Do potted-plants improve the indoor environment?
- Publication Type:
- Thesis
- Issue Date:
- 2011
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With increasing prevalence of urban air pollution (UAP), associated problems are
becoming of major international concern environmentally, economically and with
respect to human health. About 50% of the world's population (including 80% of
Australians) live in urban areas and spend approximately 90% of their life indoors,
where indoor air quality (IAQ) is almost always more polluted than outdoors, even in
urban centres with the high reliance on fossil fuels for transport and industry. An
increasing proportion of urban dwellers work in sealed buildings, dependent for air
supply and thermal comfort on heating, ventilating, and air conditioning (HVAC)
systems. This project investigated the potential benefits for more sustainable cities,
that could be achieved by using potted-plants as a supplement to HVAC systems, with
the added benefits of decreasing the incidence of sick building syndrome (SBS), and of
lowering the carbon footprint of a city.
The research considered three major aspects of IAQ. Indoor plants have been shown to
be able to significantly reduce levels of C02 and volatile organic compounds (VOCs),
two classes of contaminants almost always found in higher concentrations indoors
than outside. However, they have also been named as a likely source of pathogenic
mould spores, and this was also investigated. An office field study was conducted in
which the effects were tested of four plant treatments using Dracaena marginate
'Janet Craig' and Spathiphyllum wa/lisii 'petite' (plus reference offices) on a range of
IAQ parameters: C02, VOCs, temperature, relative humidity; plus airborne mould spore
abundance and diversity. Laboratory studies were also carried out, on the capabilities
of plants to: reduce C02 at different light intensities and from two different light
acclimation intensities; remove benzene (as model VOC) applied at various dosages;
and contribute to air-borne mould spore concentrations and species diversity.
Through the laboratory test-chamber studies it was shown that the three species
tested; Aglaonema modestum~ Chamaedorea elegans and Philodendron 'Congo' had
the ability to remove the 8-hour averaged exposure limit after an induction period.
Also plants were readily capable of reducing chamber C02 by up to 9CJ>/o within one
hour, under favourable lighting intensities and after two light acclimation levels. The
mould studies revealed that, compared with outdoor air, there were 8-15 times lower
mould spore loads indoors, and there was little correlation between the mould genera
found in potting mix soil with those found in office air. The results indicate that it is
unlikely that potted-plants are significantly contributing to the levels of moulds found
in the air in Sydney. The office study, in two relatively new buildings, demonstrated
that, with modern HVAC systems, indoor plants had little to no impact on IAQ, with no
significant differences between offices with plants and those without. This is at
variance with a previous study from this laboratory using two buildings with much
older HVAC systems, and one with no air conditioning. Thus it appears that modern
HVACs can mask any benefits of plants on IAQ. This result opens up the possibility of
reducing the energy load on the HVAC system by allowing plants to play a greater role
in cleaning indoor air. The results obtained in this study are very promising for future
indoor environmental management. The possibility of reducing urban air pollution by
lowering energy requirements of city buildings is also encouraging and, in a time of
emission trading schemes and carbon taxes, nature's ability to cost-effectively mitigate
urban pollution is impressive, and its development is urgently needed.
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