Fine and coarse aerosols control of cloud water by evaporation-precipitation dynamics

Abstract

Fine aerosols (FA, radius <1 µm) may enhance cloud albedo for a given liquid water path (LWP), thereby partially offsetting greenhouse gas-induced warming. However, the aerosol-driven LWP adjustment is currently heavily debated due to conflicting observations. Here, we observationally found that both FA and coarse sea spray aerosols (CSA, radius > 1 µm) exhibit bidirectional regulation on LWP adjustments through precipitation-evaporation competition. In marine stratocumulus with moderate thickness, under dry cloud-top environments (RH < 20%) where evaporation dominates, FA decreases LWP by ~15% while CSA induces a slight ~8% increase. Conversely, in humid cloud-top environments (RH > 80%) favoring precipitation processes, the addition of FA more than doubles LWP, whereas the addition of CSA nearly halves it. Thin cloud LWP changes are primarily driven by droplet evaporation, while deep cloud LWP changes are dominated by precipitation. Our findings underscore the necessity to resolve precipitation-evaporation dynamics and opposing FA and CSA effects for credible aerosol-cloud interaction simulations.