Aerosol Analysis with the High Resolution Time-of-Flight Aerosol Mass Spectrometer at the Urban SuperSite (T0) in Mexico City during MILAGRO

Non-refractory submicron (approx. PM1) ambient aerosol was analyzed from March 10 - 30, 2006 in Mexico City at the T0 (IMP) urban supersite with the High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS, DeCarlo et al., 2006). The HR-ToF-AMS can resolve the elemental composition of most mass fragments, especially for the low m/z (below 100) where the majority of the signal occurs in the AMS when using electron ionization (EI). Mass concentrations and size distributions of inorganic species (Ammonium, Chloride, Nitrate, Sulfate) are similar to results from MCMA-2003 (Salcedo et al., 2006). Positive Matrix Factorization (PMF) analysis of the Organic mass indicates that primary emissions and urban SOA formation are important for this dataset, while the impact of large biomass burning plumes is more episodic and correlates with satellite fire counts. A regional highly oxygenated organic aerosol is also observed. C-14 filter analysis results are generally consistent with the PMF results. Organic amines are detected in the aerosol during some mornings. Lead is also detected and correlates well with measurements from other techniques. The chemically-resolved aerosol volatility is characterized using a thermal denuder in front of the AMS. A new organic elemental analysis technique developed by our group is also applied to the organic aerosol (Aiken et al., 2007) to determine the oxygen-to-carbon (O/C) and organic mass to organic carbon (OM/OC) ratios.