Imperial College London

Dr Gregor Stewart

Faculty of MedicineSchool of Public Health

Senior Air Quality Scientist



g.stewart Website




Building E - Sir Michael UrenWhite City Campus





I am a researcher in the Environmental Research Group's Air Quality Modelling team with 8 years’ experience in emissions inventory and air quality model development.  I am also jointly responsible for development of the London Hybrid Exposure Model (LHEM).

The LHEM is currently being used in NERC-funded (APEx) and MRC-funded (CLUE) projects.  It extends ERG’s CMAQ-Urban air quality model to provide exposure estimates of people outdoors, in vehicles, on the underground and in residential and commercial buildings. It utilises spacetime-activity data from TfL's London Travel Demand Survey (LTDS), which is generated through interviews with approximately 8,000 households per annum. Weighting factors allow the scaling of the LTDS dataset to represent the population of London.

I have developed our air quality and emissions models in London, and delivered outputs on a range of projects which estimated the impacts of future transport policies on emissions and air quality.  These include the London Atmospheric Emissions Inventory (2013, 2016 and 2019 versions), consultations on the Ultra Low Emission Zone (ULEZ) and the London Environment Strategy (LES).

Current Research Projects

2020 - 2022 DUKEMS: Developing a UK Community Emissions Modelling System; NERC/Met.Office (role: key researcher)

2019-2022 APEx: An Air Pollution Exposure model to integrate protection of vulnerable groups into the UK Clean Air Programme; NERC (role: key researcher)

2017-2020 CLUE: Cognitive Development in the Urban Environment; MRC (role: key researcher)

Research projects within ERG

Scientific Reports

D Dajnak, N Kitwiroon, N Assareh, G Stewart, W Hicks, Evangelopoulos, Wood, H Walton and S Beevers (2022). Pathway to WHO: achieving clean air in the UK - Modelling air quality costs and benefits. Web Link


Project supervisor on MSc in Environmental Technology



Vu TV, Stewart GB, Kitwiroon N, et al., 2022, Assessing the contributions of outdoor and indoor sources to air quality in London homes of the SCAMP cohort, Building and Environment, Vol:222, ISSN:0360-1323, Pages:1-8

Drysdale WS, Vaughan AR, Squires FA, et al., 2022, Eddy covariance measurements highlight sources of nitrogen oxide emissions missing from inventories for central London, Atmospheric Chemistry and Physics, Vol:22, ISSN:1680-7316, Pages:9413-9433

Hicks W, Beevers S, Tremper A, et al., 2021, Quantification of non-exhaust particulate matter traffic emissions and the impact of COVID-19 lockdown at London Marylebone Road, Atmosphere, Vol:12, ISSN:2073-4433, Pages:1-19

Popoola OAM, Stewart GB, Mead MI, et al., 2016, Development of a baseline-temperature correction methodology for electrochemical sensors and its implications for long-term stability, Atmospheric Environment, Vol:147, ISSN:1352-2310, Pages:330-343


Dajnak D, Stewart G, Beevers S, 2017, Policies for london nitrogen dioxide (NO<inf>2</inf>)compliance, Pages:218-222

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