Occurrence and Atmospheric Patterns Associated with Individual and Compound Heatwave–Ozone Events in São Paulo Megacity
2025
Vanessa Silveira Barreto Carvalho | Paola do Nascimento Silva | Aline Araújo de Freitas | Vitor Lucas dos Santos Rosa Tenório | Michelle Simões Reboita | Taciana Toledo de Almeida Albuquerque | Leila Droprinchinski Martins
High ozone (O3) concentrations are frequently recorded in Sã:o Paulo Megacity, with extreme O3 levels often linked to high temperatures and heatwaves, phenomena expected to intensify with climate change. The co-occurrence of extreme O3 and heatwaves poses amplified risks to environmental and human health. Hence, this study aims to analyze individual and compound extreme O3 and heatwave events and assess the associated atmospheric patterns. Hourly O3 and temperature (T) data from 20 sites (1998&ndash:2023) were used to calculate the maximum daily 8 h average O3 (MD8A-O3) and maximum daily temperature (Tmax). The Mann&ndash:Kendall test identified trends for these variables. The 90th percentile of data from September to March defined thresholds for extreme events. Events were classified as extreme when MD8A-O3 and Tmax exceeded their thresholds for at least six consecutive days. ERA5 data were used to evaluate atmospheric patterns during these events. The results show positive trends in MD8A-O3 in 62% of sites, with values exceeding WHO Air Quality Guidelines, alongside positive Tmax trends in 90% of sites. Over the study period, four compound events, seven heatwaves, and four extreme O3 events were identified. Compound and individual events were associated with the South America Subtropical Anticyclone and positive temperature anomalies. Individual O3 events were linked to cold anomalies south of 30°: S and positive geopotential height anomalies at 850 hPa. These findings highlight the increasing occurrence of extreme O3 and heatwaves in Sã:o Paulo and their atmospheric drivers, offering insights to enhance awareness, forecasting, and policy responses to mitigate health and environmental impacts.
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