Size-differentiated Inorganic Chemical Composition of Atmospheric Particles at the T1 Supersite during the MILAGRO Field Campaign

Cascade impactors with eight cut stages were used to sample atmospheric particles at Tecámac (T1 supersite), State of Mexico, during the MILAGRO field campaign in March 2006. The sampling site is located in the northeast (NE) edge of Mexico City; it experiences both fresh local emission and aged pollutants produced in Mexico City. Samples were analyzed to determine total mass, Ca²⁺, Na⁺, Mg²⁺, NH₄⁺, K⁺, Cl^-, SO₄^2-, and NO₃^- concentrations. Mexico City pollution plume contributes with particle mass in all aerodynamic diameter sizes, but local emissions are quite important. PM₁₀ average mass concentration was 30.3 µg m^-3; for coarse mode (3.2 – 10 µm) was 11.7 µg m^-3 and fine mode (0.18 – 1.8 µm) was 18.6 µg m^-3. The ions NO₃^-, SO₄^2-, Na⁺, and NH₄⁺ were found in high concentrations on fine mode, and high concentrations of Cl^-, K⁺, Ca²⁺, and Mg²⁺ were found on coarse mode.