Abstract: Tropospheric ozone is an atmospheric pollutant causing harmful effects on human health and the environment. Plants can exhibit sensitivity to ozone, as it reacts with cellular compounds upon entering plant cells, leading to the formation of the reactive oxygen species in a cascade effect that can damage plant tissues. Due to this sensitivity, metrics aimed at agricultural and forestry protection have been created to minimize economic losses caused by ozone’s oxidative reactions. AOT40 is one of the most used metrics in the world, assessing long-term exposure for important plant specie. This study aimed to evaluate AOT40 over all possible quarters between 2018 and 2022 in the São Paulo State, Brazil. Fifty ozone monitoring stations from the Environmental Company of the São Paulo State (CETESB) were selected, obtaining hourly surface ozone concentration measurements for the study period through their Air Quality Information System (QUALAR). The data were tabulated checking each quarter (60 quarters) for all stations to determine if there was at least 70% of hourly data presence between 8:00 AM and 8:00 PM for AOT40 estimation. Stations with quarters, where AOT40 estimation was not possible, underwent a data imputation process using Kalman Smoothing (ARIMA model) and Seasonal Decomposed (Kalman Smoothing algorithm) techniques. With imputed data and AOT40 estimated for all stations, a clustering analysis was performed using a non-hierarchical clustering method by k-means algorithm. In this process, four clusters were generated with distinct characteristics in terms of values, behavior, and geographical distribution of the AOT40 index. Cluster 1 consisted of 21 stations, 18 stations in the interior of the state and 3 in the Metropolitan Area of São Paulo (MASP). These stations cover regions with agriculture and industry as their land cover types. The quarterly average AOT40 was 3009.75 (μg/m3), showing the lowest average, maximum, and minimum AOT40 values among the four clusters generated. Cluster 2 consisted of 7 stations located entirely in the interior of the state (Intermediate Regions of Araraquara, Campinas, and Ribeirão Preto) in areas with a vocational unit of industry or industrialization, presenting a quarterly average AOT40 of 7084.19 μg/m3. Cluster 3 also consisted of 7 stations in the cities of Americana, Campinas, Jundiaí, and São Paulo (4), all in industrial land cover types. This cluster exhibited the highest average, maximum, and minimum values of the AOT40 index, with an average value of 10043.76 μg/m3 and a maximum average value of 23923.49 μg/m3 in the September-October-November quarter of 2020. Cluster 4 comprised 15 stations distributed exclusively in the Metropolitan Area of São Paulo, with a quarterly average AOT40 of 5722.96 μg/m3. Individually analyzed, 47 out of the 50 stations presented at least one quarter with values exceeding the reference value for the protection of agricultural productivity (VRPP) of 6000 μg/m3. For cluster 1 the stations presented an average of 8 exceedances, with 3 stations (1 in Cubatão and 2 in Santos) not exceeding the VRPP. Cluster 2 presented an average of 27 exceedances, while Cluster 3 presented an average of 45 exceedances, the highest among the clusters. Cluster 4 showed an average of 25 exceedances. Overall, AOT40 exceedances are indicative of negative exposure to ozone for natural and planted vegetation in the State of São Paulo, suggesting possible production losses. It is important to conduct further studies to comprehend the index variation over the years, observe trends and seasonality, and quantify economic losses resulting from ozone exposure in agricultural production.

Keywords: ozone, critical levels, AOT40, São Paulo State.