EC-17. Introducing AMATI, a new tool for rapid thermodynamic calculations on large field datasets

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, viscosity and ambient light extinction. They control the partitioning between gas- and particle-phase for inorganic nitrogen and chlorine, and can also affect the partitioning of organic species, such as amines. Importantly, both aerosol water content and acidity influence the viability of a large range of heterogeneous and aqueous-phase chemical processes and reactions in the atmosphere. Hence, an accurate knowledge of these quantities is key to understanding aerosol chemical regimes in a particular region. Both aerosol water content (LWC) and acidity (in particular, its most direct proxy, pH) can be measured directly with specialized instrumentation, but especially in the case of pH such instrumentation is still not suitable for routine 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). The aim is to simplify performing rapid, robust LWC and pH calculations for 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 sensors. It can handle a large array of gas-phase inputs for inorganic nitrogen and chloride, and can also calculate pH iteratively with fast convergence if one or several of these inputs are missing. Lastly, it provides a large set of diagnostic tools to evaluate the model output. Examples from the recent NASA ATom and FIREX campaigns are used to demonstrate the performance and potential applications of the package, with an emphasis on the free troposphere.