# How COVID-19 related policies reshaped organic aerosol source contributions in central London

Gang Chen, Anja H Tremper, Max Priestman, Anna Font, David C Green

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Gang Chen, Anja H Tremper, Max Priestman, Anna Font, David C Green. How COVID-19 related policies reshaped organic aerosol source contributions in central London. European Aerosol Conference, Aug 2024, Tampere (Finlande), Finland. hal-04700498

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Submitted on 17 Sep 2024

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# How COVID-19 related policies reshaped organic aerosol source contributions in central London

Gang Chen¹*, Anja Tremper¹, Max Priestman¹, Anna Font², and David C. Green¹,³

¹MRC Centre for Environment and Health, Environmental Research Group, Imperial College London, London, W12 0BZ, UK

²IMT Nord Europe, Institut Mines-Télécom, Univ. Lille, Centre for Education, Research and Innovation in Energy and Environment (CERI EE), 59000, Lille, France

³NIHR HPRU in Environmental Exposures and Health, Imperial College London, UK

Keywords: COVID-19, Source Apportionment, PMF, Cooking Organic Aerosol

Associated conference topics: 2.9

Presenting author: gang.chen@imperial.ac.uk

Improving air quality can potentially save millions of lives, given that 97% of the urban population in Europe is exposed to a higher annual PM<sub>2.5</sub> concentration than the World Health Organization guidelines (5 µg/m<sup>3</sup>) (WHO, 2021). As the largest city in Europe, London is on the front line to mitigate the health impacts of PM<sub>2.5</sub>. Knowledge of pollution sources is crucial to design the most cost-effective mitigation strategies. Positive matrix factorization (PMF) of Aerosol Mass Spectrometer (AMS) or Aerosol Chemical Speciation Monitor (ACSM) data is a powerful approach to quantitatively identify and apportion sources of organic aerosol (OA), which makes up over half of PM<sub>2.5</sub>. Using the most advanced PMF techniques (i.e., rolling PMF, ME-2, and bootstrap, Canonaco et al., 2021) by following the standardized protocol (Chen et al., 2022) could provide high-quality source information of OA.

The year-long Quadrupole ACSM (Ng et al., 2011) data from the roadside supersite in London Marylebone Road (51.523 N, -0.155 E) collected from Aug 1st, 2019, to Oct 22nd, 2020, provides us with a unique opportunity to investigate how COVID-related policies impacted human activities and, therefore, OA sources. The period covered the first COVID-19 lockdown (Mar 26th, 2020 to Jun 23rd, 2020) and the Eat Out to Help Out (EOTHO) Scheme (Mon-Wed during Aug 3rd, 2020 to Aug 31st, 2020) (Table 1), which was a British government scheme to support the hospitality industry during the COVID-19 pandemic (https://www.gov.uk/guidance/get-a-discount-with-the-eat-out-to-help-out-scheme).

<table><caption>Table 1 Dates of the COVID-related policies in London.</caption><thead><tr><th>COVID Policies</th><th>Date</th></tr></thead><tbody><tr><td>Pre-Lockdown</td><td>Aug 1st, 2019 – Mar 25th, 2020</td></tr><tr><td>Lockdown</td><td>Mar 26th, 2020 – Jun 23rd, 2020</td></tr><tr><td>Priori scheme</td><td>Jun 24th, 2020 – Aug 2nd, 2020</td></tr><tr><td>Post-Lockdown</td><td></td></tr><tr><td>EOTHO scheme</td><td>Aug 3rd, 2020 – Aug 31st, 2020</td></tr><tr><td>After scheme</td><td>Sep 1st, 2020 – Oct 22nd, 2020</td></tr></tbody></table>

Five OA factors were identified including hydrocarbon-like OA (HOA, traffic-related, 10.5% to OA), cooking OA (COA, 19.5% to OA), biomass burning OA (BBOA, 11.5% to OA), more-oxidized oxygenated OA (MO-OOA, 37.7% to OA), and less-oxidized oxygenated OA (LO-OOA, 20.8% to OA). All factors showed distinct diurnal patterns before, during and

after lockdown. It is worth noticing that the morning rush-hour peak for HOA and noon peak for COA both disappeared during the lockdown. Moreover, the EOTHO scheme elevated the COA mass concentration after the lockdown (Fig. 1) by 44.9% but concentrations remained lower than those observed before lockdown. After the scheme ended, COA concentrations remained.

<figure><img src="image_2.png" /><figcaption>Figure 1 Diel cycles for cooking organic aerosol (COA) during different periods</figcaption></figure>

This study demonstrated the power of rolling PMF in reflecting the influences of policies in human activities and therefore, OA sources. Special attention should be paid to cooking emissions (8.5% of total PM) in urban environment. Thus, it is important to continuously resolve OA sources to inform policymakers of the effectiveness of the policies.

This work is supported by the UK Natural Environment Research Council Grant OCSA NE/T001909/2.

## References

Canonaco et al., Atmos Meas Tech, 14, https://doi.org/10.5194/amt-14-923-2021, 2021.

Chen et al., Environ Int, 166, 107325, https://doi.org/10.1016/j.envint.2022.107325, 2022.

Ng et al., Aerosol Science and Technology, 45, 780–794, https://doi.org/10.1080/02786826.2011.560211, 2011.

World Health Organization (WHO), 2021.