How sunlight on dirty buildings is creating dirty air
A new study has confirmed a previously held suspicion as to what helps drive up air pollution: the sun.
Scientists have found that natural sunlight may play a key role in cities鈥� smog levels, and its covert accomplice is something most city-dwellers walk past everyday: the grime clinging to urban structures, such as buildings or statues.
The action happens when sunlight hits the overlying grime on these surfaces, causing nitrogen gases to discharge, and later form into smog, researchers said Monday.
鈥淭he current understanding of urban air pollution does not include the recycling of nitrogen oxides and potentially other compounds from building surfaces,鈥� . 鈥淏ut based on our field studies in a real-world environment, this is happening.鈥�
Experiments now substantiate a hypothesis researchers had previously tested in the lab, shining artificial sunlight onto grime samples to determine grime's effect on chemical output.
And they鈥檝e also discovered the truth behind the long-circulating rumor that nitrates in urban grime are inert or inactive, said the scientists.
Instead of being 鈥渓ocked鈥� in place, nitrates are 鈥渂eing removed very quickly鈥� and 鈥渁lso deposited very quickly,鈥� Dr. Donaldson at a conference for the American Chemical Society. 鈥淭he lifetime of the nitrates 鈥� is very, very short.鈥�
While his team is still working to quantify the exact extent of sunlight-fueled smog, 鈥渋t may be quite a significant, and unaccounted for, contributor to air pollution in cities,鈥� said Donaldson. 鈥淚f our suspicions are correct, it means that the current understanding of urban air pollution is missing a big chunk of information.鈥�
One disparity researchers found as they set up tracking stations on the rooftops of Toronto and Leipzig, Germany, is that Leipzig has 鈥�20 times more grime than Toronto,鈥� .
The team now is hoping to study the influence of varying pollution levels across the world, 鈥渋n someplace that is and someplace that is 鈥榬eally clean.鈥欌��
Dr. Donaldson announced at the conference that his group is in talks to begin an experiment in Shanghai.
Upcoming fieldwork will also focus on whether climate conditions, such as relative humidity, are at play in determining the amount of smog arising from sunlit grime, said the professor.
鈥淚 think in dry climates, there could be very different sorts of chemistry happening. We have indications of that from our laboratory experiments,鈥� he said.
