Impact of the implementation of Madrid's low emission zone on NO2 concentration using Sentinel-5P/TROPOMI data
Carlos Morillas, Sergio Álvarez, José C.M. Pires, Adrian Garcia, Sara Martínez
Abstract
In recent years, measures and policies have been implemented to maintain healthy NO2 levels, such as creating low emission zones (LEZs). In November 2018, a traffic-restricted area known as the Special Protection Low Emission Zone (SPLEZ) was established in the core of the city of Madrid, embracing most of its central district. This study aims to assess whether the air quality has improved with implementing the LEZ by analyzing the NO2 concentration in several case scenarios. For this purpose, data from the TROPOspheric Monitoring Instrument (TROPOMI) onboard the Sentinel-5 precursor (Sentinel-5P) were used. The seasonal analysis performed before and after the LEZ implementation (from July 2018 to May 2019) and 2022 as a complete year revealed that the epicenter of transport-related concentrations did not reside within its boundaries. However, emissions within the SPLEZ increased during winter, where heating and meteorological factors played a significant role. Additionally, the findings from the case study of the COVID-19 pandemic demonstrated the influence of human activities on the NO2 concentration in both the SPLEZ and the entire metropolitan area. NO2 emissions decreased during the strict lockdown period and steadily increased as activities resumed. Satellite data was compared to surface-level measurements in each case study, resulting in a linear correlation coefficient of 0.72. It was found that TROPOMI data reflected changes more closely aligned with surface-level findings as pollution levels increased, in contrast to better air quality scenarios with better. Despite certain limitations, it can serve as a valuable tool for offering complementary information to surface-level data, particularly in characterizing changes in emission distribution patterns.