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Presentation on the air quality, climate, and health and wellbeing ecosystem services afforded by living roofs and walls, presented at the Scottish Green Roof Forum (SGRF) inaugural conference - Edinburgh, March 2011.
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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
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
Air Quality
Filtrexx Green Loxx Living Walls , Denbow Planet Friendly
Solutions, Canada
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”
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
Urban Air Quality in Scotland
Particulate Matter PM10
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)
Urban Air Quality in Scotland
Nitrogen Dioxide (NO2)
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)
Air Quality in Scotland
Ground level ozone (O3)
Source: Key Scottish Environment Statistics 2010
(www.scotland.gov.uk/Publications/2010/09/08094058/0)
PM2.5
**No safe limit**
Red blood cells – approx
8 µm diameter
Air Pollutant Removal Mechanisms ba
• Dry Deposition – transfer of gases and particles to the Earth’s surface due to turbulent air motion
• Wet Deposition
Dry Deposition
1. Interception
- Trapping
- Surface reaction
by
plants and the growing medium (soil or substrate)
2. Stomatal
uptake
Secondary Pollutant Formation (Indirect Effect) Transpiration + shade = lower surface temperatures
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
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
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
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
Smailholm Tower, Borders
House near Scoraig, Highlands
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)
Species Selection
• Environmental Toxicity
– Air quality e.g. roadside
– Accummulation of pollutants in the soil/ growing medium
Climate
Global Urban micro-climate
Urban Heat Island
Climate Change Mitigation
Uptake / absorption of greenhouse gases
Carbon Dioxide Ozone
Black Carbon (Particulate Matter)
Green Roofs & Carbon Sequestration
Carbon Sequestration Potential of Extensive Green Roofs – Michigan
& Maryland, USA (Getter et al, 2008)
• 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
Figure from Bauder’s ‘The benefits of a green
roof system’
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
Climate Change Adaptation
• 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
Reduced Urban Heat Island (UHI) (or albedo) effect
Urban Heat Island & Scotland
Do we need to be concerned?
St. Andrews UHI experiment, January 11, 2008
Climate Change in Scotland
UKCIP projections (UKCP09): Change in mean summer temperature, medium emissions scenario - 50% probability
Urban Heat Island & Scotland
• 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
Do we need to be concerned?
YES, to some degree, because of the warming climate
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)
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
Climate & Species Selection
Scara Brae sedum roof, Orkney
(photo by Redman & Sutherland Architects, Shetland)
Keep it simple & stick with nature?
Health & Wellbeing
Unknown Illustration, Yuko Shimizu
Green Spaces and Health & Wellbeing
Wellbeing (Happy?
Satisfied? ‘Flourishing’?)
Physical Health
Psychological/mental Health
Cognition
Emotion/mood
Heart rate, blood pressure,
etc...
Musculo-skeletal system
Green Spaces and Health & Wellbeing
Ward Thompson, Aspinall & Bell (2010)
Ward Thompson & Travlou (2007)
Green Spaces and Health & Wellbeing
Summary and full report freely available online at:
http://webarchive.nationalarchives.gov.uk/20110118095356/http:/www.cabe.org.uk/publications/community-green
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”
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
Edinburgh City Centre
Glasgow City Centre
Living Roofs and Health & Wellbeing
• 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
Wellbeing & productivity in the workplace - Angela Loder PhD
research (University of Toronto)
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
Living Roofs and Health & Wellbeing
Nursing Home (US Veteran’s Administration), Washington
Maggie’s Cancer Care Centre Dundee
Summary & Conclusions
• Air Quality – Particulates, NO2 and O3 – Roadsides, LAQM zones – Possible Issues: Bioaerosol, O3 (VOC’s)
• Climate Change – Mitigation: CO2 and O3 absorption – Adaptation: reduced UHI effect – Possible issues: Increased GHG budget (festiliser -> N2O); Natural VOC
emissions (-> O3); embodied energy of roof
• Health & Wellbeing – Inner city dwellers – Office workers
• 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
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 cost-benefit 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)