Observed impacts of aerosol regimes on energy and carbon fluxes in the Amazon forest

Abstract. Atmospheric aerosols play a crucial role in modulating the energy available to the Earth’s surface, influencing the hydrological cycle, ecosystems, and climate. In the Amazon, previous studies have mainly examined how aerosols scatter and absorb radiation. However, little is known about their interactions with energy partitioning (i.e., sensible and latent heat fluxes). Here, we investigate how regimes of high (AOD >0.40) and low (AOD <0.13) aerosol optical depth (AOD) affect surface energy and carbon dioxide (CO2) fluxes in an undisturbed Amazon rainforest. For this, we used long-term meteorological measurements from the Amazon Tall Tower Observatory (ATTO) collected between 2016 and 2022. We find that enhanced aerosol presence reduces both sensible heat flux and energy available for evapotranspiration by approximately 13.5 % and 2.1 % respectively, while increasing CO2 uptake (i.e., CO2 flux becoming more negative) by about 39.5 %. The impact of aerosols on turbulent surface fluxes is reflected in a cooling of approximately 0.9 °C at the canopy top, caused by a 2.8 % reduction in incoming shortwave radiation. These results demonstrate that aerosols modify turbulent energy exchange, with consequences for the forest microclimate and the coupled carbon and water cycles.