AQC has updated its analysis of the impacts of COVID-19 restrictions on air quality. The March lockdown had a large effect on NOx and NO2, with concentrations reducing at roadside, industrial and urban sites, with an increase in roadside O3. NOx and NO2 concentrations have remained below pre-lockdown levels since March at most sites; however, since July, increasing NOx and NO2 and reducing O3 concentrations brought concentrations close to pre-lockdown levels at some roadside sites.
There continues to be widespread reporting of reductions in NOx and NO2 concentrations as a result of the COVID-19 pandemic, yet much of this continues to focus on comparing concentrations measured during two separate periods of time without consideration of confounding factors such as meteorology which can have a significant effect.
Air Quality Consultants Ltd published a report in April 2020 that presented an analysis of trends in NOx, NO2 and O3 concentrations at 247 sites across the UK during the early stages of the COVID-19 social and travel restrictions. This analysis has now been updated to consider the changes up to the end of September 2020, in a report available here.
At first glance, the updated analysis appears to display visible trends in raw NOx, NO2 and O3 concentrations, with NOx and NO2 concentrations generally high pre-lockdown, then low through to July/August and increasing again into September, with O3 doing the opposite. However, it is important to note that such a trend is typical of UK seasonal conditions. This trend is controlled for in the BRT-adjusted data, which are likely to show the residual effect caused by changing social and travel restrictions.
The lockdown in late March had a dramatic effect on concentrations, with NOx and NO2 concentrations reducing notably at all roadside, industrial and urban sites, although the effect is especially clear at roadside sites. Roadside O3 concentrations also increased appreciably immediately after lockdown was implemented.
There is then a general trend for increasing NOx and NO2 concentrations, and reducing O3 concentrations, at roadside monitors from late June/early July, which corresponds to when social and travel restrictions were widely lifted. Despite these increases, BRT-adjusted NOx and NO2 concentrations at most sites have remained below pre-lockdown levels, although by the end of September, concentrations at some sites were close to (or in a few cases exceeding) pre-lockdown conditions.
Concentrations at Rural sites do not appear to have been significantly affected by the social and travel restrictions, although the low concentrations typically measured at these sites would be expected to make it difficult to establish noteworthy changes.
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