Atmospheric particles can contribute to environmental degradation. An aerosol mass spectrometer was used with positive matrix factorization to explore submicron particle sources in Rocky Mountain National Park, finding that ammonium (3.9%), nitrate (4.3%), sulfate (16.6%), and two types of oxidized organic aerosol (66.9% total) are transported on upslope winds from the urban Front Range, while local campfires contribute 8.4% of mass.