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H 2 SO 4 –H 2 O–NH 3 ternary ion-mediated nucleation (TIMN): kinetic-based model and comparison with CLOUD measurements
New particle formation (NPF) is known to be an important source of atmospheric particles that impacts air quality, hydrological cycle, and climate. Although laboratory measurements indicate that ammonia enhances NPF, the physicochemical processes underlying the observed effect of ammonia on NPF are...
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Published in: | Atmospheric chemistry and physics 2018-12, Vol.18 (23), p.17451-17474 |
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Main Authors: | , , , , , |
Format: | Article |
Language: | English |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | New particle formation (NPF) is known to be an important source
of atmospheric particles that impacts air quality, hydrological cycle, and
climate. Although laboratory measurements indicate that ammonia enhances NPF,
the physicochemical processes underlying the observed effect of ammonia on
NPF are yet to be understood. Here we present a comprehensive
kinetically based H2SO4–H2O–NH3
ternary ion-mediated nucleation (TIMN) model that is based on the
thermodynamic data derived from both quantum-chemical calculations and
laboratory measurements. NH3 was found to reduce nucleation
barriers for neutral, positively charged, and negatively charged clusters
differently, due to large differences in the binding strength of
NH3, H2O, and H2SO4 to small clusters of
different charging states. The model reveals the general favor of nucleation
of negative ions, followed by nucleation on positive ions and neutral
nucleation, for which higher NH3 concentrations are needed, in
excellent agreement with Cosmics Leaving OUtdoor Droplets (CLOUD)
measurements. The TIMN model explicitly resolves dependences of nucleation
rates on all the key controlling parameters and captures the absolute
values of nucleation rates as well as the dependence of TIMN rates on
concentrations of NH3 and H2SO4, ionization
rates, temperature, and relative humidity observed in the well-controlled
CLOUD measurements well. The kinetic model offers physicochemical insights into
the ternary nucleation process and provides a physics-based approach to
calculate TIMN rates under a wide range of atmospheric conditions. |
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ISSN: | 1680-7324 1680-7324 |
DOI: | 10.5194/acp-18-17451-2018 |