Chemistry – Page 2

CO2 – the Keeling Curve

Many things lie at the heart of climate change. Fundamental in this is global warming due to the rise in atmospheric carbon dioxide (CO2). The primary source of the CO2 is the consumption of fossil fuels by each and every one of us. We drive our cars, and CO2 is emitted in the exhaust. We turn on lights and use electricity generated from burning coal or gas. These methods of generating electricity result in the emission of CO2. These emissions have a direct effect on wildlife, the oceans, and the weather.

The mention of automobiles might put us in the mind that this problem only started since cars have been around. But it is not just the recent use of fossil fuels, we have been burning coal for a long time. Once emitted by burning of fossil fuels CO2 does not dissipated; it accumulates. Some of the CO2 may be taken up by trees and other plants in their respiration cycle. They take in CO2 and during photosynthesis the CO2 is converted into oxygen (O2). Carbon can be locked up in dead plant material too. When a tree falls in the forest its use is not over. There are kingdoms of plants and animals that will use the dead tree for food and homes in their own lives. As these plants and animals devour the now decomposing tree, they consume the carbon and lock it in their own bodies. But then as they die their carcasses, as small as they are, store some tiny bit of carbon to be released into the atmosphere and earth as the plants and creatures decompose into the earth. Over millions of years the decomposition of ancient organic matter, dead plants and animals, has produced the current fossil fuels that we use.

But how do we know that the level of atmospheric CO2 is increasing? First we can read the levels of atmospheric CO2 in ice cores. These cores are from specialized drills that penetrate deep into glaciers. When the core is drilled and extracted for examination, the levels of CO2 from past centuries can be measured. As the drill goes deeper and deeper into the glaciers the cores show what the atmosphere was like in the times past. The deeper the core is drilled, the further back in time the sample goes. When snow and ice accumulated on the surface of the glacier centuries ago it captured a signature of the gases that made up the atmosphere. From these cores the CO2 from ancient fires, and human use of wood and coal as a fuel, and emissions by ancient volcanoes can be studied. It has been established that accumulation of CO2 in the atmosphere has been going on from preindustrial times, hundreds of years ago. Since the introduction of factories and industry that used fossil fuels to operate and manufacture goods, the CO2 in the atmosphere has increased at a higher rate.

A key tool in understanding the increase of CO2 in the atmosphere has been the work of Charles D. Keeling. In 1956 he began a program to measure atmospheric gases, including CO2, at the Mauna Loa observatory in Hawaii. As these observations are plotted over time, they show an increasing level of CO2 with each passing year. The graph that shows this increase, known as the Keeling Curve, also shows the change of the seasons in the northern hemisphere. The upwards spikes of the saw-tooth curve indicate rising CO2 in the Winter months when the leaves are off the trees and are not converting CO2 into O2. The downward slope of each “tooth” indicates the activity of the trees and other plants in the growing seasons of Spring and Summer as they remove CO2 from the atmosphere and convert it into O2. But with each passing year the curve goes every upward.

From these two studies, we can determine that CO2 continues to increase based primarily on human activity. The rising levels of CO2 in the atmosphere result in a continually rising average global temperature. This is due to the greenhouse effect as the CO2 and other gases trap energy from the sun in the atmosphere. The rising levels of CO2 also result in ocean acidification.

A copy is the Keeling Curve from the Scripps Institute CO2 program is inserted below.

The Scripps Institute CO2 program website may be found at http://scrippsco2.ucsd.edu/

That gooie plastic sandwich box

Several years ago I went on a camping trip with our cub scouts. One of the other leaders loaned me a plastic chair. As I relaxed, suddenly it cracked and fell apart. It was made of some sort of plastic/poly, and when we looked at it we could tell that years in the sunshine had made it weak. It was obvious that the sunlight had broken down some chemical bond in the plastic. When I applied my weight to the chair, it just broke down. Down being the operative word! But why? Evidently the ultraviolet (UV) rays of the sun caused a photochemical effect within the polymer structure of the chair – and crack!

I got up and dusted myself off, and carried the broken chair to my car. I would take it home and dispose of it. Then I went on my way without thinking much beyond being able to put the broken chair at the curb for pickup to be recycled. However, others have taken this photochemical effect and enhanced it to help reduce the problem of plastic pollution.

Flash forward to a road trip I recently took out west. Often we would stop and buy tomatoes and cheese and english muffins and make a classic roadside sandwich for lunch. Other times we would get a pre-made sandwich to go from a convenience store when we stopped for supplies or for gasoline for the car. In a roadside rest stop I would sit at a picnic table and relax in the shade of a tree while enjoying my lunch. Ham and cheese with mustard is always a favorite of mine. But after I have peeled back the plastic film from the formed, plastic package, and after I have enjoyed the sandwich, what to do with the plastic sandwich box? It has bits of mustard and bread and cheese crumbs stuck to it. Our county’s recycling protocols ask that I do not recycle this with other “clean” plastic waste. My sandwich container is contaminated. The organics, and the chemicals in the mustard will cause problems down the recycling line as this waste plastic cannot be recycled because of the contaminants. The contaminants create weaknesses in the reformed plastics. So my sandwich container, along with other plastics contaminated with food and other organic and chemical residues is NONRECYCLABLE!

But there are clever people who work on the issue of recycling old plastic into new, and they have developed a process that addresses the issue of contaminated, nonrecyclable plastic. An article in Chemistry World reports on work that may help reduce the burden of nonrecyclable plastics on the waste streams, public spaces, and the world’s oceans.

The process being studied not only reduces the pollution burden but also aids in the recovery of the energy that was put into the making of the plastic in the first place.

Moritz Kuehnel and Erwin Reisneer of Swansea University and the University of Cambridge respectively and their colleagues have devised a process that uses a photocatalyst to degrade otherwise nonrecyclable plastics. Their testing included pure plastic product as well as plastic that was contaminated with various organic and chemical residues which would normally cause the plastic to not be recycled into new usable products. Their process uses cadmium sulfide (CdS) quantum dots as a photcatalyst for sunlight. These quantum dots are high quality nanoparticles which are generally fabricated to act as catalysts in chemical processes. There are four elements to the process; the plastic, the CdS quantum dots, water, and sunlight. From the process, called photoreforming, hydrogen is generated.

The hydrogen has many applications including, as we look down the road, as fuel for hydrogen fuel cell cars! However, there continues to be a debate on whether hydrogen fuel cell powered cars or electric vehicles are the next giant leap forward in zero carbon transportation. But the process reported in Chemistry World may help address the energy intensive generation of hydrogen from water. The chemistry in the reported process has been shown to work, and now the team as well as others is working to scale up the process so it is economical and beneficial as it has the potential to convert huge amount of contaminated and nonrecyclable plastic wastes into useful chemicals and fuels.

The Chemistry World article may be found at https://www.chemistryworld.com/news/sunlight-converts-plastic-waste-to-hydrogen-fuel/3009467.article

Tree Foam

The first time I noticed tree foam I was hiking in the mountains of Virginia. It was Fall and delightfully cool, and to make it better it was raining. A hike in the rain can be terrific. You can give yourself over to the rain. The rainfall creates a smaller world with you at the center. All around you is the random fall of the drops. They drum on the leaf canopy above and then drip down onto the understory below – including you. The rain and the trees and the understory have created a universe that is bounded by a curtain of the rhythm of the rain. As the drops beat on the leaves they create a barrier against the outside world of noise from cars and planes, and from the general hub-bub of humanity. It becomes just you in the much smaller, much cleaner universe that is centered on your hearing. You can turn and look around and look up and see the dimensions of your new world. And for a while you can enjoy the true uniqueness and quietude of a world that is all your own.

As you look around, you may see what looks like sea foam building up at the base of a tree. It’s a small but growing mass of white bubbles right at the roots. I mainly notice it on the pine trees. And the foam is not just at the base. The foam collects at the base, but it can be seen coming down the tree as pale, flowing streaks of rain water. The mass of foam at the base of the tree billows and grows at more than one spot. As I look further, I realize there is foam at the base of several of the trees. What is it? Is it a disease? Is it a fungus? Not necessarily. It’s a common occurrence brought on by the chemistry of the tree, the roughness of the bark of the tree, and the surface tension of the water that usually holds the shape of the drops as they roll down the tree.

When it rains in the woods few if any of the drops reach the ground directly from the sky. The rain that falls directly to the forest floor by-passing the canopy of the trees and the growth of the understory is considered “through-fall”. Some of the rain falling into the canopy is captured and remains on the leaves and branches. Other droplets flow down the tree’s exterior to reach the ground. The drops that do not flow all the way to the ground are given up to the atmosphere though evaporation. The water droplets that roll down twig and branch and then flow down the trunk in numerous little rivulets is “stem flow”.

As the water’s stem flow passes over the tree’s bark it picks up tiny bits of organic material and the chemical residue from the surface of the tree. These bits create a chemical change in the water’s molecular bonds which reduces the surface tension of the water droplets. The reduced surface tension allows more air to become entrained in the water. The droplets gather into larger rivulets and flow over and around the bark of the tree. This acts like waves in the ocean or rivulets in a stream and exposes more and more of the surface of the water droplets to the air. This stirring action creates the foam that can be seen flowing down the trunk and which accumulates as the mass of bubbles at the base of the tree.

The rain water that reaches the base of the tree may run off on the surface of the forest floor to be absorbed into the ground where it may be taken up by the tree’s root structure. Other run-off that is absorbed by the ground will infiltrate further downwards to mix with the water table and perhaps enter a stream that flows down towards the ocean. Eventually, through root uptake and transpiration by the tree, or through evaporation from a stream or the ocean, the water is taken back up into the atmosphere and from there to fall again as rain on the joyful hiker.

Information on tree foam may be found in a NOAA site, www.oceanservice.noaa.gov/facts/seafoam.html.

A similar article can also be found at a terrific hiking blog, http://ramblinghemlock.blogspot.com/.