Abstract. The lockdown measures taken to prevent a rapid spreading
of the coronavirus in Europe in spring 2020 led to large emission
reductions, particularly in road traffic and aviation. Atmospheric
concentrations of NO2 and PM2.5 were mostly reduced when
compared to observations taken for the same time period in previous years;
however, concentration reductions may not only be caused by emission
reductions but also by specific weather situations. In order to identify the role of emission reductions and the meteorological
situation for air quality improvements in central Europe, the meteorology
chemistry transport model system COSMO-CLM/CMAQ was applied to Europe for
the period 1 January to 30 June 2020. Emission data for 2020 were
extrapolated from most recent reported emission data, and lockdown adjustment
factors were computed from reported activity data changes, e.g. Google
mobility reports. Meteorological factors were investigated through
additional simulations with meteorological data from previous years. The results showed that lockdown effects varied significantly among
countries and were most prominent for NO2 concentrations in urban areas with 2-week-average reductions up to 55 % in the second half of March. Ozone concentrations were less strongly influenced (up to ±15 %) and
showed both increasing and decreasing concentrations due to lockdown
measures. This depended strongly on the meteorological situation and on the
NOx / VOC emission ratio. PM2.5 revealed 2 %–12 % reductions of 2-week-average concentrations in March and April, which is much less than
a different weather situation could cause. Unusually low PM2.5
concentrations as observed in northern central Europe were only marginally
caused by lockdown effects. The lockdown can be seen as a big experiment about air quality improvements
that can be achieved through drastic traffic emission reductions. From this
investigation, it can be concluded that NO2 concentrations can be
largely reduced, but effects on annual average values are small when the
measures last only a few weeks. Secondary pollutants like ozone and
PM2.5 depend more strongly on weather conditions and show a limited
response to emission changes in single sectors.
From Black to Blue Skies: Civil Society Perceptions of Air Pollution in Shanghai
