Project aguila: In situ measurements of Mexico City air pollution by a research aircraft

Measurements of aerosol concentrations, chemical species and meteorological quantities in the air above Mexico City were obtained from an instrumented research aircraft. Concentrations of particles in the size range between 0.12 and 3.12 μm were nearly invariant with height, and typical values were of the order of 5000 cm −3. However, particles smaller than 0.12 μm were confined to the lowest few hundred meters of the atmosphere until the morning temperature inversion dissipated, after which time those particles, together with newly formed particles created by secondary processes, mixed to a greater height above the city. Total particle concentrations near the surface attained values in excess of 60,000 cm −3. An examination of the corresponding profiles of SO 2 suggests that combustion processes are likely sources for the additional small particles.