396
G. Fanourgakis et al.
63.1 Introduction
The organic component represents a significant amount of the total submicron dry
aerosol mass which, depending on the location and the atmospheric conditions, may
reach the 30–70% of the total mass [1]. The contribution of the organic mass to
the particles number concentrations and to the cloud condensation nuclei (CCN) are
here quantified by performing simulations with the global 3-dimensional chemistry
transport model TM4-ECPL [2, 6, 7] with and without emissions of primary organic
particles and formation of secondary organic aerosols. The model is coupled to the
aerosol microphysics module M7 [5]. All major aerosol components namely mineral
dust, black carbon, sea-salt, organics, and sulfate are considered in the model as
internally or externally mixed particles represented by log-normal mass and number
distributions that evolve by coagulation, condensation and nucleation.
63.2 Results
63.2.1 Surface Distribution of CCN at Supersaturation Ratio
0.2%
The annual surface distribution of the CCN at 0.2% supersaturation ratio (denoted
as CCN 0.2 ) obtained from the two simulations with the TM4-ECPL model, with
and without organic mass, are shown in Fig. 63.1a, b respectively. Calculations of
the CCN were performed using the κ-Köhler theory as developed by Petters et al.
[3] that expresses the hygroscopicity κ of the aerosol particles as a function of the
volume-weighted fraction hygroscopic parameter of each aerosol component. The
hygroscopicity parameters used in the present study are κ SO4 = 0.6 (sulfate), κ BC =
0.0 (black carbon), κ DU = 0.0 (dust), κ SS = 1.0 (sea-salt), κ ORG = 0.1 (organics).
When organics are considered in the simulation (Fig. 63.1a, with organics), nearsurface CCN 0.2 number concentrations are reaching ~3500 cm
−3 at the polluted
areas, which is close to the value of ~3000 cm
−3 computed as the multi-model
mean maximum during a model intercomparison based on the results of 15 global
models [7]. Neglecting the contribution of organics to the formation of the CCN 0.2 ,
the maximum of the near-surface global CCN 0.2 distribution drops to ~1200 cm
−3
(Fig. 63.1b, without organics). In Fig. 63.1c is shown the percentage difference of
the CCN 0.2 distribution between these two simulations. Over land, this difference
is found to be >50% with the highest differences that reach 90% calculated in high
polluted areas.
G. Fanourgakis et al.
63.1 Introduction
The organic component represents a significant amount of the total submicron dry
aerosol mass which, depending on the location and the atmospheric conditions, may
reach the 30–70% of the total mass [1]. The contribution of the organic mass to
the particles number concentrations and to the cloud condensation nuclei (CCN) are
here quantified by performing simulations with the global 3-dimensional chemistry
transport model TM4-ECPL [2, 6, 7] with and without emissions of primary organic
particles and formation of secondary organic aerosols. The model is coupled to the
aerosol microphysics module M7 [5]. All major aerosol components namely mineral
dust, black carbon, sea-salt, organics, and sulfate are considered in the model as
internally or externally mixed particles represented by log-normal mass and number
distributions that evolve by coagulation, condensation and nucleation.
63.2 Results
63.2.1 Surface Distribution of CCN at Supersaturation Ratio
0.2%
The annual surface distribution of the CCN at 0.2% supersaturation ratio (denoted
as CCN 0.2 ) obtained from the two simulations with the TM4-ECPL model, with
and without organic mass, are shown in Fig. 63.1a, b respectively. Calculations of
the CCN were performed using the κ-Köhler theory as developed by Petters et al.
[3] that expresses the hygroscopicity κ of the aerosol particles as a function of the
volume-weighted fraction hygroscopic parameter of each aerosol component. The
hygroscopicity parameters used in the present study are κ SO4 = 0.6 (sulfate), κ BC =
0.0 (black carbon), κ DU = 0.0 (dust), κ SS = 1.0 (sea-salt), κ ORG = 0.1 (organics).
When organics are considered in the simulation (Fig. 63.1a, with organics), nearsurface CCN 0.2 number concentrations are reaching ~3500 cm
−3 at the polluted
areas, which is close to the value of ~3000 cm
−3 computed as the multi-model
mean maximum during a model intercomparison based on the results of 15 global
models [7]. Neglecting the contribution of organics to the formation of the CCN 0.2 ,
the maximum of the near-surface global CCN 0.2 distribution drops to ~1200 cm
−3
(Fig. 63.1b, without organics). In Fig. 63.1c is shown the percentage difference of
the CCN 0.2 distribution between these two simulations. Over land, this difference
is found to be >50% with the highest differences that reach 90% calculated in high
polluted areas.