How have surface NO2 concentrations changed as a result of the UK’s COVID-19 travel restrictions?

H F Dacre,L S Neal,A H Mortimer

doi:10.1088/1748-9326/abb6a2

H F Dacre, L S Neal + Show 1 more

Open Access

https://doi.org/10.1088/1748-9326/abb6a2

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Abstract

Restrictions as a result of the COVID-19 pandemic have led to fewer vehicles on UK roads. Since fuel combustion is responsible for a large fraction of UK emissions it is expected that surface NO2 concentrations would reduce as a result. However, over parts of the UK, surface NO2 concentrations have increased following the implementation of travel restrictions. NO2 measurements from 142 Automatic Urban and Rural Network sites are combined with meteorological data from the Met Office high-resolution weather prediction model to build site specific models. These models predict NO2 concentrations given no change in emissions. It is found that both meteorological and emission changes contribute to the observed changes in NO2 concentrations. Given no change in emissions, changes in meteorology between pre- and post-lockdown periods would have led to a mean increase in NO2 concentrations of +6%. Conversely, changes in emissions would have led to a mean reduction in NO2 concentrations of -18%, resulting in the observed total change in NO2 concentrations of −12%. However at some sites the reduction in emissions is smaller than the increase in NO2 concentrations due to meteorology. The largest increases associated with changes in the meteorology are seen at rural sites (+20%) where NO2 measurements are representative of large areas and thus dominated by the regional advection of secondary NO2 from Europe. Conversely, the largest decreases associated with reduced emissions are found at urban traffic and urban background sites (−27% and −14% respectively) where NO2 concentrations are representative of local areas and thus dominated by local reduction in emissions from vehicles. As lockdown measures are relaxed, NO2 concentrations are likely to return to pre-COVID levels, but these results demonstrate that changes in our behaviour can result in positive impacts on air quality and illustrate the effectiveness of travel-reducing strategies in urban areas.

Highlights

The coronavirus disease 2019 (COVID-19) outbreak began in late 2019 and by March 2020 the virus had been declared a global pandemic by the World Health Organization (WHO 2020)
In the north of England NO2 concentrations have reduced by an average of 20%, but in the south of England and parts of Wales, several AURN sites show an increase in NO2 concentrations after lockdown of over 20%
The aim of this work is to investigate the spatial distribution of changes in NO2 concentration in the UK between the 6-weeks prior to COVID-19 travel restrictions (01/02/20 – 16/03/20, referred to as ‘prelockdown’) and the 6-weeks after travel restrictions were imposed (17/03/20 – 30/04/20, referred to as ‘post-lockdown’)

Summary

Introduction

The coronavirus disease 2019 (COVID-19) outbreak began in late 2019 and by March 2020 the virus had been declared a global pandemic by the World Health Organization (WHO 2020). Countries all over the world have implemented lockdown restrictions to slow down its infection and mitigate its effects These restrictions have caused an unprecedented reduction in global economic activity and travel (Nicola et al 2020). NO2 is formed in the atmosphere in a chemical reaction between nitric oxide (NO) and ozone (O3). Because this NO2 is not released straight into the atmosphere, but is formed there by a chemical reaction, it is known as secondary NO2 Both primary emissions and secondary formation influence NO2 concentrations. Meteorology modifies atmospheric chemistry processes such as photolysis and wet deposition. The combination of these processes can make it difficult to identify the contribution from individual components on NO2 concentrations

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