UK surface NO2 levels dropped by 42 % during the COVID-19 lockdown: impact on surface O3

• Published in: Atmospheric chemistry and physics 2020-12, Vol.20 (24), p.15743-15759
• Main Authors: Lee, James D, Drysdale, Will S, Finch, Doug P, Wilde, Shona E, Palmer, Paul I
• Format: Article
• Language: English
• Subjects: Air; Air pollution; Air quality; Coronaviruses; COVID-19; Disease transmission; Emissions; Emissions control; Nitrogen compounds; Nitrogen dioxide; Nitrogen oxides; Nitrogen oxides emissions; Oxidants; Oxidizing agents; Ozone; Pandemics; Photochemicals; Photochemistry; Pollutants; Radiation; Roads & highways; Roadsides; Severe acute respiratory syndrome coronavirus 2; Shelter in place; Ultraviolet radiation; Urban areas
• ISSN: 1680-7316; 1680-7324
• DOI: 10.5194/acp-20-15743-2020

We report changes in surface nitrogen dioxide (NO2) across the UK during the COVID-19 pandemic when large and rapid emission reductions accompanied a nationwide lockdown (23 March–31 May 2020, inclusively), and compare them with values from an equivalent period over the previous 5 years. Data are from the Automatic Urban and Rural Network (AURN), which forms the basis of checking nationwide compliance with ambient air quality directives. We calculate thatNO2 reduced by 42%±9.8% on average across all 126 urban AURN sites, with a slightly larger (48%±9.5%) reduction at sites close to the roadside (urban traffic). We also find that ozone (O3) increased by 11 % on average across the urban background network during the lockdown period. Total oxidant levels (Ox=NO2+O3) increased only slightly on average (3.2%±0.2%), suggesting the majority of this change can be attributed to photochemical repartitioning due to the reduction in NOx. Generally, we find larger, positiveOx changes in southern UK cities, which we attribute to increased UV radiation and temperature in 2020 compared to previous years. The net effect of the NO2 andO3 changes is a sharp decrease in exceedances of the NO2 air quality objective limit for the UK, with only one exceedance in London in 2020 up until the end of May. Concurrent increases in O3 exceedances in London emphasize the potential for O3 to become an air pollutant of concern as NOx emissions are reduced in the next 10–20 years.