Navigation Links
Dirty air brings rain -- then again, maybe not

An international team of scientists, headed by Prof. Daniel Rosenfeld of the Institute of Earth Sciences at the Hebrew University of Jerusalem, has come up with a surprising finding to the disputed issue of whether air pollution increases or decreases rainfall. The conclusion: both can be true, depending on local environmental conditions.

The determination of this issue is one with significant consequences in an era of climate change and specifically in areas suffering from manmade pollution and water shortages, including Israel.

In an article appearing in the Sept 5 issue of the journal Science, the scientific team, which included researchers from Germany, has published the results of its research untangling the contradictions surrounding the conundrum. They do this by following the energy flow through the atmosphere and the ways it is influenced by aerosol (airborne) particles. This allows the development of more exact predictions of how air pollution affects weather, water resources and future climates.

Mankind releases huge amounts of particles into the air that are so tiny that they float. Before being influenced by man, air above land contained up to twice as many of these so called aerosol particles as air above oceans. Nowadays, this ratio has increased to as much as a hundredfold.

Natural and manmade aerosols influence our climate that much is agreed. But which way do they push it? They produce more clouds and more rain, some say. They produce fewer clouds and less rain, say others. This disputed role of aerosols has been the greatest source of uncertainties in our understanding of the climate system, including the question of global warming.

"Both camps are right", says Prof. Meinrat O. Andreae, director of the Max Planck Institute for Chemistry in Germany, a coauthor of the publication. "But you have to consider how many aerosol particles there are." The lead author, Prof. Rosenfeld of the Hebrew University, adds: "The amount of aerosols is the critical factor controlling how the energy is distributed in the atmosphere." Clouds, and therefore precipitation, come about when moist, warm air rises from ground level and water condenses or freezes on the aerosols aloft. The energy responsible for evaporating the water from the earth's surface and lifting the air is provided by the sun.

Aerosols act twofold: On the one hand, they act like a sunscreen reducing the amount of sun energy reaching the ground. Accordingly, less water evaporates and the air at ground level stays cooler and drier, with less of a tendency to rise and form clouds.

On the other hand, there would be no cloud droplets without aerosols. Some of them act as gathering points for air humidity, so called condensation nuclei. On these tiny particles with diameters of less than a thousandth of a millimeter the water condenses similar to dew on cold ground releasing energy in the process. This is the same energy that was earlier used to evaporate the water from the earth's surface. The released heat warms the air parcel so that it can rise further, taking the cloud droplets with it.

But if there is a surplus of these gathering points, the droplets never reach the critical mass needed to fall to earth as rain there just is not enough water to share between all the aerosol particles. Also, with a rising number of droplets their overall surface increases, which increases the amount of sunlight reflected back to space and thus cooling and drying the earth.

In a nutshell, then, the study results show the following: With rising pollution, the amount of precipitation at first rises, than maxes out and finally falls off sharply at very high aerosol concentrations. The practical result is that in relatively clean air, adding aerosols up to the amount that releases the maximum of available energy increases precipitation. Beyond that point, increasing the aerosol load even further lessens precipitation. Therefore, in areas with high atmospheric aerosol content, due to natural or manmade conditions, the continuation or even aggravation of those conditions can lead to lower than normal rainfall or even drought.

Prof. Rosenfeld states: "These results have great significance for countries like Israel where rainfall is scarce and can be easily affected by over-production of aerosols. Our study should act as a red light to all of those responsible for controlling the amounts of pollution we release into the atmosphere."

"With these results we can finally improve our understanding of aerosol effects on precipitation and climate," summarizes Andreae, "since the direct contradiction of the different aerosol effects has seriously hindered us from giving more accurate predictions for the future of our climate, and especially for the availability of water."


Contact: Jerry Barach
The Hebrew University of Jerusalem

Related biology news :

1. New ORNL process brings nanoparticles into focus
2. First-ever symposium brings together military and civilian medical experts
3. Astronomy technology brings nanoparticle probes into sharper focus
4. Chemist Brings SAFETY Act Expertise to Homeland Security Firm
5. Scientist brings 50 million year old spider back to life
6. Major genetic breakthrough for ankylosing spondylitis brings treatment hope
7. Contraception: progress brings hope for new methods for men
8. UCs NIH grant brings technology from outer space to playgrounds
9. Shuttle brings space-grown strep bacteria back for study
10. Bison can thrive again, study says
11. In nature -- and maybe the corner office -- scientists find that generalists can thrive
Post Your Comments:
Related Image:
Dirty air brings rain -- then again, maybe not
(Date:4/4/2017)... NEW YORK , April 4, 2017   ... solutions, today announced that the United States Patent and ... The patent broadly covers the linking of an iris ... the same transaction) and represents the company,s 45 th ... our latest patent is very timely given the multi-modal ...
(Date:3/30/2017)... 30, 2017 Trends, opportunities and forecast in ... by technology (fingerprint, AFIS, iris recognition, facial recognition, hand ... by end use industry (government and law enforcement, commercial ... banking, and others), and by region ( North ... Asia Pacific , and the Rest of ...
(Date:3/24/2017)... The Controller General of Immigration from Maldives Mr. Mohamed Anwar ... prestigious international IAIR Award for the most innovative high security ePassport and ... ... Maldives Immigration Controller General, Mr. Mohamed ... the right) have received the IAIR award for the "Most innovative high ...
Breaking Biology News(10 mins):
(Date:10/12/2017)... ... October 12, 2017 , ... ... with the addition of its newest module, US Hemostats & Sealants. , SmartTRAK’s ... hemostats, absorbable hemostats, fibrin sealants, synthetic sealants and biologic sealants used in surgical ...
(Date:10/11/2017)... ... 11, 2017 , ... The CRISPR-Cas9 system has ... and avoiding the use of exogenous expression plasmids. The simplicity of programming this ... gain-of-function studies. , This complement to loss-of-function studies, such as with RNAi ...
(Date:10/11/2017)... INDIANAPOLIS , Oct. 11, 2017  VMS BioMarketing, a ... of a nationwide oncology Clinical Nurse Educator (CNE) network, which ... growing need for communication among health care professionals to enhance ... physicians, nurses, office staff, and other health care professionals to ... for breast cancer. ...
(Date:10/11/2017)... ... October 11, 2017 , ... Singh Biotechnology today announced that ... SBT-100, its novel anti-STAT3 (Signal Transducer and Activator of Transcription 3) B VHH13 ... cross the cell membrane and bind intracellular STAT3 and inhibit its function. Dysregulation ...
Breaking Biology Technology: