Do downdrafts always induce near-surface ozone enhancements above the Amazon region?

The investigation of atmospheric gases in the central Amazon, with emphasis on tropospheric ozone (O₃), is fundamental to understanding impacts of climate change and anthropogenic activities. While previous studies associated downdrafts with near-surface O₃-enhancement, cases of O₃-decrease are still less explored. This study was conducted during the field mission from GoAmazon 2014/15 project. Experimental data and vertical O₃ profiles from ERA5 reanalysis were used. 73 downdraft events were identified, of which around 51% were associated with near-surface O₃-enhancement and the rest with decrease or minor variations. Numerical simulations were performed using the WRF-Chem model to investigate the three-dimensional dynamics of O₃ during downdraft events. Two representative cases in O₃ concentrations were selected to assess the model's performance. The study revealed that the variability of near-surface O₃ is driven by the O₃ concentration in the middle troposphere as well as the wind direction patterns that precede the downdrafts. Our analysis shows that downdrafts carry air masses that have higher or lower concentrations of O₃ than those near the surface. It was observed that wind direction, O₃ concentration in the middle troposphere, and O₃ concentration near the surface are identified as key factors that define whether the occurrence of a downdraft will result in an increase or decrease in surface O₃. Enhancement events were associated with an increase of 11 ppbv, while decrease events showed reductions of 10 ppbv. These results may contribute to better parameterizations of some chemical processes in atmospheric models.