Impact of COVID-19 pandemic related to lockdown measures on tropospheric NO2 columns over Île-de-France.

The evolution of NO₂, considered as proxy for air pollution, was analyzed to evaluate the impact of 1^st lockdown (March 17^th - May 10^th 2020) over île-de-France region (Paris and surroundings). Tropospheric NO₂ columns measured by two UV-Visible SAOZ spectrometers were analyzed to compare the evolution of NO₂ between urban and suburban sites during the lockdown. The urban site is the observation platform QUALAIR (48°50' N/2°21' E) on the Pierre et Marie Curie Campus of Sorbonne University in the center of Paris. The suburban site is located at Guyancourt (48°46' N/2°03' E), University of Versailles Saint Quentin, 24 km south-west of Paris. Tropospheric NO₂ columns above Paris and Guyancourt have shown similar values during the whole lockdown period from March to May 2020. One decade datasets were filtered to consider air masses at both sites with similar meteorological conditions. The median NO₂ columns, as well as the surface measurements of AIPARIF (Air Quality Observatory in Ile de France) during the lockdown period in 2020 were compared to the extrapolated values estimated from a linear trend analysis for the 2011-2019 period at each station. Negative NO₂ trends of -1.5 Pmolec cm^-2 yr^-1 (~-6.3 % yr^-1) are observed from the columns and of -2.2 μg m^-3 yr^-1 (~-3.6 % yr^-1) from the surface concentration. The negative anomaly in tropospheric columns in 2020 attributed to lockdown (and related emission reductions) was found to be 56 % at Paris and 46 % at Guyancourt, respectively. Similar anomaly was found in the data of surface concentrations, amounting for 53 % and 28 % at the urban and suburban sites, accordingly. [ABSTRACT FROM AUTHOR]