16 | New Scientist | 14 March 2020
EnvironmentA WIDESPREAD switch to burning
hydrogen to heat UK homes to
meet new climate targets risks
releasing harmful nitrogen oxide
(NOx) pollution in urban areas,
according to a leaked report
obtained by New Scientist.
The report by air quality experts
for the government’s Department
for Environment, Food and Rural
Affairs (DEFRA) lays out pros and
cons for pollution of the UK’s
new legal target of cutting carbon
emissions to net zero by 2050.
Hydrogen, which is backed by
industry and government advisers
as a key fuel to replace natural gas
to decarbonise heating, could lead
to NOx emissions if used in boilers
in homes and businesses, it says.
“The use of hydrogen as a
significant energy source for
domestic and commercial
space heating would potentially
lead to NOx emissions being
concentrated in higher density
population areas,” the report says.
What’s more, it says building
large, clean-energy projects could
also cause local air pollution to
rise. Nuclear plants are cited as a
concern due to long build times.
For example, the number of trucks
coming and going at Hinkley
Point C, a nuclear power station
being constructed in Somerset,
is up 20 per cent since 2016.
However, the air quality experts
say the shift to electric cars will
bring “unambiguous benefits”
by eliminating the release of one
form of NOx, toxic nitrogen
dioxide (NO 2 ), which is mostly
pumped out by diesel engines.
That said, they caution that
particulate matter, which can
lead to serious illness or death,
will remain a problem unless there
is a switch away from vehicles to
more walking and cycling. This is
because a lot of particulates come
not from exhausts on modern
cars, but from dust released bythe tyres, brakes and road surfaces.
The authors say that as
buildings become more energy
efficient, they must be designed
to avoid accumulation of indoor
air pollutants due to inadequate
ventilation. However, well-
designed building upgrades
can avoid the risk. “Poor indoor
air quality is by no means an
inevitable consequence of energy
efficiency,” the report says.
Other measures for cutting
carbon emissions from homes,such as district heating schemes,
could also have a temporary
negative effect on air quality
because they may use polluting
fuels such as biomass before later
transitioning to cleaner sources.
Growing more bioenergy crops
also poses a potential threat for
air quality, as some fast-growing
plants can release volatile organic
compounds (VOCs) into the air.
These chemicals can lead toformation of ozone at ground
level, which is another pollutant.
Even so, the researchers say that,
overall, moving to net-zero carbon
will create “major opportunities”
for cleaner air. Attempts to clean
up farming are largely seen as a
universal good, with low-carbon
efforts like manure management
also cutting air pollutants,
including NO 2 and ammonia.
Using hydrogen in the gas
supply network would, despite the
concerns over NOx, “completely
eliminate” VOCs such as ethane,
propane and butane, which leak
from pipes, according to the
analysis. Another technology to
clean up heating – heat pumps –
is seen as “highly beneficial” for
cutting both VOCs and NOx.
More energy efficient homes
should curb the use of wood-
burning stoves, a rising source of
air pollution in cities. And moves
to far more renewable electricity
generation will bring a range of
air quality benefits, it adds.
The report is based on one
scenario of how to get to net zero,
provided by the UK government’s
climate adviser, the Committeeon Climate Change. DEFRA didn’t
respond to requests for comment.
Robert Gross at the UK Energy
Research Centre, who wasn’t
involved in the report, says it
is important to guard against
unintended consequences. For
example, past policies promoted
diesel cars to cut carbon emissions
but inadvertently made other
forms of air pollution worse.
While the impact of hydrogen
boilers on air quality is worth
looking at, he says it is unlikely
that we should be “desperately
worried” about it. “For the most
part, the solutions we need to be
moving to net zero involve
moving away from combustion-
based energy conversion
altogether and therefore are quite
likely to have beneficial local air
quality implications,” he says.
In response to the report, boiler
maker Worcester Bosch said lab
tests of its hydrogen boiler had
found NOx emissions were half
those from a natural gas boiler. ❚Air quality might be at
risk as the UK moves to
a low-carbon economyAdam VaughanDBURKE/ALAMYNews
“ It is important to guard
against the unintended
consequences of our
environmental policies”Net-zero push may raise pollution
Some ways to meet UK carbon-free goal could end up polluting air, says leaked report
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