Light Pollution May Worsen Air Pollution

3 photolysis)—a form of nitrogen oxide only present in darkness—normally breaks down damaging chemicals that create smog. Recent measurements taken over Los Angeles have shown that, like sunlight, city lights suppress the nitrate radical—reducing night cleansing by up to 7% and increasing the following day’s ozone pollution precursor chemicals by up to 5%. (More research is needed to quantify the relative amount of ozone found the next day.) The darker sky over Boulder, Colorado, was used as a control in the research. Researchers found that the nitrate radical is less affected by red light, but unfortunately, red light is not a desirable color for nighttime city lights. The negative effects from light pollution are found above ground level, so light pollution reduction measures, including broader use of “dark sky” lighting that is aimed and shielded downward, should mitigate the effect. The study, “Nighttime photochemistry: nitrate radical destruction by anthropogenic light sources,” is available at adsabs.harvard.edu/.