Amazonian river winds unraveled by air pollution observations

River winds are induced by the daily thermal contrast between the land and the river. During the daytime, warmer temperatures over the land lead to lighter air masses that are lifted. The air masses in turn drive onshore air movement from the river toward the land. Subsequently, the air subsides over the river. The result is a closed local air circulation cell in the vertical plane (Figure 1). At night, the land cools more rapidly, and the air circulation reverses because the river is warmer. Because these driving forces combine with larger and smaller atmospheric flows of trade winds and local topography, the combined river winds remain elusive and difficult to understand, measure and simulate. A key question then arise: How to obtain accurate observational evidence of these river wind circulations?