Carbonaceous Aerosol Processing in the Mexico City Metropolitan Area
Abstract
Mexico City Metropolitan Area (MCMA) is a mega-city environment with significant air pollution. Emissions of primary particles and secondary particle precursors are high and build up in the boundary layer during the night with the concentrations peaking during the early morning. Daily photochemistry alters the chemical, physical, and optical properties of these primary particles. The Aerodyne mobile laboratory, outfitted with a suite of gas and particle instruments, investigated the processing of these primary particles at the T0 site as part of the Mexico City Metropolitan Area (MCMA) component of the MILAGRO campaign (March 2006). Aerosol particle mass, chemistry (bulk and surface PAHs), absorption and scattering, and size-distributions (mobility and vacuum aerodynamic) were measured. Simultaneous measurements by the AMS and SMPS instruments on mobility-selected particles yielded the particle mass, volume, density, composition, dynamic shape factor, and fractal dimension. Early morning primary particle emissions were dominated by fractal particles containing significant surface bound PAHs, similar in morphology and composition to diesel-generated particles. During the morning, these particles were observed to grow in mass and become more spherical via gas-to-particle condensation of photochemical products (oxidized organic compounds and ammonium nitrate). Particles with fractal morphologies and surface bound PAH signals were no longer evident after late morning and at down wind locations. Emission ratios, correlations with carbon monoxide, and organic aerosol chemical classifications will be presented. The rapid processing and fate of these primary particles will be discussed with an emphasis on gaining insight into the processing mechanisms.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.A24C..06O
- Keywords:
-
- 0305 Aerosols and particles (0345;
- 4801;
- 4906);
- 0317 Chemical kinetic and photochemical properties;
- 0345 Pollution: urban and regional (0305;
- 0478;
- 4251);
- 0365 Troposphere: composition and chemistry