Potential alteration of ice clouds by
aircraft soot
Joyce E. Penner and Xiaohong Liu
Department of Atmospheric, Oceanic and Space Sciences
University of Michigan
Aviation, Atmosphere and Climate
30 June - 3 July 2003
Friedrichshafen, Germany
Evidence for alteration of ice clouds by
aircraft emissions
• Soot associated with increasing ice concentrations in
regions of enhanced soot most probably due to
aircraft (Ström and Ohlsson, 1998)
• Trend difference in high clouds observed over
regions with Computed Contrail cover > 0.5% was
3.5%/decade (land) and 1.6%/decade (ocean)
between 1984 and1990 (ISCCP data) (Fahey and
Schumann et al. (2001))
• Model results:
– Jensen and Toon [1997]
– Lohmann [2000]
Mechanisms forming ice clouds
• Homogeneous nucleation
– Jhaze = Jw(Teff); Teff= T+lDTm
• Deposition nucleation
– Js’=(4p2rN2Zse)/(2pln(kT))1/2ag2cl,sexp[-DFg,S/kT]
– Fg,S=[16pMw2si/v3]/[3(RTriln Sv,i)2]f(mi,v,x); mi,v =0.9
– or: Meyer’s empirical formulation:
• Nid=exp{a+b[100(RHi-1]}
• Immersion nucleation
– Js’=(4p2rN2kT)/(h)  c1,S exp[-Dg*/(RT)-DFg,S/(kT)]
– Fg.S=[16pMw2si/v3]/(3[Lm,0ri ln (T0/Te)]2) f(mi,w,x); mi,w =0.5
• Contact nucleation
Warm case (w=20 cm/s)
800
600
600
z (m)
800
400
200
0
0.001
0.01
0.1
1
10
400
200
hf only
hf+deposition
hf+immersion
hf only
hf+deposition
hf+immersion
0
0.001
100
0.01
Warm case (w=100 cm/s)
0.1
Ni (1/cc)
Ni (1/cc)
800
600
z (m)
z (m)
Warm case (w=4 cm/s)
400
200
0
0.001
hf only
hf+deposition
hf+immersion
0.01
0.1
Ni (1/cc)
1
10
100
1
10
100
Cold case (w=20 cm/s)
Cold case (w=4 cm/s)
800
800
z (m)
600
400
400
200
200
hf+deposition
hf+deposition
hf+immersion
hf+immersion
0
0.001
0.01
0.1
hf only
hf only
1
10
0
0.001
0.01
0.1
Ni (1/cc)
100
Cold case (w=100 cm/s)
Ni (1/cc)
800
600
z (m)
z (m)
600
400
200
hf only
hf+deposition
hf+immersion
0
0.001
0.01
0.1
Ni (1/cc)
1
10
100
1
10
100
Parameterization for homogeneous ice
formation
• T ≥ 6.07 ln w - 55.0 (fast growth; high T low w):
– Ni=min{exp(a2+b2T+c2lnw)Naa1+b1T+c1lnw , Na}
• T<6.07 ln w - 55.0 (slow growth; low T high w):
– Ni=min{exp(a4+(b4+b5lnw) T+c4lnw)Naa3+b3T+c3lnw , Na}
Homogeneous + deposition nucleation
• Lower updraft velocities and higher
temperatures=> deposition nucleation only:
–
–
–
–
Threshold: T  14.387 ln(w) - 18.825; and w  0.3 m/s
Si (%) = a  T + b;
where a and b are a function of w
Use with Meyer’s (1992) parameterization
• Use homogeneous parameterization at higher
updrafts and lower temperatures
Homogeneous, deposition, and immersion freezing
•
Threshold temperature for immersion, deposition freezing:
– T  a ln(w) + b
– a, b are functions of the number of soot particles Ns
•
Immersion freezing:
– Ni,s=min{exp(a22)Nsb22exp(bT)wc, Ns}
– b, c are functions of ln Ns
•
Deposition freezing:
– Maximum supersaturation; Simax(%) = A T2 + BT + C
•
– A, B, C are functions of w
– Number of ice crystals from Meyer’s (1992) parameterization for
deposition
Use homogeneous parameterization at lower T
Immersion nucleation: ice crystal number
Ice numer concentration (cm-3)
100
10
D = -60C
 = -40C
W=0.5 m s-1
1
W=-0.04 m s-1
0.1
0.01
0.001
0.001
Sulphate = 200 cm-3
0.01
0.1
1
Total soot concentration (cm-3)
10
Homogeneous nucleation: ice crystal number
W=1.0 m s-1
W=0.04 m s-1
10
1000
T=-40C
Ice crystal number density (cm-3)
229.3 K
214.2 K
194.1 K
-1
1
Ice crystal number density (cm-3)
-1
w = 0.04 m s
w = 1.0 m s
229.3 K
214.2 K
194.1 K
100
T=-60C
0.1
T=-80C
T=-40C
T=-60C
10
T=-80C
1
0.01
10
100
Sulfate aerosol
concentration (cm-3)
1000
10
100
-3
Total sulfate aerosol concentration (cm
)
Sulfate aerosol
concentration (cm-3)
1000
IMPACT/DAO
• Uses NASA DAO 1997 meteorological fields
• Uses IPCC-recommended emissions inventories
except for dust (from Ginoux for 1997 DAO winds)
• Emissions put into BL for dust and biomass burning
• Wet scavenging as in Harvard GEOS-CHEM model
except that large scale scavenging uses 0.5 g/m3 for
LWC
• Dry deposition as in Zhang, Gong et al. [AE, 2001]
Unique features
• DAO version has improved LWC for sulfate chemistry
• GMI model is based on IMPACT
• We can compare these results with more than one
set of meteorological fields:
– IMPACT/DAO=GMI/DAO
– GMI/MACCCM3
– GMI/GISSII’
Comparison of burdens: GMI models for 1995 ff BC
Burden
(Tg)
DAO
wet
(Tg/yr)
dry
(Tg/yr)
Lifetime
(days)
0.058
7.17
1.75
2.40
GISS 0.080
6.92
2.04
3.26
NCAR 0.060
7.31
1.88
2.4
GRANTOUR/CCM1 ffBC+bbBC:
0.20
9.56
2.66
DAO* 0.14
5.00
1.65
5.97
7.52
DAO
NCAR
GISS
Fuel tracer: ng/g
BC Burdens:
DAO
3.3e-4 Tg
GISS
5.7e-4 Tg
NCAR
4.1e-4 Tg
Zonal mean SO4 number concentration (cm-3)
Zonal mean ice number (cm-3), homogeneous nucleation only
Relative humidity wrt water (%)
Zonal mean soot number concentration (cm-3)
Zonal mean ice number (cm-3), heterogeneous +
homogeneous nucleation, surface sources
Difference in ice concentration between heterogeneous +
homogeneous and homogeneous only (cm-3), surface sources
Concentration of soot from aircraft (cm-3)
Concentration of ice (cm-3)
Aircraft + surface sources
Surface aerosol sources
Difference in ice concentration between surface +
aircraft aerosol sources and surface only sources (cm-3)
Conclusion
• An initial assessment of the potential impact
of aircraft emissions on ice concentrations
indicates significant increases (O˜100%) in
zonal mean concentrations near flight
corridors
• Better quantification requires a better
simulation of upper tropospheric humidity
together with full representation of all aerosol
types and their mode of nucleation