Wood In Architecture Issue 1, 2022

SUSTAINABILITY
year. Thus, planting multiple tree species in
urban areas can help in CO2 mitigation and the
subsequent climate change.
we plant forests to prevent polluted air from
getting into the atmosphere and swirling
around and spreading to the clean forest?
Can we draw a hard line between the air that
is polluted and air that is not? And is CO2
different in the wood itself with different
levels of pollution?
Looking at a map from Global Forest Watch,
China has enormous areas of land covered
in trees but unfortunately, most of it is in
central China, which is far away from the
main pollution centres. China has grown its
forest by 40% over the last 30 years. That
equals an area of 629,367km 2 , and to put it
into perspective it is about the area of Texas,
US. I then wonder, how much pollution
does this forest collect and store? Does it
help China to get cleaner air? Or does all
the pollution in this global world enter the
atmosphere and spread equally around the
world and find a tree to store it in no matter
if it is a red oak tree in the Appalachian or a
beech tree in Denmark?
With these questions in mind, I called our
freelance consultant Krishnanunni Ravindran
to ask him about this.
Most air pollution and
harmful GHG comes from
towns and industries
Per Friis Knudsen: Would it help to plant
more trees near very polluted areas, such
as urban and industrial areas, to absorb the
CO2 emissions at an early stage to prevent
the CO2 to get into the atmosphere?
Krishnanunni Ravindran: Yes, growing trees
in towns and industrial areas can significantly
address the problem of urban air pollution.
Trees can absorb CO2 and other toxic
particles, odours, and pollutant gases, thereby
effectively filtering these chemicals from the
air. Trees growing in the street proximity can
absorb more pollutant gases than distant
trees growing miles away from the source of
pollution. Thus, trees absorb CO2 from the
atmosphere and release oxygen in return
through the process of photosynthesis.
Depending on the attributes of the tree — the
species, age, leaf type, canopy structure, and
others — and the environmental conditions,
the amount of CO2 absorbed by trees may
differ. Some trees are sensitive to changing
environmental conditions and absorb different
amounts of CO2 in different seasons. Some
are insensitive to seasonal changes in
environmental conditions and absorb more
or less the same amount of CO2 around the
Knudsen: We hear terms like CO2, nitrogen
dioxide (NO2), methane (CH4), and sulphur
dioxide (SO2) from time to time, but we
always focus on CO2. What are the other
elements? Where do they come from and
what impact do they have on us? Can they
be absorbed? Which of these gases is the
biggest problem for the environment?
Ravindran: Apart from CO2, there are a lot
of gases in the atmosphere such as nitrogen
oxides, ammonia, CH4, SO2, ozone (O3), water
vapour (H2O), chlorofluorocarbons (CFCs), and
others. They are released from many natural
sources such as volcanoes, decomposition
of organic matter, respiration, and the
combustion of fossil fuels. All these gases are
now commonly known as greenhouse gases
(GHGs) because of the warming effect it has
on our environment. Well, these gases are
purposely meant for keeping us warm and
comfortable on earth. Without these gases in
the atmosphere, we would have experienced
zero-degree Fahrenheit, making life impossible
on earth. However, a gradual increase in the
amount of these gases in the atmosphere
could increase the temperature of the earth,
causing serious problems to mankind.
Trees can absorb CO2 and other toxic particles,
odours, and pollutant gases, and when planted near
industrial areas, can address urban air pollution
WOOD IN ARCHITECTURE • ISSUE 1 – 2022 29