Metal and PAH content in PM10 measured in Bristol in 2021.

Particulate matter in the atmosphere is a major health concern, and the chemical composition of particles will affect its toxicology. Chemical composition of PM₁₀ can indicate likely sources of pollutants; high concentrations of metals can come from fuel mixtures, lubricants, abrasion and engine wear from cars [1], while polycyclic aromatic hydrocarbons (PAH) are produced by combustion sources [2]. Measurements can be interpreted through use of air flow measurements within the city and supported modelling [3].

PM₁₀ samples were collected weekly, every Thursday, for 24 hours from a 1^st floor balcony at the We the Curious science museum in central Bristol, UK. Samples were collected using a Sven Leckel LVS3 PM₁₀ sampler on a 47 mm quartz filter and weighed to calculate the mass concentration. Quartz filters were halved and analysed for metals using ICP-MS and for PAH using GC-MS. Local meteorology was measured on the roof using a Gill Maximet 501 weather station.

Measurements took place from February 2021 until February 2022. Within the UK the third COVID-19 lockdown started on 6^th January 2021 and was incrementally lifted from 8^th March until 21^st June when all restrictions were removed.

Taking the average of samples that were detected above noise average metal concentrations from lowest (Co, 40 ng/m³) to highest (Fe 195 µg/m³) were Co < Li < Ce < Cd < La < Rb < Bi < Se < V < Sb < As < Sr < Sn < Pb < Mn < Ba< Cu < Zn < Al < Mg< Fe. Average PAH concentrations from lowest to highest were Anthracene < Fluoranthene < Pyrene < Acenaphthene < Dibenzo-a,h-Anthracene <  Benzo[k]Fluoranthene < Indeno-123-cd-Pyrene < Chrysene < Benzo[a]Pyrene < Benzo-ghi-Perylene < Benzo[a]Anthracene < Benzo[b]Fluoranthene, average total PAH concentration was 4.8 ng/m³).

For the sample collected from 13^th January 2022, many metals and PAH levels were elevated. This coincided with a multivehicle fire in Totterdown, around 2 km South East of the measurement position, that started in the evening of the 13th. Total PAH, Mn, Co, Cu, As, Rb, Cd, Sn, Sb, Ba, Ce, Pb and Bi were more than 2 standard deviations higher than the weekly mean concentrations, many showing a 2-3 fold increase. Measurements of Nitric Oxide from the UK government AURN air quality site in St Pauls, ~2 km from the We the Curious site ~3 km north of the incident site, confirmed that pollutants were dispersed city wide, not local to the measurement position. The predominant wind direction was south westerly on the 13^th January, but air masses can spread through a complex city terrain against wind directions [3].

Measurements in a single location can provide information on pollution in the city, extreme peaks in concentrations were identified with fires being a likely source.

[1] Pulles T, van der Gon HD, Appelman W, Verheul M 2012. Atmos Environ 61, 641–651.

[2] Jang, E., Alam, M.S. and Harrison, R.M., 2013. Atmospheric Environment, 79, 271-285.

[3] Matthews, J.C., Wright, M.D., Martin, et al. 2020. Boundary-Layer Meteorology, 175, 113-134.