Tag Archives: leaf

Leaf blowers are not only annoying but also bad for you (and the environment)

The seemingly-innocuous leaf blower may actually cause a lot more damage than you’d think — to both your health and the climate.

A groundskeeper blows autumn leaves in the Homewood Cemetery, Pittsburgh.
Image via Wikimedia.

It’s that time of the year: trees are shedding their leaves, and people are blowing them off the pavement. According to the Centers for Disease Control and Prevention (CDC), this quaint image actually hides several health concerns for operators and the public at large.

The inefficient gas engines typically used on leaf blowers generate large amounts of air pollution and particulate matter. The noise they generate can lead to serious hearing problems, including permanent hearing loss, according to the CDC.

Sounds bad

Some noise may not seem like much of an issue, but the dose can make it poison. The CDC explains that using your conventional, commercial (and gas-powered) leaf-blower for two hours has an adverse impact on your hearing. Some emit between 80 and 85 decibels (dB) while in use. Most cheap or mid-range leaf blowers, however, can expose users to up to 112 decibels (a plane taking off generates 105 decibels). At this level, they can cause instant “pain and ear injury,” with “hearing loss possible in less than [2 to] 5 minutes”.

The low-frequency sound they emit fades slowly over long distances or through building walls. Even at 800 meters away, a conventional leaf blower is still over the 55 dB limit considered safe by the World Health Organization, according to one 2017 study. Because they’re so loud, they can be heard “many homes away” from where they are being used, Quartz explains.

This ties into the greater issue of noise pollution. The 2016 Greater Boston Noise Report (link plays audio,) which surveyed 1,050 residents across the Boston area, found that most felt they “could not control noise or get away from it,” with leaf blowers being a major source of noise. Some 79% of responders said they believed no one cared that it bothered them. Leaf blowers are also seeing more use — in some cases becoming a daily occurrence. As homeowners and landscaping crews create an overlap of noise, these devices can be heard for several hours a day.

Image credits S. Hermann & F. Richter / Pixabay.

With over 11 million leaf blowers in the U.S. as of 2018, this adds up to a lot of annoyed people. Most cities don’t have legislation in place that deals with leaf blower noise specifically, and existing noise ordinances are practically unenforceable for these devices. However, there are cities across the U.S. that have some kind of leaf blower noise restrictions in place or going into effect.

Noisy environments can cause both mental and physical health complications, contributing to tinnitus, hypertension, and generating stress (which leads to annoyance and disturbed sleep).

Very polluting

A report published by the California Environmental Protection Agency (CalEPA) in the year 2000 lists several potential hazards regarding air quality when using leaf blowers:

  • Particulate Matter (PM): “Particles of 10 Fm and smaller are inhalable and able to deposit and remain on airway surfaces,” the study explains, while “smaller particles (2.5 Fm or less) are able to penetrate deep into the lungs and move into intercellular spaces.” More on the health impact of PM here.
  • Carbon Monoxide: a gas that binds to the hemoglobin protein in our red blood cells. This prevents the cell from ‘loading’ oxygen or carbon dioxide — essentially preventing respiration.
  • Unburned fuel: toxic compounds from gasoline that leak in the air, either through evaporation or due to incomplete combustion in the engine. Several of these compounds are probable carcinogens and are known irritants for eyes, skin, and the respiratory tract.

To give you an idea of the levels of exposure involved here, the study explains that landscape workers running a leaf blower are exposed to ten times more ultra-fine particles than someone standing next to a busy road.

Additionally, these tools are important sources of smog-forming compounds. It’s not a serious issue right now, but as more people buy and use leaf blowers, lawnmowers, and other small gas-powered engines, these are expected to overtake cars as the leading cause of smog in the United States.

What to do about it

Well, the easiest option is to use a rake — or just leave the leaves where they are, which is healthier for the environment.

But leaf blowers didn’t get to where they are today because people like to rake. Electrical versions, either corded or battery-powered, would address the air quality and virtually all of the noise concerns (albeit in exchange for less power).

While government regulation might help with emission levels, noise concerns might best be dealt with using more social approaches. Establishing neighborhood-wide leaf blowing intervals, or limiting the activity to a single day per week, would help make our lives a little better. As an added benefit, this would also help people feel that their concerns are being heard, and foster a sense of community.

An artificial leaf can turn carbon dioxide into fuel

Seeking innovative ways to deal with the rise in greenhouse gas emissions, a group of scientists has developed a so-called “artificial leaf” that can convert carbon dioxide (CO2) into a useful alternative fuel – with almost no costs.

Credit Wikipedia Commons

The research, published in the journal Nature Energy, was inspired by the way plants use energy from sunlight to turn carbon dioxide into food.

“We call it an artificial leaf because it mimics real leaves and the process of photosynthesis,” said Yimin Wu, an engineering professor at the University of Waterloo who led the research. “A leaf produces glucose and oxygen. We produce methanol and oxygen.”

Carbon dioxide is the primary contributor to global warming. Making methanol out of it would both reduce greenhouse gas emissions and provide a substitute for the fossil fuels that create them. The key to the process is a cheap, optimized red powder called cuprous oxide.

The powder is created by a chemical reaction when four substances – glucose, copper acetate, sodium hydroxide, and sodium dodecyl sulfate – are added to water that has been heated to a particular temperature. It’s engineered to have as many eight-sided particles as possible

Then, the powder serves as the catalyst, or trigger, for another chemical reaction when it is mixed with water into which carbon dioxide is blown and a beam of white light is directed with a solar simulator.

“This is the chemical reaction that we discovered,” said Wu, who has worked on the project since 2015. “Nobody has done this before.”

The reaction produces oxygen, as in photosynthesis, while also converting carbon dioxide in the water-powder solution into methanol. The methanol is collected as it evaporates when the solution is heated.

Looking ahead, the next steps in the research include increasing the methanol yield and commercializing the patented process to convert carbon dioxide collected from major greenhouse gas sources such as power plants, vehicles, and oil drilling.

“I’m extremely excited about the potential of this discovery to change the game,” said Wu, a professor of mechanical and mechatronics engineering, and a member of the Waterloo Institute for Nanotechnology. “Climate change is an urgent problem and we can help reduce CO2 emissions while also creating an alternative fuel.”


New design hotfix could make artificial leaves better than actual leaves

A new design could bring artificial leaves out of the lab to convert CO2 into raw materials for fuel.


Image credits Jeon Sang-O.

The idea behind artificial leaves isn’t very complicated — just make them do the same job regular leaves perform, but faster, if possible. Despite this, we’ve had a hard time actually delivering on the idea outside of laboratory conditions. New research, however, could improve on the technology enough to make it viable in the real world.

Leaf it to the catalysts

The sore point with our present artificial leaves is that they simply don’t gobble up CO2 at the concentrations it’s found in the atmosphere.

“So far, all designs for artificial leaves that have been tested in the lab use carbon dioxide from pressurized tanks. In order to implement successfully in the real world, these devices need to be able to draw carbon dioxide from much more dilute sources, such as air and flue gas, which is the gas given off by coal-burning power plants,” said Meenesh Singh, assistant professor of chemical engineering in the UIC College of Engineering and corresponding author on the paper.

While artificial leaves are meant to mimic photosynthesis, even our most refined leaves only work if supplied with pure, pressurized CO2 from tanks in the lab. It’s good that they work, it means we’re on the right track, but they’re not useable in practical applications. Because they only work with high concentrations of CO2, they can’t be used to scrub this gas out of the wider atmosphere, which is what we want to do with them.

Researchers at the University of Illinois at Chicago, however, propose a design solution that could fix this shortcoming. Their relatively simple addition to the design would make artificial leaves over 10 times more efficient than their natural counterparts at absorbing CO2. The gas can then be converted to fuel, they add.

Singh and his colleague Aditya Prajapati, a graduate student in his lab, say that encapsulating artificial leaves inside a transparent, semi-permeable capsule filled with water is all we need to do. The membrane allows water inside to evaporate which, as it passes through the quaternary ammonium resin membrane, pulls in CO2 from the air.

Artificial leaf.

A schematic showing the main principles behind this process.
Carbon dioxide (red and black) enters the leaf as water (white and red) evaporates from the bottom of the leaf. An artificial photosystem (purple circle at the center of the leaf) made of a light absorber coated with catalysts converts carbon dioxide to carbon monoxide and converts water to oxygen (double red spheres) using sunlight.
Image credits Meenesh Singh.

The artificial photosynthetic unit inside the capsule then converts carbon dioxide to carbon monoxide, which can be siphoned off and used to make fuel. Oxygen is also produced and can either be collected or released into the surrounding environment.

“By enveloping traditional artificial leaf technology inside this specialized membrane, the whole unit is able to function outside, like a natural leaf,” Singh said.

The duo estimates that 360 such leaves, each measuring 1.7 meters by 0.2 meters (5.5 by 0.6 feet), could produce around half a ton of carbon monoxide per day. Spread over a 500 sq meter area, the leaves could reduce CO2 levels by 10% within 100 meters of the array in a single day, they add.

“Our conceptual design uses readily available materials and technology, that when combined can produce an artificial leaf that is ready to be deployed outside the lab where it can play a significant role in reducing greenhouse gases in the atmosphere,” Singh said.

The paper “Assessment of Artificial Photosynthetic Systems for Integrated Carbon Capture and Conversion” has been published in the journal ACS Sustainable Chemistry & Engineering.

A banana leaf a million times bigger than a common heather leaf. Credit: Pixabay.

Why leaves come in so many different sizes, explained by new study

There are hundreds of thousands of plant species growing on our planet whose leaf surface area varies from as small as one square millimeter to one square meter. Previously, scientists have identified that the amount of sunlight and available water are prime factors that determine how large a leaf can get but this isn’t a complete picture.

A banana leaf a million times bigger than a common heather leaf. Credit: Pixabay.

A banana leaf a million times bigger than a common heather leaf. Credit: Pixabay.

A new study that analyzed leaf size for more than 7,000 plants found both daytime and nighttime temperatures play a critical role. Specifically, plants have to strike a delicate balance in order to both reduce the risk of overheating and the risk of freezing.

Just right

The findings help explain why plants in the tropics grow far larger leaves than in any other area of the globe. The banana’s leaf, for instance, is a million times bigger than that of the common heather.

Because it has loads of available water, for all practical purposes in indefinite amounts, the banana leaf can grow to huge sizes. Practically, according to the Australian researchers at the University of Queensland who carried out the research, there’s no limit to how large a leaf can grow if there’s enough water — that’s if only water availability were important.

The real limit is governed by both day time and night time temperature, though.

Since the surface area is greater, large leaves are more vulnerable to freezing at night when the temperature dips. Larger leaves are also thicker, which entails a slower heat exchange with the ambient air.  Likewise, during the daytime, leaves risk overheating if temperatures climb over a threshold.

The researchers learned of this relationship after they plugged a series of equations which predict the maximum viable leaf size anywhere in the world based on the risk of daytime overheating and night-time freezing into a computer model. Their predictions matched the observed data.

The main predictor for leaf size is frost risk

Previously, the textbook theory explained leaf size variability in terms of available water and the risk of overheating. In those places with high rainfall, such as in the tropics, leaves grow larger while small-leaved plants flourish in arid and high altitude environments. However, this explanation does not capture the entire complexity of leaf size variability.

Instead, the authors reported in the journal Science that:

  • daytime temperatures place an upper boundary on leaf size for plants growing in arid environments since optimal transpiration is not possible when water supply is limited;
  • in wet environments, however, its night-time temperatures that constrain leaf growth to achieve effective transpirational cooling;
  • in both wet and warm environments, such as the tropics, there seem to be no thermal constraints. Instead, physical limits likely impose a maximum leaf size.

This neat map put together by the researchers shows that as we move to areas with higher average annual temperatures, average leaf size increases.

lead size map


These findings are very important in today’s climate change context helping scientists better understand how well equipped plants are in the face of an ever warming world. Specifically, scientists ought now to be able to build better models that predict how different types of vegetation may shift in response to climate change.

For Dr Elizabeth Law, a postdoc fellow at UQ School of Biological Sciences and lead author of the study, it’s also about the thrill of contributing to a new ecological theory.

“Not just observing patterns and changes, but really being able to explain why they happen,” she said.

“It’s the first step towards better predictions of the future.”

The prototype for the first practical "artificial leaf," which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

Artificial leaf and bacteria turn sunlight into liquid fuel

Using only energy from the sun, a pioneering artificial leaf system splits water to generate hydrogen – a highly energy dense fuel. When Daniel Nocera, then a professor at MIT, announced his device for the first time four years ago, people were really hyped about it but it soon became clear that making hydrogen was only part of the solution. “The problem with the artificial leaf,” Nocera says, is that “it makes hydrogen. You guys don’t have an infrastructure to use hydrogen.” Why aren’t we seeing more hydrogen cars on the streets? Because there aren’t any hydrogen fueling stations. Why aren’t any hydrogen pumps? Because hydrogen is one bad mother. It’s the smallest stable molecule and it naturally wants to escape into the atmosphere. To contain it you need to compress it to at least 10,000 PSI (more like 100,000 PSI to be sure) which makes it extremely expensive and prohibitive.

Sunlight to liquid fuel

The prototype for the first practical "artificial leaf," which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

The prototype for the first practical “artificial leaf,” which has been hyped in the media since its flashy debut at the American Chemical Society national meeting last year. Image: MIT

Conspiracies aside, diesel and gasoline are here to stay for a long while because they’re so convenient – they’re cheap, readily available and liquid at normal temperature and pressure. Also, while hydrogen  has more energy per unit mass than other fuels, it’s much less dense than other fuels. A gallon of gasoline has a mass of 6.0 pounds, the same gallon of liquid hydrogen only has a mass of 0.567 pounds or only 9.45% of the mass of gasoline.  Therefore one gallon of gasoline yields 125,400 BTUs of energy while a gallon of liquid hydrogen yields only 34,643 BTUs or 27.6% of the energy in a gallon of gasoline. What are we to do with an artificial leaf that makes hydrogen, then? Well, Nocera and his new colleagues at Harvard now report pairing their hydrogen-generating leaf with an engineered bacteria called Ralstonia eutropha to generate biomass and isopropyl alcohol, respectively – an alcohol fuel comparable to ethanol. This way, the extra step converts the hydrogen in a much more manageable fuel. Though, far from efficient right now, the system might become a viable means of storing energy from the sun – still a lifelong engineering problem.

Biofuels like ethanol are made from biomass. We call biomass any biological material derived from living, or recently living organisms – most often than not plants. In nature, plants use photosynthesis to capture CO2 and use it with water in the presence of energy from the sun to make organic compounds of carbons. These are stored and can then be used to generate energy. Sticking with ethanol, this can be broken down from starchy corn kernels. The Harvard system bypasses the biomass step and goes straight to liquid fuel thanks to their engineered bacterium.

The simple setup consists of a  triple-junction solar cell, connected with two catalysts: cobalt-borate for splitting the water molecule and a nickel-molybdenum-zinc alloy to form the hydrogen gas. The bacteria then absorbs the hydrogen, combines it with carbon dioxide, eventually producing the isopropyl alcohol. The resulting system would look like an algae farm, Nocera says, except that the bacteria wouldn’t need the continuous light or maintenance that algae require.

While it all sounds extremely appealing, there are still many challenges that the researchers need to overcome. One has already been met. In initial runs the bacteria kept dying. They eventually identified  reactive oxygen as being the culprit, but what was surprising was its source. Reactive oxygen species were coming out of the hydrogen side of the water splitting, not the oxygen side. “We were shocked,” Nocera said for National Geographic. “That confused us for a while.”

Next, they need to improve the system’s flow such that it might become efficient and make sense economically. Right now, there’s more energy going into growing the microbes and extracting the fuel than going out. Findings appeared in PNAS.

Transverse cross-section of a very thin sunflower leaf (Helianthus annuus) to a thick tea leaf (Camellia sasquana). Along with total leaf thickness and leaf area, the leaves differ dramatically in cell size and in the thickness of cell walls according to specific mathematical equations newly discovered by the UCLA research team. Credit: Lawren Sack, Grace John, Christine Scoffoni/UCLA Life Sciences

Hidden mathematical rules that govern leaf design uncovered

After performing an exhaustive quantitative research across numerous plant species, scientists at  UCLA’s College of Letters and Science  have found that leaf design is governed by a set of fundamental mathematical expressions, underling once again the elegance of nature.

Transverse cross-section of a very thin sunflower leaf (Helianthus annuus) to a thick tea leaf (Camellia sasquana). Along with total leaf thickness and leaf area, the leaves differ dramatically in cell size and in the thickness of cell walls according to specific mathematical equations newly discovered by the UCLA research team.  Credit: Lawren Sack, Grace John, Christine Scoffoni/UCLA Life Sciences

Transverse cross-section of a very thin sunflower leaf (Helianthus annuus) to a thick tea leaf (Camellia sasquana). Along with total leaf thickness and leaf area, the leaves differ dramatically in cell size and in the thickness of cell walls according to specific mathematical equations newly discovered by the UCLA research team.
Credit: Lawren Sack, Grace John, Christine Scoffoni/UCLA Life Sciences

The basis of their research was  “allometric analysis”, that is to say the study of an object’s evolution in size by studying its constituting parts and how they vary in proportionality. While it is easy to observe major differences in leaf surface area among species, they said, differences in leaf thickness are less obvious but equally important. Leaf thickness is actually where the researchers struck gold.

“Once you start rubbing leaves between your fingers, you can feel that some leaves are floppy and thin, while others are rigid and thick,” said Grace John, a UCLA doctoral student in ecology and evolutionary biology and lead author of the research. “We started with the simplest questions — but ones that had never been answered clearly — such as whether leaves that are thicker or larger in area are constructed of different sizes or types of cells.”

A leaf is made out of three distinct parts: the outer layer that makes the leaf surface also called an epidermis, the  mesophyll which is comprised of photosynthesis capable cells and vascular tissue, whose cells are involved in water and sugar transport. The team found, after cutting cross-sections thinner than a single cell to observe each leaf’s microscopic layout, that the thicker the leaf, the larger the size of the cells in all of its tissues — except in the vascular tissue.

These relationships can be described by new, simple mathematical equations, effectively allowing scientists to predict the dimension of cells and cell walls based on the thickness of a leaf.

“This means that if a leaf has a larger cell in one tissue, it has a larger cell in another tissue, in direct proportion, as if you blew up the leaf and all its cells using Photoshop,” said Christine Scoffoni, a doctoral student at UCLA and member of the research team.

The new ability to predict the internal anatomy of leaves from their thickness can give clues to the function of the leaf, because leaf thickness affects both the overall photosynthetic rate and the lifespan, said Sack.

“A minor difference in thickness tells us more about the layout inside the leaf than a much more dramatic difference in leaf area,” John said.

The design of the leaf provides insights into how larger structures can be constructed without losing function or stability.

“Fundamental discoveries like these highlight the elegant solutions evolved by natural systems,” Sack said. “Plant anatomy often has been perceived as boring. Quantitative discoveries like these prove how exciting this science can be. We need to start re-establishing skill sets in this type of fundamental science to extract practical lessons from the mysteries of nature.

“There are so many properties of leaves we cannot yet imitate synthetically,” he added. “Leaves are providing us with the blueprints for bigger, better things. We just have to look close enough to read them.”
The study’s findings, which were published in the journal Botany, are o great worth since they provide key insights into how leaf design works at a cellular level. Insights such as these might cross biology and enter biotech, since we’re already seeing things like solar cells inspired by leaf biology, for instance.
“What makes the cross-sections especially exciting is the huge variation from one species to the next,” John said. “Some have relatively enormous cells in certain tissues, and cell shapes vary from cylindrical to star-shaped. Each species is beautiful in its distinctiveness. All of this variation needs decoding.”

Ants use bacteria to grow gardens

leafAnts are most amazing creatures, and there’s so much we could learn from them I wouldn’t even know where to start. As it is, we’ve just started to scratch the surface of what we know about ants, and strangely enouch, researchers are discovering more and more things human and ant societies have in common.

Leaf cutter ants are one of the most remarkable ant species, and scientists have recently found a new quality (or ‘skill’, if you wish) to add to their inventory: they use nitrogen-fixing bacteria to make their gardens grow. You know who else does something similar? Humans.

The finding was reported on 20 November in Science by bacteriologist Cameron Currie from the University of Wisconsin-Madison and analyzes a previously unknown very interesting symbiosis between ants and bacteria, providing a totally new insight on leaf cutter ants and how they managed to be the dominant ant species in the American tropics and subtropics.

“Nitrogen is a limiting resource,” says Garret Suen, a UW-Madison postdoctoral fellow and a co-author of the new study. “If you don’t have it, you can’t survive.”

Indeed, this ‘business relationship’ allows the ants to be impressively successful, while the bacteria thrives too.

“This is the first indication of bacterial garden symbionts in the fungus-growing ant system,” says Currie, a UW-Madison professor of bacteriology.


The fungus growing ants are technically herbivores, but without the bacteria, there is absolutely no way they could get the necessary nutrients.

“Without nitrogen, there is no way these guys could achieve such large colony sizes. These ants are one of the most dominant insects in the Neotropics. The ability to have colonies with millions of ants is predicted to require a tremendous amount of nitrogen.”

So how do they do it ? The gardens in question are initially sowed by the ants, which bring leaf pieces into their underground nests. From the leaf, a fungus called Leucoagaricus gongylophorus starts growing – which was traditionally viewed as the ants’ food, ever since 1890s research; only recently did researchers start taking into consideration the more complex interactions between the fungus, the bacteria and ants.

But things get even more complicated from here on – genetic analysis of proteins found in bacteria revealed even more complex interactions.

“Our results show that calling these ‘fungal gardens’ is pretty misleading; ‘fungus-bacterial communities’ would be far more accurate,” said Kristin Burnum, a bioanalytical chemist at the Department of Energy’s Pacific Northwest National Laboratory. . “Bacteria are not only integral residents of these communities, but they perform essential tasks that keep the communities — and the ants that help cultivate them — living.”


Researchers hope that understanding how this (sort of) symbiosis works can not only boost our understanding of complex ant societies and biological mechanism, but also lead to more effective development of biofuels.