COVID-19 and Air Pollution - views of possible futures?

The COVID-19 pandemic forced governments around the world to impose restrictions on daily life to prevent the spread of the virus. This resulted in unprecedented reductions in anthropogenic activity, and reduced emissions of certain air pollutants, namely oxides of nitrogen. The UK 'lockdown' was enforced in March 2020, which led to restrictions on movement, social interaction, and 'non-essential' businesses and services. Such dramatic reduction in certain air pollutants across the species emissions spectrum, over such a relatively short time interval and across so many different countries, is unprecedented. Much focus has been on improvements in air quality, owing to a reduction in road transport and hence NOx and particulate matter (PM) emissions; however, the picture is not as simple as first thought. Indeed, reductions in NOx emissions have resulted in a perturbation to the 'normal' state of lower atmospheric chemistry, which has resulted in an increase in atmospheric reactivity and the photochemical production of ozone (Wyche et al., 2020), which in terms of its function as a respiratory pollutant, has been shown to be a more harmful than NOx species. Further, the reductions observed in ambient PM levels has implications for ultrafine particles (UFP), i.e. PM acts to supress UFP (and hence control their number, as shown in recent research by Guo et al., 2020). This is particularly concerning as UFP are now believed to be more harmful than other, larger fractions of particles; indeed, evidence is mounting to demonstrate their ability to penetrate deeply into the body and impair the function of our major organs.
The project will look to answer the following research questions:
1. What changes have occurred in atmospheric trace composition and reactivity owing to the COVID-19 lockdown and does this represent a window into the future to see the impact of reduced NOx emissions in moving towards a low carbon economy? What lessons can be learnt and how can these be used to help develop policy and measures to protect the environment and public health?
2. Do reduced PM concentrations under 'real-world'/pandemic conditions lead to an increase in UFP numbers and if so to what extent?
3. Is there a link between UFP (and other air pollutants) and COVID-19 cases?