Tuesday, 18 February 2014

Will we ever understand road vehicle pollution?

Alaric Lester

Principal Consultant (Air Quality)

When the UK’s first national air quality strategy was published in 1997, the country finally had a framework for dealing with air pollution. European and national policies and standards were expected to deal with the majority of problem areas, while local authorities would sort localised hotspots. Road vehicles were the predominant source of air pollution, but experts expected air quality problems to be all but gone by 2010.

How did we progress? With carbon monoxide, the advent of catalytic converters in the 1990s quickly removed any areas of high concentrations. For PM10 – particles smaller than ten microns, which are possibly of more concern for health across Europe than any other airborne pollutant – progress has been slower. PM10 levels have fallen steadily but slowly, and there are still more than 100 PM10 air quality management areas (AQMAs) – areas that local authorities have identified as not meeting set standards.

For nitrogen dioxide (NO2), progress has been well short of even pessimistic expectations. Data from the national Automatic and Urban Rural Network and London Air Quality Network tell a story of diminishing returns. After some early progress up to around 2005, NO2 levels have been static or even increasing ever since. There are now well over 500 AQMAs for NO2 across the UK. The European Commission has threatened infraction proceedings against the UK government for failing to deal with NO2 problems. Road vehicles remain the predominant source of NO2 and PM10.

Fifteen years ago we thought we had a reasonable understanding of vehicle emissions. Now, owing to rapid developments in engine and emissions abatement technology, our understanding is arguably worse. Regulations on vehicle emissions limits are based on idealised tests that bear no resemblance to real-world driving; measured real-world vehicle emissions data is scarce; and most experts agree that UK and European emissions factors for road vehicles are highly inaccurate.

Vehicle emissions factors are based on laboratory test bed measurements. These tests give a fair approximation of road driving, but NO2 is not measured directly. We need better data on vehicle emissions to have confidence that intervention measures will actually deliver.

Remote sensing equipment from the University of Leeds Institute for Transport Studies recently featured on the One Show. Remote sensing allows measurement of exhaust emissions at a specific location. It gives a useful snapshot, but does not provide information on how vehicle emissions perform over a range of driving conditions. Instantaneous emissions models, such as Graz University of Technology’s PHEM and TRL’s IEM, do have emissions information over all driving conditions, but they are models and based on very limited measured emissions data.

PEMS (portable emissions measurement system) equipment is ideal for capturing large amounts of real-world emissions data. It can be installed on vehicles driving on the road. Its restriction is expense – a laboratory-standard PEMS costs around £250k. A few universities, such as Imperial College, have experimental (less accurate) PEMS equipment and have been capturing useful data. We need far more data, though, to produce reliable emissions factors that could robustly test the effectiveness of measures such as Boris Johnson’s proposed ultra-low-emission zone. We need more data to challenge current policy and bring about effective change. Might we see a European project collecting PEMS data across the EU over a 12-month period (to allow for seasonal emissions effects) and a team of experts mining the data to generate a new, robust set of emissions factors that bears more than a passing resemblance to reality? Will anyone propose it, and would Europe fund it? The air quality community has a duty to build a robust case.

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