Exposure in London.

Using TfL data to better understand our exposure to air pollution


Studies that estimate the harmful effects of air pollution are based on methods, which assume that we only breathe in the air in our local neighbourhoods. But how much time do people actually spend there? Funded by the NERC Traffic Pollution & Health in London project, using anonymous activity data (provided by Transport for London ), and advanced air pollution and micro-environmental modelling, we have built the London Hybrid Exposure Model (LHEM) to begin to look at this problem from a different angle. We have looked at where Londoners spend their time, and the air that they are breathing whilst in these places.

Our findings show that, on average, many studies are over-estimating Londoners exposure to outdoor air pollution, but that there are also many people whose exposure is being under-estimated. These people tend to spend long periods in transport, such as in the car or on the bus, where they are exposed to high levels of NO2 and PM2.5 . We also conclude that since most people spend a lot of time indoors that sources of pollution in the home, office or school are very important in estimating peoples exposure to air pollution, but that this is not currently considered in the studies of people’s health.

There is more work to do to better disentangle exposure to air pollution and its health effects, but we believe that this is a step in the right direction.

Below we have taken a subset of 45,000 Londoners and have created some interactive graphs for you to explore. Data within the graphs is labelled 'LHEM' for showing results from our new exposure model, and 'residential' for the same people’s exposures in their local neighbourhood. If you click on the legend items, you can explore the data by selecting and deselecting different age groups.

Scatter Chart Visualisation

Typical Daily PM2.5 Exposure

By default we plot the first 1000 datapoints, increase the datapoints by selecting the values

Typical Daily NO2 Exposure

By default we plot the first 1000 datapoints, increase the datapoints by selecting the values

Histogram Visualisation

The graphs below show histograms of our results. Using the 'Grouped' option, each age group is plotted as a single bar showing the number of people with that level of exposure. Using the 'stacked' option, people with the same exposure are grouped and plotted as bars on top of each other. We think they allow you to better understand how levels of exposure vary by age group. As with the graphs above, you can interact with the legends to show different age groups.

Typical Daily NO2 Exposure

Typical Daily PM2.5 Exposure


The London Hybrid Exposure Model (LHEM): Improving human exposure estimates to NO2 and PM2.5 in an urban setting
James David Smith, Christina Mitsakou, Nutthida Kitwiroon, Ben M. Barratt, Heather A Walton, Jonathon G Taylor, Hugh Ross Anderson, Frank J. Kelly, and Sean D. Beevers. 2016. Environmental Science & Technology


James Smith
0207 848 4005

© Imperial College London, Environmental Research Group. All rights reserved 2020.