key: cord-1012571-8im9m5jr
authors: Ordóñez, Carlos; Garrido-Perez, Jose M.; García-Herrera, Ricardo
title: Early spring near-surface ozone in Europe during the COVID-19 shutdown: Meteorological effects outweigh emission changes
date: 2020-07-28
journal: Sci Total Environ
DOI: 10.1016/j.scitotenv.2020.141322
sha: 1335fee7b3c80bb034a134aadb2ce8a2c7931045
doc_id: 1012571
cord_uid: 8im9m5jr

Abstract This paper analyses the impact of the control measures during the COVID-19 lockdown in Europe (15 March–30 April 2020) on 1-h daily maximum nitrogen dioxide (NO2) and maximum daily 8-h running average ozone (MDA8 O3) observations obtained from the European Environment Agency's air quality database (AirBase). Daily maximum NO2 decreased consistently over the whole continent, with relative reductions ranging from 5% to 55% with respect to the same period in 2015–2019 for 80% of the sites considered (10th – 90th percentiles). However, MDA8 O3 concentrations showed a different pattern, decreasing over Iberia and increasing elsewhere. In particular, a large region from northwestern to central Europe experienced increases of 10–22% at urban background stations, reaching typical values of the summer season. The analysis of the expected NO2 and O3 concentrations in the absence of the lockdown, using generalised additive models fed by reanalysis meteorological data, shows that the low NO2 concentrations were mostly attributed to the emission reductions while O3 anomalies were dominated by the meteorology. The relevance of each meteorological variable depends on the location. The positive O3 anomalies in northwestern and central Europe were mostly associated with elevated temperatures, low specific humidity and enhanced solar radiation. This pattern could be an analogue to study the limits of pollution control policies under climate change scenarios. On the other hand, the O3 reduction in Iberia is mostly attributable to the low solar radiation and high specific humidity, although the reduced zonal wind also played a role in the proximity of the Iberian Mediterranean coast.

In December 2019, a novel virus named SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) causing COVID-19 (coronavirus disease 2019) was first reported in Wuhan, China. Since then, the virus has spread worldwide, leading the World Health Organization (WHO) to declare the COVID-19 outbreak a global pandemic on 11 March 2020 (Sohrabi et al., 2020) . This airborne illness has not only caused an international health crisis, but also a great impact on society and the environment (Ivanov, 2020; Nicola et al., 2020; Yang et al., 2020) . Most national governments have taken social distancing measures to reduce further spread and avoid the collapse of healthcare systems. As a consequence of the lockdown, unprecedented falls in industrial activity and vehicle usetwo of the main sources of air pollutionhave been reported. Consequently, the concentrations of several air pollutants have decreased in the affected countries (Bauwens et al., 2020; Chauhan and Singh, 2020; Petetin et al., 2020; Shi and Brasseur, 2020; Sicard et al., 2020; Tobías et al., 2020; Wang et al., 2020) . As an illustration, Chauhan and Singh (2020) following the emission reductions. This has led to a convergence of ozone pollution for the different types of sites in Europe, although the concentrations remain higher at rural than at urban background sites (Sicard et al., 2013; Paoletti et al., 2014; Monks et al., 2015; Boleti et al., 2018) .

While the enforcement of air pollution regulation is often aimed at gradual reductions of air pollutant concentrations, there have been specific events with stricter emission restrictions in the past, such as the 2008 Beijing Olympics (e.g. Wang et al., 2009; Witte et al., 2009) . Nevertheless, the intensity, duration and extension of the decay in the emissions of primary pollutants during the COVID-19 lockdown are unprecedented, offering a unique opportunity to study the impact of reduced anthropogenic emissions on the O 3 concentrations at continental scales. On the other hand, the confounding effect of J o u r n a l P r e -p r o o f 6 NO 2 and O 3 across Europe. For that purpose, we have used generalised additive models (GAMs) fed by reanalysis meteorological data to estimate the NO 2 and O 3 concentrations that would be expected in the absence of the lockdown.

The response of European countries to the coronavirus outbreak has been diverse. Figure   S1 displays the spatial distribution of the monthly MDA8 O 3 means at those sites, illustrating that the March-April period investigated here can be considered as a transition time between the low ozone months (Oct-Feb) and the high ozone season (from April to September, depending on the region). The analyses presented in this work have first been performed separately for urban background and rural stations. Since both types of sites exhibit the same patterns, we will show the results for the combination of them throughout the manuscript.

For the characterization of the meteorological conditions, we have extracted the following fields from the ERA5 meteorological reanalysis (Hersbach et al., 2020) , at 0.75º × 0.75º horizontal resolution, for the 1981-2020 period: daily maximum air temperature at 2m (T2max); daily mean fields of the zonal (U10) and meridional (V10) wind components at 10m, 500 hPa geopotential height (Z500), 2-m specific humidity (q) and downward solar radiation flux (SR), and daily accumulated precipitation (Prec). Although ERA5 data may have some deficiencies in capturing the local meteorology at some sites, the resolution used here seems to be appropriate as shown by previous analyses on the influence of meteorology on surface ozone observations in Europe (Otero et al., 2016; Boleti et al., J o u r n a l P r e -p r o o f 8 2019). Furthermore, additional analyses based on NCEP/NCAR meteorological data at 2.5º × 2.5º (Kalnay et al., 1996) confirm that the results presented in this work are not very sensitive to the choice of the reanalysis dataset (not shown). has been done only for those countries with good coverage of urban background and rural measurement sites (>25 stations for both NO 2 and O 3 ). The table confirms the strongest NO 2 decreases found for the three mentioned countries (Spain, France and Italy), with a fall of more than 40% from the baseline for urban background stations. This order of magnitude is comparable to that of the ~50% NO 2 reductions (ranging from 30% to 69%) reported by Sicard et al. (2020) and Tobías et al. (2020) for five cities in the same countries.

Conversely, averaged O 3 concentrations increased both at urban background and rural sites in all countries except for Spain. This needs to be further investigated, bearing in mind that ozone concentrations do not respond linearly to changes in precursor emissions (e.g. Lin et al., 1988; Trainer et al., 1993; Parrish et al., 1999; Vogel et al., 1999; Sillman, 1999; Kleinman et al., 2002) . The fact that O 3 increased more at urban than at rural sites in 9 of the 10 countries considered (and decreased less at urban than at rural sites in Spain)

indicates Spain -51.6 ± 11.2 -38.4 ± 27.9 -7.1 ± 10.7 -11.6 ± 6.9 -50.0 ± 11.9 -39.4 ± 26.6 -1.7 ± 11.6 -7.8 ± 7.3 France -43.1 ± 11.4 -36.7 ± 19.6 6.6 ± 9.6 3.1 ± 7.7 -46.9 ± 9.8 -42.3 ± 17.0 1.7 ± 6.8 -2.1 ± 5.0

United Kingdom -31.2 ± 12.9 -21.5 ± 12.7 12.3 ± 13.9 3.1 ± 6.7 -35.0 ± 11.9 -31.7 ± 11.0 4.7 ± 11.4 -1. 

Here we conduct more in-depth analyses for Spain and Germany as representative The observed ozone concentrations in Germany during spring 2020 are considerably higher than the reference ones (Figure 4c ). The rise from March to April is steeper than in the reference climatology, resulting in median values during the last weeks of April well above the summer medians of the reference period. This is remarkable because, despite the moderate seasonality of ozone during spring and summer in Germany, the peak ozone season over most of the country occurs between June and August (see also Figure S1 ) 

As Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Observed changes (%) Meteorology-adjusted changes (%) Spain -51.6 ± 11.2 -38.4 ± 27.9 -7.1 ± 10.7 -11.6 ± 6.9 -50.0 ± 11.9 -39.4 ± 26.6 -1.7 ± 11.6 -7.8 ± 7.3 France -43.1 ± 11.4 -36.7 ± 19.6 6.6 ± 9.6 3.1 ± 7.7 -46.9 ± 9.8 -42.3 ± 17.0 1.7 ± 6.8 -2.1 ± 5.0

United Kingdom -31.2 ± 12.9 -21.5 ± 12.7 12.3 ± 13.9 3.1 ± 6.7 -35.0 ± 11.9 -31.7 ± 11.0 4.7 ± 11.4 -1.2 ± 5.5

Italy -44.2 ± 13.9 -25.7 ± 25.8 5.0 ± 13.1 1. 

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This work was supported by the Spanish Ministerio de Economía y Competitividad