Satellite Data
Section 1
Air pollution is recognised as being the fifth leading risk factor for mortality worldwide,Ambient air pollution contributes to about 5 million deaths globally – or one in ten deaths.In Europe, air pollution-related diseases claim one in eight deaths, according to the latest report of the European Environmental Agency. This brings air pollution in the spotlight of environmental problems of high societal relevance. Analyses based on satellite observations from the TROPOMI instrument, aboard the Copernicus Sentinel-5P satellite, launched in 2017, have been vital in tracking the evolution of air pollution across the world.
In 2020, satellite data has been widely used to monitor the changes in air quality that resulted from the COVID- 19 measures that affected more than half of world’s population. Scientists from the Royal Belgian Institute for Space Aeronomy (BIRA-IASB) used satellite data from TROPOMI.
Section 2
In March-April 2020, during the tight phase of the lockdowns in Europe, very strong reductions of satellite NO2 levels of the order of 40-50% were recorded in large cities of Spain, Italy and France, and moderate reductions of the order of 20% in Belgian cities, like Brussels and Antwerp (Figure 1 and 2). The main reason is well identified: vehicular traffic, one of the main sources of nitrogen oxides (NO and NO2), has been dramatically reduced during the first phase of the lockdown period. The analysis has also drawn attention to the remarkable technological progress made to measure pollution – satellite measurements made possible to monitor NO2 levels in near real-time globally.
The concentrations appear to return to near-normal levels in July-August 2020, due to the progressive relaxation of the lockdown measures, but are still lower by 10% over large cities where human activities have not yet fully resumed.
Section 3
In New Delhi and Lima, two megacities where public health measures to contain the pandemic were strongly enforced, he NO2 levels show a significant drop during first phase of the lockdowns, and remain unusually low in July-August This indicates that economy hasn’t returned to full capacity yet, despite the partial lifting of the restrictions, The impact of meteorology on NO2 concentrations is also important and should not be overlooked. This is why it is necessary to analyse data over sufficiently long periods, In order to better estimate the impact of human activity.
By comparing the monthly average of 2019 and 2020, we estimate an uncertainty on the COVID-19 induced reduction of around 15–20%,The decreases observed by satellites and the decreases observed in measuring stations in different cities correspond well if we take into account their uncertainties.
Section 4
COVID-19 measures are being relaxed in many countries, we would like to pay attention to the, Improved air quality in the last months,All over the world,countries have to a greater or lesser extent taken measures to reduce the spread of the coronavirus. In particular, transportation and people’s movements have, been restricted worldwide. Traffic, the main source of nitrogen dioxide (NO2) in the urban environment, decreased significantly. This is clearly visible on satellite images, as well as decline in industrial activities, another important source of NO2 in the atmosphere.
Political and societal efforts to improve air quality can also lead to lower NO2 concentrations, Therefore, computer models will be used in the future in order to distinguish the effects of imposed COVID-19 measures from other factors.