In the last two years, we’ve all been keenly aware of anyone who coughs or sneezes next to us, and that the air we breathe may contain dangerous viruses we need to protect ourselves from. Yet, apart from COVID-19 which took the world by storm, there are countless microscopic creatures of various kinds in the air around us, and many cause diseases in humans or plants.
A new study using an innovative method published by researchers from Singapore, Brazil and Germany revealed the composition of microorganisms in the air column. The researchers concluded from the study data and previous information that as global temperatures continue to rise due to global warming, various disease agents will multiply and spread around the world to areas where they aren’t present now, and may threaten our health and ability to grow food.
Like water, soil, as well as intestines of humans and other animals, the air is also an environment where a variety of microorganisms live, microscopic creatures like bacteria, viruses and fungi.
"When bread is left on the counter in the kitchen, it will be covered in mold within a few days," says Prof. Yoav Yair, dean of the School of Sustainability at Reichman University. "Where did the spores that caused it come from? Well, they're in the air all the time. We all breathe air that has huge amounts of particles in it."
Prof Stefan Schuster, one of the lead researchers of the new study, discovered that Singapore residents breathe between 100,000 and a million microorganisms from about 725 different species every day, most of which aren’t harmful. "It can be assumed that in Israel these are similar numbers," says Yair.
The largest concentration of microorganisms in the air is close to the ground in the "boundary layer" section of the atmosphere. "This is the lowest layer of the atmosphere, the one that comes in contact with the ground and the sea surface and there is an exchange of energy and substances on the largest scale," Yair explains.
This isn’t a "permanent" layer, but its dimensions vary according to various factors. Yair states that at certain hours of severe air pollution incidents, it’s easy to identify the boundary layer. "When you travel in the morning from Jerusalem to Tel Aviv and see a kind of brown soup over Gush Dan, this is the border layer."
Warmer, higher, farther away
In the new study published in the scientific journal PNAS, researchers used a 200-meter-high tower with meteorological measurements including humidity, wind speed, temperature and solar radiation and a research aircraft equipped with 38 sampling systems that sampled air at various heights from the ground at 3500 meters at different times of the day including microorganisms. Next, they analyzed the amount and type of DNA that each sample contained, and drew according to the samples on a vertical map (i.e., divided by height) with a high resolution of the microorganisms' presence at different heights during the day.
In fact, researchers have been trying to figure out how height affects bacteria and viruses before they fall back to the ground. The importance of this measurement lies in the fact that the higher a particular microorganism is, the greater the chance that it will land in a place farther from its starting point.
"A basic fact in meteorology is that the wind speed increases as you move away from the surface because the air close to the ground meets it and diffuses the energy," Yair explains. "So, if the boundary layer reaches higher, the particles in it can move for longer ranges."
Researchers found that temperature is the only environmental factor that’s significant in determining the peak altitude that microorganisms reach in the air during the day. The explanation is simple to understand when one remembers the simple principle that heat rises. During the day, heat from the sun is absorbed by the surface of the earth, heats the air above the ground and produces a certain spread and mixing of the boundary layer in the atmosphere above that.
"Normally, there are mixing processes in the atmosphere, from the molecular level to the scale of clouds," Yair explains. "As surface heating increases, the boundary layer rises, and with it comes pollution, dust and bacteria."
Increased risk of spreading diseases
Based on the findings, scientists warn that in a warmer atmosphere, a result of rising global temperatures due to the climate crisis increases the risk of disease to humans and plants in large areas where they didn’t previously exist. Beyond that, various studies suggest that rising global temperatures are allowing disease agents to survive in areas that were previously too cold for them. These harmful effects can be seen around the world today.
"Malaria, for example, is sensitive to low temperatures and today it’s spreading to more northern latitudes because the temperature is rising," says Yair. "A similar phenomenon is seen with different species of harmful insects worldwide."
Rising temperatures are one way the climate crisis may lead to rising morbidity. Another way due to the changing climate, which Yair researched together with other scientists, is the phenomenon of "lightning storm asthma.”
"During lightning storms, the wind drops and blows many particles of dust, pollen and spores of fungi, some of which are very allergenic," he says. In 2015, an extreme lightning storm in Israel led to many people being admitted to hospitals due to asthma. "The climate crisis will increase the incidence of lightning storms and prolong the flowering period of many plants, some of which are allergenic." That is, he says, there’s a high probability of lightning storm asthma events.
Along with the dangers expected, it's important to remember that most of the microorganisms in the air aren’t harmful to humans at all. "Most people have adapted to the phenomenon because evolution has made us immune to many of the microorganisms in the air," says Yair. "However, sensitive and vulnerable people may suffer from it."
The article was prepared by Zavit, the PR division of the Israeli Association of Ecology and Environmental Sciences.