"It's usually difficult to detect what's going on in that spectral region because the molecular systems of interest frequently have weak spectral features there, so they're tough to see," said Francisco, who contributed the study's computations. "The upshot is that a lot of atmospheric models ignore this region altogether, assuming that because nothing can be seen, nothing must be happening."
The laser technique, however, enabled the team to characterize the minute quantities of radiation absorbed by a substance called methyl hydroperoxide when it breaks up in sunlight and forms OH radicals. Methyl hydroperoxide is one of the substances that can absorb light in the lower UV spectrum, and the team theorizes that the sensitive laser technique, called action spectroscopy, could reveal OH radical production from other chemically related molecules as well.
"This study is important because it shows that the atmosphere could be generating far more OH radicals than we thought before because the models are underestimating the amount of chemistry that’s happening," said Sinha, who is an associate professor of chemistry and biochemistry. "It could imply that the atmosphere is more effective at breaking down pollution than models have shown. We hope the results will improve our understanding of how the atmosphere works."
Sinha cautioned, however, that the results do not mean we can now safely ignore atmospheric pollution.
"This study in no way implies that we are out of the woods with regard to atmospheric pollution," he said. "What it means is that we need to do a much more careful job with our measurements in order to accurately account for all the reactive chemicals present in the air."
Francisco said he hopes the study also would encourage other refinements to atmospheric models.
"Models are only as good as the information we put into them, and we must always keep a cautious perspective about the results models return