Sudden changes in nitrogen dioxide emissions over Greece due to lockdown after the outbreak of COVID-19
release_56rjgnfqz5e3pkksyh5jr5h7dm
by
Maria Elissavet Koukouli, Ioanna Skoulidou, Andreas Karavias, Isaak Parcharidis, Dimitris Balis, Astrid Manders, Arjo Segers, Henk Eskes, Jos van Geffen
Abstract
Abstract. The unprecedented order, in modern peaceful times, for
a near-total lockdown of the Greek population as a means of protection against severe acute respiratory syndrome coronavirus 2, commonly known as
COVID-19, has generated unintentional positive side-effects with respect to the
country's air quality levels. Sentinel-5 Precursor/Tropospheric Monitoring Instrument (S5P/TROPOMI) monthly mean tropospheric nitrogen
dioxide (NO2) observations show an average change of −34 % to
+20 % and −39 % to −5 % with an average decrease of −15 % and −11 %
for March and April 2020 respectively, compared with the previous year, over
the six larger Greek metropolitan areas; this is mostly attributable to vehicular
emission reductions. For the capital city of Athens, weekly analysis was
statistically possible for the S5P/TROPOMI observations and revealed a
marked decline in the NO2 load of between −8 % and −43 % for 7 of the
8 weeks studied; this is in agreement with the equivalent
Ozone Monitoring Instrument (OMI)/Aura observations as
well as the ground-based estimates of a multi-axis differential optical
absorption spectroscopy ground-based instrument. Chemical transport
modelling of the NO2 columns, provided by the Long Term Ozone Simulation European Operational Smog (LOTOS-EUROS) chemical
transport model, shows that the magnitude of these reductions cannot solely
be attributed to the difference in meteorological factors affecting NO2
levels during March and April 2020 and the equivalent time periods of the
previous year. Taking this factor into account, the resulting decline was
estimated to range between ∼ −25 % and −65 % for 5
of the 8 weeks studied, with the remaining 3 weeks showing a
positive average of ∼ 10 %; this positive average was postulated to be due to the
uncertainty of the methodology, which is based on differences. As a result
this analysis, we conclude that the effect of the COVID-19 lockdown and the
restriction of transport emissions over Greece is ∼ −10 %.
As transport is the second largest sector (after industry)
affecting Greece's air quality, this occasion may well help policymakers to
enforce more targeted measures to aid Greece in further reducing emissions
according to international air quality standards.
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