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PM2.5 on the London Underground

PM2.5 on the London Underground
PM2.5 on the London Underground
INTRODUCTION: Despite the London Underground (LU) handling on average 2.8 million passenger journeys per day, the characteristics and potential health effects of the elevated concentrations of metal-rich PM2.5 found in this subway system are not well understood.

METHODS: Spatial monitoring campaigns were carried out to characterise the health-relevant chemical and physical properties of PM2.5 across the LU network, including diurnal and day-to-day variability and spatial distribution (above ground, depth below ground and subway line). Population-weighted station PM2.5 rankings were produced to understand the
relative importance of concentrations at different stations and on different lines.

RESULTS: The PM2.5 mass in the LU (mean 88 μg m-3, median 28 μg m-3) was greater than at ambient background locations (mean 19 μg m-3, median 14 μg m-3) and roadside environments in central London (mean 22 μg m-3, median 14 μg m-3). Concentrations varied between lines and locations, with the deepest and shallowest submerged lines being the District (median 4 μg m-3) and Victoria (median 361 μg m-3 but up to 885 μg m-3). Broadly in agreement with other subway systems around the world, sampled LU PM2.5 comprised 47% iron oxide, 7% elemental carbon, 11% organic carbon, and 14% metallic and mineral oxides. Although a relationship between line depth and air quality inside the tube trains was evident, there were clear influences relating to the distance from cleaner outside air and the exchange with cabin air when the doors open. The passenger population-weighted exposure analysis demonstrated a method to identify stations that should be prioritised for remediation to improve air quality.

CONCLUSION: PM2.5 concentrations in the LU are many times higher than in other London transport environments. Failure to include this environment in epidemiological studies of the relationship between PM2.5 and health in London is therefore likely to lead to a large exposure misclassification error. Given the significant contribution of underground PM2.5 to daily exposure, and the differences in composition compared to urban PM2.5, there is a clear need for well-designed studies to better understand the health effects of underground exposure.
0160-4120
Smith, James
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Barratt, Benjamin
2e639122-13b5-48e5-903e-3bb549e73cf0
Fuller, Gary
c729f6ca-78c1-49a8-9554-563def2c894d
Kelly, Frank
15749088-29c9-43d8-9c87-8f44369e7bb5
Loxham, Matthew
8ef02171-9040-4c1d-8452-2ca34c56facb
Nicolosi, Eleonora
37c80004-025b-4eb6-87ba-b5744bbb1e51
Priestman, Max
bcfd71e1-1ff5-47a8-907f-f817881bff2b
Tremper, Anja
6b528f39-826e-4cd5-8655-ff22a8411006
Green, David
96646307-e2fd-4b57-99ca-76456dfa2a8f
Smith, James
5edecb32-58bf-4c2c-96e7-b8b88322f62b
Barratt, Benjamin
2e639122-13b5-48e5-903e-3bb549e73cf0
Fuller, Gary
c729f6ca-78c1-49a8-9554-563def2c894d
Kelly, Frank
15749088-29c9-43d8-9c87-8f44369e7bb5
Loxham, Matthew
8ef02171-9040-4c1d-8452-2ca34c56facb
Nicolosi, Eleonora
37c80004-025b-4eb6-87ba-b5744bbb1e51
Priestman, Max
bcfd71e1-1ff5-47a8-907f-f817881bff2b
Tremper, Anja
6b528f39-826e-4cd5-8655-ff22a8411006
Green, David
96646307-e2fd-4b57-99ca-76456dfa2a8f

Smith, James, Barratt, Benjamin, Fuller, Gary, Kelly, Frank, Loxham, Matthew, Nicolosi, Eleonora, Priestman, Max, Tremper, Anja and Green, David (2019) PM2.5 on the London Underground. Environment International. (In Press)

Record type: Article

Abstract

INTRODUCTION: Despite the London Underground (LU) handling on average 2.8 million passenger journeys per day, the characteristics and potential health effects of the elevated concentrations of metal-rich PM2.5 found in this subway system are not well understood.

METHODS: Spatial monitoring campaigns were carried out to characterise the health-relevant chemical and physical properties of PM2.5 across the LU network, including diurnal and day-to-day variability and spatial distribution (above ground, depth below ground and subway line). Population-weighted station PM2.5 rankings were produced to understand the
relative importance of concentrations at different stations and on different lines.

RESULTS: The PM2.5 mass in the LU (mean 88 μg m-3, median 28 μg m-3) was greater than at ambient background locations (mean 19 μg m-3, median 14 μg m-3) and roadside environments in central London (mean 22 μg m-3, median 14 μg m-3). Concentrations varied between lines and locations, with the deepest and shallowest submerged lines being the District (median 4 μg m-3) and Victoria (median 361 μg m-3 but up to 885 μg m-3). Broadly in agreement with other subway systems around the world, sampled LU PM2.5 comprised 47% iron oxide, 7% elemental carbon, 11% organic carbon, and 14% metallic and mineral oxides. Although a relationship between line depth and air quality inside the tube trains was evident, there were clear influences relating to the distance from cleaner outside air and the exchange with cabin air when the doors open. The passenger population-weighted exposure analysis demonstrated a method to identify stations that should be prioritised for remediation to improve air quality.

CONCLUSION: PM2.5 concentrations in the LU are many times higher than in other London transport environments. Failure to include this environment in epidemiological studies of the relationship between PM2.5 and health in London is therefore likely to lead to a large exposure misclassification error. Given the significant contribution of underground PM2.5 to daily exposure, and the differences in composition compared to urban PM2.5, there is a clear need for well-designed studies to better understand the health effects of underground exposure.

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Accepted/In Press date: 13 September 2019

Identifiers

Local EPrints ID: 434381
URI: https://eprints.soton.ac.uk/id/eprint/434381
ISSN: 0160-4120
PURE UUID: 6c7e2ed9-7b11-4a42-a672-493c16410f5f
ORCID for Matthew Loxham: ORCID iD orcid.org/0000-0001-6459-538X

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Date deposited: 23 Sep 2019 16:30
Last modified: 24 Sep 2019 00:36

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