North Atlantic, consistent with enhanced SWCRE. This suggests that interactive BVOC emissions reshape regional temperature responses primarily through combined BVOC–SOA–cloud and ozone feedbacks.
Overall, compared with the offline inventory approach, online coupled BVOC emissions in EC-Earth3-AerChem significantly change spatial patterns of regional radiative impact and temperature response, indicating that the dynamics in BVOC emissions themselves may be an important source of regional uncertainty in chemistry-coupled climate simulations.