A two decades study on ozone variability and trend over the main urban areas of the São Paulo state, Brazil

In this paper, we analyze the variability of the ozone concentration over São Paulo Macrometropolis, as well the factors, whichdetermined the tendency observed in the last two decades. Time series of hourly ozone concentrations measured at 16 automatedstations from an air quality network from 1996 to 2017 were analyzed. The temporal variability of ozone concentrations exhibitswell-defined daily and seasonal patterns. Ozone presents a significant positive correlation between the number of cases (thresh-olds of 100–160μgm−3) and the fuel sales of gasohol and diesel. The ozone concentrations do not exhibit significant long-termtrends, but some sites present positive trends that occurs in sites in the proximity of busy roads and negative trends that occurs insites located in residential areas or next to trees. The effect of atmospheric process of transport and ozone formation was analyzedusing a quantile regression model (QRM). This statistical model can deal with the nonlinearities that appear in the relationship ofozone and other variables and is applicable to time series with non-normal distribution. The resulting model explains 0.76% ofthe ozone concentration variability (with global coefficient of determinationR1= 0.76) providing a better representation than anordinary least square regression model (with coefficient of determinationR2= 0.52); the effect of radiation and temperature arethe most critical in determining the highest ozone quantiles