River winds and pollutant recirculation near the Manaus city in the central Amazon

Tianning Zhao,Scot T Martin,Alex B Guenther,Yongjing Ma,Jianhuai Ye,Jordi Vilà-Guerau De Arellano,Carla E Batista,Hui-Ming Hung,Matthew P Stewart,Patricia C Guimarães,Rodrigo A F De Souza,Igor O Ribeiro

doi:10.1038/s43247-021-00277-6

Abstract

Local atmospheric recirculation flows (i.e., river winds) induced by thermal contrast between wide Amazon rivers and adjacent forests could affect pollutant dispersion, but observational platforms for investigating this possibility have been lacking. Here we collected daytime vertical profiles of meteorological variables and chemical concentrations up to 500 m with a copter-type unmanned aerial vehicle during the 2019 dry season. Cluster analysis showed that a river-forest recirculation flow occurred for 23% (13 of 56) of the profiles. In fair weather, the thermally driven river winds fully developed for synoptic wind speeds below 4 m s−1, and during these periods the vertical profiles of carbon monoxide and total oxidants (defined as ozone and nitrogen dioxide) were altered. Numerical modeling shows that the river winds can recirculate pollution back toward the riverbank. There are implications regarding air quality for the many human settlements along the rivers throughout northern Brazil.

Highlights

IntroductionLocal atmospheric recirculation flows (i.e., river winds) induced by thermal contrast between wide Amazon rivers and adjacent forests could affect pollutant dispersion, but observational platforms for investigating this possibility have been lacking
Local atmospheric recirculation flows induced by thermal contrast between wide Amazon rivers and adjacent forests could affect pollutant dispersion, but observational platforms for investigating this possibility have been lacking
Vertical profiles of 1-m resolution were collected by the Unmanned aerial vehicles (UAVs) once per hour from surface elevation to 500 m for 56 flights

Summary

Introduction

Local atmospheric recirculation flows (i.e., river winds) induced by thermal contrast between wide Amazon rivers and adjacent forests could affect pollutant dispersion, but observational platforms for investigating this possibility have been lacking. In the absence of further complicating effects of local topography and other factors, such as frequent inclement weather during the wet season and weakened thermal contrast under cloudy skies, a return wind from the land to the river can develop overhead at several hundred meters in altitude In this way, closed recirculating sub-cells of river winds at the small mesoscale are possible. Vertical profiles of meteorological and chemical data from surface elevation to 500 m were collected by a UAV during the daytime over a wide river in the central Amazon of northern Brazil in the dry season. Implications for the air quality of nearby human populations were quantitatively examined through a pairing between the observations and an idealized, local large eddy simulation

Methods

Results

Conclusion