Guest blogger Eloise Marais shares insights from a recently published paper, examining the causes of air quality change during the first UK lockdown.
There was widespread reporting of the air quality improvements in Spring 2020 in comparison to the previous year during the lockdown imposed from 23 March 2020 in the UK. Researchers at Universities of Leicester and Leeds, UCL and the National Centre for Earth Observation examined this dramatic drop in air pollution with a detailed model and measurements air pollution to find that lockdown measures only explain half the improvement in air quality.
This research, recently accepted by the journal Environmental Research Letters (https://iopscience.iop.org/article/10.1088/1748-9326/abde5d), used the GEOS-Chem chemical transport model and observations from the space-based TROPOMI instrument onboard the ESA Sentinel-5P satellite. The model includes detailed representation of sources and chemical and physical processes in the atmosphere that affect regional air quality. This allowed the researchers to tease out the factors that contributed to improvements in air quality. They estimated that emissions decreased by 20-30% on average across the UK, but by much more (>40%) in London and only marginally in Scotland. They also found that differences in meteorology and long-range transport of pollution between the two years contributed at least half of the observed air quality improvements. The relative contribution of emissions and other factors for UK regions and two UK cities (London and Manchester) are shown in the figure below for the air pollutant PM2.5.
These findings support the need to consider emissions as well as meteorology in developing air pollution mitigation measures and enforcing air quality policy standards, especially if the UK adopts a stricter PM2.5 standard.