Urban pollution in the Amazon wet season: minimal impact on aerosol, cloud and rain

Anthropogenic emissions* influence aerosol formation, cloud properties, and rainfall, but their effects are highly variable and uncertain.

During the wet season of the Amazon rainforest, pollution from the Brazilian city Manaus can substantially increase cloud condensation nuclei compared to the natural background, yet the response of clouds and precipitation remains unclear. Using high-resolution simulations, Wang X. et al. tested different emission scenarios and found that while doubling emissions raised aerosol concentrations and cloud droplet numbers, the overall impact on cloud water and rainfall was minimal. Even extreme reductions in aerosols only slightly altered rainfall, suggesting that complex microphysical processes buffer the system.

These findings highlight that Amazonian convective clouds are resilient to localized aerosol perturbations, making it difficult to predict linear cause–effect relationships between pollution and rainfall.

*Anthropogenic emissions are tiny particles in the air released by human activities. Take our quiz to learn more!