The Santa Monica Mountains hiking trails are some of the most popular in the city (and definitely with famous people), but those same trails also might be at a heightened risk for fire because they're so close to car traffic. Researchers from the National Park Service, UC Riverside, and the US Forest Service working in the Santa Monica range found that levels of atmospheric nitrogen, one of the main substances in smog and a product of combustion-engine cars, increased incrementally the further they got from the ocean, until, in the easternmost part of the mountains, levels of were three times what they were in the east, reports KPCC. And nitrogen doesn't just affect visibility. An experiment conducted by the researchers found that, besides making the air look brown and cloudy, atmospheric nitrogen also threatens native, more fire-resistant plants, while allowing non-native, quick-burning grasses to flourish—meaning that areas with more of this kind of air pollution might be more susceptible to fires. Now it's a matter of figuring out the numbers: How much does the risk of fire increase when nitrogen pollution goes up?

· Air pollution may boost fire risk in local mountains [SCPR]