New Worlds: Pollution worsens drought & flooding

Research provides clear evidence of how aerosols can affect weather and climate.

By JUDY SIEGEL-ITZKOVICH
Rain in Tel Aviv 311 (photo credit: JOANNA PARASZCZUK)
Rain in Tel Aviv 311
(photo credit: JOANNA PARASZCZUK)
Dirty air works both ways: Particulate matter in the atmosphere affects the development of clouds by reducing the amount of rain in cool and relatively dry regions, such as Israel in winter. But it can also increase rain and the intensity of severe storms in warm and moist regions or seasons, such as the eastern half of the US during summer, according to a new study by researchers at the Hebrew University of Jerusalem and the University of Maryland.
The research provides clear evidence of how aerosols – soot, dust and other small particles in the atmosphere – can affect weather and climate. The findings have important implications for the availability, management and use of water resources around the world, the scientists say.Using a decade-long dataset of extensive atmosphere measurements from America’s Southern Great Plains Research Center in Oklahoma (run by the US Department of Energy’s atmospheric radiation measurement program), the researchers uncovered for the first time the long-term net impact of aerosols on cloud height and thickness and the resulting changes in the frequency and intensity of rainfall. This study confirmed and showed the importance of the theory developed by HU Prof. Daniel Rosenfeld in his previous studies. The new study appeared in a recent issue of Nature Geoscience.
The team members say the findings have major policy implications for sustainable development and water resources, especially for those developing regions susceptible to extreme events, such as drought and flood. Increases in manufacturing, urbanization, building of power plants and other industrial developments are often accompanied with increases in pollution whose adverse impacts on weather and climate, as revealed in this study, can hurt the economy.
Aerosols – not spray cans but tiny solid or liquid particles suspended in air – include soot, dust and sulfate particles and are what we commonly think of when we talk about air pollution. Aerosols may come from the combustion of fossil fuels, industrial and agricultural processes and accidental or deliberate burning of fields and forests. They can be hazardous to both human health and the environment. Aerosols also affect cloud microphysics, as they serve as nuclei around which water droplets or ice particles form. Both processes can affect cloud properties and rainfall. Different processes may work in harmony or offset each other, leading to a complex yet inconclusive interpretation of their long-term net effect.
“When the air rises, water vapor condenses on aerosol particles to form cloud drops. In cleaner air, the drops are larger because there are fewer drops, and they have better chances of colliding to form large rain drops. In polluted air, more and smaller drops are formed. They float in the air and are slow to coalesce into rain drops,” says Rosenfeld.
“With a small amount of moisture, most cloud drops never become large enough for efficient precipitation, thus the amount of rainfall is reduced. Rain withheld in moist, polluted and thick clouds freezes at higher altitudes to form ice crystals or even hail.
The energy released by freezing fuels the clouds to grow taller and create larger ice particles that produce more intense precipitation.
This explains why air pollution can exacerbate both drought and flood,” says Rosenfeld. This may partially explain his finding in another study that there are more severe convective storms during summer on weekdays compared to weekends in the eastern US; more pollution is emitted during the weekdays than during the weekend.
MOLECULAR COOKING
Cola turned into spaghetti, raspberry drink “miraculously” reduced to clear water, making cottage cheese from milk and “cooking” raw eggs in alcohol were some of the feats presented during Hanukka at Jerusalem’s Bloomfield Science Museum, with many of them continuing through March.
A workshop attracting both young children and adults on “experiential molecular cooking,” in which scientific methods are used to create “caviar” from various colorful fruits, will continue to be offered on Saturdays by “Dr. Molecule” through the winter.

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Other events and exhibits will remain on the museum’s regular visiting days until March.
The live performances by Dr. Sergio Broido, who has a doctorate in molecular biology from the Hebrew University and has won a bronze medal at a cooking competition abroad – ran through the festival of lights and wowed young audiences.
Broido used guar gum and seaweed to change the form of foods from liquid to a rubber-like texture. “Juice” from cooked red cabbage helped change water to colors and back again, depending on whether the water was acidic or alkaline.
Continuing through the summer is a exhibit showing Israel’s 50 greatest inventions.
Another exhibit explains how electricity has become the fuel that moves nearly the whole of technology.