Non‐Fossil Origin Explains the Large Seasonal Variation of Highly Processed Organic Aerosol in the Northeastern Tibetan Plateau (3,200 m a.s.l.)

Abstract

Abstract Carbonaceous aerosol plays an important role in climate, but its sources and atmospheric processes are least understood in the Tibetan Plateau (TP), a remote yet climatically sensitive region. This study presents the first seasonal cycle of radiocarbon and stable isotope 13C of organic and elemental carbon (OC and EC) in the atmosphere of the northeastern TP. Large seasonal variations of EC and OC concentrations were explained by non‐fossil sources. Regardless of the season, fossil contribution to OC was strongly correlated with inverse OC concentrations. This allowed the separating a constant background source and a source responsible for OC variability that was mostly of non‐fossil origin. The 13C signature of OC shows that OC was highly atmospherically processed and thus less volatile than OC found near sources or in urban areas. The 13C‐depleted secondary sources contributed strongly to more volatile OC, whereas the 13C‐enriched less volatile OC suggests the influence of atmospheric aging.