Near-Infrared Laser Desorption/Ionization Aerosol Mass Spectrometry for Investigating Primary and Secondary Organic Aerosols under Low Loading Conditions

摘要

A new method, near-infrared laser desorption/ionizationnaerosol mass spectrometry (NIR-LDI-AMS), is describednfor the real time analysis of organic aerosols at atmosphericallynrelevant mass loadings. Use of a single NIRnlaser pulse to vaporize and ionize particle componentsndeposited on an aluminum probe results in minimalnfragmentation to produce exclusively intact pseudomolecularnanions at [M - H]-. Limits of detection (totalnparticulate mass sampled) for oxidized compounds ofnrelevance to atmospheric primary and secondary organicnaerosol range from 89 fg for pinic acid to 8.8 pgnfor cholesterol. NIR-LDI-AMS was used in conjunctionnwith the University of Vermont Environmental Chambernto study secondary organic aerosol (SOA) formationnfrom ozonolysis of limonene at total aerosol massnloadings ranging from 3.2 to 25.0 μg m-3 and with antime resolution of several minutes. NIR-LDI-AMSnpermitted direct delineation between gas-phase, homogeneousnSOA formation and subsequent heterogeneousnaerosol processing by ozone.