AQC has further updated its analysis of the impacts of COVID-19 social and travel restrictions on air quality. Trends in raw NOx, NO2 and O3 concentrations in 2020 to date continue to show no obvious influence of the social and travel restrictions implemented in response to the COVID-19 pandemic. However, isolating and removing meteorological and temporal effects has revealed significant reductions in NOx and NO2 concentrations at a very large number of monitoring sites across the UK.
There continues to be widespread reporting of reductions in NOx and NO2 concentrations as a result of the COVID-19 pandemic. Much of this has focussed on comparing concentrations measured during two separate periods of time without consideration of confounding factors such as meteorology. Such comparisons can be misleading; they are likely to be little more than a comparison of the influence of weather during those two periods.
Air Quality Consultants Ltd has previously carried out a much more detailed analysis to isolate the variation caused by meteorological and seasonal factors from the measured ambient concentrations, to demonstrate whether there are real changes in concentrations as a result of reducing emissions. This analysis has now been further expanded to consider 247 UK sites in a report available here.
Isolating and removing meteorological and temporal effects has revealed reductions in NOx and NO2 concentrations at a very large number of monitoring sites across the UK in the second half of March. This compares with the changes in raw NOx, NO2 and O3 concentrations in 2020, which have shown no obvious influence of the social and travel restrictions implemented in the UK in response to the COVID-19 pandemic.
The reductions in NOx and NO2 concentrations at roadside monitors appear to be substantial and coincide with reductions in traffic volumes on UK roads. As roadside NOx concentrations have fallen, roadside O3 concentrations have increased to be closer to those recorded at rural sites. This is a predictable response to the removal of fresh NOx emissions, which typically depress roadside O3.
Given that NO2 and O3 have both been linked with negative health effects, reductions in NO2 concentrations are welcome, but increases in ground-level O3 concentrations are not.
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