Archive for ‘water’

March, 2014

The vital role of trees: from atmospheric chemistry to architecture

Dr James Levine

As an atmospheric chemist, I am interested in the influence that trees have on the quality of air we breathe and the climate we either enjoy or ‘weather’, depending on where we live.  First off, there’s the appealing synergy between people and trees: as we breathe in oxygen and breathe out CO2, trees draw down CO2 from the atmosphere and top up our oxygen supply.  If we have an immediate need for oxygen, we have a long-term need for a habitable climate, and trees again play a vital role.  In drawing down, or sequestering CO2, they reduce the burden of this greenhouse gas (GHG) that is at the forefront of our minds as we consider the climate our children, and children’s children, will inherit.  But trees have a further, much more subtle means of influencing both air quality and climate.

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The atmosphere is predominantly cleansed of gases harmful to human health, and some potent GHGs (e.g. methane), by a perhaps surprising simple chemical species, the OH radical (just an oxygen atom joined to a hydrogen atom).  Trees emit gases, so called volatile organic compounds (VOCs), that influence the abundance of OH radicals globally.  As part of Prof Rob MacKenzie’s group here at the University of Birmingham, I am involved in the Cooperative LBA Atmospheric Regional Experiment exploring the influence that the Amazon rainforest has in this regard; this is a collaboration with the University of Sao Paulo (Brazil), the University of Lancaster and the Centre for Ecology and Hydrology.  Of course, whilst trees affect the climate, the climate also affects trees; changes in climate also ‘feedback’ on the chemistry stemming from the VOCs trees emit.  Under Rob’s direction, the new Birmingham Institute for Forest Research will explore some of these feedbacks.  In particular, it is tasked with exploring the impact of climate change on UK woodland, both directly via changes in physical conditions (e.g. air temperature and humidity), and indirectly via changes in the incidence of, and resilience to, pests and disease.

I now have a confession to make: I lead a bit of a double life.  Atmospheric chemist by day, I’m an architecture student by night.  Trees and timber have important parts to play in architecture too, including one pertinent to reducing anthropogenic CO2 emissions.  Construction of the built environment, and the energy used to maintain a comfortable environment within it, account for around half the UK’s (and global) CO2 emissions.  If sustainably and locally sourced, timber embodies very little energy, or CO2 emissions; the CO2 locked up in the timber and ultimately released to the atmosphere (upon decay at the end of a building’s life), may be drawn down from the atmosphere by a tree grown in its place.  Timber construction is also readily compatible with approaches to radically reducing the ‘operational energy demands’ of maintaining a comfortable environment, reliant on high levels of insulation and air-tightness.  Built to the Passivhaus standard, for example, a house in the UK may require no more heating, year-round, than the warmth its occupants alone provide.  And it doesn’t stop there.

The use of trees and timber in architecture has a part to play in improving our quality of life and providing uplifting, life-affirming spaces.  Be it the oxygen they ‘breathe out’, the microclimates they yield, or the sense of well-being they inspire, research suggests trees benefit people living and working in their vicinity.  In schools, for example, they appear to increase children’s concentration and ability to learn.  The architect, Louis Kahn (1960), envisaged that “Schools began with a man under a tree who did not know he was a teacher discussing his realization with a few who did not know they were students.”  I wonder what role he imagined the tree played.  Did it simply provide shelter or did it also help cultivate a sense of security, that commodity which is recognised as key to learning?  We only have to look at David Nash’s Ash Dome  to see the potential the boughs of a tree have to offer both shelter and that peculiar sense of ‘rootedness’ a connection to the outdoors inspires.  For an exploration of the many and varied qualities we associate with trees and timber, Roger Deakin’s Wildwood – A Journey Through Trees makes a visceral and evocative read.

So what has motivated this brief reflection on the role of trees in relation to my dual interests in atmospheric chemistry and architecture?  It is the Trees, People and the Built Environment II conference, taking place in Birmingham this week.  Trees clearly have a vital role, be it at present or with a view to the future, and I look forward to learning in the next few days about many more, perhaps equally diverse, facets to this.

Kahn, L. I. (1960). Form and Design (1960). In R. Twombly (Ed.), Kahn (pp. 62-74). New York: W. W. Norton and Company.

Dr James Levine is a Research Fellow at the School of Geography, Earth and Environmental Sciences, University of Birmingham.

January, 2014

Saving humans through saving water

Dr Zoe Schnepp

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Generating clean drinking water for everyone on this planet is one of the biggest global challenges. It’s also a particular interest of mine since there are so many ways in which chemistry can contribute. 

One of the big problems with water is the presence of microbes – bacteria, viruses and parasites – which can cause a range of diseases. Gastrointestinal infections related to poor sanitation kill 2.2 million people a year.[i] However, there are also many other sources of water contamination. These can be man-made pollutants, such as fabric dyes or agricultural run-off. There is also increasing concern about drug molecules such as hormones entering the water supply from both animal and human excrement. Another important source of water contamination is from nature. The earth contains plenty of toxic elements and these can leach into water from rocks. It would be impossible to talk about all the fascinating chemistry research into combatting all of these water problems so I’m just going to focus on one: arsenic. 

Arsenic is found in many different minerals in the Earth’s crust. It’s also used in a range of different industries but as I mentioned above, the main source of arsenic contamination in water actually comes from the element leaching from rocks into groundwater. This is widespread, including countries such as Bangladesh, India, China and Argentina.[ii] The actual concentrations of arsenic in groundwater are quite low – too low to cause acute arsenic poisoning. The problem comes from long-term consumption of arsenic-contaminated water, as well as use of groundwater to irrigate crops. This can cause a range of unpleasant health problems and, since arsenic is carcinogenic, it has been linked to cancers of the skin, lungs and bladder. 

A particularly interesting example of tackling arsenic removal actually uses the same chemistry as I mentioned in this blog yesterday – photocatalysis. Many research groups around the world are working on ways to use sunlight to help remove arsenic from water. It’s similar chemistry to self-cleaning windows, where sunlight activates catalysts on the surface of the window to break down molecules of dirt that have accumulated. Since arsenic is an element, we are not looking at breaking it down, but we can convert it into a different form. Once it’s in that form, it’s much easier to remove. 

The chemistry works by using a photocatalyst – a material that can absorb energy from the sun and use that energy to drive a chemical reaction. Arsenic in groundwater is mainly present as positively charged ions – each ion having a charge of +3 (As3+). In this form, arsenic is very mobile – it’s not absorbed very well by normal water filters and it can move easily into the body. The purpose of the new photocatalyst chemistry is to convert arsenic into a different form that is more easily absorbed onto water filters. By shining sunlight onto these photocatalysts, arsenic is converted from +3 ions to +5 ions. These are much more easily removed. 

The beauty of this chemistry is that it uses sunlight as the energy source. It could also be integrated with some conventional water-filtration materials such as activated carbons. The challenge is now to get the materials (the photocatalysts) optimized. Catalysts work best with a high surface area and so a lot of current research into these photocatalysts is in structuring the material – more on this tomorrow!

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