Using Sentinel 5P satellite and vehicle flow data to map NO2 air pollution near highways in the Metropolitan Region of Campinas, Brazil

Nitrogen dioxide (NO₂), an atmospheric pollutant produced by fossil fuel combustion in vehicles and industrial processes, is harmful to human health, worsening respiratory and cardiovascular diseases. The main effects of NO₂ pollution on human health are respiratory infections, airway inflammation, asthma, and low birth weight, among others. Vehicle traffic in cities is one of the main sources of NO₂, affecting the health of the population living near highways. The highest NO₂ concentration occurs at distances between 200 and 500 meters from high-traffic highways. The study area, the metropolitan region of Campinas (MRC), Brazil, is a technological, industrial and economic hub with 3.3 million inhabitants and busy transport corridors that connect the southeast and central-west regions of the country. It is composed of 20 municipalities and is located in São Paulo state, the most developed and populated Brazilian state. The aims of this work are to map atmospheric NO₂ pollution and estimate NO₂ concentrations near the highways in the MRC using average daily vehicle flow (DVF) and NO₂ concentrations estimated from satellite images. Data on the tropospheric vertical column of nitrogen dioxide (in mol/cm²) values from 32 daily images from the Sentinel 5P satellite TROPOMI spectrometer that were collected from April 15 to May 20, 2024, were used. During that period, there was no rain, and the sky remained clear and cloudless. The images were processed to produce NO₂ median images during the study period. The NO₂ pollution map was produced by the spline interpolation algorithm method. To estimate the concentration of NO₂ near the MRC highways, a road map was used, and a 500 m buffer was drawn around the highways. The NO₂ pollution map was combined with the buffer map, and the median NO₂ concentration within the 500 m buffer around the highways was estimated. Pearson regression analysis was performed between the average DVF and the NO₂ concentration. The results revealed a positive and significant correlation (r=0.692; p= 0.004) between the DVF and NO₂ concentration near the highways estimated from satellite data. The highest NO₂ concentrations were observed near highways SP-083 (1.5591 mol/cm²; 45,000 vehicles/day), SP-330 (1.521 mol/cm²; 38,815 vehicles/day), and SP-075 (1.485 mol/cm²; 37,813 vehicles/day). The results of this study can be used in epidemiological research to identify neighborhoods and populations that live near high NO₂ concentration highways and are exposed to respiratory and cardiovascular disease risks. In the next step of this research, the NO₂ concentration values ​​estimated from Sentinel 5P images in mol/cm² units will be converted to µg/m³ units using data from ground-based measurement stations located in the MRC. In the future, this methodology can be used to produce highway NO₂ pollution maps for areas in which ground measurement station data are unavailable.