Air Quality Analysis in Lima, Peru Using the NO₂ Levels during the COVID-19 Pandemic Lockdown

The emergence of the new COVID-19 virus in Peru forced the Peruvian government to take swift measures to stop its proliferation. Consequently, a state of emergency was declared, which included mandatory social isolation and quarantine. This action meant that people would transit only in emergency cases. In this context, this study’s objective is to analyze the air quality changes in terms of the capital city’s NO₂ levels due to these government decisions using satellite imagery data obtained from the Sentinel-5P satellite. One critical problem is the lack of spatially distributed air quality data. The Peruvian Meteorological Service only monitors air quality in Lima, the capital city. In addition, the air quality ground stations are not always functioning. Thus, there is a need to find new reliable methods to complement the official data obtained. One method of doing so is the use of remote sensing products, although the accuracy and applicability are yet to be determined; therefore, this is the article’s focus. A temporal and spatial analysis was developed quantitatively and qualitatively to measure the levels of NO₂ in eighteen regions of Lima to contrast the quarantine’s effect on polluting gas emission levels. The measurements are also compared with the official Peruvian data from ground sensors using Pearson correlation coefficients, thus, showing that Sentinel-5P data can be used for changes in the mean daily concentration of NO₂. We also developed the first version of an open platform that converts the satellite data into a friendly format for visualization. The results show NO₂ ambient concentration reductions compared to 2019 of between 60% and 40% in the first two weeks and between 50% and 25% in the following two weeks of the COVID-19 lockdown. However, this effect could not be observed two months after the start of the lockdown.