New parameterization of sulfuric acid‐ammonia‐water ternary nucleation rates at tropospheric conditions

Recently, the classical theory of sulfuric acid‐ammonia‐water (H 2 SO 4 ‐NH 3 ‐H 2 O) nucleation was reinvestigated by including the effect of stable ammonium bisulfate formation into calculations. The predicted nucleation rates lowered by many orders of magnitude, bringing them close to agreement with the available experiments on H 2 SO 4 ‐NH 3 ‐H 2 O nucleation. However, because of complex thermodynamics involved, the theoretical calculations of nucleation rates are computationally demanding, and sometimes the theory breaks down at specific concentrations and temperatures. Here we present parameterized equations of ternary H 2 SO 4 ‐NH 3 ‐H 2 O nucleation rates, critical cluster sizes, and critical cluster compositions. Our parameterizations reduce the computing time of these values by a factor of 10 5 compared with the calculations with the full thermodynamic model. Also, our parameterizations provide reliable estimates for ternary nucleation rates in cases when the full theory fails in isolated points of the parameter space. The parameterized nucleation rates are accurate to one order of magnitude in nucleation rate. Because of their computational efficiency, our parameterizations are particularly suitable for large‐scale models of atmosphere. They are valid for temperatures above 235 K, sulfuric acid concentrations 5 · 10 4 –10 9 cm −3 , ammonia mixing ratios 0.1–1000 ppt, relative humidities 5%–95%, and nucleation rates over 10 −5 cm −3 s −1 . At these conditions, no significant nucleation occurs above 295 K.