How COVID-19 Related Policies Reshaped Organic Aerosol Source Contributions in Central London

IAN (GANG) CHEN, Anja Tremper, Max Priestman, Anna Font, David Green, Imperial College London

     Abstract Number: 277
     Working Group: Source Apportionment

Abstract
As the largest city in Europe, London is at the forefront of mitigating the health impacts of PM2.5. Knowledge of pollution sources is crucial to design the most cost-effective mitigation strategies. Positive matrix factorization (PMF) of Aerosol Chemical Speciation Monitor (ACSM) data is a powerful approach to quantitatively identify and quantify sources of organic aerosol (OA), which makes up over half of PM2.5. Using the most advanced PMF techniques (i.e., rolling PMF, ME-2, and bootstrap) by following the standardized protocol could provide high-quality source information on OA. The year-long Quadrupole ACSM 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 from Aug 3rd, 2020 to Aug 31st, 2020), which was a British government scheme to support the hospitality industry during COVID-19. Five OA factors were identified including hydrocarbon-like OA (HOA, traffic-related, 10.5% to OA), cooking OA (COA, 19.5%), biomass burning OA (BBOA, 11.5%), more-oxidized oxygenated OA (MO-OOA, 37.7%), and less-oxidized oxygenated OA (LO-OOA, 20.8%). All factors showed distinct diurnal patterns before, during and after lockdown. Moreover, the EOTHO scheme elevated the COA mass concentration after the lockdown by 44.9 % but concentrations remained lower than those observed before lockdown. After the scheme ended, COA concentrations remained. This study suggests special attention should be paid to cooking emissions (8.5% of total PM) in urban environments. Thus, it is important to continuously resolve OA sources to inform policymakers of the effectiveness of the policies.