Featured Research

from universities, journals, and other organizations

Air Pollution Can Prevent Rainfall

Date:
March 14, 2000
Source:
American Association For The Advancement Of Science
Summary:
Urban and industrial air pollution can stifle rain and snowfall, a new study shows, because the pollution particles prevent cloud water from condensing into raindrops and snowflakes. These findings are reported in the 10 March issue of Science.

Washington D.C. - Urban and industrial air pollution can stifle rain and snowfall, a new study shows, because the pollution particles prevent cloud water from condensing into raindrops and snowflakes. These findings are reported in the 10 March issue of Science.

The new study, by Daniel Rosenfeld, of the Hebrew University of Jerusalem, presents satellite images and measurements of "pollution tracks" downstream from major urban areas and air pollution sources such as power plants, lead smelters, and oil refineries. The tracks consist of polluted clouds that have shut off virtually all precipitation because they contain abnormally small water droplets.

The droplets' small size is caused by pollution particles that act as "seeding" sites around which cloud moisture condenses. Approximately one million small droplets must collide and coalesce in order to make a precipitation-sized drop-that is, one large enough to fall below the cloud base and reach the ground before evaporating. In polluted clouds, there are too many small droplets and not enough larger ones. These small droplets float in the air with low probability of bumping into each other and merging into raindrops. The smaller droplets are also slower to freeze into ice crystals, resulting in less sleet and snowfall.

Because urban and industrial air pollution is a significant problem in many regions of the world, Rosenfeld's findings suggest that human activity may be affecting rainfall patterns on a global scale.

These data are the first direct evidence of how urban and industrial pollution affects rainfall levels, a question scientists have debated for several decades. In fact, some previous studies have concluded that air pollution might increase rainfall, but the debate has continued due to a lack of convincing data.

"In the past, scientists had to collect information by poking little holes in clouds from airplanes, or using statistics about rainfall patterns because you can't replicate rain-clouds in the lab. Now, new satellite instruments allow us to have a comprehensive look at the problem. For the first time, we can measure cloud precipitation and microstructure simultaneously over large areas," Rosenfeld said.

In his Science paper, Rosenfeld presents the first images of pollution tracks over land. The images, taken over regions in Turkey, Canada, and Australia, all contain known sources of industrial or urban air pollution. The tracks stream away from these pollution sources in long narrow plumes.

Rosenfeld took yet a closer look at the pollution tracks in Australia, where the plumes were particularly striking. Further measurements from a bevy of satellite instruments showed that precipitation of both raindrops and ice crystals-which was occurring in the unpolluted clouds-was practically shut off in the clouds within the pollution tracks. However, the total amount of moisture in the polluted clouds was sufficient to produce rain and snow.

Rosenfeld also notes that in other parts of the world air pollution is more widespread and not as easy to distinguish as it is against the relatively clean Australian atmosphere. Thus the well-defined tracks identified in the study "serve as a Rosetta stone for the potential impact of more widely distributed aerosol pollution on clouds," writes Owen Toon, of the University of Colorado at Boulder, in a related commentary article.


Story Source:

The above story is based on materials provided by American Association For The Advancement Of Science. Note: Materials may be edited for content and length.


Cite This Page:

American Association For The Advancement Of Science. "Air Pollution Can Prevent Rainfall." ScienceDaily. ScienceDaily, 14 March 2000. <www.sciencedaily.com/releases/2000/03/000314065455.htm>.
American Association For The Advancement Of Science. (2000, March 14). Air Pollution Can Prevent Rainfall. ScienceDaily. Retrieved July 22, 2014 from www.sciencedaily.com/releases/2000/03/000314065455.htm
American Association For The Advancement Of Science. "Air Pollution Can Prevent Rainfall." ScienceDaily. www.sciencedaily.com/releases/2000/03/000314065455.htm (accessed July 22, 2014).

Share This




More Earth & Climate News

Tuesday, July 22, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

New Orleans Plans to Recycle Cigarette Butts

New Orleans Plans to Recycle Cigarette Butts

AP (July 21, 2014) New Orleans is the first U.S. city to participate in a large-scale recycling effort for cigarette butts. The city is rolling out dozens of containers for smokers to use when they discard their butts. (July 21) Video provided by AP
Powered by NewsLook.com
Shark Sightings a Big Catch for Cape Tourism

Shark Sightings a Big Catch for Cape Tourism

AP (July 21, 2014) A rise in shark sightings along the shores of Chatham, Massachusetts is driving a surge of eager vacationers to the beach town looking to catch a glimpse of a great white. (July 21) Video provided by AP
Powered by NewsLook.com
Spectacular Lightning Storm Hits London

Spectacular Lightning Storm Hits London

AFP (July 19, 2014) A spectaCular lightning storm struck the UK overnight Friday. Images of lightning strikes over the Shard and Tower Bridge in central London. Duration: 00:23 Video provided by AFP
Powered by NewsLook.com
A Centuries' Old British Tradition Is Far from a Swan Song

A Centuries' Old British Tradition Is Far from a Swan Song

AFP (July 19, 2014) As if it weren't enough that the Queen is the Sovereign of the UK and 15 other Commonwealth realms, she is also the owner of all Britain's unmarked swans. Duration: 02:18 Video provided by AFP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins