Henry's Law Constant of Atmospheric Amines and their Dependence on Temperature, pH, and Ionic Strength

In the atmosphere, amines are emitted from various anthropogenic (automobiles, industries, combustion, animal husbandry, cooking, tobacco smoke, treatment of sewage and waste, and CO2 capture), biogenic (ocean, biomass burning, and vegetation), and geologic sources. Atmospheric amines are basic, so they have acid-neutralizing capacity and potential to engage in acid-base reactions in the condensed phase, which could contribute to formation of new aerosol particles. Atmospheric amines can also participate in cloud chemistry and contribute to brown carbon formation. Despite the importance, amines are usually not incorporated into regional and global atmospheric chemical transport models largely due to lack of their thermodynamic properties such as The Henry`s law constants (KH). In this work, we choose six different amines and measure their KH in pure water and in 1-octanol for the temperatures pertinent to the lower troposphere (278 - 298 K) using a bubble column system coupled to an FTIR spectrometer. The KH values display strong dependence on temperature, pH and ionic strength. The characteristic time for amines to establish gas-droplet equilibrium is relatively short, and it can be significantly extended at lower temperatures or pHs. The evaluation of amines partitioning between gas phase and condensed phase implies that amines predominantly resides in rainwater, and loss to organic aerosol is negligible.