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  • Melinda Mills

Showcasing ‘low-to-zero’ emission public transport solutions at COP26, Glasgow


If the UK expects to make serious CO2 emission cuts, to avoid 1.5 degrees of warming and safeguard population health, while also retaining the ability to move easily throughout the country, the transportation sector will require a major overhaul.


So, what are our options?


Currently, the transportation sector focusses on three dominant ‘low emission’ technologies. They are electric and hydrogen powered batteries.

  • You may have already heard of electric vehicles or ‘EVs’, where the engine runs on batteries charged by being plugged into an electric power source, similar to charging a mobile phone.

  • The second type is: vehicles powered by hydrogen fuel cells, which combine ‘hydrogen’ and ‘oxygen’ to generate electricity (see graphic below). This method requires pure hydrogen to be pumped into the vehicles reserve tanks, similar to vehicles that run on liquid petroleum.

  • A third type of low(er) emission transportation are ‘hybrid’ vehicles, which run on a combination of electricity and petroleum (which emits CO2 directly into the atmosphere).

Illustrations by Jon Halls, courtesy Metaphor


The question is: out of these three ‘low emission’ transportation technologies, which one emits the least amount of CO2, not just in operation, but on a ‘whole lifecycle’ basis (i.e., factoring in CO2 emissions associated with manufacturing/transport of parts and dismantling/recycling at end of life)?


Petrol is evidently the highest CO2 emitting source, with its combustion producing CO2 – pumped directly into the air as well as other air pollutants such as nitrogen oxides. While EVs themselves may not directly emit CO2 into the atmosphere, the fuel used to generate the electricity on which they run might. All vehicles, including EVs also emit ‘Non-Exhaust Emissions’ (NEEs) into the atmosphere, that is, ‘particulates’ (i.e., little bits of plastic, metal and other materials) from the tyres, brakes and road surfaces which make their way into the air and oceans. The batteries used in EVs make the vehicle heavier, thus generating more friction than in non-EV vehicles, which ultimately results in more NEEs. Just like electricity, hydrogen can also be generated through sustainable or unsustainable means. When generated sustainably (e.g., from windfarms) it is referred to as ‘green hydrogen’. When generated using fossil fuels, but CO2 capture methods are also employed, it’s dubbed ‘blue hydrogen’, and when no carbon capture occurs, it is called ‘grey hydrogen’ (see graphic below).


Illustrations by Jon Halls, courtesy Metaphor


Why has this not taken off?


There has been some debate whether hydrogen fuel cells are a viable solution for cutting emissions. At present, a major barrier to the proliferation of personally owned hydrogen fuel cell powered vehicles, is a lack of hydrogen fuel stations.


Up until now we’ve only discussed these technologies within the context of personal vehicles. Another crucial piece to addressing the climate crisis, will be a transition towards more widespread use of public transportation and active travel.


Implementing hydrogen fuel cell technology in buses and trains like HydroFLEX, the UK’s first hydrogen powered train, is cost-effective and scalable.


How does this relate to the study of demography & populations?


The short answer is that decreasing transport-related emissions matters for population health on several fronts. First, the reduction of tailpipe emissions and short-lived pollutants - notably nitrogen dioxide - will improve air quality in urban areas and along streets carrying high traffic volumes. This translates into a direct health benefit for those residing near or travelling through such areas. In addition, the proportion of more deprived communities is often higher along busy roadways, in which we find higher incidences of pre-existing medical conditions such as heart and lung disease rendering them more vulnerable to the health impacts of air pollution. By reducing short-lived pollutants, we can alleviate the extra burden upon these vulnerable individuals in the population.


Second, reducing CO2 emissions and other 'radiatively-forcing', long-lived pollutants (usually referred to as greenhouse gases, or GHGs) can help reduce further climate change. Many areas of the world will experience warmings, which will be exacerbated in urban areas by the so-called 'urban heat island effect' (linked to enhanced heat absorption by, and/or heat capacity of, the built urban form). Local emissions can

affect local microclimates, for example, via changes in cloud condensation nuclei, but most gases of significant global warming potential have long atmospheric lifetimes so their climatic impacts are spread around the world.


Climate change is already contributing to human patterns of migration, fertility, and mortality around the world via the consequences of flooding, heat waves and other extreme weather events. A recent article in Nature calculated the mortality cost of carbon, which estimated that “adding 4,434 metric tons of carbon dioxide in 2020—equivalent to the average lifetime emissions of 12.8 average world people or 3.5 Americans—causes one excess death globally in expectation between 2020 and 2100.” In addition, there is a direct relationship between CO2 emissions from the burning of fossil fuels and poor air quality, with the WHO estimating 4.2 million deaths occur each year due to outdoor air pollution.


For more information on this topic, check out these cool, short videos about Hydrogen Fuel Cell technology:

LCDS DPhil Candidate Kayla Schulte will be showcasing ‘low to zero’ emissions solutions for public transport as a part of the COP26 Universities Network on behalf of the TRANSITION Clean Air Network, alongside Regional Clean Air Champion Dr. Suzanne Bartington, Dr. Stuart Hillmansen, Dr. James Levine, Dr. Ajit Singh & PhD candidate Rabee Jibrin.


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