Elsevier

Environmental Research

Volume 142, October 2015, Pages 495-510
Environmental Research

Urban air quality comparison for bus, tram, subway and pedestrian commutes in Barcelona

https://doi.org/10.1016/j.envres.2015.07.022Get rights and content
Under a Creative Commons license
open access

Highlights

  • Big differences in the aerosols inhaled in bus, subway, tram and walking journeys

  • Particle number concentration is lowest in subway trains and highest in diesel bus

  • City centre traffic crossings show particle transient peaks >1×105 part./cm3

  • Tram is the cleanest form of city public transport when compared to bus and subway

  • Subway particles are rich in Fe–Mn, and diesel bus particles are richer in Sb–Cu

Abstract

Access to detailed comparisons in air quality variations encountered when commuting through a city offers the urban traveller more informed choice on how to minimise personal exposure to inhalable pollutants. In this study we report on an experiment designed to compare atmospheric contaminants inhaled during bus, subway train, tram and walking journeys through the city of Barcelona. Average number concentrations of particles 10-300 nm in size, N, are lowest in the commute using subway trains (N<2.5×104 part. cm−3), higher during tram travel and suburban walking (2.5×104 cm−3<N<5.0×104 cm−3), and highest in diesel bus or walking in the city centre (N>5.0×104 cm−3), with extreme transient peaks at busy traffic crossings commonly exceeding 1.0×105 cm−3 and accompanied by peaks in Black Carbon and CO. Subway particles are coarser (mode 90 nm) than in buses, trams or outdoors (<70 nm), and concentrations of fine particulate matter (PM2.5) and Black Carbon are lower in the tram when compared to both bus and subway. CO2 levels in public transport reflect passenger numbers, more than tripling from outdoor levels to >1200 ppm in crowded buses and trains. There are also striking differences in inhalable particle chemistry depending on the route chosen, ranging from aluminosiliceous at roadsides and near pavement works, ferruginous with enhanced Mn, Co, Zn, Sr and Ba in the subway environment, and higher levels of Sb and Cu inside the bus. We graphically display such chemical variations using a ternary diagram to emphasise how “air quality” in the city involves a consideration of both physical and chemical parameters, and is not simply a question of measuring particle number or mass.

Abbreviations

PM2.5
particulate matter with a diameter below 2.5 microns
PEM
Personal Environmental Monitor
ICP-AES
Inductively Coupled Plasma Atomic Emission Spectroscopy
ICP-MS
Inductively Coupled Plasma Mass Spectrometry
CPC
condensation particle counter
N
particle number concentrations
BC
Black Carbon
SCRT®
Selective Catalytic Reduction+Continuously Regenerating Trap
ADSA
alveolar deposited surface area

Keywords

Commuting
Ultrafine particles
Metalliferous PM2.5
Exposure
City transport pollution

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