It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Thursday, August 13, 2020
Scientists Identify Successful and Cost-Effective Ways to Restore Coral Reefs
Written by AZoCleantechAug 13 2020
The most successful and cost-effective ways to restore coral reefs have been identified by an international group of scientists, after analysing restoration projects in Latin America.
The University of Queensland's Dr Elisa Bayraktarov led the team that investigated 12 coral reef restoration case studies in five countries.
"Coral reefs worldwide are degrading due to climate change, overfishing, pollution, coastal development, coral bleaching and diseases," Dr Bayraktarov said.
"Coral reef restoration - or rebuilding what we have lost - may become critical, especially for coral species that are threatened with extinction.
"Much of this work is led by environmental non-Government organisations (ENGOs), tourism operators, community groups, national resource management groups and governments who rarely publish their great depth of knowledge.
"So we decided to bridge the gap between academia, ENGOs and other groups that restore coral reefs."
The researchers analysed the motivations and techniques used for each project, providing estimates on total annual project cost per unit area of reef restored, project duration and the spatial extent of interventions.
The team found the most successful projects had high coral survival rates or an increase in coral cover, but that they also offered socioeconomic benefits for their surrounding communities.
"Projects that train local fishermen or recreational divers to participate in restoration, or engage with dive operators or hotels to support the maintenance of the coral nurseries, were much more effective and long-lived," Dr Bayraktarov said.
"We also found that coral reef restoration efforts in Latin American countries and territories were cheaper than previously thought - with the median cost of a project around US$93,000 (~AUD$130,000) to restore one hectare of coral reef.
A one-year-old coral "The projects also had run for much longer than assumed, with some active for up to 17 years.
"And best of all, an analysis of all the studied projects revealed a high likelihood of overall project success of 70 per cent."
Co-author Dr Phanor Montoya-Maya, director and founder of the Colombian-based organisation Corales de Paz, said he was excited about the project's collaborative nature.
"Twenty-five Latin-American coral reef restoration scientists and practitioners from 17 institutions in five countries worked on this research," he said.
"We wanted to showcase the efforts of Spanish-speaking countries that depend on their local coral reefs to the global coral reef restoration community.
"And to share the diversity of objectives, techniques, tools used, and methods to measure success in Latin America to encourage others to carry out similar work.
"We're providing critical project information - such as total annual project cost per unit area of reef restored, spatial extent of restored site and duration - on how to best save our degraded reefs.
"Collaboration and communication is helping make their futures brighter."
The research has been published in PLOS One (DOI: 10.1371/journal.pone.0228477). See a full list of supporting organisations.
HumanCAPITALIST Influence Identified as Key Agent of Future Ocean Warming Patterns
Written by AZoCleantechAug 13 2020
The oceans play an important role in regulating our climate and its change by absorbing heat and carbon.
The implications of their results, published today in Nature, are significant because regional sea level, affecting coastal populations around the world, depends on patterns of ocean warming. In this study they show how these patterns are likely to change.
The results imply widespread ocean warming and sea level rise, compared to the past, including increased warming near the Eastern edges of ocean basins leading to more sea level rise along the Western coastlines of continents in the North Atlantic and Pacific Oceans.
Co-author, Laure Zanna, Visiting Professor in Climate Physics at Oxford University and Professor in the Center of Atmosphere Ocean Science at NYU Courant, said: 'In the future, the imprint of rising atmospheric temperatures on ocean warming will likely dominate that of changes in ocean circulation. Initially, we might think that as the climate warms more, changes in ocean currents and their impact on ocean warming patterns will become larger. However, we show that that this is not the case in several regions of the ocean.'
A new method, developed by scientists at Oxford University, uses climate models to suggest that ocean warming patterns will increasingly be influenced by simple uptake of atmospheric warming - making them easier to predict. This is in contrast to now and the past when circulation changes were key factors in shaping ocean warming patterns.
Changes in ocean warming due to the simple uptake of atmospheric warming are easier to model and so the scientists hope that where previous models have struggled, they might become more accurate for future projections.
Lead author, Dr Ben Bronselaer, who began conducting this research while a PhD student at Oxford University, said: 'I think it is an encouraging possibility that climate models, which struggle to simulate past ocean warming, might be better at predicting future warming patterns. Better prediction of warming patterns implies better prediction of regional sea level rise, which will help to mitigate climate impacts such as flooding on individual communities. Of course, we do need to understand predictions of ocean circulation better to solidify this result.
'During our research, we found a surprising relationship between ocean heat and carbon storage which appears to be unique. While there is a connection between these two quantities that is not yet fully understood, we think we have made significant progress towards uncovering it.'
The Nature study shows that the global ocean heat and carbon uptake go hand-in-hand, and the uptake rates are set by the present state of the ocean. This relationship is at the core of the method developed in this study. As humans change the ocean state by adding more heat and carbon, the ability of the ocean to take up both heat and carbon will be altered. A possible implication could be that the later emissions are reduced, the slower the reductions in atmospheric surface temperature are likely to be, due to the coupling between heat and carbon uptake by the ocean.
These results highlight a deep and fundamental connection between ocean and carbon uptake, which has implications for atmospheric heat and carbon. While ocean carbon and heat are separate systems, this study shows that they are deeply interconnected, via the capacity of the ocean to absorb these quantities. These results help explain why atmospheric warming depends linearly on cumulative carbon emissions.
Prof Laure Zanna said: 'We find that the ocean's capacity to absorb heat and carbon are coupled, and constrained by the ocean state. This implies that the present ocean state will regulate surface warming whether CO2 emissions continue to rise or decline.
'The rates of ocean warming over the past 60 years have been significantly altered by changes in ocean circulation, particularly in the North Atlantic and parts of the Pacific Ocean, where we can identify cooling over some decades. However, in the future changes in ocean currents appear to play a smaller role on patterns of ocean warming, and the oceans will transport the excess anthropogenic heat in the ocean in a rather passive manner in these regions.'
The modelling in this study relied on a set of creative simulations done by colleagues at The Geophysical Fluid Dynamics Laboratory (GFDL), and other published work. Using these simulations, the scientists were able to draw hypotheses on how the patterns of heat and carbon are related and how they differ.
Building on this research, the scientists will now attempt to understand how the storage of heat and carbon in the ocean will affect the decline of atmospheric temperature and CO2 levels if carbon emissions start going down.
They will also use the component of ocean warming that is driven by circulation changes to better understand ocean circulation changes, which are difficult to measure directly, and their impact on regional sea level in the Tropics.
A study of five different seafoods has found traces of plastic in every sample tested.
Researchers bought oysters, prawns, squid, crabs and sardines from a market in Australia and analysed them using a newly developed method that identifies and measures five different plastic types simultaneously.
The study - by the University of Exeter and the University of Queensland - found plastic levels of 0.04 milligrams (mg) per gram of tissue in squid, 0.07 mg in prawns, 0.1 mg in oysters, 0.3 mg in crabs and 2.9 mg in sardines.
"Considering an average serving, a seafood eater could be exposed to approximately 0.7 mg of plastic when ingesting an average serving of oysters or squid, and up to 30 mg of plastic when eating sardines, respectively," said lead author Francisca Ribeiro, a QUEX Institute PhD student.
"For comparison, 30 mg is the average weight of a grain of rice.
"Our findings show that the amount of plastics present varies greatly among species, and differs between individuals of the same species.
"From the seafood species tested, sardines had the highest plastic content, which was a surprising result."
Co-author Professor Tamara Galloway, of Exeter's Global Systems Institute, said: "We do not fully understand the risks to human health of ingesting plastic, but this new method will make it easier for us to find out."
The researchers bought raw seafood - five wild blue crabs, ten oysters, ten farmed tiger prawns, ten wild squid and ten wild sardines.
They then analysed them for the five different kinds of plastics that can be identified by the new method.
All of the plastics are commonly used in plastic packaging and synthetic textiles and are frequently found in marine litter: polystyrene, polyethylene, polyvinyl chloride, polypropylene and poly(methyl methacrylate).
In the new method, edible tissues are treated with chemicals to dissolve the plastics present in the samples. The resulting solution is analysed using a highly sensitive technique called Pyrolysis Gas Chromatography Mass Spectrometry which can identify the different kinds of plastic in the sample at the same time.
Polyvinyl chloride was found in all samples, while the plastic found in highest concentrations was polyethylene.
Microplastics are very small pieces of plastic that pollute much of the planet, including the sea where they are eaten by marine creatures of all types, from small larvae and planktonic organisms to large mammals.
Studies to date show that microplastics not only enter our diet from seafood, but also from bottled water, sea salt, beer and honey, as well the dust that settles on our meals.
The new testing method is a step towards defining what microplastic levels can be considered harmful and assessing the possible risks of ingesting microplastics in food.
The paper, published in the journal Environmental Science & Technology, is entitled: "Quantitative Analysis of Selected Plastics in High-Commercial-Value Australian Seafood by Pyrolysis Gas Chromatography Mass Spectrometry."
High Concentrations of Microplastics can Impact the Marine Food Web
Written by AZoCleantechAug 12 2020
Tinyplastic particles measure around 0.1 mm in length, the same size as that of phytoplankton, which happens to be the favorite food of the copepods.
Image Credit: DTU Aqua.
Scientists from the DTU Aqua, DTU Environment, Aalborg University, and the Greenland Institute of Natural Resources detected such microplastics in water sampled from the fjord Nuup Kangerlua (or Godthåbsfjorden), running beyond Nuuk and further into the sea west of Greenland.
The researchers discovered around 1 particle for each 10 L of water, the concentration of which was similar to the one previously detected in seawater elsewhere in the North Atlantic.
However, the team had anticipated finding relatively higher concentrations, because German scientists have quantified extremely high concentrations of microplastics in ice and snow on the glaciers that are melting into Nuup Kangerlua.
The study results were recently published in Environmental Pollution—a scientific journal.
There’s plastic in the fjord. Not as much as we would have expected based on the concentrations found by the Germans in snow and ice. But it’s there. And the plastic particles are generally very small. They are exactly of a size that the copepods in the area can eat, which means they can enter the marine food webs that way.
Torkel Gissel Nielsen, Professor, DTU Aqua
Nielsen emphasizes that plastic concentrations that have been detected so far may not have considerable adverse impacts. However, if these concentrations become relatively worse, this may lead be a serious problem.
We can also see that there are 10,000 times as many phytoplankton in the water as there is plastic. So assuming that the copepods eat whatever they come across and given the abundance of food available to them, they are unlikely to end up ingesting too many plastic particles at all. And so the risk of the MPs entering the marine food webs and being distributed around is infinitely small.
The research team from the VELUX project, called MarinePlastic, obtained samples from five locations along Nuup Kangerlua. They employed uniquely designed pumps featuring filters that can collect even the smallest microplastics.
However, for comparative reasons, the team also used conventional Bongo nets to collect samples. Such Bongo nets can collect a thousand times fewer microplastics when compared to the pumps. The nets only trapped microplastics that measured above 300 μm.
Nielsen added, “Using pumps like we’ve done in this case, you’ll find far higher concentrations of very small MPs—which is what is most bio-available and potentially able to enter the marine food webs via copepods.”
Nuuk is a Point Source of Plastic
The research vessel cruised from inside the fjord, wherein the glacier water runs into the fjord, beyond Nuuk, and finally reaches the mouth of the fjord. In five locations, along the route, samples were gathered, and the highest concentration of microplastics was detected around Nuuk and also further out towards the sea.
Nuuk is the largest city in Greenland and has around 18,000 inhabitants. However, it lacks effective sewage treatment plants.
Polyester, the most abundant kind of plastic, is utilized, for instance, in plastic bottles and synthetic fabrics. Nylon or polyamide is the second-most abundant type of plastic and is used in fishing nets, for instance.
We also found that MP concentrations were roughly comparable with concentrations previously found in the North Atlantic, about 1 particle per 10 litres of water. And Nuuk was identified as a point source. Compared to the measuring stations further into the fjord, MP abundance—and especially the smallest size fractions of MPs—increased close to Nuuk.
Torkel Gissel Nielsen, Professor, DTU Aqua
Journal Reference:
Rist, S., et al. (2020) Quantification of plankton-sized microplastics in a productive coastal Arctic marine ecosystem. Environmental Pollution. doi.org/10.1016/j.envpol.2020.115248.
Warming Climate in Tropical Forests Could Increase Harmful Emissions of Soil Carbon
Written by AZoCleantechAug 13 2020
Billions of tonnes of carbon dioxide risk being lost into the atmosphere due to tropical forest soils being significantly more sensitive to climate change than previously thought.
Carbon emissions from soils in tropical forests - which store one quarter of the world's soil carbon - could increase dramatically if temperatures continue to rise in line with current predictions, researchers say.
A new experiment conducted in Panama suggests these harmful emissions of soil carbon could rise by 55 per cent if the climate warms by four degrees Celsius.
Carbon dioxide is released naturally by soils through decomposition and plant root activity. However, the release of so much extra carbon dioxide - which the study found was coming from increased decomposition of soil organic matter - could trigger further global warming.
Previous research has shown that rising temperatures threaten to release carbon locked away in cooler or frozen soils - such as in the Arctic tundra. Until now, tropical soils were thought to be less sensitive to the effects of climate warming.
A team led by researchers from the University of Edinburgh conducted a large-scale experiment in a tropical forest on Barro Colorado Island in the Panama Canal.
They built heating devices and buried them one metre into the forest soil. Over a two-year period the equipment - fitted with heating cables and a thermostat - kept the experimental areas four degrees warmer than the surrounding soil.
The findings show that as much as an extra eight tonnes of soil carbon could be released as carbon dioxide from every hectare of tropical forest each year at the higher temperatures.
Researchers expect the rate of emissions will eventually decline in the experimentally warmed soils, but they do not yet know how long this will take, or the long-term impact of soil warming on climate change.
They will continue the experiment - known as the Soil Warming Experiment in Lowland Tropical Rainforest, or SWELTR - to better understand how tropical forests respond to a warming world.
The study, published in the journal Nature, also involved researchers from the Smithsonian Tropical Research Institute (STRI) in Panama and the Australian National University (ANU). It was funded by the European Union and the Natural Environment Research Council, the Smithsonian Institution and STRI, and ANU-Biology.
Dr Andrew Nottingham, of the University of Edinburgh's School of GeoSciences, who led the study, said: "The results demonstrate the high sensitivity of these ecosystems to warming. It should be a wake-up call for us to take action to mitigate climate change and preserve tropical forests, which are one of the most important components in Earth's carbon cycle."
Study co-author Professor Patrick Meir, also of the School of GeoSciences at Edinburgh and the Australian National University, said: "The high carbon emissions from warmed tropical forest soil differ from expectations, and indicate a need to re-examine current predictions".
Social protection programs can facilitate progress towards the Sustainable Development Goals (SDGs) but can also create trade-offs across divergent social and environmental goals that can undermine their effectiveness, say the authors of new research published in the journal PNAS. This is one of the largest studies on the sustainability implications of social protection, funded by the Grantham Centre for Sustainable Futures at The University of Sheffield .
Focusing on Brazil's flagship Zero Hunger (ZH) social protection scheme, designed to alleviate food insecurity and hunger through cash transfers and agricultural support, the study highlights the importance of considering the social and environmental outcomes of development policies. The authors used data spanning 13 years (2000-2013) and covering around 4,000 rural municipalities in Brazil. Their results draw out implications for Brazil's progress towards the SDGs, specifically: no poverty (SDG 1), zero hunger (SDG 2), good health and wellbeing (SDG 3) and life on land (SDG 15).
The ZH program was implemented in 2004 with the primary target beneficiaries being small-scale family farmers with the goal of lifting 44 million Brazilians out of poverty and food insecurity. This is a globally important group with 12% of the world's agricultural land managed by some 475 million smallholders. The programme has been praised for playing a key role in enabling Brazil to meet its Millennium Development Goals in 2015.
The study found that successful elements of the ZH program include evidence of an increase in food production (SDG 2) and slightly reduced poverty (SDG 1). However, this can be contrasted with more variable outcomes in food security dimensions across regions, depending on whether cash transfer or agricultural support were used. In addition, they were widespread trade-offs with other sustainable development goals, notably environmental protection (SDG 15).
Dr. Cecilie Dyngeland (who conducted the research as part of her PhD at the University of Sheffield) said:
"Alleviating poverty is essential, but we rarely think about the unintended environmental consequences of poverty alleviation policies. A key strength of our analysis is that it allows us to understand how policies affect multiple social and environmental outcomes simultaneously."
Despite these evident shortcomings, the authors suggest there are ways to balance human development with environmental integrity.
Dr. Johan Oldekop (at the Global Development Institute, University of Manchester) said:
"We find that the same programme can lead to contrasting outcomes in different regions of Brazil. It is critical for us to understand what processes have enabled joint positive social and environmental outcomes, in order to learn from these synergies and develop incentives that avoid trade-offs."
The research team's analysis of the ZH programme provides insights on how to achieve multiple sustainability outcomes whilst being directly relevant to the design and implementation of social protection mechanisms around the world. This is particularly salient in Africa, where social protection programs based on ZH currently operate in several countries. The research compared two different types of protection programmes and found that cash transfers were less likely than agricultural support to generate synergies across development and environmental objectives.
As Dr Karl Evans (from the Animal and Plant Science Department at the University of Sheffield) added,
"This research demonstrates that development policies can enhance or degrade the natural environments which are vital for the well-being and livelihoods of many vulnerable people. Development policies need to focus on strategies that enhance rather than degrade this capacity. Linking social protection to environmental conditionalities is one potential mechanism to achieve poverty alleviation without degrading the natural environment."
Governments, international donors and financial organisations are making large investments in social protection to mitigate the economic impacts of the COVID-19 pandemic. For social protection programmes to continue to contribute to progress on multiple development objectives, their trade-offs and synergies will need to be at the front and centre of the design and implementation of poverty alleviation strategies moving forward.
To ensure robust policy impact evaluation, the measurement of intended and unintended sustainable development outcomes of initiatives needs to become the norm.
By the end of 2020, it is estimated that 102,000 tons of Li-ion batteries will be retired from EVs annually, rising to 7.8 million tons by 2040. This exponential growth means that consideration must be given to what to do with the retired batteries.
Electric vehicles are becoming increasingly common on the roads worldwide, and their presence is only likely to grow. As a result, there is increased demand for lithium-ion (Li-ion) batteries that power them. But as the first wave of such batteries near the end of their life, there is the question of what to do with the most expensive component of an electric vehicle; should they be repurposed or recycled?
Powering an Electric Vehicle
Electric vehicles (EV) are powered in one of two ways: they are either a battery electric vehicle (BEV), powered solely by a battery, or a plug-in hybrid electric vehicle (PHEV), which combines a gasoline or diesel engine with an electric motor and large rechargeable battery.
Li-ion batteries function for around eight to 10 years and can no longer satisfy the power requirements of an EV, i.e., the loss of capacity limits the vehicle’s driving range. Recycling End-of-Life Electric Vehicle Batteries
The default option is to recycle batteries to extract their raw materials – particularly cobalt - for reuse.
Electric vehicle and clean energy company Tesla claims all its batteries will be directly recycled. The global Li-ion battery recycling market will be worth an estimated $31 billion annually by 2040.
Recycling is a crucial solution to ensuring raw material supply security. Recovering metals such as lithium, cobalt, nickel, manganese, copper and aluminum offer manufacturers protection from supply disruption and a way to avoid price fluctuations while generating additional revenue streams. It is, however, necessary to extract large volumes of high-quality materials to make the process worthwhile.
In many countries, extended producer responsibility (EPR) means OEMs are responsible for retired batteries. This can simplify the recycling process, providing a specific collection network where professionals handle EV batteries. This system is an essential factor in how efficient the process will be - a low volume of cells or high collection costs could damage the economy of recycling.
In theory, recycling is the least sustainable measure in a circular economy and should be a last resort when the battery cannot be utilized further. In practice, it is not simple. The recycling value chain must be considered from a lifecycle perspective – from mining and processing to battery materials and production, battery usage to recycling, or reuse and recycling in some cases.
Lithium iron phosphate (LFP) is a popular battery chemistry employed by Chinese EV manufacturers in particular. Such batteries have a low recycling value as they contain few very high-value metals. In this instance, giving the batteries a second life is a more attractive option, as they have a better lifecycle and safety performance than other batteries. This is crucial if being repurposed for stationary energy storage.
Although all batteries will need to be recycled at some point, the variety of designs and high voltage of EV battery packs means safe disassembly can be complicated and time-consuming. Furthermore, most recycling capacity is in China, although there is increasing interest from other countries.
Repurposing Electric Vehicles Batteries
Unlike those used in consumer electronics, when an EV battery reaches the end of its useful life in vehicle service, it still retains between 70 and 80% of its original capacity. This means they could have a second life in a less-demanding application before they are ultimately recycled.
Manufacturers such as Nissan, Renault, BMW and Volkswagen are enthusiastically exploring scenarios in which retired batteries are utilized in applications ranging from residential to commercial and grid-scale energy storage.
Second-life batteries represent a considerable value opportunity across both the automotive industry and energy storage sector. The potential value of these batteries is impacted by their design and use in their previous life, how they are collected and utilized in their second life application, in addition to their recycling value.
Many technological, economic and regulatory challenges have been identified, and companies are developing means of improving the value of a second-life battery. Technologically speaking, repurposing an EV for another use will not affect its recycling – it will just delay the process, while potentially causing a knock-on effect on the logistics and economics of recycling.
Many batteries are now reaching the end of their useful life as a power source for EVs, and their number is only going to increase as the presence of these vehicles increases.
The decision to recycle or repurpose depends on the value of the battery pack itself. LFP batteries have a low precious metal value, so they are best repurposed, while those with high proportions of metals such as cobalt might be best recycled.
Regardless of whether or not they have been given a second life after they have served their useful purpose in an electric vehicle, EV batteries ultimately face the same destiny – to be recycled.
Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.
Written by Kerry Taylor-Smith Kerry has been a freelance writer, editor, and proofreader since 2016, specializing in science and health-related subjects. She has a degree in Natural Sciences at the University of Bath and is based in the UK.
SARS-CoV-2 droplets travel further and last longer than thought, and even more in humid air
The ongoing COVID-19 pandemic is spread by respiratory aerosols, in which tiny droplets of saliva and mucus containing the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are expelled from the upper respiratory tract. Though quite a few studies have investigated the viral load of such droplets, not much is known about how far these droplets move or how long they linger in the air, even though such information is crucial to determining how infectious they are.
Now, a new study by researchers at the University of Twente and University of Rome Tor Vergata and published on the preprint server medRxiv* in August 2020 shows that earlier assumptions about these droplets were wrong. In fact, under 50% relative humidity, the smallest droplets survive 50 times longer, and at 90% relative humidity, up to 150 times longer. In other words, the two-meter or six-foot social distancing rule is grossly inadequate, given the actual advective range of the droplets within one second. And the range, as well as lifetime of the droplet, only increases with smaller droplet size. Visualisations of droplets in a heavy cough for RH = 50%: a-d, Snapshots of the droplet-laden cough simulation. At time t = 100 ms, the cough contains hot air with high moisture content. The hot moist air propagates (t ~ 200 ms) and dissipates (t ~ 400 ms) into the ambient surroundings. At t ~ 400 ms, we show larger droplets falling out from the puff whereas smaller droplets remain protected and are carried along by the puff. Preventing Respiratory Transmission
The current rules of social distancing originated with a 1919 paper dealing with the Spanish flu of that time. This, in turn, was based on a theory of droplet transmission of viruses developed by William F. Wells in connection with the spread of tuberculosis. He thought that the wide range of particles produced by a cough or sneeze in a tuberculosis patient would determine the behavior of the droplets. Small droplets would rapidly evaporate and leave behind less infectious dried aerosol particles with lower transmission risk. Larger droplets would be like bullets. In the current study, droplets measuring over 5-10 micrometers are called respiratory droplets and can cause host-to-host spread. Small droplets, or respiratory droplets, transfer the virus through aerosols.
Despite the age of this principle, the evidence is building that it is faulty. Not only has viral spread continued to take place, especially with superspreaders, but the droplets are known to last longer and spread farther than a few seconds and two meters – namely, up to 8 meters and for up to 10 minutes, respectively. This is because droplets are typically expelled as a cloud, within warm and humid air, which delays their drying out and prolongs their infectious period. In fact, droplet lifetime is dependent on the mixing process within this turbulent air, while the earlier drying behavior is that of a single droplet. Airborne transmission
This change in fundamental assumptions is supported by empirical studies, medical knowledge, and physics – "long-distance airborne transmission through multiphase turbulent droplet cloud emission is an essential factor." Some researchers have shown that very infectious patients may spread the virus in their aerosols over large distances. In fact, the results of such spread may be even more severe disease due to the tiny droplets of the aerosol, which leads to their entry deep into the lungs. Lifetime ratio for 10 µm and 20 µm droplets: a, Extended lifetime as a function of relative humidity up to RH = 90%. The curves in the figure are fitted according to the function y = a1/(1 − x) + a2, where a1 and a2 are the fitting parameters. Visualisations of humid puff for ambient RH = 50% and 90% at time 600 ms: b, The humid puff maintains coherence for longer time and at much longer distances for larger ambient RH. Note the different humidity color scales for two shown cases. Humidity and Infectiousness
The current study deals not only with the accumulating nature of aerosols, which remains infectious indoors over hours but also with the little-understood contribution of humidity. Because of the immense difficulty in tracing the movement of thousands of tiny droplets in space and over time, while simultaneously keeping track of or adjusting the conditions such as flow rate, distribution width of the droplets, temperature and relative humidity, the researchers chose to use numerical simulations instead. Assessing Small Scale Droplet Physics
They tweaked existing methods to ensure that the small scale of the droplet mixing process, as well as the coupling of temperature and humidity, which are so essential to the evaporation of the droplets and thus their lifetime and effects, are properly captured. This involved the development of a very efficient numerical tool that will be of use in revealing the flow physics of an event occurring with breathing, and also what decides the enormous enhancement of the lifetime of a respiratory droplet relative to considering the droplet isolated from its surrounding puff velocity, temperature, and humidity. This tool can also be used to simulate more complicated respiratory events, especially those which take place indoors.
The conditions of the experiment included a duration of 0.6 seconds, simulating a turbulent puff of air into ambient air, full of 5,000 droplets of water, as well as hot air saturated with vapor, in order to replicate a strong cough. The initial temperature was 34 oC. The temperature of the ambient air was set at 20oC, with the relative humidity between 50% and 90%. The heat and vapor in the turbulent puff are exchanged to the ambient air. The researchers tracked the droplets for several seconds to understand the physics underlying their evaporation en masse.
Fall Pattern of Large and Small Particles
The first result at a RH of 50% is the falling out of larger droplets over 100 μm in diameter, in a ballistic manner, because of their weight compared to the airflow, at 0.1 m to 0.7 m from the source. These evaporate faster, compromising the survival of the infectious particles. This agrees with the earliest predictions (Wells, 1930), and the current social distancing guidelines by the World Health Organization (WHO), Center for Disease Prevention and Control (CDC) and the European Centre for Disease Prevention and Control (ECDC).
When smaller than this, however, the droplets form spirals tracing a mostly horizontal path, which means they also promote airborne rather than droplet transmission – unlike the current WHO hypothesis. This is due to their slower settling speed compared to the velocity of the fluid in which they are carried, which means further advection by the turbulent airstream. This latter is essential in airborne transmission of infection.
This small droplet behavior means they have much higher lifetimes than isolated droplets. In fact, 10 μm droplets at RH 50% and 90% have 60 to 200 times the survival times of the Wells value. These move slower related to the fluid flow, and so shrink less due to reduced convection and evaporation.
With successive coughs, therefore, the puff may reach over 2 m from the source at the leading edge, with most of the smaller droplets being in humid surroundings and thus living longer.
Implications and Recommendations
Thus, the study shows that the humidity field around the droplet plus the turbulent velocity, and not just the droplet diameter, determines the respiratory droplet lifetime. This boosts their lifetime by orders of magnitude. The ambient RH further extends the lifetime, and the researchers comment, "This finding may explain why many COVID-19 superspreading events have been reported in indoor environments with large ambient relative humidity." They quote the high spread in meat-processing plants with cooled air, which increases the indoor RH immensely.
This means that aerosol and droplet concentration must be controlled indoors, especially in the coming fall and winter. Again, older medical experts like Soper (1919) are proved right with their claim, originally pertaining to the Spanish flu pandemic of those years, that "there is danger in the air in which they cough and sneeze." Even further, according to the current study, "we must also add "speak," "sing," scream," and even "breath." In fact, Soper recommended open windows at home and work, and masks for suspected patients – an excellent protocol for today at well.
The current study thus confirms and explains Soper's mitigation strategies for use in controlling COVID-19 transmission. The researchers say face masks block respiratory droplets indoors, and some may even reduce the inhalation of these droplets, an essential role for healthcare workers in the pandemic.
Excellent ventilation is equally important to ensure the infectious puff advects out of the room or becomes rapidly and highly diluted. A possible unfavorable effect of this is that good ventilation may increase the length of the propagation path of the droplets, and these two effects of ventilation on transmission properties must be investigated in parallel.
Finally, a lower ambient RH will help speed up the evaporation of the droplets and aerosols, reducing infectivity by decreasing the lifetime of infectious particles and aerosols.
The study sums up, "Our results help to understand why these various mitigation strategies against COVID-19 are successful…. Our present tool and approach will be a starting point for larger parameter studies and for further optimizing mitigation strategies ." *Important Notice
medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information. Journal reference:
Dr. Liji Thomas is an OB-GYN, who graduated from the Government Medical College, University of Calicut, Kerala, in 2001. Liji practiced as a full-time consultant in obstetrics/gynecology in a private hospital for a few years following her graduation. She has counseled hundreds of patients facing issues from pregnancy-related problems and infertility, and has been in charge of over 2,000 deliveries, striving always to achieve a normal delivery rather than operative.
