ADCHAM - A multilayer aerosol dynamics, gas and particle chemistry chamber model
P. Roldin1, E.Z. Nordin2, A.C. Eriksson1, D. Mogensen3, A. Rusanen3, E. Swietlicki1, M. Boy3 and J. Pagels2
1
Division of Nuclear Physics, Lund University, P.O. Box 118 SE-221 00 Lund, Sweden
2
Ergonomics and Aerosol Technology, Lund University, Lund, Sweden
3
Atmospheric Sciences Division, Department of Physics, University of Helsinki, Finland
Keywords: Secondary organic aerosol, multilayer, aerosol dynamics, gas phase chemistry
Laboratory experiments show that SOA
particles can form a solid or semi-solid amorphous
phase (e.g. Virtanen et al., 2010). If an amorphous
solid phase is formed gas to particle partitioning will
not be well represented by a thermodynamic
equilibrium process (Pöschl, 2011).
ADCHAM combines an updated version of the
aerosol dynamics and particle phase chemistry
module from ADCHEM (Roldin et al., 2011) and the
gas phase Master Chemical Mechanism (MCMv3.2).
ADCHAM explicitly treats the bulk diffusion of all
compounds (including O3) between different particle
layers and bulk reactions analogous to Shiraiwa et al.
(2010). For all compounds except O3 the gas-surface
exchange is modeled with a condensation/evaporation
equation which considers the gas-surface diffusion
limitations and non-unity dissolution probability in
the surface bulk layer (mass accommodation). In each
particle layer the model considers oligomerization,
equilibrium reactions between crystalline inorganic
salts and their dissolved ions, and oxidation of SOA
with O3. The oligomerization and solid salt formation
increases the viscosity of the particle bulk which
limits the diffusion of the liquid compounds. We
estimate the pure liquid saturation vapor pressures,
, using either the group contribution method
SIMPOL (Pankow & Asher, 2008) or the method by
Nannoolal et al. (2008). The corresponding
equilibrium vapor pressures over each particle size
are derived with Raoult’s law, using the activity
coefficients calculated with AIOMFAC (Zuend et al.,
2011) and the Kelvin effect.
ADCHAM is currently used to model smog
chamber experiments for both anthropogenic and
biogenic SOA. Figure 1 shows the model layer
structure when modeling SOA and NH4NO3
formation on dry (NH4)2SO4 particles. Figure 2a
illustrates modeled evaporation time scales for αpinene SOA particles in vacuum, 1) when SOA is
liquid-like, 2) when SOA is amorphous (solid), 3)
when SOA particles are amorphous and partly
oxidized with O3 forming 50 % non-volatile and 50 %
more volatile (
1 ) oxidation products, and 4)
when SOA is amorphous and partly oligomerized.
The slow evaporation of amorphous particles is due to
the accumulation of low or non-volatile (NV)
compounds in the particle surface layer (Fig 2b).
Gas phase
Monom. NH3 HNO3 H2SO4 O3
Near surf. gas phase Monom. NH3 HNO3 H2SO4
Surf. mono layer
O3
O3
Bulk , 1
Monom.→Oligom., Monom.+O3→Ox. Prod
NH4NO3(s) ↔ NH4+ (aq) + NO3-(aq)
(NH4)2SO4(s) ↔ 2NH4+ (aq) + SO4-2(aq)
Bulk, 2
Monom.→Oligom., Monom.+O3→Ox. Prod
NH4NO3(s) ↔ NH4+ (aq) + NO3-(aq)
(NH4)2SO4(s) ↔ 2NH4+ (aq) + SO4-2(aq)
…
Bulk, n-1
Monom.→Oligom , Monom.+O3→Ox. Prod
NH4NO3(s) ↔ NH4+ (aq) + NO3-(aq)
(NH4)2SO4(s) ↔ 2NH4+ (aq) + SO4-2(aq)
Bulk, n
Monom.→Oligom., Monom.+O3→Ox. Prod
NH4NO3(s) ↔ NH4+ (aq) + NO3-(aq)
(NH4)2SO4(s) ↔ 2NH4+ (aq) + SO4-2(aq)
Core
(NH4)2SO4(s)
Figure 1. Model layer structure.
Figure 2. a) modeled SOA evaporation, b) fraction of
SOA+O3(p) oxidation products from simulation 3 and
oligomer mass fraction from simulation 4, in each
particle layer after 3 hours of evaporation.
Nannoolal, J., Rarey, J., Ramjugernath, D., (2010),
Fuild Phase Equilibria, 269, 117-133
Pankow, J. F. & Asher, W. E. (2008), Atmos. Chem.
Phys., 8, 2773–2796
Pöschl, U., (2011), Atmos. Res. 101, 562–573.
Roldin et al., (2011), Atmos. Chem. Phys., 11, 58675896
Virtanen et al., (2010), Nature, 467, 824-827.
Zuend et al., (2011), Atmos. Chem. Phys., 11, 9155–
9206
Shiraiwa, M., Pfrang, C., Pöschl, U., (2010), Atmos.
Chem. Phys., 10, 3673–3691