a The saturation vapor pressure (in Pa) of the amine at 298 K [Ge et al., 2011b; Linstrom and Mallard, 2018].
b The gaseous basicity (in kJ∙mol−1) at 298 K [Hunter and Lias, 1998].
c The aqueous base hydrolysis constant (in mol∙kg−1) of the amine at 298.15 K [Ge et al., 2011b].
d The solid/gas equilibrium dissociation constant (in Pa2) of the nitrate salt of the amine at 298.15 K [Ge et al., 2011b].
e The transitional temperature (in K) of nitric acid condensation, defined as the temperature at which the moles of total nitrate in the condensed phases equals to 5% of the initial moles of nitric acid and determined in this study. Details on uncertainty estimations are in the Supporting Information (Table S1).
f classified based on the Tc of the amine: Group I amines with Tc ≤ 278 K and Group II with Tc > 288 K.
At 266 K; Extrapolated to 298 K based on the Antoine Equation [Linstrom and Mallard, 2018];* At 293 K.
Since the salts of amines with NA [Salo et al., 2011] showed comparable or lower saturation vapor pressure than that of ammonium nitrate, it is conceivable that the cluster growth in the ASN nucleation system can be enhanced by amines due to the condensation of amines and NA, at least at low temperature. Amines may, therefore, contribute to both the formation and growth of FNCs. Also, due to the various amines observed in the atmosphere, it is uncertain how their chemical structures may play a role in their contribution to the ASN nucleation system. Furthermore, since ambient amines are typically much lower in concentrations than ammonia, investigation on the effect of excess ammonia on the possible condensation of amines and NA under ambient conditions is also warranted.
In this study, the contribution of amines to the condensation of NA on nanoparticles was investigated using Extended Aerosol Inorganics Models (E-AIM) [Wexler and Clegg, 2002; Ge et al., 2011b] under conditions that closely resemble typical ambient conditions, especially those found in an urban environment. Our results showed that monoamines and NA can condense at comparable temperature to ammonia. Much to our surprises, significant condensation of NA was observed, at room temperature, with amines that can form additional hydrogen bonds. Such process seems to enhance the water uptake by nanoparticles at lower relative humidity (RH) and unaffected by the presence of excess ammonia. Our results suggest that RNCs may facilitate the NPF by co-condensing with NA on nanoparticles at a wide range of temperatures. Our results may be important in regions commonly polluted with amine emissions, such as megacities, agricultural lands and heavily industrialized areas.