REPORT TO

INTERIOR PLANTSCAPE ASSOCIATION (IPA)

(Revised – Re-submitted – June 2016)

Towards Development of Indoor Plant Walls for

Improved Indoor Air Quality

Research team

Researcher: Mr Michael Zavattaro (MSc. Scholar)

Compiler & for correspondence: Prof. Margaret Burchett

(Margaret.Burchett@uts.edu.au)

Program Director: Dr Fraser Torpy

Plants and Urban Air Quality Group

School of Life Sciences

University of Technology Sydney

PO Box 123, Broadway, NSW 2007, Australia

mailto:Margaret.Burchett@uts.edu.au

SUMMARY

Over the last three decades, international research (including our own) has demonstrated that

indoor plants can reduce levels of all types of urban air pollutants tested and, of particular

importance, carbon dioxide and air toxics (e.g. volatile organic compounds, VOCs), which

are always in higher concentrations indoors than outside, even in the city centre. Indoor plants

have the potential to improve indoor environmental quality as a whole, and hence the health

and well-being of building occupants. The use of indoor plants to refresh indoor air in air-

conditioned city buildings could also reduce the energy load on the building, and its footprint,

contributing to the goal of urban sustainability. The UN estimates that the building sector

accounts for about 40 % of global energy use, and that the proportion needs to be reduced.

Aims of the project reported here are to contribute to the baseline scientific information

needed to underpin the development of indoor plant-walls and equivalent living-green

installations, as a means of bringing about significant reductions in air pollution levels in

commercial buildings. The reductions would also lower costs of building air-conditioning

ventilation systems. This is a preliminary study; there have been extremely few reports of in-

situ investigations on this aspect of plant-wall benefits.

Air sampling was conducted in seven Sydney city buildings, which all had indoor plant-wall

(IPW) installations and were also equipped with building-wide air-conditioning systems. As it

happened, the buildings all housed different types of business enterprises. In each building

comparisons were made of air pollutant levels on the floor containing the plant-wall, which

also had numbers of human occupants, and on a ‘reference’ floor with no plants. The plant-

wall dimensions were found to vary greatly, ranging from 72 m2 down to 5 m

2.

Results In the two buildings with the largest plant-walls, the planted floors showed reductions

in CO2 levels of from 13 to 23 percent, while two other buildings showed some minor CO2

reductions. In the three buildings with the largest plant-walls, there was a trend towards

reductions of extremely fine airborne particulate matter (PM10 and PM2.5), which are known

to be serious health hazards of urban air. The results are encouraging, since they were

obtained in the presence of continuous air-conditioning, the systems of which had unknown

‘refresh’ ventilation rates.

Future R&D Our studies are continuing for the development of the horticultural technology

needed to ensure that plant-walls and equivalent living-green interiorscapes become standard

installations in city buildings. This will improve urban energy efficiency and the health of

urban dwellers.

1. BACKGROUND

Over the last three decades there has been increasing evidence of the benefits of living plants

in the work-place, including:

Reducing indoor air pollution (e.g. Tarran et al., 2007; Burchett et al., 2008; Irga et al, 2013; Torpy et al., 2013a, 2014, 2015);

Providing a peaceful aesthetic (e.g. Aitken & Palmer, 1989; Dijkstra et al., 2008);

Improving attitudes and performance of staff, students, clients (e.g. Fjeld, 2002; Dravigne et al., 2008).

The last two decades have also seen increasing development and use of several types of plant-

walls (Loh, 2008) (also called biowalls; vertical gardens; green-walls, etc.; here called

‘Indoor Plant-Walls’- IPWs). Over the same time there have been advancements in more

conventional indoor plantscape designs, which will remain more flexible in various

interiorscape situations.

Our own research findings (e.g. Wood et al., 2002, 2006; Orwell et al., 2006; Tarran et al.,

2007; Burchett et al., 2008, Irga et al., 2013; Torpy et al., 2013 (a), (b); 2014; 2015), and

those of other investigators (e.g. Yoo et al., 2006; Yang et al., 2009; Llewellyn & Dixon,

2011) indicate that now is the time to spearhead the development of IPW installations in

city buildings, in order to provide significant reductions in indoor air pollution. At

present it is standard building practice to rely on the central Heating, Ventilation and Air-

Conditioning (HVAC) systems to remove air pollutants. Although effective, this system is

very energy intensive since, for example, outdoor air brought in for air refreshment must be

heated or cooled to the building’s normal temperature (even if the building is already at that

temperature). If part of the ventilation process were to be replaced with IPWs, the building

energy load could be reduced, which would lower its carbon-footprint, and contribute to the

goal of urban sustainability in this country (Aust. Gov., 2011).

The aim of our research program is to advance the information needed for the continuing

development of indoor plant-walls, to bring about significant improvements in IAQ in urban

commercial buildings. This will lower costs of building air-conditioning, through a lessening

of ventilation requirements. The development and utilisation of IPWs will contribute to

achieving our national sustainability goal of the ‘Triple-bottom-line: For People-Profits-

Planet’.

Urbanisation and the ‘Indoor Habitat’ According to UN estimates (2001), in the year 1800 only 2 % of the world’s population lived

in urban areas. Until then, almost everyone was perforce surrounded by living greenery –

farms, village greens, home gardens, church or temple gardens, grasslands, forests or

woodlands (apart from sparse desert dwellers which comprised of very little food and water).

The UN also estimated that now, 54 % of global population lives in urban areas, with the

proportion expected to rise to about 65-70 % by 2050. It is perhaps not surprising that Hartig

et al., (2014), in the Ann. Rev. of Public Health, reported that: “urbanization, resource

exploitation, and lifestyle changes have diminished possibilities for human contact with

nature”.

The authors reviewed a wide range of research articles which showed relationships between

contact with nature and the maintenance or improvement of health and wellbeing, including:

better air quality;

more opportunity for physical activity;

promoting social cohesion, with parks, other open planted-areas, street trees, etc.; and

stress reduction.

There are numbers of advantages to urban living, but there are also adverse health and

wellbeing issues arising from urban dwellings. There is an increasing incidence of chronic

conditions from sedentary living - obesity, diabetes, cardiovascular disease (Manson et al.,

2004; Aust. Gov., 2015); plus increased street and domestic violence (Winton, 2004); and

mental illness (WHO, 2001, Srivastava, 2009). There are also negative effects from what has

been termed a widespread “disengagement with nature” (Gladwell et al., 2013), which may

be adversely affecting a new generation of city dwellers (Grinde & Grindal Patil, 2009;

National Trust UK, 2012). Anecdotally, we have been told that some Sydney primary-school

children are reluctant to go on class excursions to parks or nature-reserves, because they

believe that: “Plants are dangerous - and there may be animals too, that can get on you”

(Educ. Officer, Bicentenn. Park Authority; pers. comm).

Health Hazards of Urban Air Pollution

In Australia, as in much of the western world, 80 % of us already live in urban areas, and

spend about 90 % of our time indoors (Environ. Aust., 2003; USEPA, 2016). Consequently

indoor environmental quality is crucial to our health and wellbeing. It was estimated by the

OECD (2014) that the costs of deaths from urban air pollution (UAP) in Australia (3,000 per

annum; Begg et al., 2003) are almost $6 billion p.a. and there are similar cost levels caused

by illness and associated loss of productivity (Olesen, 2006; Bernstein et al., 2008). Acute

responses to air pollution include asthma, strokes, heart attacks and other sudden

cardiovascular malfunctions (NSW Health, 2009). Chronic effects include lung and other

cancers, more cardiovascular problems, pre-term births and low birth weights (Bobak, 2000;

NSW State of Environ, 2015). Lung and cardiovascular disease, as well as the increasing

incidence of autism, have been linked in particular with levels of airborne particulate matter

(PM) (Volk et al., 2013).

Gaseous pollutants Approximately 90 % of UAP comes from fossil fuel combustion. The

emissions include a mixture of nitrogen and sulfur oxides, carbon dioxide and monoxide, a

cluster of ‘air toxics’ from partial burning of fuel, including a range of volatile organic

compounds (VOCs), and ‘secondary’ photochemical products e.g. ozone and peroxyacetyl

nitrate (PAN). The commonest VOCs (produced from vehicle emissions), are the lightest -

the BTEX group - Benzene, Toluene, Ethylbenzene, and Xylene.

Suspended particulate matter (PM) – is the primary cause of city haze. The main health

hazards are from the most minute particulates: PM10 (diameters 10 micrometres [μm] or less:

at and down from just 1/50 the thickness of a human hair); and PM2.5 (diams. 2.5 μm or less:

at or below 1/200 the thickness of a hair). The PM10 fraction is known as the ‘coarse

particulates’, and PM2.5 as the ‘fine particulates’. Both these (overlapping) size ranges can

lodge in lungs and cause disease. PM2.5 particles also move easily from lungs into the blood

stream, causing not only more vascular disease but lowered brain function as well ( alder n-

arcidue as et al., 2008). PM comprises continually changing mixtures of the tiny solid and

liquid particles derived from fossil fuel emissions; fragments thrown up from tyres and

roadways; natural dust from soils, and ‘bio-particles’ - fungal spores and, more seasonally,

pollens. The character of the mixtures also varies with city, local industry, and seasons.

Indoor air pollution Air pollution levels inside buildings are always higher than those

outdoors, even in the CBD - often 2 to 10 times higher, and sometimes up to 100 times higher

than outdoors (US EPA, 2015a). This is because, as air enters the building it brings its

‘outdoor’ air pollution load, which mixes with more pollutants emanating from indoor

sources (WHO, 2000; 2005). The indoor-sourced pollution is mainly composed of more

VOCs, which are continually outgassing from synthetic furnishings, finishes, paints, solvents,

and equipment; plus higher CO2 concentrations from occupants’ breathing (and any non-flued

gas appliances). Excess CO2 causes drowsiness, and VOCs, even at imperceptibly low levels

(less than 250 parts per billion; ppb), cause some occupants to experience ‘sick building

syndrome’ pstein, orb ck ordstr m, 2008). SBS produces symptoms

such as headaches, dizziness, nausea, loss of concentration, and/or sore eyes, nose or throat.

From a 100-building study by the USEPA, it was found that for every increase in CO2

concentration of 100 parts per million (ppm), there was a 10 to 20 % increase in mucous

membrane and lower respiratory “building-related symptoms” [‘ R ’ or ‘SBS’] among

occupants (Erdmann & Apte, 2004).

Plants Improve Indoor Air Quality (IAQ)

Since the pioneering work of Wolverton and colleagues (1989; 1993) on removal of VOCs by

indoor plants, numerous studies have shown that plants can reduce concentrations of all urban

air pollutants tested. These include carbon monoxide (Bidwell et al., 1972; Sanhueza et al,

1998); nitrogen oxides (Coward et al., 1996); sulfur dioxide (Lee & Sim, 1999); ozone

(Elkiey & Ormrod, 1981), single and mixed VOCs (Yoo et al, 2006; Wood et al, 2006;

Orwell et al., 2006; Irga et al., 2013); formaldehyde (testing 86 species; Kim et al., 2008);

ammonia (Yoneyama et al, 2002); PM (Lohr & Pearson-Mims, 1996); PAHs and other

organic compounds (Barro et al., 2009). A laboratory study by Oyabu et al. (2003) using

three plant species, found they could also reduce concentrations of three pollutants classified

in Japan as “offensive odours” i.e. not from fossil fuel combustion, but from human

occupants: ‘bioeffluents’ .

All air pollutants from fossil fuel sources are toxic, and numbers of VOCs are known to be

carcinogenic (Berkeley Laboratory, 2016). Our previous laboratory chamber studies, with

approximately 20 plant species/varieties, have shown that VOC removal by indoor plants in

the same- sized pots, in either potting-mix or hydroculture, achieve almost equal removal

rates after a second or third ‘inducing’ dose (no more than a week). We also found that VOC

removal rates remain equal day and night, and rise further if a higher dose concentration is

applied. It is the normal bacteria in the root-zone that are the primary removal agents, the

plant contributing mainly by secreting various sugars into the substrate so that its soil

microbial community will flourish (a symbiotic plant-microbe relationship). Odours from

occupants, and from cosmetics (in the form of VOCs), can also be degraded by indoor plants

and their root-zone microflora. Since bacteria can reproduce about every 20 minutes if

stimulated by a whiff of an organic contaminant, the species that can best digest the airborne

VOCs present will quickly increase their numbers to enjoy the feast thereby increase rates of

VOC removal.

Ventilation in Big Buildings

The problems of IAQ in commercial buildings are more complex than at home, where one

can usually just open a window. The primary aim of air-conditioning in city buildings is to

keep the indoor environment at a comfortable temperature for staff and clients (22-23 oC).

However, where whole-building HVAC mechanical ventilation systems are used, which is

usually the case, the buildings must be sealed. This means the HVAC also has to supply the

indoor air, which must be of acceptable quality. This involves regularly removing the

increasingly stale, polluted indoor air, and bringing in ‘fresh’ outside air, in an effort to

maintain healthy IAQ. Maximum CO2 levels are used as an indicator of overall indoor air

pollution concentrations (incl. VOCs, PM, and inorganics). As in the USA, the guidelines for

indoor maximum CO2 concentrations in Australia are 800-1,000 ppm (ASHRAE, 2001; Petty,

2015). The HVAC is designed either to maintain CO2 levels significantly below the

building’s set maximum, or to trigger increased ventilation rates whenever the maximum is

reached. Both the thermal and air quality requirements of city buildings are costly of fuel

energy and budgets.

2. SAMPLING METHODS

Access to the seven buildings studied was made available by Mr Jock Gammon, Founder &

Managing Director of Junglefy Pty Ltd (Aust.), who designed, installed and maintains the

plant-walls sampled. The IPWs were all of different dimensions (Table 1), and had a

somewhat varied species composition (Table 2). There was no assisted ventilation to either

the plants or substrate in any of the plant-walls sampled. Permission for access was also

obtained from individual building managers. The buildings all had HVAC systems, and each

building was involved in a different type of business activity (Table 1).

Sampling methods Air sampling was conducted over a two-week period in July 2015, and

always between 10.00 am to 3.00 pm, to minimise any complications that might arise from

differences in seasonal conditions. A set of portable monitors was used for all measurements.

In each building sampling was carried on two floors, as follows.

the floor with the plant-wall installation, which also had numbers of occupants, including on the sampling days;

a ‘reference’ floor –a mainly unoccupied space on another level of the building, e.g. in a boardroom or corridor (no plants).

Pollutants sampled The pollutants selected are found world-wide in urban air, and are under

surveillance by the NSW EPA. They are all toxic (hazardous), producing adverse health

effects at very low concentrations. Individual air-sampling period for each pollutant was 2

minutes. Samplings included:

Gases (ppm): Carbon dioxide (CO2), Carbon monoxide (CO), Nitrous oxide (NO), Nitrogen

dioxide (NO2), Sulfur dioxide (SO2), and Total VOCs.

PM10 & PM2.5 (as micrograms per cubic metre of air; μg /m3).

Physical measurements Temperature (oC); relative humidity (RH %); and light intensity

using the Internat. Units System (IU) - micromoles of light quanta (or micro-Einsteins), per

square metre, per second μmol q/m2/s).

Sampling pattern In each building sets of three replicate readings were made for each of the

11 contaminants, at each of 3 heights from the floor: 7.5, 130, & 180 cm, respectively*, as

follows:

on the plant-wall floor - 60 cm out from the foliage surface, and at the centre of the room-space.

on the reference floor - at the centre of the room-space.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -- - - - - - - - - - - - - - - - - **Following the USA/ASHRAE Standard, ANSI/ASHRAE Standard 62.1-2013. The 3 sampling heights ‘from the floor’, are taken to represent air quality measured at: 7.5 cm - ‘floor level’ (but clearing carpets, etc);

130 cm - ‘breathing zone’ at head height when seated at desk; and 180 cm - breathing zone at standing height.

3. FINDINGS Some low pollution levels The concentrations of carbon monoxide, nitrogen and sulfur

oxides, and total VOCs, were found to be from very low almost to zero, in all the buildings.

They were therefore of negligible health risk, so are not tabulated here. This was a pleasing

result, since gaseous pollutants are not removed by HVAC filters or other A/C systems. The

results indicate that in general air pollution levels in Sydney as a whole, were low over the

sampling period.

Table 1 shows the major results obtained from the investigation:

Column 1. lists the commercial use of each building. It seems that a growing range of

business types are choosing to install IPWs as part of their interior design.

Col. 2. shows the plant-wall dimensions. Areas varied from 72 m2 down to 5 m

2 – a 14-fold

difference. The range presumably reflects differences in available space, outlook regarding

aesthetic value, aims for enhancing staff and client satisfaction, costs, or a combination of

factors. The modules were 50 x 50 x 13 cm, each with 16 cavities for single plants (see Plates

1-7), and used a hydroculture, coco-fibre substrate. Each IPW was irrigated via channels

along the tops of the modules, with multiple holes at the bottom for easy drainage, collection,

and recycling as appropriate. Col. 3. lists the room-spaces sampled on IPW and reference floors.

Col. 4. presents the average light intensities for IPW and reference floors in each building,

both near (60 cm out from) the plant-wall, and in the centre of the room-space. The reference

spaces could be expected to have low light intensities, depending on use, or non-use, of those

areas. All the plant-walls were fitted with some type of targeted lighting, installed

individually by building management. However, over-all the light intensities of the room-

spaces were variable and rather low.

Outdoor sunlight at noon has a light intensity of approximately 2,000 μmol q/m2/s (about

100,000 Lux). Our previous studies (Torpy et al, 2014) have found that average UTS office

lighting levels range from about to 1 μmol q/m2/s (10 μmol q/m

2/s equals ~380 Lux). The

State Government of Victoria (2009) recommends minimum light levels for “routine office

work” of from 3 –400 Lux (8.5-10.5 μmol q/m2/s). In the tested buildings values of from

4.5 to 9.7 μmol q/m2/s were recorded within 60 cm from the plant-walls, however levels from

2.3 to 6.5 μmol q/m2/s, which were recorded in the centre of occupied spaces, are

unsatisfactorily low for office occupants. The results also indicate that although the plant-wall

lighting provides highlights over the planted surfaces (Plates 1-7), it evidently has little effect

on room-space illumination as a whole.

Cols. 5, 6 list concentrations of PM10 and PM2.5 respectively. All the values for PM10 were at

or below the Australian tandard maximum of 5 μg/m3. However, as can be seen from

Table 1, the pairs of concentrations for PM10 and PM2.5 were very similar to each other, which

indicates that a majority of the particles captured in the PM10 sampling were in fact extremely

fine, in the PM2.5 range (Harrison et al., 1997). HVAC systems are equipped with filters that

remove some of the dust that would otherwise come indoors, but some particulates are not

captured by the filters, as exemplified by these results. The PM results also point to possible

health risks in Sydney at these concentrations. The Australian maximum for 24-hour-

averaged outdoor concentration for PM2.5 is 5 μg/m3 (Aust. Gov., 1998; 2013 - under review,

towards stricter limits).

Cols. 7,8 show CO2 levels in the sampled buildings, and percentage differences between

planted and reference floors. The current ambient global CO2 concentration (May 2016;

Scripps Inst. Oceanography, Mauna Loa Observatory) is fluctuating between 405-408 ppm.

The CO2 values on reference floors in the 7 buildings ranged from 480 ppm (not too far

above world ambient) to 835 ppm (nearly twice ambient, and above the trigger values for

increased ventilation in some Sydney buildings, e.g. UTS). These differences reflect a

mixture of different HVAC settings and cycles, and/or different occupant numbers and

activities at particular times. No HVAC system can provide identical air conditions

throughout a building at any given moment, although floors with occupants might normally

have higher CO2 levels than unoccupied spaces. However, the results in Col. 7 show some

variations from the expected norm. In the first building, the Library, on the floor which held

the largest plant-wall installation, CO2 concentrations both near the plant-wall and in the

centre of the room-space were 13 % lower than on the reference floor. In the second building,

the Insurance office, with a plant-wall area only 35 % that of the Library, CO2 levels near the

plant-wall remained equal to those on the reference floor, and were 23 % lower in the centre

of the room-space than on the unoccupied floor.

In this project it was not possible to disentangle the operations of the HVAC systems in the

various buildings and the potential contribution of the plant-walls in reducing CO2 by

photosynthetic uptake or dissolution in water associated with the substrate. However, the CO2

reductions recorded on planted floors in these first two buildings suggest that these plant-

plant installations indeed have the capacity to make a contribution to refreshing indoor air. In

the next three buildings, which had diminishing plant-wall areas, CO2 values were higher

near the plant-walls than on reference floors, though in two of the three buildings, values

were lower in the centre of planted space than near the plant-walls. The two buildings with

the least planted areas, the Childcare Centre and UTS Conference Centre, maintained near-

equal levels of CO2 on planted and reference floors. A combination of light intensity and

species-specific light threshold levels for CO2 uptake, are major determinants of plant CO2

responses in indoor air.

Table 2 lists plant species found in each of the seven buildings. A total of 15 species/varieties

were used, with highest diversity, 11 species, being found in the Insurance building. The three

commonest species were Philodendron spp. (3 spp; 6 buildings); C. comosum (5 buildings);

and E. aureum (5 buildings). Two ferns, Davallia sp. and Phlebodium aureum were used in 2

buildings.

Table 1: Sites and dimensions of plant-walls in the 7 buildings; light intensities; concentrations of

PM10 and PM2.5; CO2; percentage differences in CO2 concentrations between plant-walled floors

(60 cm from plants & in centre of space) and reference floors (centre space only).

(Where PM and CO2 concentrations on IPW floors are equal to, or lower than, those on reference

floors, values are shown in blue).

1. Sites 2.Plant-

wall areas

(m2)

3. Spaces:

Ref. flr;

IPW flr;

Near-wall

/ Centre.

4. Light

Intensity

μmol

q/m2/s)

5. PM10

Conc.

(μg/m3)

6. PM2.5

Conc.

(μg/m3)

7. CO2

Conc

(ppm)

8. % Diffs.

CO2 Ref. fl./

IPW fl.

i. Public Library 72 Ref. spce.

IPW spce:

60 cm

Centre

2.7

4.5

3.7

30

20

20

30

20

20

570

500

500

-13

-13

ii. Insurance 24.5 Ref. spce.

IPW spce:

60 cm

Centre

1.1

9.0

3.0

40

30

30

30

30

30

835

845

570

=

-23

iii. Couriers-

Packaging

21 Ref. spce.

IPW spce:

60 cm

Centre

10.5

6.0

6.5

20

20

20

20

20

20

610

750

570

+23

-7

iv. Café

Hunter St

12.3 Ref. spce.

IPW spce:

60 cm

Centre

6.5

7.3

6.0

50

50

50

50

40

-

520

710

585

+20

v. UTS

Admin Centre

12 Ref. spce.

IPW spce:

60 cm

Centre

1.8

9.7

2.3

30

50

40

30

40

30

480

660

650

+36

+35

vi. Childcare

Centre

6 Ref. spce.

IPW spce:

60 cm

Centre

3.5

7.2

3.0

30

40

40

20

40

40

600

-

655

+9

vii. UTS

Conf. Centre

5 Ref. spce.

IPW spce:

60 cm

Centre

9.5

6.5

5.7

40

-

20

40

20

20

545

550

585

=

+8

Table 2. Plants used among buildings in the IPW modules.

Building Species/variety

Public library Chlorophytum comosum

Epipremnum aureum

Philodendron bipinnatifidum

Philodendron scandens

Philodendron xanadu

Neomarica sp.

Peperomia sp.

Spathiphyllum cochlearispathum

Insurance Chlorophytum comosum.

Philodendron bipinnatifidum

Philodendron xanadu

Anthurium sp.

Aglaonema sp.

Davallia sp.

Iresine sp.

Peperomia sp.

Phlebodium aureum

Spathiphyllum cochlearispathum

Syngonium podophyllum

Couriers/Packaging Chlorophytum comosum (varigated)

Epipremnum aureum.

Philodendron bipinnatifidum

Philodendron xanadu

Peperomia sp.

Davallia sp

Phlebodium aureum

Spathiphyllum cochlearispathum

Syngonium podophyllum

Café, Hunter Street Chlorophytum comosum

Chlorophytum comosum (variegated)

Epipremnum aureum

Ctenanthe sp.

Peperomia sp.

Phlebodium aureum

UTS 10, Admin. Epipremnum aureum

Ctenanthe sp.

Neomarica sp.

Childcare Centre Chlorophytum comosum (variegated)

Philodendron xanadu

Ctenanthe sp.

Peperomia sp.

UTS Conf. Centre Epipremnum aureum

Philodendron scandens

Philodendron xanadu

Neomarica sp.

4. SIGNIFICANCE OF FINDINGS

PM pollution The results in Col. 5, 6, show that airborne PM contamination in these Sydney

buildings was largely composed of very fine particulates – the PM2.5 fraction. Although only

from ‘snapshot’ sampling, the values suggest that only three of the buildings, the Library,

Couriers, and the UTS Conference Centre, would be under the Australian PM2.5 maximum. In

these buildings planted floors had lower PM2.5 levels than reference floors, which point to

plant presence possibly being involved. The other four buildings were significantly above the

Australian PM2.5 limit, and by the USA standards would be classed as ‘Unhealthy for

Sensitive Groups’. The PM10 and PM2.5 risk categories have been developed internationally

over the last two decades, as it has become recognised that suspended fine and ultrafine

particles are considerably more hazardous to health than previously understood (NSW Health,

2015; NSW EPA, 2015).

Indoor CO2 levels – relationships with photosynthesis in indoor plants. In this era of

concern over rising CO2 levels and climate change, the world now appreciates that all green

plants can absorb carbon dioxide. With adequate lighting for the particular species, any

green shoot will open its leaf stomates (pores), which will simultaneously start:

a flow of water (and minerals) up from its roots (‘translocation’) the dragging force being evaporation of water from the leaves; and

uptake of CO2, as the starting-material of photosynthesis.

Non-green parts - brown stems, coloured flowers or fruit, roots and root-zone

microorganisms (bacteria and fungi) do not photosynthesise. They continually respire

(24/7), emitting CO2 (and their cellular-respiration chemistry is almost identical with our

own). Hence with respect to net CO2 uptake and sugar production, there are opposed

processes at play in the plant, as follows:

Light energy

PHOTOSYNTHESIS: 6CO2 + 6H2O ------------> [C6H12O6] + 6O2-----

Chlorophylls [sugar] (Oxygen– by-product) -- (+enzymes)

Day & Night

RESPIRATION: [C6H12O6] +6O2 ---------------> 6CO2 + 6H2O + [36 ATP]

[sugar] (+other enzymes) [‘ nergy’ molecules]

A successful plant is one which always produces more photosynthetic product (glucose

sugar) during lighted hours, than it uses to power continuous whole-plant respiration. The

‘Light Compensation Point’ (LCP) of a plant is the light intensity at which the green shoot’s

rate of CO2 uptake exactly equals the whole-plant’s respiratory CO2 output. The light level

must be routinely higher than the LCP for the plant to survive. Our studies have shown that a

number of indoor species need light intensities of ~15 to 3 μmol q/m2/s to show any

measurable net CO2 uptake (Torpy et al., 2014). Light intensities near the surface of the plant-

walls of from 4.5 to 9.7 μmol q/m2/s (avr. about 7.5; Tab. 1, Col. 4) suggest that some species

might be at or below their LCPs. Every species has its own LCP, its own optimum light

intensity, and its intrinsic photosynthetic processing rate. The photosynthetic capacity of a

species depends on a range of other factors as well, including leaf area; temperatures; water

balance; fertilisation; and rates of sugar transport from leaves to other parts of the plant.

Is variegated foliage useful in CO2 reduction? The IPWs surveyed included variegated C.

comosum in three buildings (Table 2), and some other species showed some variegation also.

For optimising CO2 removal, it must be remembered that white-striped or patchy leaves have

less photosynthetic ability than green leaves. The white areas, caused by mutations, are

‘albino’, lacking chlorophyll and associated pigments (carotenes and xanthophylls). The

Botanic Gardens of the University of California LA, 15 states that: “Variegated leaves

occur rarely in nature but are extremely common among indoor and outdoor ornamentals,

where they have been saved as horticultural oddities”. In more kindly vein, Ombrello 15

comments: “We as a species, however, protect and perpetuate these [variegated] oddities of

nature. Our interest in the unusual assures their survival under our care”. To advance the

‘plant-wall for indoor air-cleansing’ program, more detailed information is needed on

the photosynthetic propensities of popular indoor species (both green and variegated).

Indoor plants and HVACs. In comparing planted and reference floors in the seven buildings

(Table 1), clear CO2 reductions were found in the first two buildings, of from 13 to 23 %.

However, there was considerable CO2 variability generally among the buildings, as follows:

- Among reference floors alone;

- On planted floors alone, between those near the IPW, and those in the centre of the space;

- For either of the two sampling points, i.e near-IPW and centre.

The differences provide some idea of possible plant responses to the indoor air conditions,

and also something of the flexibility of HVACs and the different settings under which they

are operating in different buildings.

5. FUTURE RESEARCH

Towards urban sustainability

The horticultural development of indoor plants for improved Indoor Environmental Quality

(IEQ) is less than three decades old, whereas for roses, carnations, pomegranates, etc., there

have been thousands of years of selection and cultivation. However, there is now evidence

that indoor plants are already, and will increasingly be, needed to cleanse indoor air and help

ensure future urban sustainability (Hartig et al., 2003; Sahely et al., 2005; Aust. Gov, 2011;

Specht et al, 2014; Dunham et al., 2014). It has also been estimated that improved

productivity gains from simply having plants in the nearby space, more than repay the cost of

indoor plant presence, in terms of occupant wellbeing and performance (Lohr et al., 1996;

Rodgers et al., 2012). Nieuwenhuis et al. (2014) concluded, from a 3-part investigation of

offices with and without plants, that: “The results demonstrate how office landscaping

strategies that involve transforming a lean office into a green one, contribute not only to

employee welfare, but also to organizational output. Lean, it appears, is meaner than

green, not only because it is less pleasant but also because it is less productive.”

Species strengths and weaknesses

(i) CO2 uptake The next step is to profile the CLPs and photosynthetic capacity of the most

used indoor species/varieties, so that they can be reliably utilised to bring about significant

reduction of CO2. For each species, laboratory trials would be made of:

- Leaf- and whole-plant CO2 removal responses to a range of light intensities;

- Leaf areas and biomasses, and the pot or module sizes involved;

- CO2 uptake with varying numbers of plants in an experimental room-space.

(ii) Occupant-related VOCs (ORVOCs) This project with would investigate to what extent

plants of various species can reduce or remove levels of household spray cleaners, room

deodorants perfumes, after-shaves, etc. While generally considered safe, recent evidence has

shown that some of the chemicals commonly used as fragrances can be converted to toxic

VOCs in the air (eg. Limonene).

(iii) PM reduction This study would estimate the proficiency of species to reduce levels of

PM10 and PM2.5. Outdoor plant leaves accumulate particulates and so contribute to cleaning

city air (Beckett et al., 1998; Irga et al 2015). There has also been one report of indoor plants

reducing particulate concentrations by up to 20 percent in some indoor sampling zones (Lohr

& Pearson-Mims, 1996). It is likely that not only leaf area but also leaf surface

characteristics, and possible growth medium factors, would influence PM accumulation

abilities.

Performance in the ‘Real –World’

(iv) CO2 uptake This would involve in situ studies of CO2 concentrations on floors with and

without plant-walls, in selected buildings with and without HVAC systems. Investigations

would involve:

Obtaining details of the HVACs/alternative air-conditioning systems, and their operations in each building;

Measuring CO2 levels at sampling points similar to those used in the present study;

Measuring CO2 uptake of IPWs in the buildings, at various light intensities, using a portable, adjustable, lighting stand.

(v) PM10 & PM2.5 reductions Sampling of particulates would be conducted in buildings at the

same times as the CO2 uptake trials are taking place.

(vi) Are indoor-plants a possible source of fungal spores?

High concentrations of airborne fungal spores, such as those found in damp buildings, are a

health hazard which can lead to symptoms of sick-building syndrome (Takeda et al., 2009).

Pathogenic fungi such as Aspergillus fumigatus can cause serious allergic reactions, and in

severely immunocompromised individuals fungal infections can lead to death (Maschmeyer

et al., 2007). Several authors (Staib et al. 1978, Summerbell et al. 1989, Engelhart et al. 2009)

have stated that indoor plants are therefore a serious health risk that should never be used

inside buildings. It is clearly essential that immunocompromised patients (e.g. after organ

transplants, or suffering from HIV) must be protected from exposure to any ‘raw’ natural

biological material, such as salad vegetables, fruit, cut-flowers, or potted-plants. However, for

the vast majority of building occupants, indoor plants have been shown not only to reduce air

pollution, but also to lower noise levels (Costa & James, 1999), reduce sick-leave, improve

job-satisfaction and performance, increase pain tolerance (Park et al., 2002), and lift spirits

(Kaplan, 1995; Bringslimark et al., 2009).

We have conducted what appears to be the first systematic study of the possible effects of

indoor plants on indoor airborne fungal spore counts (Torpy et al., 2013b). Over 50 single-

staff offices, in two UTS buildings, were supplied with 0, 1, or 3 potted plants of Dracaena

deremensis or Spathiphyllum wallisii ‘Petite’. No significant differences were found with the

presence or different amounts of plant material, in terms of fungal spore numbers or their

species composition. In addition, all the indoor spore concentrations were some three to ten

times lower than in parallel ‘reference’ samples taken outdoors in adjacent streets. New

research in this area would include:

a laboratory study of possible emission rates of fungal spores from ‘IPW’ species plus-

an in situ study into possible airborne fungal loads in buildings with plant-walls, to assess whether there might be some limit to the advisable area of IPW in any given

volume of room-space.

Goal of research directions

The central aim of our research is to harness the use plant photosynthesis to help reduce

indoor CO2 levels in HVAC and similarly air-conditioned city buildings. Other benefits

would also accrue. If the energy load of a building’s air-con system could be lowered by

perhaps 10 %, the C-footprint of the building would be substantially reduced, and ventilation

costs reduced by a similar percentage. The U P 11 states that: “The Buildings sector of

today has an oversized ecological footprint. The buildings sector is the single largest

contributor to global greenhouse gas emissions (GHG), with approximately one third of

global energy end use taking place within buildings..... There are significant opportunities to

improve energy-efficiency in buildings”.

Indoor plants can play a significant role in improving building efficiency, while making

the ‘indoor habitat’ a much more pleasant place in to live and work. Research funding

would be required for the proposed studies, and we are currently seeking funding sources.

ACKNOWLEDGEMENTS

We thank Interior Plantscape Association (IPA) and the previous New Zealand Association

(PAWA) for funding the Indoor-Plant-Walls project. Special thanks to Ms Nerida Hills,

President, and Ms Elaine Tunn, IPA Executive Officer, for their assistance and patience as

the work has very slowly been completed. We thank Mr Jock Gammon, Junglefy Pty Ltd., for

advice and providing access to the plant-wall installations studied. The co-operation of

Junglefy staff member Mr Andrew Wands, and the building managers, in assisting with

building access and sampling arrangements, are also much appreciated. This project, although

short-term and limited in scope, has produced valuable information, which has helped propel

our Plants and Urban Air Quality Group, UTS, into new phases of indoor plant research.

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Figure 1: Public library.

Figure 2: Insurance company.

Figure 3: Couriers-packaging facility.

Figure 4: Hunter St café.

Figure 5: UTS Administration Centre.

Figure 6: Childcare centre.

Figure 7: UTS Conference Centre.