The UK government has responded to the Action on Air Quality report of its Environmental Audit Committee. The last two decades of UK/EU air quality policy, and the industry response, reminds me of nothing so much as the kind of school-swot one-upmanship we all remember hearing from clever but immature peers when we were young. ‘Hah!’ says the regulator, ‘I’m going to make you dirty car manufacturers squeeze through tighter emissions tests before your new models can be sold.’

‘No problem’, replies the industry. ‘We’re so clever, we’ll pass any test you set, and there will still be bigger, heavier, compliant-on-paper cars on your roads – ya boo!’ As long as we think of air pollution as a technological ‘hitch’ requiring a technological fix, we will fail to grasp the true nature of the problem.

The pollutant nitrogen dioxide is the cause of the vast majority of air quality black spots in the UK and in cities elsewhere in the developed world. Emissions of nitrogen oxides from petrol vehicles have been controlled effectively by engine and exhaust technology, but, unlike petrol engines, diesels produce the toxic oxide – NO2 – directly, and diesel engines in use show no improvement as a result of the imposition of stricter EU regulations.

The key statistic, right at the start of the government’s response, is that pollutant emissions have fallen by half, but roadside concentrations of NO2 have fallen by only 15%. In the jargon, this is known as non-linear roll-back and means that air concentrations don’t decrease in line with emissions reductions. Usually, this effect arises because of complicated atmospheric chemistry but in this case it arises because the emissions are calculated by adding up all the car/truck emissions test results and multiplying by the miles travelled by each vehicle type in each square kilometre of the UK.

Although there is a small contribution to the trend in concentrations from changing atmospheric chemistry, by far the biggest effects are that we have followed the tax incentives and switched to lower CO2 but higher NOx diesel engines; that emissions tests do not capture the emissions of real-world driving, and that we all subvert the best efforts of clean engine technology by driving bigger cars.

The government recognises the difference between real-world and test emissions and is absolutely correct that more realistic emissions estimates are crucial if substantive progress is to be made.

The Committee also recommended that the government take concrete steps towards a rebalancing of fuel and excise duties in order to provide parity between carbon dioxide and other pollutants in the tax regimes applied to diesel and petrol engines.

It is disappointing, therefore, that the government’s response fails to consider changes to duty or the introduction of a diesel scrappage scheme and focuses instead on encouraging a general switch away from diesel and petrol as our vehicle fuels of choice. Undoubtedly the best overall option is for a reduction of all petrol or diesel traffic in cities, but I don’t see any evidence that ministers are interested in finding the least harmful path towards such a goal. Nor do I see any rapid progress towards reconfigured urban spaces not reliant on private car ownership and road freight transport.

This lack of a transformative perspective is even clearer in response to the recommendation that planning guidance should be strengthened to protect urban green space and to make it impossible to construct buildings used by vulnerable communities (the old, the very young) close to pollution hot spots. The official response seems to suggest that protecting vulnerable communities is largely a matter of the proper siting of ventilation systems and of opening windows positioned away from busy streets.

Configuring urban space is emphatically not just a case of making sure that school ventilation intakes are placed in the least worst position. Tools are available to help decision-makers understand how to make their urban space more pleasant to live in, but there seems to be no awareness or promotion of this ‘systems-thinking’ in this part of government. I would have expected to see reference to the landmark reports from the Trees and Design Action Group and to the iTree tool that is, belatedly, being taken up in the UK. These tools are not perfect, but not to use them at all is far worse.

The use of green infrastructure in air pollution mitigation requires fresh collaboration between local authorities, national government, private sector developers and the research community. We might then be able to move away, once and for all, from the ‘ya-boo’ game-playing of the car manufacturing industry and its regulators.

Professor Rob MacKenzie
Professor of Atmospheric Science and Director, Birmingham Institute of Forest Research, University of Birmingham