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

Abstract

The evolution of NO2, considered as a proxy for air pollution, was analyzed to evaluate the impact of the first lockdown (17 March–10 May 2020) over the Île-de-France region (Paris and surroundings). Tropospheric NO2 columns measured by two UV-Visible Système d'Analyse par Observation Zénithale (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) at the Sorbonne University Pierre and Marie Curie Campus in the center of Paris. The suburban site is located at Guyancourt (48∘46′N / 2∘03′E), Versailles Saint-Quentin-en-Yvelines University, 24 km southwest of Paris. Tropospheric NO2 columns above Paris and Guyancourt have shown similar values during the whole lockdown period from March to May 2020. A decade of data sets were filtered to consider air masses at both sites with similar meteorological conditions. The median NO2 columns and the surface measurements of Airparif (Air Quality Observatory in Île 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 trends of −2.2 µg m−3 yr−1 (∼ −3.6 % yr−1) are observed from the surface concentration. The negative anomaly in tropospheric columns in 2020 attributed to the lockdown (and related emission reductions) was found to be 56 % at Paris and 46 % at Guyancourt, respectively. A similar anomaly was found in the data of surface concentrations, amounting to 53 % and 28 % at the urban and suburban sites, accordingly.