Meteorology-normalized impact of the COVID-19 lockdown upon NO<sub>2</sub> pollution in Spain

Abstract

Abstract. The spread of the new coronavirus SARS-CoV-2 that causes COVID-19 forced the Spanish Government to implement extensive lockdown measures to reduce the number of hospital admissions, starting on 14 March 2020. Over the following days and weeks, strong reductions in nitrogen dioxide (NO2) pollution were reported in many regions of Spain. A substantial part of these reductions was obviously due to decreased local and regional anthropogenic emissions. Yet, the confounding effect of meteorological variability hinders a reliable quantification of the lockdown's impact upon the observed pollution levels. Our study uses machine-learning (ML) models fed by meteorological data along with other time features to estimate the “business-as-usual” NO2 mixing ratios that would have been observed in the absence of the lockdown. We then quantify the so-called meteorology-normalized NO2 reductions induced by the lockdown measures by comparing the estimated business-as-usual values with the observed NO2 mixing ratios. We applied this analysis for a selection of urban background and traffic stations covering the more than 50 Spanish provinces and islands. The ML predictive models were found to perform remarkably well in most locations, with an overall bias, root mean square error and correlation of +4 %, 29 % and 0.86, respectively. During the period of study, from the enforcement of the state of alarm in Spain on 14 March to 23 April, we found the lockdown measures to be responsible for a 50 % reduction in NO2 levels on average over all provinces and islands. The lockdown in Spain has gone through several phases with different levels of severity with respect to mobility restrictions. As expected, the meteorology-normalized change in NO2 was found to be stronger during phase II (the most stringent phase) and phase III of the lockdown than during phase I. In the largest agglomerations, where both urban background and traffic stations were available, a stronger meteorology-normalized NO2 change is highlighted at traffic stations compared with urban background sites. Our results are consistent with foreseen (although still uncertain) changes in anthropogenic emissions induced by the lockdown. We also show the importance of taking the meteorological variability into account for accurately assessing the impact of the lockdown on NO2 levels, in particular at fine spatial and temporal scales. Meteorology-normalized estimates such as those presented here are crucial to reliably quantify the health implications of the lockdown due to reduced air pollution.

UK surface NO2 levels dropped by 42 % during the COVID-19 lockdown: impact on surface O3

“…In Europe, reductions of NO 2 are typically slightly larger than we have seen in the UK in our study, perhaps reflecting more stringent lockdown policy. In Spain, NO 2 was reduced by 50 % at both urban traffic and urban background sites (Petetin et al, 2020); in Rome, Turin and Nice, NO 2 was reduced by 46, 30 and 63 %, respectively (Sicard et al, 2020). In all of these studies similarmagnitude increases of O 3 were observed, mainly attributed to the decreased nitric oxide (NO).…”

What can we learn about urban air quality with regard to the first outbreak of the COVID-19 pandemic? A case study from central Europe

“…At the same time, PM 10 mass represents disintegration sources, e.g. windblown soil, crustal rock, mineral and roadside dust, resuspended dust by car movement, agricultural activities in the region, construction work and material wear such as tire abrasion of cars at kerbside sites (Salma and Maenhaut, 2006;Putaud et al, 2010;Harrison et al, 2012;Salma et al, 2020a). They all can be important, particularly under dry weather conditions.…”

“…As a consequence of the implemented measures, road traffic in many cities worldwide was reduced in a substantial manner and for a considerable time interval. In parallel, lower concentrations of several air pollutants were reported from both satellite observations and in situ measurements (Conticini et al, 2020;Frontera et al, 2020;Keller et al, 2020;Lal et al, 2020;Le et al, 2020;Lee et al, 2020;Liu et al, 2020;Mahato et al, 2020;Morawska and Cao, 2020;Nakada and Urban, 2020;Petetin et al, 2020;Tobías et al, 2020;Wang et al, 2020).…”

Relations between Air Quality and Covid-19 Lockdown Measures in Valencia, Spain

“…Only essential businesses, including grocery stores and food trade, pharmacies, and other industries, were authorized to be open. While other non-essential businesses such as retail shops, bars, restaurants, and commercial companies, had to close [17]. After the lockdown, businesses in some nonessential sectors, including construction and industry, were gradually allowed to return to work.…”