The Institute - December 2020 - TI-12

tech takes on COVID-19

Yes, COVID-19 Shutdowns
Improved Air Quality Worldwide




COVID-19 pandemic, scientists
and civilians on the ground have
observed a sharp improvement in
air quality, especially over quarantined regions. A likely explanation was the
shutdowns in response to the pandemic, which
reduced traffic and power production. But it
may not have been the only explanation for
the observed improvement. Weather systems
can shift away pollution and improve air quality over cities.
Now, a recent analysis by the German Aerospace Center (DLR) that combined weather
data and models, pollution measurements
from ground stations, and spectral data from
satellites supports the idea that the shutdowns
were responsible, ruling out weather as a confounding factor.
Pandemic shutdowns have called attention
to air-quality issues around the world. Photo
comparisons of cities before and during quarantine measures show stark reductions in visible smog, while entire continents including
North America, Europe, and Asia are reportStill images from a GIF comparing nitrogen dioxide emissions in Europe in March
ing lower pollutant concentrations throughout.
and April of 2019 (top) and 2020
Using data from TROPOMI onboard the
Copernicus Sentinel 5-Precursor (S5P) satellite and data from GOME-2 onboard the MetOp satellites,
NO2 that reaches the sunny upper regions of the tropowhich can detect the spectral signatures of specific gases,
sphere can dissociate to form ozone (O3), another respiratory
the DLR researchers measured global nitrogen dioxide
pollutant at ground level, and nitric oxide (NO), which returns
(NO2) levels. They were on average 30 percent to 50 percent
to the ground level as acid rain. According to the World Health
lower during the shutdown period than during the same
Organization, all three molecules-ozone, nitric oxide, and
periods in 2019 and previous years. Locally, the impact of
nitrogen dioxide-are linked to early mortality for exposed
shutdowns on air quality varies widely and likely depends
populations, in addition to worse outcomes for respiratory
on the different progressions of the pandemic in each region.
and cardiovascular illnesses.
But a decrease in measured emissions levels might not
Tracking emission levels by satellite comes with its own chalmean there has been an actual reduction in emissions. Most
lenges. The troposphere, home to most weather events, can
NO2-which is emitted primarily by burning coal, gas, diesel,
quickly turn air pollution into soil and ocean pollution-still
and other biofuels-stays relatively close to its source. But this
harmful but now invisible to satellite spectrometers.
changes as the gas moves upward through the troposphere,
" Air contaminants get easily transported by winds or are
the innermost section of Earth's atmosphere. There, the air
washed out by precipitation, " says IEEE Senior Member Diego
is in constant motion, and NO2 can be spread across large
Loyola, lead researcher of the DLR analysis. His team at the Gerdistances and between atmospheric layers.
man Aerospace Center Earth Observation Center is monitoring

The Institute - December 2020

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