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

• Main Authors: J. D. Lee, W. S. Drysdale, D. P. Finch, S. E. Wilde, P. I. Palmer
• Format: Article
• Language: English
• Published: Copernicus Publications 2020-12-01
• Series: Atmospheric Chemistry and Physics
• Online Access: https://acp.copernicus.org/articles/20/15743/2020/acp-20-15743-2020.pdf

<p>We report changes in surface nitrogen dioxide (<span class="inline-formula">NO₂</span>) 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 that <span class="inline-formula">NO₂</span> reduced by <span class="inline-formula">42 <i>%</i>±9.8 <i>%</i></span> on average across all 126 urban AURN sites, with a slightly larger (<span class="inline-formula">48 <i>%</i>±9.5 <i>%</i></span>) reduction at sites close to the roadside (urban traffic). We also find that ozone (<span class="inline-formula">O₃</span>) increased by 11 % on average across the urban background network during the lockdown period. Total oxidant levels (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mtext mathvariant="italic">x</mtext></msub></mrow><mo>=</mo><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub></mrow><mo>+</mo><mrow class="chem"><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">3</mn></msub></mrow></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="73pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="2b548850d308edc75bc21be3fb575c2b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-20-15743-2020-ie00001.svg" width="73pt" height="13pt" src="acp-20-15743-2020-ie00001.png"/></svg:svg></span></span>) increased only slightly on average (<span class="inline-formula">3.2 <i>%</i>±0.2 <i>%</i></span>), suggesting the majority of this change can be attributed to photochemical repartitioning due to the reduction in <span class="inline-formula">NO_<i>x</i></span>. Generally, we find larger, positive <span class="inline-formula">O_<i>x</i></span> 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 <span class="inline-formula">NO₂</span> and <span class="inline-formula">O₃</span> changes is a sharp decrease in exceedances of the <span class="inline-formula">NO₂</span> air quality objective limit for the UK, with only one exceedance in London in 2020 up until the end of May. Concurrent increases in <span class="inline-formula">O₃</span> exceedances in London emphasize the potential for <span class="inline-formula">O₃</span> to become an air pollutant of concern as <span class="inline-formula">NO_<i>x</i></span> emissions are reduced in the next 10–20 years.</p>