![]() It appears that (1) thermodynamic models constrained by gas aerosol measurements and (2) the phase partitioning of ammonia provide the best available predictions of aerosol pH. The modeled pH values from both E-AIM and ISORROPIA-II run with gas aerosol inputs agreed well with the aerosol pH predicted by the phase partitioning of ammonia. Using only measured aerosol chemical composition as inputs without any constraint for the gas phase, the E-AIM (Extended Aerosol Inorganics Model) and ISORROPIA-II thermodynamic equilibrium models tend to predict aerosol pH levels that are inconsistent with the observed NH3-NH4+ partitioning. Similarly, no relationship is observed between the cation / anion molar ratio and predicted aerosol pH. Based on the MILAGRO measurements, no correlation is observed between H+ levels inferred with the ion balance and aerosol pH predicted by the thermodynamic models and NH3-NH4+ partitioning. The ion balance and molar ratio methods assume that any deficit in inorganic cations relative to anions is due to the presence of H+ and that a higher H+ loading and lower cation / anion ratio both correspond to increasingly acidic particles (i.e., lower pH). All methods are evaluated against predictions of thermodynamic models and against direct observations of aerosol-gas equilibrium partitioning acquired in Mexico City during the Megacity Initiative: Local and Global Research Objectives (MILAGRO) study. In this study, four of the most common aerosol acidity proxies are evaluated and compared: (1) the ion balance method, (2) the molar ratio method, (3) thermodynamic equilibrium models, and (4) the phase partitioning of ammonia. M7, coupled to equilibrium simplified gas/aerosol partitioning model (EQSAM), which includes mineral dust components, sea salt and lumped organics in addition to the ammonium-sulfate-nitrate-water system.Given significant challenges with available measurements of aerosol acidity, proxy methods are frequently used to estimate the acidity of atmospheric particles. ![]() ![]() It consists of a modal aerosol dynamical model (with 7 modes), i.e. The aerosol scheme includes inorganic and organic secondary aerosols. ![]() To investigate these effects for the Amazonian atmosphere and climate, we apply the Mainz version of the ECHAM5 chemistry climate-model, which includes a modular earth submodel system (MESSy), in which on-line emissions, chemical transformations and deposition of gases and aerosols have been included. Subsequently, hygroscopic growth of aerosols and cloud formation are affected. Chemical box model studies indicate the importance of organic aerosol compounds for the total cation/anion balance and gas/aerosol partitioning during burning periods. Metzger, Max-Planck Institute for Chemistry, Mainz, Germany, Max-Planck Institute for Chemistry, Mainz, Germany, Max-Planck Institute for Chemistry, Mainz, Germany, Max-Planck Institute for Chemistry, Mainz, Germany, Max-Planck Institute for Meteorology, Hamburg, Germany, Max-Planck Institute for Chemistry, Mainz, Germany, Max-Planck Institute for Chemistry, Mainz, Germany, Instituto de Física, Universidade de São Paulo, São Paulo, Brasil, deforestation leads to unique changes in atmospheric gas and aqueous phase chemistry with consequences for gas/aerosol partitioning and cloud formation. ![]() Role of aerosol chemical composition on the formation of cloud condensation nuclei during biomass burning periods ![]()
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