Changes in ambient air quality and atmospheric composition and reactivity in the South East of the UK as a result of the COVID-19 lockdown - LPS

Kevin Wyche, Mark Nichols, Harley Parfiff, Paul Beckett, Douglas Gregg, Kirsty Smallbone, Paul Monks

Research output: Contribution to conferenceAbstractpeer-review


By the 1st July 2020, there were in excess of 10 million confirmed cases of COVID-19 worldwide. Of these cases, it was reported that the virus had claimed an estimated 511,037 lives. In an effort to halt the spread of the disease, governments across the globe put into place a range of measures based on ‘social distancing’ and ‘self-isolation’, which resulted in many industries suspending operations and most citizens (i.e., non ‘key-workers’) staying in their homes. As such, anthropogenic activity around the globe decreased rapidly, to such an extent that emissions of air pollutants began to decline dramatically, with this period now being referred to as an ‘anthropause’. In the early stages of the pandemic, remote sensing data from satellites indicated that nitrogen dioxide (NO₂) concentrations had fallen by as much as 30% across China and by as much as 50% across areas of central Europe. Early work using in-situ measurements confirmed these findings, with studies from China, Korea, India, the USA and Europe all reporting decreases in ambient NOx concentrations. The UK government advised that the general population should avoid ‘non-essential’ travel and social contact, on 16th March 2020. At this point, the total number of confirmed cases in the UK had surpassed 1500. Subsequently, on 23rd March 2020, the government announced a UK-wide partial ‘lockdown’, to contain the spread of the virus. The Health Protection (Coronavirus, Restrictions) (England) Regulations 2020, the statutory instrument to enforce the lockdown, was enacted shortly after.
In this work, we combine findings from the University of Brighton’s Brighton Atmospheric Observatory and the ESA's Sentinel-5P satellite, to investigate changes in tropospheric Nitrogen Dioxide concentrations in the South East of the UK during the COVID-19 pandemic.
BAO (formerly the JOAQUIN Advanced Air Quality reSearch Laboratory; JAAQS) was established in Brighton in 2015. It comprises a climate controlled, clean laboratory instrumented with a suite of state-of-the-art analytical instruments for making detailed, real-time measurements of tropospheric composition. It is equipped with long-path Differential Optical Absorption Spectroscopy (DOAS; Opsis AB) for remote sensing of trace gas parameters (path length ~ 300 m), including NO₂, O₃, SO₂, formaldehyde (HCHO), nitrous acid (HONO) and benzene (C₆H₆; indicative data only); total and size-resolved particle counters (7 ≤ n ≤ 1000 nm; TSI 3031 and TSI 3783); a black carbon monitor (Thermo MAAP 5012); a PM2.5 monitor (Met One ES-642); and a meteorology station (Campbell Scientific; data from 01/01/2019). BAO is situated in a suburban background environment, roughly 5 km from Brighton city centre. Data were recorded at 5-minute averaging intervals and were screened for service periods and anomalies prior to analysis.
Level-2 (L2) TROPOMI NO₂ products were sourced from the Sentinel-5P Pre-Operations Data Hub for dates between 23rd March and 22nd April of both 2019 and 2020. The pixels covering the South East quadrant of the UK were extracted from each dataset and filtered to remove problematic and cloud-influenced observations, i.e., where pixel values were negative or associated with a Quality Assurance flag < 0.75. The filtered data were appropriately averaged, and units converted to molec m^-2. Percentage change in tropospheric column NO2 values over the region were determined by expressing the concentration difference between 2020 and 2019 as a fraction of the 2019 value. The values of cells within the filtered daily raster files which covered Brighton and Hove were recorded next to the appropriate date, which meant these values could be plotted alongside DOAS measurements.
The attached figure shows regional daily average NO₂ concentrations as recorded by TROPOMI over (a) the period 25/03/2019–22/04/2019 (i.e. the pre-pandemic baseline) and (b) 23/03/2020–20/04/2020 (i.e. post-implementation of lockdown restrictions). The percentage change between the two periods is also shown (c), as are the locally integrated values over the city of Brighton and Hove, plotted alongside long-path DOAS measurements made on the ground (over a total path length 300 m) for the same time period (d). The data shown in Figure 1 confirms findings from analysis of in-situ monitor observations made by the Sussex-Air Network and DEFRA Automatic Urban and Rural Network (AURN), extending the reach of the data capture to the entire South East of the UK on a 7 × 7 km resolution scale. In-line with the in-situ monitors, TROPOMI measured a decrease in the concentrations of NO2 across the entire region during the lockdown, with the regional average value falling by 33%, from 4.9 × 10^16 to 3.3 × 10^16 molec m^-2. Figure 1(c) shows that the largest changes in NO2 were observed in the centre of the region, in the areas surrounding London and at certain coastal locations.
As seen in Figure 1(d), when integrated across the city scale (Brighton and Hove in this instance), TROPOMI is relatively successful in capturing local daily variations when compared to remote sensing conducted on the ground, in this case by long-path DOAS. Here, TROPOMI measured NO2 values across the city during the 2020 lockdown period to be 59% of those measured over roughly the same time period the previous year (with mean values falling from 4.4 × 10^16 to 2.9 × 10^16 molecule m^-2), comparing favourably with DOAS, which recorded NO₂ values that were ~64% of those measured during the previous two years over roughly the same time period.
The methodology is also extended to London, Birmingham and Manchester, which are the 1st, 2nd and 6th largest cities within the UK.
Original languageEnglish
Publication statusPublished - 23 May 2022
EventThe European Space Agency Living Planet Symposium - Bonn, Germany, Bonn, Germany
Duration: 23 May 202227 May 2022


ConferenceThe European Space Agency Living Planet Symposium
Abbreviated titleLPS 2022
Internet address


  • air quality
  • atmospheric science
  • COVID-19
  • lockdown
  • anthropause
  • air pollution


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