Tuesday, January 11, 2011

Light as a Contributer to Urban Air Pollution

The distribution of atmospheric ozone in parti...
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City Lights Affect Air Pollution (American Geophysical Union Fall Meeting, Dec. 13, 2010)

Also discussed here: City lighting 'boosts pollution' - Bright city lights exacerbate air pollution, according to a study by US scientists (BBC News, Dec. 14, 2010)

And here: Nitrogen oxides in the nocturnal boundary layer: Simultaneous in situ measurements of NO3, N2O5, NO2, NO, and O3 (Abstract, Journal of Geophysical Research, Vol. 108, 4299, 11 Pp., 2003)

The impact of light pollution, particularly around cities, is seen usually as an impact on astronomy and a health threat on sleep for residents living close to the light source. The article under review today suggests that light projected up through the atmosphere may, in addition, interrupt the normal nocturnal  atmospheric chemistry processes where a nitrate radical breaks down the formation of ozone- thus resulting in more ozone than if there had been no light.  If validated, this would seem to point to greater restrictions as part of air pollution regulations concerning the widespread use of lighting in large cities.

Key Quotes:

“human-made lighting is influencing chemical reactions in the atmosphere, altering nighttime compositions and concentrations of some airborne pollutants”

“These findings could indicate increasing shifts in air-pollution’s distinctive night-versus-day chemical profiles”

"Our first results indicate that city lights can slow down the night-time cleansing by up to 7% and they can also increase the starting chemicals for ozone pollution the next day by up to 5%"

“It uses a special form of nitrogen oxide, called the nitrate radical, to break down chemicals that would otherwise go on to form the smog and ozone that can make city air such an irritant on the chest.”

"[This effect] is more important up in the air than it is directly on the ground so if you manage to keep the light pointing downward and not reflected back up into sky, into the higher parts of the air, then you would certainly have a much smaller effect of this,"

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