Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO2 Ratios

Freitas, Arthur Dias; Zacharias, Daniel Constantino; Paim, Bruna Lüdtke; Borbon, Agnès; Fornaro, Adalgiza

doi:10.3390/rs18101603

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Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios

by

Arthur Dias Freitas

^1,*

,

Daniel Constantino Zacharias

²

,

Bruna Lüdtke Paim

¹

,

Agnès Borbon

³

and

Adalgiza Fornaro

¹

Departamento de Ciências Atmosféricas, Instituto de Astronomia, Geofísica e Ciências Atmosféricas (IAG), Universidade de São Paulo (USP), Rua do Matão, 1226, Cidade Universitária, São Paulo 05508-090, SP, Brazil

²

Centro de Ciências Ambientais, Universidade Federal do Sul da Bahia, Rodovia BR-367 Km 10 Zona Rural, Porto Seguro 45810-000, BA, Brazil

³

Laboratoire de Météorologie Physique (LaMP), CNRS, Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Université Clermont Auvergne (UCA), 63178 Clermont-Ferrand, France

^*

Author to whom correspondence should be addressed.

Remote Sens. 2026, 18(10), 1603; https://doi.org/10.3390/rs18101603

Submission received: 20 February 2026 / Revised: 4 April 2026 / Accepted: 8 April 2026 / Published: 16 May 2026

(This article belongs to the Special Issue Monitoring Urban Environment from Space)

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Abstract

The Metropolitan Area of São Paulo (MASP), located in southeastern Brazil, faces significant air quality challenges due to its large vehicle fleet and complex fuel composition, including widespread ethanol use. Air pollution dynamics in this context are investigated, focusing on spatio-temporal variations in formaldehyde (HCHO) and nitrogen dioxide (NO

_{2}

), and their role in ozone (O

_{3}

) formation. High-resolution data from the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor satellite are used to analyze HCHO and NO

_{2}

vertical column densities (VCDs) over a 5-year period (2019–2023). Results reveal high HCHO and NO

_{2}

VCDs over MASP, with spatial patterns related to land use and higher concentrations during the dry season, with HCHO mean VCD reaching 14.21 × 10

^{15}

molecules cm

^{- 2}

and NO

_{2}

mean VCD reaching 8.91 × 10

^{15}

molecules cm

^{- 2}

. The Formaldehyde to Nitrogen dioxide Ratio (FNR) thresholds were derived based on observations from 24 CETESB surface O

_{3}

monitoring stations, providing region-specific constraints for O

_{3}

sensitivity classification in MASP, with lower and upper thresholds of 1.6 and 2.4. Based on these thresholds, the analysis indicates a predominance of VOC-sensitive conditions in the urban core, alongside transition and NOx-limited regimes in other areas.

Keywords: air quality; FNR; formaldehyde; pollution; satellite; thresholds; urban

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MDPI and ACS Style

Freitas, A.D.; Zacharias, D.C.; Paim, B.L.; Borbon, A.; Fornaro, A. Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios. Remote Sens. 2026, 18, 1603. https://doi.org/10.3390/rs18101603

AMA Style

Freitas AD, Zacharias DC, Paim BL, Borbon A, Fornaro A. Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios. Remote Sensing. 2026; 18(10):1603. https://doi.org/10.3390/rs18101603

Chicago/Turabian Style

Freitas, Arthur Dias, Daniel Constantino Zacharias, Bruna Lüdtke Paim, Agnès Borbon, and Adalgiza Fornaro. 2026. "Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios" Remote Sensing 18, no. 10: 1603. https://doi.org/10.3390/rs18101603

APA Style

Freitas, A. D., Zacharias, D. C., Paim, B. L., Borbon, A., & Fornaro, A. (2026). Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios. Remote Sensing, 18(10), 1603. https://doi.org/10.3390/rs18101603

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Investigating Ozone Formation Regimes in the Metropolitan Area of São Paulo Using Five Years of TROPOMI HCHO/NO₂ Ratios

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