Fog, Temperature and Air Quality Over the Metropolitan Area of São Paulo: a Trend Analysis from 1998 to 2018

This study investigates the long-term development of fog occurrences in the Metropolitan Area of São Paulo (MASP). Specifically, it analyzes the roles of meteorological and air quality parameters as potential drivers for fog formation. A dataset reaching back to the year 1933 shows that the overall trends of the annual fog occurrences (AFO) coincide with those of the annual mean temperature. Air quality data have been available since 1998, allowing us to perform a statistical analysis of the contributions of meteorology and air quality to AFO for the period from 1998 to 2018. The logistic regression model shows that the binary dependent variable (daily fog occurrence, FO) is explained by its independent predictors PM10, relative humidity (rH), and daily minimum temperature (Tmin), in that order. FO was not found to be significantly influenced by atmospheric pressure (aP) and nitrogen oxides (NOx). While the influence of SO2 was minor and associated with less confidence, it was negative. Potential causes for these surprising results are discussed. We conclude that the parameters PM10, rH, and Tmin are significant drivers of fog formation in the MASP, whereby the total explanatory power of the drivers for the dichotomous variable FO is 16%.