A Computationally Efficient Multicomponent Equilibrium Solver for Aerosols (MESA)
This paper describes the development and application of a new multicomponent equilibrium solver for aerosol-phase (MESA) to predict the complex solid-liquid partitioning in atmospheric particles containing H+, NH4+, Na+, Ca2+, SO4=, HSO4-, NO3-, and Cl- ions. The algorithm of MESA involves integrating the set of ordinary differential equations describing the transient precipitation and dissolution reactions for each salt until the system satisfies the equilibrium or mass convergence criteria. Arbitrary values are chosen for the dissolution and precipitation rate constants such that their ratio is equal to the equilibrium constant. Numerically, this approach is equivalent to iterating all the equilibrium reactions simultaneously with a single iteration loop. Because CaSO4 is sparingly soluble, it is assumed to exist as a solid over the entire RH range to simplify the algorithm for calcium containing particles. Temperature-dependent mutual deliquescence relative humidity polynomials (valid from 240 to 310 K) for all the possible salt mixtures were constructed using the comprehensive Pitzer-Simonson-Clegg (PSC) activity coefficient model at 298.15 K and temperature-dependent equilibrium constants in MESA. Performance of MESA is evaluated for 16 representative mixed-electrolyte systems commonly found in tropospheric aerosols using PSC and two other multicomponent activity coefficient methods – Multicomponent Taylor Expansion Method (MTEM) of Zaveri et al. [2004], and the widely-used Kusik and Meissner method (KM), and the results are compared against the predictions of the Web-based AIM Model III or available experimental data. Excellent agreement was found between AIM, MESA-PSC, and MESA-MTEM predictions of the multistage deliquescence growth as a function of RH. On the other hand, MESA-KM displayed up to 20% deviations in the mass growth factors for common salt mixtures in the sulfate-poor cases while significant discrepancies were found in the predicted multistage deliquescence points as well as mass growth factors for the sulfate-rich systems. The MESA-MTEM configuration required only 5 to 10 single-level iterations to obtain the equilibrium solution for ~44% of the 328 multiphase problems solved in the 16 test cases at RH values ranging between 20% and 90%, while ~85% of the problems solved required less than 20 iterations. Based on the accuracy and computational efficiency considerations, the MESA-MTEM configuration is attractive for use in 3-D aerosol/air quality models.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 877587
- Report Number(s):
- PNNL-SA-42795; KP1202010; TRN: US200608%%432
- Journal Information:
- Journal of Geophysical Research - Atmospheres, Vol. 110, Issue D24; ISSN 0747-7309
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE
AEROSOLS
EQUILIBRIUM
ALGORITHMS
PHASE STUDIES
ATMOSPHERIC CHEMISTRY
ATMOSPHERIC PRECIPITATIONS
thermodynamic equilibrium
solid-liquid partitioning
aerosol composition
numerical methods
computational efficiency