Reducing Air Pollution vs Reducing Greenhouse Gases

The devil is in the diesel

Some cities around the world are now looking to ban diesel cars from their centres from 2025 and London Mayor Sadiq Khan has said he would like to introduce a pollution charge for diesel vehicles by the end of 2017. The problem with diesel engines is the particles and NOx emissions and the resulting air pollution they create. However they produce less CO2 than petrol engines. This was why many of us to bought diesel cars in the first place.

So if we ban diesel cars from our cities, we encourage more people to buy a petrol car and we have more CO2 emissions, we are just replacing one problem with another. So are there any other options?

What are the alternatives?

Hybrid (HEV) – petrol engine with an electric motor charged off the alternator and extra energy from the engine when braking.

Plug-in hybrid (PHEV) – electric motor charged via a plug to mains electricity that then converts to a petrol engine when battery is depleted.

Extended range electric vehicle (EREV )- very like a PHEV but the battery gets you further.

Electric Vehicle (EV) – electric motor only charged off the mains electricity.

Which car to choose depends on the access you have to charging points, the number of miles you drive and finances, let’s be honest these cars are not cheap to buy, but they are cheaper to run. It is difficult to get reliable figures for comparison so when choosing a car for CO2 emissions [Best to Worst]:

EV1>EREV1> PHEV1 >HEV> Diesel/ Biodiesel> Petrol .

For local air pollution emissions [Best to Worst]:

EV/EREV2>PHEV2>HEV > Petrol> Biodiesel >Diesel

1 charged using renewable energy

2 assuming you drive within the range of the battery


When it comes to biodiesel there are many different types depending on what they are made of, which determines how good they are for emissions. Biodiesel made from waste cooking oil is taking something that would have been thrown away and reusing it and it has half the particulates of standard diesel.

Biodiesel made from maize/corn is another matter. It is argued that once you take into account the CO2 emissions from sowing, harvesting and converting the crop that it can actually be worse in carbon terms, than standard oil derived diesel.

In some countries cars run on bioethanol. Again it depends on what it is made from as to how good it is. Bioethanol made from sugar cane waste is an excellent example of resource efficiency as long as there is enough waste generated to keep up with demand.

Hydrogen fuelled cars do not seem to have made it off the ground (no pun intended). The infrastructure being a major challenge, in terms of refuelling points, and the energy needed to manufacture and store hydrogen. There is also the challenge as regards fuel cells. These contain some scarce elements which could present a resource constraint given the world market for cars.

What else could we do?

Car sharing would be another way to address the problem. Most cars, at peak times, are only occupied by the driver. If each car had a passenger too then that is air pollution and congestion lowered immediately. Ask on local forums if anyone does the same or similar commute to you, it’ll save you money too.

Many public transport companies run electric buses, many rail routes in the UK are electrified and increasing numbers of cities have trams. These are all being run off the grid which in one regard only pushes the pollution back to the power station, but it is a far more efficient means of moving large numbers of people than individual transport modes, and in that sense far greener. They also have the benefit of reducing local air pollution that is a major challenge in our urban areas. Sadly, public transport (and electric based public transport in particular) in the UK these options are simply not available to many people.

Governments need to help

Public transport could be an area that government could fund to get us out of our cars, making services regular and affordable. Maybe this could be funded by the reduced cost to the NHS from the health benefits that would be seen by not so many people visiting hospital with pollution related problems.

We could look to Norway for inspiration. Not only do Norwegians have a financial incentive to buy an electric vehicle, they pay no tax and there are lots of charging points. Given that most of their electricity comes from hydropower this motoring is as green as it gets.

Many electric vehicles are designed with recycling and reuse in mind. Tesla’s cars are designed in such a way that you keep the bones of the car all your life and take off and bolt on the parts you need. If only I could afford one!

For support on environmental issues or to measure the environmental impact of your workplace and gain a green award, contact or call us on 01746 552423, see our website for testimonials, a video and more!

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