Cars and canyons: Understanding roadside impacts of automobile pollution in grand canyon national park

Nitrogen oxides (NOx) in air pollution contribute to haze that diminishes the views at Grand Canyon National Park. NOx pollution negatively impacts vegetation and ecological communities, but these effects are not well understood. Some sources of this pollution, like regional airborne emissions from urban areas and coal-fi red power plants, are beyond the direct jurisdiction of the National Park Service (NPS). However, NOx emitted from vehicular exhaust is one source of pollution that the park can potentially manage as it strives to provide alternative transportation options for the public. We sampled atmospheric NOx and foliar δ¹⁵N signatures (the ratio of nitrogen isotopes 15N to 14N can be used to identify emission sources) along a traffi c gradient at the south rim of the national park to assess the extent to which vehicles on park roads may be adding nitrogen (N) to transportation corridors. Atmospheric NOx was found to be elevated within a few meters of the roadside and at the south entrance where automobile traffi c was the greatest. We also found that foliar nitrogen isotope signatures along the roadside gradient matched known signatures from vehicular emissions, indicating that cars and other vehicles are primary sources of nitrogen in the ecosystem near roadways. Haze-reducing legislation has recently been enacted to reduce emissions from regional coal-fi red power plants, but the National Park Service can further reduce park pollution by encouraging nonmotorized recreation and greater public use of alternative transportation options.