Living roofs and walls can provide benefits for air quality, climate change mitigation and adaptation, and human health and wellbeing. They improve air quality by filtering pollutants like particulate matter and absorbing gases. Regarding climate, vegetation on roofs and walls can sequester carbon and reduce the urban heat island effect. Exposure to natural environments has also been shown to provide psychological benefits and reduce stress. However, more research is still needed to fully understand these impacts and how to maximize benefits through species selection that considers factors like emissions and climate resilience.

1. Living Roofs & Walls: benefits to
Air Quality, Climate,
and
Health & Wellbeing
Lynette Robertson
OPENspace
Research Centre for Inclusive Access to the Outdoors
Edinburgh College of Art & Heriot-Watt University

2. Outline
• Air Quality
• Climate
– Global: greenhouse gas uptake (Mitigative measure)
– Urban micro-climate: reduced Urban Heat Island (UHI) effect (Adaptive
measure)
• Health & wellbeing
• Summary and conclusions
• Topics for research

3. Air Quality
Filtrexx Green Loxx Living Walls , Denbow Planet Friendly
Solutions, Canada

4. Air Quality & Health
•
Lung diseases
•
Exacerbates respiratory illnesses
•
Increased incidence of cardiovascular disease
•
DEFRA ‘Air Pollution: Action in a Changing
Climate’ Report (2010):
– Average reduction in life expectancy in the UK = 6
months, annual cost £15 billion (economic cost of
physical inactivity and obesity in urban areas
estimated to be in excess £10 billion)
– The reduction in life expectancy due to air pollution
has decreased with improvements in air quality, but
further benefits are increasingly costly to achieve
[abatement technology]
•
Institute of Occupational Medicine:
– “gains in life expectancy from eliminating man made
fine particles are larger than those possible from
eliminating motor vehicle traffic accidents or second
hand cigarette smoke”

5. Main Pollutants
• Particulate Matter
– Type:
• Solid
• Liquid (secondary pollutants)
– Size:
• PM10 – 10 micrometres (µm) and less
• PM2.5 – 2.5 µm and less
• Gases
–
–
–
–
NOx – Nitrogen Oxide (NO) + Nitrogen Dioxide (NO2)
VOCs – Volatile Organic Compounds
O3 – Ozone (secondary pollutant)
SO2 – Sulphur Dioxide

6. Urban Air Quality in Scotland
Particulate Matter PM10
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)

7. Urban Air Quality in Scotland
Nitrogen Dioxide (NO2)
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)

8. Air Quality in Scotland
Ground level ozone (O3)
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)

9. PM2.5
**No safe limit**
Red blood cells – approx
8 µm diameter

10. Air Pollutant Removal Mechanisms
ba
• Dry Deposition – transfer of gases and particles to the Earth’s surface due
to turbulent air motion
• Wet Deposition

11. Dry Deposition
1. Interception
- Trapping
- Surface reaction
by
plants and the growing medium (soil
or substrate)
2. Stomatal
uptake

12. Secondary Pollutant Formation (Indirect Effect)
Transpiration + shade = lower surface temperatures

13. Green Roofs & Air Quality
• 1 m2 uncut grass roof can remove
up to 2 kg of air borne particulates
per year (Johnson & Newton, 1996)
• Intensive roofs offer greatest
benefits
• Species type is crucial
– Size
– Leaf structure -> surface area
– Phytoremediation properies
House with turf roof, Old Quarter, Tórshavn

14. Living Roofs & Walls: Modelling Studies
• Chicago – Green Roofs, dry deposition model (Yang et al, 2008)
– 20 ha of green roofs removed 1675kg of air pollutants in one year
– Mostly O3 (52%), but also significant reductions in NO2 (27%), PM10
(14%) and SO2 (7%)
Chicago City Hall

15. Living Roofs & Walls: Modelling Studies
• Toronto – Roofs & Walls, UFORE model (Bass & Currie, 2008)
– Modelled concentrations of various pollutants (PM10 , NO2 , O3 , SO2 , CO),
and the economic value of removal
– Greatest removal by intensive roofs but extensive roofs can aid trees and
shrubs in pollution mitigation
– A 10-20% increase in green roof surface area in the city centre would
contribute significantly to the social, financial and environmental health of
citizens

16. Living Roofs & Walls: Scotland
• Improvements in AQ are increasingly
costly to achieve through technological
means
• No safe limit for PM2.5
• 1 m2 grass roof can remove up to 2 kg /
year
House near Scoraig, Highlands
Smailholm Tower, Borders

17. Urban Green Space & Air Quality: Possible Issues
ba
• Bioaerosol
–
–
–
–
Pollen
Spores
Mites
etc
• Volatile Organic Compounds (VOC’s)
-> O3 formation

*Select species carefully*
(low isoprene and monoterpene emitters)

18. Species Selection
• Environmental Toxicity
– Air quality e.g. roadside
– Accummulation of
pollutants in the soil/
growing medium

19. Climate
Global
Urban micro-climate

Urban Heat Island

20. Climate Change Mitigation
Uptake / absorption of greenhouse gases
Carbon Dioxide
Ozone
Black Carbon
(Particulate Matter)

21. Green Roofs & Carbon Sequestration
Carbon Sequestration Potential of
Extensive Green Roofs – Michigan
& Maryland, USA
(Getter et al, 2008)
•
•
•
•
•
•
•
Figure from Bauder’s ‘The benefits of a green
roof system’
•
12 extensive roofs over 2 years
Mostly Sedum
Mean plant biomass: 162 g C m-2
Mean below ground biomass: 107 g C m-2
Substrate: 100 g C m-2
Sequestration varied with species
Embodied energy = 6.5 kg C m-2 -> 9 years
pay-back
BUT: Sedum is a ‘CAM’ photosynthesiser ->
C assimilation rates are only 1/2 or 1/3 that
of non-CAM species

22. Green Roofs & Ozone
• Greenhouse gas (direct warming
effect)
• Reduced CO2 absorption (indirect
warming effect)
• O3 is absorbed and destroyed by
reacting with the plant tissue

23. Climate Change Adaptation
Reduced Urban Heat Island (UHI) (or albedo)
effect
• Increasing green space shifts
the urban environment back
towards functioning more like
a natural ecosystem
1. Cooling: higher albedo,
evaporation, transpiration
2. Increased water storage ->
further cooling

24. Urban Heat Island & Scotland
Do we need to be concerned?
St. Andrews UHI experiment, January 11, 2008

25. Climate Change in Scotland
UKCIP projections (UKCP09): Change in mean summer temperature, medium
emissions scenario - 50% probability

26. Urban Heat Island & Scotland
Do we need to be concerned?
YES, to some degree, because of the warming climate
• Heat-wave events - likely to be an
increase in frequency in the UK and
across Europe
• Air Quality - higher temperatures
generally enhance ozone production
-> greater likelihood of photochemical
pollution episodes/‘smogs’ (Fowler et
al, 2008)
• Sustainability/Energy Conservation increased need for air conditioning in
summer

27. Living Roofs and Walls & the Urban Heat Island
Temperature decrease in an urban
canyon due to walls and green
roofs in diverse climates
(Alexandri & Jones, 2008)
•
7 cities: Athens, Beijing, Hong Kong,
Brasilia, Montreal, Mumbi, Riyadh
•
Magnitude of decrease depends on
climate and amount of vegetation, and in
hot climates urban geometry to a lesser
extent
•
Greatest effect of vegetation on urban
temperatures found for hotter, drier
climates, but humid climates also benefit
•
Ait temp decrease at roof level:
max = 26°C, day-time mean = 12.8°C
(Riyadh)

28. Living Roofs and Walls & Climate Change:
Possible Issues
• Impact on GHG budget
– Nitrous Oxide (N2O) - fertiliser type
– Ozone – VOC emissions from plants;
impact on C-Seq
-> **Species Type**
• Embodied energy of roof/wall
Life cycle cost-benefit analysis
• Irrigation
• Fertiliser
• Resilience of plants to a warmer,
wetter, more variable and more
extreme climate
-> droughts
-> downpours
-> storms

29. Climate & Species Selection
Scara Brae sedum roof, Orkney
(photo by Redman & Sutherland Architects, Shetland)
Keep it simple & stick with nature?

30. Health &
Wellbeing
Unknown Illustration, Yuko Shimizu

31. Green Spaces and Health & Wellbeing
Cognition
Emotion/
mood
Heart rate,
blood pressure,
etc...
Psychological
/mental
Health
Physical
Health
Wellbeing
(Happy?
Satisfied?
‘Flourishing’?)
Musculoskeletal
system

32. Green Spaces and Health & Wellbeing
Ward Thompson & Travlou (2007)
Ward Thompson, Aspinall & Bell (2010)

33. Green Spaces and Health & Wellbeing
CABE ‘Community Green’
report
(Ward Thompson et al, 2010)
• Focused on social inequality and
quality of green spaces
• “Urban green space represents an
important & cost effective
opportunity for people to
transform their local
neighbourhoods and improve
quality of life”
Summary and full report freely available online at:
http://webarchive.nationalarchives.gov.uk/20110118095356/http:/www.cabe.org.uk/publications/community-green

34. Living Roofs & Walls and Health & Wellbeing
• Main, sometimes only, means of
expanding urban green space in
high density urban areas
• Natural England recommendation:
town and city dwellers should have
access to a natural green space
within 300m of home

35. Edinburgh City Centre

36. Glasgow City Centre

37. Living Roofs and Health & Wellbeing
Wellbeing & productivity in the workplace - Angela Loder PhD
research (University of Toronto)
•
Three case studies: Chicago, Toronto,
London
•
Qualitative interviews and
quantitative surveys of office
worker’s perceptions of green roofs
•
Most workers who overlook green
roofs from their workplace felt the
sight of greenery amid concrete and
glass gave them a ‘calming’ and
‘peaceful’ mental break from the
work day, and helped workers gain
perspective and clarity
•
This was particularly the case if the
green roof was accessible

38. Living Roofs and Health & Wellbeing
Greenspace and psychological health benefits
(Fuller et al, 2007)
• Sheffield green spaces
• Psychological benefits
increase with species
richness of plants, and to a
lesser extent birds

39. Living Roofs and Health & Wellbeing
Nursing Home (US Veteran’s Administration), Washington

40. Maggie’s Cancer Care Centre Dundee

41. Summary & Conclusions
•
Air Quality
•
Climate Change
•
Health & Wellbeing
•
Intensive roofs offer most benefits, but extensive roofs are still good
•
Species selection is crucial in order to maximise environmental benefits and
avoid wasting money
•
Research is needed
– Particulates, NO2 and O3
– Roadsides, LAQM zones
– Possible Issues: Bioaerosol, O3 (VOC’s)
– Mitigation: CO2 and O3 absorption
– Adaptation: reduced UHI effect
– Possible issues: Increased GHG budget (festiliser -> N2O); Natural VOC
emissions (-> O3); embodied energy of roof
– Inner city dwellers
– Office workers

42. Topics for Research
• Air quality
– Species selection: VOC’s, bioaerosol
– Impact of increased coverage on
health (should incorporate H&WB
benefits)
• Climate Change
– Species selection: maximising
mitigation (CO2, N2O, O3); resilience to
current and changing climate
– Embodied energy: life cycle costbenefit analysis
• Plant microbial fuel cells (PMFCs) ->
electricity generation
• Reflective roofs
• Health & wellbeing
– Opportunities for research into
psychological and physical
mechanisms
Caixa Forum, Madrid (Patrick Blanc)