City dimming lights can help reduce smog (Scientific American)

SAN FRANCISCO - city lights can do more to hide a dark sky: they could worsen indirectly daytime smog. Measurements of light pollution in Los Angeles showed a better than expected chemists - bright enough to destroy chemical products that would otherwise be to purify the air during a night glow.

"Light pollution can slow night cleaning," said Harald Stark of the National Oceanic and Atmospheric Administration. He is based in Boulder, Colorado and the results reported on 14 December here to a meeting of the American Geophysical Union.

"I think that someone had thought about it," says Jochen Stotz, an atmospheric chemist at the University of California, Los Angeles. "It shows that it is really important to what happens during the night" for the quality of air, adds Stotz, who was not involved in the study of NOAA. "We see how important."

Surprising is the only moment that - a hypothesis, Stark told a press conference. The chemistry of the formation of smog is very complex and the effects of the lights of the city are difficult to quantify without research, he said.

For several flights this summer NOAA aircraft, the Stark and his team discovered that the glow of Los Angeles is 10 000 times smaller than the light of the Sun, but still 25 times brighter than the full moon. The researchers calculated that so much light would be sufficient to break the nitrite in the air. Nitrite (NO3) indirectly reduces the levels of ozone during the day, because it reacts with other nitrogen compounds which are involved in the formation of ozone reactions. So then that areas dark nitrite is a cleaner night in L.A. it can be reduced, with the effect of exacerbating smog.

Impact could be worst cities to the North in winter, said stark, because the clouds and snow cover have a multiplier effect on light pollution.

Stotz, said that he and his colleagues now plan to include the effects of light pollution in their atmospheric chemistry models for attempting to quantify the results of the NOAA. Even if the result is an increase of several percentage points in ozone levels, it can make a significant difference to the communities who are already struggling to remain within the limits imposed by the U.S. Environmental Protection Agency, says Stark.

Cities can discover outside lighting control may have more advantages than the savings of energy and keep bright stars.

Image: Typical Western United States, such as Los Angeles, cities are defined through the streets of yellow-orange sodium vapor-bed in grids. Tracks can be distinguished as dark lines where, surprisingly, it is preferable to put an airplane on a runway darker than a well lit. The city's edge lights fade abruptly into the surrounding desert. Credit: NASA