Sudden changes in nitrogen dioxide emissions over Greece due to lockdown
after the outbreak of COVID-19
Koukouli, M.-E., Skoulidou, I., Karavias, A.,
Parcharidis, I., Balis, D., Manders, A., Segers, A., Eskes, H. and
van Geffen, J.: 2021,
Atmos. Chem. Phys. 21, 1759-1774.
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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created: 9 February 2021
last modified: 6 April 2021