Estimation of changes in air pollution emissions, concentrations and exposure during the COVID-19 outbreak in the UK

There have been significant changes in the emissions of air pollutants from several sectors, but, with the exception of the transport sector which showed a marked decrease, availability of activity and emissions data for the lockdown period is still limited.
- UK air quality has been negatively influenced by a significant change in meteorology between the weeks preceding and following the lockdown in addition to changes (both positive and negative) arising from actions in response to COVID-19.
- The most pronounced changes in UK air quality during lockdown have been in the urban environment, notably for nitrogen oxides (NOx). Once weather effects are accounted for, mean reductions in urban NOx averaged over the lockdown period considered have been typically 30-40%, with mean NO2 reductions of 20-30%. In general, NOx and NO2 reductions have been greater at roadside than at urban background sites. These reductions would typically correspond to decreases in concentrations of 10-20 ug m-3 if expressed relative to annual averages.
- Meteorological conditions have led to higher PM2.5 during lockdown than the average experienced in equivalent calendar periods from previous years. Analysis combining observations and models indicates however that PM2.5 concentrations were of the order 2 - 5 ug m-3 lower in Southern England than would have been expected under a business-as-usual emissions scenario. The changes to UK PM2.5 in terms of contributing sources and transboundary influences have yet to be determined.
- 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. In London, initial estimates of reduction in PM2.5 exposure compared to business-as-usual are in the range 5-24% depending on factors such as commuting mode.
- Little is known about the impact of lockdown on indoor air quality, since homes are not routinely monitored in the UK. Whilst exposure to pollution in the workplace and during commuting will have likely reduced for many people, increased time spent on activities in the home such as cooking and cleaning may have increased emissions and concentrations of pollutants such as PM2.5 and Volatile Organic Compounds (VOCs).
- Increased ozone has been observed at some urban monitoring stations, a result of lower local NO. Models suggest the responses in UK ozone for this summer compared to business-as-usual are variable, with no single direction of change, although there may be some modest increases in urban areas and in central and south-eastern parts of the UK.
- Long-term exposure to air pollution is associated with increased morbidity and mortality from chronic diseases, some of which have also been identified as increasing the risk of severe COVID-19 symptoms. Given this, it would not be surprising if there was a link between exposure to air pollution (past or present) and the occurrence or severity of COVID-19 infection. Whilst several unpublished studies have examined this effect, and have reported associations with past exposure to both PM2.5 and NO2, there is currently no consensus on the pollutant responsible or the magnitude of any effect. Such studies require very careful control for confounding influences, and further work is needed before there can be confidence in their findings.
- Very small amounts of RNA from SARS-CoV-2 have been observed in outdoor particulate matter but it is not yet known whether breathing air outdoors provides a significant route for transmission of live virus or infection. Whilst aerosol containing the virus can build up indoors in poorly ventilated rooms, dilution is rapid in an open outdoor environment, which is likely to reduce the dose of virus inhaled compared to indoors. The lifetime of active virus in the outdoor atmosphere has yet to be determined.