Clearing the air: Bristol’s “radical” air quality plan

A mix of emotions will have greeted the Mayor of Bristol’s unveiling of his plans to address poor air quality in the city last week. For many, it seemed radical, with Bristol set to become the first city to ban diesel cars from the urban centre. But given the challenges facing us, others were left asking whether it is radical enough.

The City Council passed a motion in November 2016 to address urgently the matter of poor air quality in the city and to bring it into full legal compliance by 2020. By this standard, the Mayor’s plan is more than a little late, given that it will not begin to be implemented until 2021. Under the Mayor’s plans, the preferred option will bring the council into full compliance with its legal obligations by 2027, although in all but one location, modelling suggests compliance would be achieved by 2025.

Air traffic control

The council has chosen what it calls a ‘hybrid’ option, having initially consulted on two options (which the hybrid effectively combines). The hybrid incorporates what the Government’s Framework calls a ‘Class C’ Clean Air Zone in a larger proportion of the city centre, and a ban on diesel vehicles in a smaller area within that. Between 7am and 3pm, all diesel cars will be excluded from a central area. This is supplemented by a range of measures, including a diesel car scrapping premium.

By the standard of air quality measures being taken across the UK, this is, indeed, a reasonably forward-thinking position. Within the larger CAZ area, it is envisaged that charges will apply, as shown in the table below. In most cases, vehicles whose emissions performance is towards the better end of the spectrum (ones that meet the Euro standards with higher numbers) are exempt from charges.

In line with guidance provided by the Joint Air Quality Unit (JAQU), the council assessed a range of options, seeking to quantify a range of effects associated with the options chosen. As well as the ‘hybrid’ option, which has emerged as the preferred one, JAQU required the council to consider a Clean Air Zone of Class D, in which charges would be extended to also cover certain cars. The key differences between the two options are shown in the table below.

Test case

In advance of appearing on the local news last week, I was looking over the council’s economic case for the change. There are some quirks: the narrative and the tables don’t match up, and the numbers in different tables appear internally inconsistent. But I was most interested in the environmental impacts, since adopting the preferred hybrid option only just brings the city into compliance with legally established limit values for air quality.

The combustion of fossil fuels to power vehicles leads to the emission of oxides of nitrogen (NOx) and small particles (‘particulate matter’, or ‘PM’); both cause health problems. NOx emissions give rise to secondary particulate aerosols as well. It’s the NO_x where the city has transgressed the legal limit values, and which has been the focus of the measures adopted. Also emitted in the combustion process is carbon dioxide (CO₂) the main gas contributing to climate change.

The hybrid option delivers nearly four times more abatement of NOx, the pollutant which Government is asking the city to target; but the Class D CAZ delivers eight times more abatement of CO₂.

Government sets out approaches to converting into money terms the impacts of these emissions. It seems to be the case that, across the piece, the overall value of the reduction in emissions of NOx, particulate matter and CO₂ is under the Class D approach more than doubles that achieved under the hybrid. Might another ‘hybrid’ (of elements of both options shown) have achieved better outcomes across the board?

Bristol City Council became, last year, the first in the UK to declare a climate emergency and pledged to make Bristol carbon neutral by 2030, taking into account both production and consumption emissions (scope 1, 2 and 3). This pledge covers the city as a whole, not just the council’s own emissions. The council is working hard to understand how best to move onto that trajectory, and it is therefore strange that this major intervention to address air quality isn’t also maximising GHG reductions.

CAZ and effect

The Economic Appraisal Modelling Report, released last week, shows how minimal the clean air plan’s contribution will be to reaching the 2030 target. The evolution in CO₂ emissions under the hybrid and baseline scenarios is shown below in two graphics. The first shows the Y-axis running from zero, and the difference between the scenarios is barely discernible. We have to zoom into the top sixth of the first chart’s scale to see the tiny difference the air quality proposals will make.

Figure 1: Change in CO2 Emissions (tonnes) – Version 1

Figure 2: Change in CO2 Emissions (tonnes) – Version 2

According to modelling undertaken for the Council, the hybrid option will, by 2030, have delivered a less than 1% reduction in GHG emissions from transport relative to the baseline. More importantly, the transport emissions are modelled to increase compared with today. This doesn’t feel like we’re heading in a good direction. Meanwhile, compared with the baseline, NOx falls by only 5% by 2030, while PM emissions fall by less than 1.5%.

Net Zero or ‘carbon neutral’ by 2030 will – according to most commentators – demand a more or less complete decarbonisation of transport. It is likely to need to be supported by measures to shift towards active travel (e.g. more cycling and walking), and to reduce the need to make journeys (e.g. though more home-working). Decarbonisation will massively reduce NOx and PM emissions, too, with the whole package leading to substantial health benefits, as well as wider environmental outcomes.

Missing link

If a council is serious about addressing both air quality and climate change, then it will have to bear down on both air quality and GHG emissions in a far more comprehensive manner than even Bristol’s ‘radical’ plan proposes. Achieving net zero CO₂ emissions is almost certain to require reducing use of both petrol and diesel vehicles to a bare minimum, as quickly as we sensibly can. This conversation needs to be happening now, and actions must swiftly follow.

If we don’t start saying, well in advance, what needs to be done, there is a risk of alienating people. Banning diesel cars for periods of the day may feel like a radical – even a draconian – step. If you’re a Bristolian who recently purchased a diesel vehicle, you might well feel aggrieved, and it is perhaps understandable that Bristol’s mayor would be reticent to anger more people by announcing long-term plans to go further.

But consider what action the air quality plan is intended to motivate. If our diesel driver now buys a petrol vehicle in response (as the council’s modelling suggests many people will), they’ll be doubly annoyed to be told, in a few years’ time, that in order to reduce CO₂ emissions, they soon won’t be able to use that either. It’s much better to know now so you can plan for the longer term.

It’s not clear that the pennies are dropping in central government either: pushing local authorities to just achieve air quality targets doesn’t constitute joined-up thinking when the linked challenge of climate change needs to be addressed urgently, and in a determined manner.

The lesson is simple, and applies equally in Bristol or Beijing. If you write an air quality plan, it should at least be consistent with following a pathway that leads to warming no greater than 1.5 degrees – or else you’ll soon need to change it. But if you get serious about a strategy to reduce greenhouse gas emissions from transport, you are likely to completely trounce any target for NOx emissions, regardless of your air quality plan.

Featured image: Nick (CC BY-NC-ND 2.0), via Flickr