Text S1. Specific Application of Thermodynamic State Equations in a Reduced Nitrogen Compound (RNC)-Sulfuric Acid-Nitric Acid chemical system
The Extended-Aerosol Inorganics Model (E-AIM) considers the partitions of a particular chemical in four phases: gas (g), solid (s, including its salts), aqueous solution (aq) and hydrophobic organic solution (org) at any given relative humidity and temperature in a fixed total volume of 1 m3 and at a fixed total pressure of 101,325 Pa. The E-AIM model (http://www.aim.env.uea.ac.uk/aim/aim.php) allows the users to specify the initial concentration of the chemical (as moles in 1 m3), as well as instructions regarding the properties and activity (discussed in details in following sections) of the chemical.
All possible states for water (g, aq and s) are considered by the E-AIM. However, in this study, low temperatures at which the water may start to freeze were avoided. The autoprotolysis of water and both hydrolysis equilibria of the inorganic diacid H2SO4are also considered to include H+, HSO4 and OHconcentrations in the calculations. The protonation of ammonia and the formation of ammonium nitrate and sulfate solids are considered in our simulations to represent the partition of ammonia in aqueous solution and solid phases as accurately as possible. Since NH4+, SO42− and NO3 are the primarily inorganic ions of consideration, E-AIM Model II was used throughout our study. Thermodynamic data on ammonia and its nitrate and sulfate salts have been extensively studied and their thermodynamic properties and constants are relatively well established.1 Therefore, default inputs (including the methods to estimate activities) in the existing E-AIM Model II on ammonia, sulfuric acid and nitric acid are used without further modification. Wang et al.2identified that ammonia and nitric acid in the ammonia-sulfuric acid-nitric acid ternary system could only condense at or below 278 K, but above 263 K, suggesting that our simulation results on the ammonia-sulfuric acid-nitric acid ternary system should have an uncertainty within the range of −3.8% to +1.7%.
In this study, for example, the following series of state equations are possible for ethanolamine (MEA, with its conjugated acid labeled as MEAH+):
\(\text{MEA\ }\left(g\right)\rightleftharpoons MEA\left(\text{aq}\right)\)Eq. S1
\(\text{MEA\ }\left(\text{aq}\right)+\ H^{+}(aq)\rightleftharpoons\text{MEAH}^{+}\left(\text{aq}\right)\)Eq. S2
\(\text{MEAH}^{+}\left(\text{aq}\right)+\text{NO}_{3}^{-}(aq)\rightleftharpoons MEA\bullet HNO_{3}\left(s\right)\)Eq. S3
\(MEA\bullet HNO_{3}\left(s\right)\rightleftharpoons MEA\left(g\right)+\ HNO_{3}\left(g\right)\)Eq. S4
\(2\text{MEAH}^{+}\left(\text{aq}\right)+\text{SO}_{4}^{2-}(aq)\rightleftharpoons 2MEA\bullet H_{2}SO_{4}\left(s\right)\)Eq. S5
\(2MEA\bullet H_{2}SO_{4}\left(s\right)\rightleftharpoons MEA\left(g\right)+\ H_{2}SO_{4}\left(g\right)\)Eq. S6
Each of the equation above involves an equilibrium constant Kthat is temperature dependent and may have been determined experimentally or can be derived using other thermodynamic properties of MEA.