An urban CO2 monitoring network to evaluate transport related carbon mitigation initiatives

Student thesis: Doctoral ThesisDoctor of Philosophy


Transport is the only sector of the UK economy for which current greenhouse gas emissions, primarily as CO2, are greater than in 1990; estimated at 26% of total CO2 emissions. While UK strategy in the form of the Climate Change Act details how, and to what extent, national and international initiatives to CO2 combat emissions are predicted to decrease, they provide no indication of their effects on ambient CO2 concentrations and few direct measurements of emissions currently exist to aid comparisons with, and elucidate these estimates.

The main aim of this research was to create an assessment framework capable of providing evidence for the impact of regulatory or other interventional measures within the transport sector on ambient CO2 concentrations both within and across Greater London. To accomplish this, a long-term urban CO2 monitoring network was established in London utilising five locations to represent different road types and urban background atmospheric conditions. Methods to isolate local vehicle fleet CO2 emissions from regional CO2 sources, accounting for transpiration sources, identified considerable additional CO2 loading by between 9 and 35 ppm at roadside monitoring stations in comparison to urban background locations during a typical day. During daylight hours alone, this enhancement is as high as 55 ppm at the kerbside in a street canyon.

A detailed assessment of NOX/CO2 ratios measured by a remote sensing device (RSD) aided the understanding of how emissions can be characterised from vehicles during on-road operation. The exact source of emissions could be pinpointed, i.e. specific vehicle type, fuel and even manufacturer and its contribution to the overall emission source profile. The average NOX/CO2 ratio from the RSD campaign was 0.004 in comparison with derived ambient roadside NOx/CO2 ratios of 0.0036, 0.039 and 0.0041 calculated from the roadside sites across the London CO2 network.

Trend analysis of roadside CO2 increments across the London network over a seven-year period produced negative trends of between -2.7 and -3.7% year-1. These trends compared well with the National Atmospheric Emissions Inventory but were twice that of the London Atmospheric Emissions Inventory. That these negative trends contrasted with increased vehicle number counts suggested that tailpipe emissions of CO2 and of NOX were indeed decreasing because of pollutant mitigation strategies. However, no individual action could be identified as the underlying reason for these reductions. The London CO2 monitoring network can be utilised as an on-going research resource as part of a measurement, recording and verification framework for London by providing evidence for changes in local and London-wide emissions of CO2.
Date of Award1 Jul 2018
Original languageEnglish
Awarding Institution
  • King's College London
SupervisorBenjamin Barratt (Supervisor)

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