Submicron and Single Particle Organic Functional Group Composition in MIRAGE 2006

Submicron aerosol filter samples were collected on board the NCAR C-130, over Mexico and the Gulf of Mexico during MIRAGE in March 2006. The organic functional group and total organic mass composition was measured by Fourier Transform Infrared spectrometry. The functional groups identified include alkane, alkene and aromatic, hydroxyl and carbonyl groups. The higher mass loadings were observed during high ozone concentrations. The highest organic mass concentrations ranged between 5 and 10 μg m-3 with an organic-mass-to-organic-carbon ratio equal to 1.2. Composition of samples collected upwind and downwind of the Mexico City urban area was compared. Soft X-ray spectromicroscopy (STXM-NEXAFS) was also used for single particle analysis to study the different types of particles and their morphologies. The concentration and size distribution of oxygenated organic functional groups (carboxylic and ketonic carbonyl groups) and unsaturated carbon bonds (alkenes and aromatics) were used to characterize aging in particles.