Tech could someday let people even in dry climates
get clean water straight from the atmosphere›››
Making it rainUAE researcher Linda Zou uses nanotechnology
to develop new materials for cloud seeding 21 Mar 2023
Linda Zou is a UAE researcher who uses nanotechnology to develop new materials for cloud seeding, a weather-modification technology that improves the chances a cloud will produce rain. She talked to the KUST Review about her work and the future of cloud-seeding technology.
Linda Zou is a professor in the Khalifa University Department of Civil Infrastructure and Environmental Engineering and the head of the Nano and Water Laboratory. This interview has been edited for space and clarity.
QUESTION: Walk us through the basics of cloud-seeding technology and what should people who aren’t familiar with cloud seeding know.
ANSWER: The sun shines and water vapor rises up from the Earth’s surface, and these tiny water vapors will keep on rising and finally condense to become either rain or snow.
In the presence of small particles as nuclei, water vapor condenses, turning into small liquid droplets. And that droplet will hit another small droplet during the falling process, and then they form a larger droplet. The size grows and grows. When the drops reach the lower part of the atmosphere, they’re too big, too heavy, and they fall as rainfall. And unfortunately the availability of this sort of small seeding nuclei in the atmosphere is unpredictable. It could be naturally occurring particles such as volcano ashes, dust particles or pollens. But when you need it you can’t guarantee you’ll get it.
Cloud seeding is to spread artificial seeding materials by using aircraft, flying over the bottom of suitable clouds and releasing the seeding materials, and an updraft will carry them into the cloud, to start the condensation and turn the water vapor into water droplets artificially. And this is the cloud-seeding process.
Q: How important is it to the world to tap that atmospheric moisture?
A: The World Meteorological Organization (WMO) did a survey and reported more than 45 countries are practicing some sort of weather modification. Cloud seeding is one of the major (weather-modification) technologies. This implied the advancement in the cloud-seeding materials could have a wider impact to combat the water-shortage problem globally.
Q: Is cloud seeding used primarily in desert countries or are a broad range of countries practicing it?
A: (Cloud-seeding) is technology-driven; commonly you need aircraft fleets. Countries like the US, South Africa and some European countries are very active, particularly in agricultural protection, as well. (Countries may have) a different purpose: Russia is more interested in hail-suppression. China has dry regions. For many decades, the science behind this water-related process hasn’t had much innovation, UAE is driving innovation through its UAE Rain Enhancement Science Program.
Cloud seeding can increase a region’s rainfall, but knowing when the conditions for cloud seeding are optimal can be difficult. Read more›››
Now, researchers who recently won a U.S.$1.5 million grant from the UAE’s National Center of Meteorology think they can help by tapping into artificial intelligence.
Luca Delle Monache, deputy director of the Center for Western Weather and Water Extremes (CW3E), Scripps Institute of Oceanography at the University of California, San Diego, in March received the three-year grant of the UAE Research Program for Rain Enhancement Science (UAEREP) for the project using a hybrid machine-learning framework for enhanced precipitation nowcasting.
Nowcasting in meteorology is describing the present or predicting the very near-future weather conditions. Khalifa University’s Ernesto Damiani, Linda Zou and Hussam Al Hamadi will gather data and create a prototype artificial intelligence system for data fusion and weather nowcasting for the project.
Alya Al Mazroui, UAEREP director, says the work will continue the organization’s role in advancing rain-enhancement technology, as well as “promoting the UAE’s status as a prominent hub for rain-enhancement research and helping the world tackle the challenges posed by the scarcity of potable water.” ‹‹‹ Read less
Q: That leads into the next question: What are some of the problems and limitations that your work is looking to solve?
A: The kind of seeding material adopted around the world heavily depends on atmospheric relative humidity. That means the seeding material released is only activated or useful at very high relative humidity. So a lot of cases you release (the seeds), and if it isn’t very humid conditions, it’s not useful. So because I’m thinking on the science of the interactions between materials and atmospheric relative humidity, I can see that there’s room to improve.
Q: And your proposal is to change the seeding material?
A: Yes. I proposed three ideas: Each has been investigated and concept is realized. The first is to change the surface of the material to make it more reactive (so it can work) at a lower relative humidity. Instead of 75 percent or higher, now we can use it at 65 percent.
To achieve this, we used nanotechnology to engineer a material that is activated in much broader relative-humidity conditions. Because the structure is so porous, water will melt easily, forming larger droplets, increasing the probability that it will work.
Secondly, a bioinspired hydrophilic/hydrophobic pattern was created on the seeding material to enhance the interaction with water vapor; thirdly, a porous 3D nanocomposite was developed to promote ice nucleation and growth for cloud-seeding in cold clouds.
Q: Old-technology cloud-seeding materials might be harmful to the environment. That’s another problem you’re looking to solve?
A: There are different types of seeding material used. Various salt particles are used for warm clouds; their environmental effect is less of concern. But the one you hear about is mostly silver iodide, which is mostly for cold clouds – for ice- and snow-making. Over longer periods of application, silver iodide may pose some toxic effects. It is not used in my research project, as the design of novel seeding material is to steer away from potential harmful materials.
Q: Some of your materials are inspired by natural adaptations in biological organisms. What would you say is the value of looking to nature to solve problems?
A: Nature has evolved over millions of years. Every biological system that thrives today is the positive result of evolution. Modern analytical tools enable scientists to look at the details of biology at the biochemistry level and have more understanding on how they work. This newly gained knowledge helped us to mimic the biological mechanism in designing nanomaterials. Although we’re not able to replicate biological mechanisms, I can be inspired and learn from their principles.
The United Arab Emirates’ rain-enhancement operations began in the 1990s and were developed in cooperation with such international organizations as the United States’ NASA and National Center for Atmospheric Research. Read more›››
According to the UAE Program for Rain Enhancement Science, the Emirates now have more than 60 networked weather stations, five specialized aircraft used for seeding and an integrated radar network.
Other benefits from cloud-seeding research include increased understanding of cloud microphysics; cloud dynamics and thermodynamics; the physical chain of events that lead to cloud formation and rainfall; and how cloud-condensation nuclei and ice nuclei interact with clouds.
Research impacts include improved cloud-seeding materials and delivery methods and helping meteorologists better nowcast and forecast the weather. ‹‹‹ Read less
Q: What would you say are the biggest challenges to seeding clouds?
A: One of the major problems is all cloud-seeding operations are carried out in the open atmosphere. All the conditions cannot be controlled as in a closed system.
Secondly, all clouds are different at a time and they’re also varied and unpredictable. These make the evaluation of cloud-seeding effects difficult. But we accept this unpredictability. And if the seeding materials become more and more efficient, the probability (of success) is higher for any given cloud conditions.
Q: Some of your work focuses on ice and snow instead of rain. How are these approaches different?
A: It’s different and it’s the same in some regions. Clouds that form at a few thousand meters above us are in sub-zero temperatures. Precipitation at that altitude will be ice. But when ice falls down to the earth, if it falls down in cold regions it will be snow. If it falls down to the warm regions such as UAE it will melt into rain.
So for clouds with sub-zero temperatures, different techniques have to be used. The sub-zero clouds’ conditions are different. The water vapors are oversaturated in some cold clouds, so their relative humidity is like more than 100 percent but they stay as supercooled water vapor. So at this stage if (the supercooled vapor meets) a suitable ice nuclei it will form ice crystals and grow rapidly as an ice explosion, as an avalanche of ice crystals.
So I also investigate to develop this type of ice nuclei. The ice nucleus is often silver iodide. Why? the possible theory behind is that its crystal structure is similar to the ice. So crystal grows on the other crystal due to their crystal framework lattice matching. So it’s very different from the droplets, a different mechanism.
And as we said with the silver iodide there are some problems but there aren’t many alternatives. So I designed an alternative material. This material can also help create artificial snow at ski resorts. It works well in cloud-chamber experiments.
Q: Can you describe that material?
A: The novel cloud-seeding material has a shell/core structure, it has a sodium chloride core, which is covered by a nanometer thickness of titania particles. This structure offers a synergistic effect on condensation at lower relative humidity and forms larger water droplets: Both are important to increase the probability of rainfall.
Q: Is this the sort of technology that would be used to control undesirable weather, like preventing hail?
A: Yes. That’s the case in some European countries, to protect agriculture industry from extreme weather attack, such as hail and frost.
Q: What impact would you say cloud-seeding will have on climate change?
A: I think this is a very important question. It is in the broader spectrum of climate-change strategies. If we got more water as rainfall through cloud-seeding, it would be cooling the weather and replenish the ground-water aquifer. There would be less demand for air-conditioning, less demand for desalinization. It has very positive effects.
Q: So what’s the next frontier? What’s the next exciting development?
A: The next frontier will be scaling up the production, making the seeding materials more available. Apart from airplane, the seeding materials can be released by other methods such as balloons, or drones. In addition, it can also migrate into surface-water-harvesting applications, like catching fog.
Q: Is there anything we haven’t covered that you want people to know?
A: The UAE Research Program for Rain Enhancement Science is appreciated because they provide us funding on my research project. I really wish that this will have a ripple effect. We need to transform the novel seeding materials into commercial-scale production and wider application. We have started working on that. I need government and industry support on this direction. If this becomes commercially technology, more countries and regions will benefit.
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