Tropospheric Ozone Assessment Report II: South America regional analysis

This study presents the first regional assessment of tropospheric ozone over South America for the early twenty-first century. We use observations from 14 combined satellite records, two atmospheric reanalyses, and model simulations to examine the spatial distribution, source contributions and trends in ozone and its precursors. Satellites and reanalysis data reveal enhanced tropospheric column ozone over the mid-latitudes of the west coast and the subtropical east coast, with 2005-2021 median values (±2σ) ranging from 46 [±11] to 49 [±9] nmol mol-1. By contrast, the lowest ozone levels occur over the northwest (39 [±8]-42 [±8] nmol mol-1) and the southern cone (38 [±11]-40 [±7] nmol mol-1). Tropospheric column ozone trends (±2σ) differ across South America (2005-2021), reflecting substantial subregional and partial column variability. Satellite observations suggest an overall negative trend (low certainty), whereas reanalyses show positive trends with high certainty, ranging from +0.55 [±0.85] to +0.85 [±0.70] nmol mol-1 decade-1. Model simulations identify global background methane as the dominant contributor to the South American tropospheric ozone burden, accounting for 41% (17 of 42 nmol mol-1), followed by global anthropogenically emitted nitrogen oxides (31%). These findings improve our understanding of chemical processes and provide valuable inputs for assessing air quality and climate impacts. This article is part of the theme issue 'Tropospheric Ozone Assessment Report II'.