A large fraction of primarily emitted particulates in the troposphere are long-chain hydrocarbons that can evaporate from the particle phase to the vapor phase; they can also be readily oxidized in both phases, following different reaction schemes and leading to oxygenated products with different isomeric distributions. In the present study, evaporation and oxidation of four long-chain normal alkanes (n-octadecane, n-eicosane, n-docosane, and n-tetracosane) were examined in a flow tube reactor. Particle-phase samples were comprehensively analyzed using a two-dimensional gas chromatograph coupled to a high-resolution time-of-flight mass spectrometer (GC�GC/HTOF-MS) with vacuum ultraviolet (VUV) photoionization. Both functionalization (up to third generation) and fragmentation oxygenated products were measured and quantified. More importantly, most of the oxygenated higher molecular weight constitutional isomers were separated. Ketones and alcohols with the functional group on different carbon positions were identified by their unique VUV mass spectra. The isomer distributions of ketones and alcohols are more similar to those of gas-phase oxidation for more volatile n-alkanes and are more similar to those from heterogeneous oxidation for less volatile n-alkanes.  These results suggest both evaporation and oxidation occurred simultaneously and the product isomer distribution effectively reveals the relative importance of the two processes. This work demonstrated that isomer analyses could provide a new metric to estimate evaporation and oxidation kinetics of long-chain hydrocarbons.

Understanding the evolution of long-chain n-alkanes in the atmosphere using gas chromatography-vacuum ultraviolet-mass spectrometry

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.