Ozônio troposférico com referência à proteção da vegetação no Estado de São Paulo: 2018-2022

Abstract

Ozone (O₃) is an oxidizing and reactive gas naturally produced in the Earth's atmosphere, found in both the stratosphere and the troposphere. Tropospheric ozone is regarded as an atmospheric pollutant, causing harmful effects on human health and the environment. Given the sensitivity of plants to this pollutant, metrics aimed at protecting agriculture and forests are employed to minimize economic losses caused by ozone's oxidative reactions. This research aimed to evaluate tropospheric ozone concentrations between 2018 and 2022 at air quality monitoring stations in the State of São Paulo using the AOT40 metric, based on reference values for agricultural productivity protection (6000 µg/m³·h) and forest protection (9800 µg/m³·h). To achieve this goal, data imputation was conducted using Kalman Smoothing and Seasonal Decomposition techniques to fill gaps in the AOT40 time series, enabling non-hierarchical clustering analysis using the k-means algorithm, leading to the formation of distinct clusters that were evaluated against the reference values for vegetation protection. Five clusters were identified, each with an average quarterly AOT40 value of 7,068.91 µg/m³·h (Cluster 1), 10,067.60 µg/m³·h (Cluster 2), 3,643.12 µg/m³·h (Cluster 3), 5,534.66 µg/m³·h (Cluster 4), and 2,224.29 µg/m³·h (Cluster 5). As a secondary pollutant, tropospheric ozone depends on various conditions for its formation and dispersion. It was found through the clusters that locational characteristics significantly influence ozone levels. In addition to meteorological conditions, topography, land use and occupation, and vehicular traffic were identified as factors contributing to the clustering of stations into similar groups, highlighting their influence on the AOT40 index. It was observed that some stations, particularly those in the state's interior, exhibited significant increases in the AOT40 index compared to previous assessments, necessitating more detailed monitoring of these areas. Of the 50 stations evaluated, 47 recorded quarters where reference values for vegetation protection were exceeded, indicating vegetation exposure to tropospheric ozone. The highest quarterly AOT40 values were observed during the transition from winter to spring, coinciding with the growth and reproduction phase of vegetation, when a considerable emission of biogenic volatile organic compounds occurs. Additionally, this period coincides with the planting phase of some crops and the occurrence of wildfires in the interior of the State of São Paulo. The high values observed at various stations suggest that ozone exposure may pose risks to agricultural productivity, as well as to protected areas such as parks, forests, and conservation areas. Overall, the determination and evaluation of the AOT40 index in comparison with reference values contributed to constructing a panorama of vegetation exposure in the State of São Paulo. Despite the limitations, the AOT40 index has proven useful in identifying areas susceptible to ozone pollution, and the integration of techniques applied in this study paves the way for future research.