AMATI, a New Tool for Rapid Thermodynamic Calculations on Large Field Datasets

PEDRO CAMPUZANO-JOST, Donna Sueper, Simon Clegg, Benjamin A. Nault, Hongyu Guo, Jose-Luis Jimenez, CIRES, University of Colorado, Boulder

     Abstract Number: 320
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
The hygroscopicity and acidity of ambient aerosols are key intensive properties. They have a strong impact on the physical properties of the aerosol, such as phase state and viscosity. They control the partitioning between gas- and particle-phase for inorganic nitrogen and chlorine, and also for some organic components. Importantly, both aerosol water content (LWC) and acidity (in particular, its most direct proxy, pH) influence the kinetics and thermodynamics of many heterogeneous and aqueous-phase chemical processes in the atmosphere. Hence, an accurate knowledge of these quantities is key to understanding aerosol chemical regimes in a particular region. Both LWC and pH can be measured directly with specialized instrumentation, but especially for pH such instrumentation is still not suitable for rapid field measurements. Hence, thermodynamic models (such as the Extended Aerosol Thermodynamic Model, E-AIM) have been used to predict pH and water content based on a combination of aerosol and gas measurements.

Based on our previous work using E-AIM to predict pH for a large set of aircraft missions, we have developed a general software interface for E-AIM in Igor Pro, AMATI (AMbient Aerosol Thermodynamic calculator in Igor). It simplifies performing rapid, robust LWC and pH calculations on large field datasets. It is designed to use data from the Aerodyne AMS/ACSM as the main aerosol inputs, but can easily be adapted for other particle composition sensors. It can handle a large array of gas-phase inputs for inorganic nitrogen and chloride, and can also calculate pH iteratively with fast and robust convergence if one or several of these inputs are missing. Importantly, it provides a large set of diagnostic tools to evaluate the accuracy of the model output. Examples from recent field projects are used to demonstrate the performance and potential applications of the package, with an emphasis on the free troposphere.