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.