Too much light at night time contributes to air pollution, says a study conducted by the National Oceanic and Atmospheric Administration (NOAA) and the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado.
Findings indicate that uplight from outdoor lighting that contributes to sky glow over cities also interferes with chemical reactions that naturally clean the air during nighttime hours.
Every night, chemicals from vehicle exhaust and other human created sources are broken down and prevented from becoming smog, ozone, or other irritants by a form of nitrogen oxide called the nitrate radical. Sunlight destroys the naturally occurring nitrate radical, so this process occurs only in hours of darkness.
Measurements taken over Los Angeles by aircraft show that light pollution from cities is suppressing the radical. Though the lights are 10,000 times dimmer than the Sun, the study's first results indicate that city lights can slow down the nighttime cleansing by up to 7pc and they can increase the starting chemicals for ozone pollution the next day by up to 5pc.
"[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," NOAA investigator Harald Stark told BBC News.
The finding has been presented at the American Geophysical Union meeting in San Francisco.