Releasing a rapid evidence review report this week on changes in air pollution emissions, the Air Quality Expert Group (AQEG) notes that long-term exposure to air pollution is linked to increased morbidity and mortality from chronic diseases. It adds that some of these have also been identified as increasing the risk of severe COVID-19 symptoms.

The report’s insights into the impact of air quality on viral infection were provided by the Committee on the Medical Effects of Air Pollutants, comprising academics and health experts, and chaired by Professor Frank J Kelly, of Imperial College London. The committee points to studies exploring the links between COVID-19 and both past and contemporary air pollution exposure, but it cautions that these are limited by an, as yet, “incomplete understanding of the factors controlling the transmission and progression of the disease, and especially individual risk factors”.

Concludes the committee: “In summary, although there is, as yet, no clear empirical evidence that exposure to air pollutants increases the likelihood or severity of COVID-19 infection, knowledge of the impacts of air pollution on health suggests that this is likely. In addition, infection may temporarily increase subsequent responses to air pollution, in those with pre-existing illnesses. Potential interactions between air pollution and COVID-19 may be relevant to the future management of the pandemic in the UK and elsewhere.”

According to the wider report, average levels of polluting nitrogen oxides (NOx) and nitrogen dioxide (NO2) during the UK’s lockdown period up to the end of April were between 30 and 40 per cent lower than normal in urban communities. It goes on to state that changes to population exposure to air pollution are variable and more uncertain than estimates of changes in ambient concentrations.

“Some urban locations have seen significant falls in NO₂, and wider working from home has reduced travel exposure more generally in cities,” says the report. “In London, initial estimates of reduction in PM_2.5 exposure compared to ‘business as usual’ are in the range 5-24 per cent depending on factors such as commuting mode.”

The reduction in mobility decreased vehicle traffic by about 70 per cent by mid-April, according to data from the Department for Transport (DfT), with various local authorities seeing overall reductions of 50 per cent (London), 62 per cent (Central London), 60 to 70 per cent (Leeds), 60 per cent (Newcastle), 55-60 per cent (East & West Sussex) and 60 to 75 per cent (Manchester). Traffic volumes have since increased.

Indoor air pollution

The report acknowledges, too, that while exposure to pollution in the workplace and during commuting will have likely reduced for many people, more time spent on activities in the home, such as cooking and cleaning, may have increased emissions and concentrations of pollutants such as PM_2.5 and volatile organic compounds (VOCs).

An exposure model by Kings College London that accounts for both indoor and outdoor pollution predicts a net increase in PM_2.5 exposure for most individuals (with the exception of Underground users) as a result of COVID-19, if it’s assumed that an additional domestic cooking activity is performed each day. Without the extra cooking activity, the model predicts a slight decrease. The model also predicts a net decrease in NO₂ exposure both with and without additional cooking activities.

Measures to mitigate indoor air pollution exposure could include encouraging people to spend more time outdoors, regular vacuuming of carpets, not smoking indoors, and ensuring that homes are adequately ventilated (eg, leaving windows open), particularly while cooking and cleaning. Kitchen filtration or extraction devices will help mitigate exposure, as long as they expel the emissions to the outdoors rather than recirculate them within the kitchen, says the report. Proper maintenance of cooker extraction devices is essential (cleaned/filters replaced) if they are to be effective, it adds.