Quantifying the regional emission reductions during the COVID-19 lockdown and effects for Central European surface air quality

Abstract:

During March and April 2020 several European countries implemented travel restrictions and partial lockdowns to combat the COVID-19 pandemic. Here we evaluate the effect of these restrictions for local and regional ambient air quality in Central Europe, particularly Austria and the Czech Republic. We focus on nitrogen oxides (NOx) and ozone (O₃) and compare, considering meteorological covariates, the 2020 burden to those of previous years (2017-2019). Our results show (1) a sharp contrast between NOx emission reductions observed at traffic and background sites, (2) pronounced regional differences in emission reductions within the case study region, and (3) significant changes in the diurnal cycle and daily mean and maximum 8-hour ozone concentration due to changes in the chemical regime. To quantify the regional change in NOx and O₃ burdens we perform sensitivity simulations with two state-of-the-art chemistry transport models (WRF-Chem, CAMx) driven by data from the ERA-5 reanalysis. These sensitivity simulations comprise fractional NOx emission reductions up to 50% for the Central European region. Initial results indicate that in urban areas regional emission reductions of up to 50% appear feasible. In contrast the comparison of model results and observations indicates only relatively marginal emission reductions in rural background areas.