Formation of semivolatile inorganic aerosols in the mexico city metropolitan area during the milagro campaign

V. A. Karydis, A. P. Tsimpidi, W. Lei, L. T. Molina, S. N. Pandis
2011 Atmospheric Chemistry and Physics Discussions  
One of the most challenging tasks for chemical transport models (CTMs) is the prediction of the formation and partitioning of the major semi-volatile inorganic aerosol components (nitrate, chloride, ammonium) between the gas and particulate phases. In this work the PMCAMx-2008 CTM, which includes the recently developed aerosol thermodynamic model ISORROPIA-II, is applied in the Mexico City Metropolitan Area in order to simulate the formation of the major inorganic aerosol components. The main
more » ... ponents. The main sources of SO 2 (such as the Miguel Hidalgo Refinery and the Francisco Perez Rios Power Plant) in the Mexico City Metropolitan Area (MCMA) are located in Tula, resulting in high predicted PM 1 (particulate matter with diameter less than 1 µm) sulfate concentrations (over 25 µg m −3 ) in that area. The average predicted PM 1 nitrate concentrations are up to 3 µg m −3 (with maxima up to 11 µg m −3 ) in and around the urban center, mostly produced from local photochemistry. The presence of calcium coming from the Tolteca area (7 µg m −3 ) as well as the rest of the mineral cations (1 µg m −3 potassium, 1 µg m −3 magnesium, 2 µg m −3 sodium, and 3 µg m −3 calcium) from the Texcoco Lake resulted in the formation of a significant amount of aerosol nitrate in the coarse mode with concentrations up to 3 µg m −3 over these areas. PM 1−10 (particulate matter with diameter between 1 and 10 µm) chloride is also high and its concentration exceeds 2 µg m −3 in Texcoco Lake. PM 1 ammonium concentrations peak at Correspondence to: S. N. Pandis (spyros@chemeng.upatras.gr) Published by Copernicus Publications on behalf of the European Geosciences Union. 13306 V. A. Karydis et al.: Formation of semivolatile inorganic aerosols fine aerosol is simulated using the bulk equilibrium assumption and to the remaining aerosol sections using a dynamic approach, is needed in order to accurately simulate the size distribution of the inorganic aerosols. The bulk equilibrium approach fails to reproduce the observed coarse nitrate and overpredicts the fine nitrate. Sensitivity tests indicate that sulfate concentration in Tula decreases by up to 0.5 µg m −3 after a 50 % reduction of SO 2 emissions while it can increase by up to 0.3 µg m −3 when NO x emissions are reduced by 50 %. Nitrate concentration decreases by up to 1 µg m −3 after the 50 % reduction of NO x or NH 3 emissions. Ammonium concentration decreases by up to 1 µg m −3 , 0.3 µg m −3 , and 0.1 µg m −3 after the 50 % reduction of NH 3 , NO x , and SO 2 emissions, respectively.
doi:10.5194/acpd-11-21995-2011 fatcat:eewta2adu5ae3pzuarjkfwhncm