1. EXPORT EFFICIENCY OF BLACK CARBON IN CONTINENTAL OUTFLOW: IMPLICATIONS FOR THE GLOBAL BUDGET AND FOR ARCTIC DEPOSITION
Rokjin, J. Park, Daniel J. Jacob, Paul I. Palmer, Antony D. Clarke, Rodney J. Weber, Mark A. Zondlo, Fred L. Eisele, Alan R. Bandy, Donald C. Thornton, Glen W. Sachse, and Tami C. Bond
with support from the NASA Atmospheric Chemistry Modeling and Analysis Program

2. BC IN THE ATMOSPHERE CHEMICAL AGING How long ()? How much?
BC is operationally defined as the light-absorbing fraction of carbonaceous aerosols.
PRIMARY EMISSION
CHEMICAL AGING
WET DEPOSITION
coating by sulfate
or organics
oxidation
Hydrophobic
Hydrophilic
How long ()?
How much?
Most global models assume  = 1 day for chemical conversion of hydrophobic to hydrophilic BC.

3. OBJECTIVES
Assess BC export efficiencies in Asian outflow over the NW pacific constrained by aircraft observations from the TRACE-P mission (Feb-Apr 2001).
- Comparison of the BC observations [Clarke et al., 2004] with soluble and insoluble species offers constraints on BC solubility.
Determine the model time scale () for conversion of fresh hydrophobic to hydrophilic BC as constrained by the TRACE-P observations.
Examine implications for the BC global burden and its deposition flux to the Arctic (“dirty snow”).

4. EXPORT EFFICIENCY NORMALIZED EXPORT EFFICIENCY
BC emissions over East Asia are highly uncertain [Carmichael et al, 2003].
[Koike et al., 2003; Parrish et al, 2004]
X = combustion-derived species
RX = emission ratio (X/CO)
Δ = enhancements relative to background
NORMALIZED EXPORT EFFICIENCY
INDEPENDENT OF
EMISSION RATIO, R
We use the TRACE-P P-3B data north of 30oN for which China provided a common
source region.

5. OBSERVED EXPORT EFFICIENCY BC vs SOX (≡SO2(g)+SO42-) and HNO3T (≡HNO3(g)+NO3-)
Normalized export efficiency
BC AEROSOLS ARE SIGNIFICANTLY SOLUBLE BUT NOT AS MUCH AS
SULFATE OR NITRATE.

6. MEAN PROFILES OF SOX, fine NO3-, BC GEOS-CHEM chemical tracer model vs
MEAN PROFILES OF SOX, fine NO3-, BC GEOS-CHEM chemical tracer model vs. TRACE-P observations
P3B DATA over NW Pacific (30 – 45oN, 120 – 140oE)
No significant model bias in SOx and NO3- indicates
successful simulation of scavenging in Asian outflow.
Model underestimates BC observations by factor of 2; insufficient emissions [Bond et al., 2004] or excessive scavenging?

7. BC NORMALIZED EXPORT EFFICIENCY IN ASIAN OUTFLOW (GEOS-CHEM vs TRACE-P )
Simulation with  = 1±1 days for BC scavenging provides the best fit to the TRACE-P observations.

8. IMPLICATION FOR CLIMATE
BC BURDEN & ARCTIC DEPOSITION FLUX
BC lifetime is 5.8 ± 1.8 days, 50% longer than that of sulfate,
global burden is 0.11 ± 0.03 Tg using Bond et al. [2004] inventory, and resulting decrease in Arctic snow albedo = 3.2 ± 2.5%
with  = 1 ± 1 days from the TRACE-P constraints

9. CONCLUSIONS Global model simulations of BC for assessment of climate
impacts are highly sensitive to the assumed scavenging
efficiency of BC by precipitation.
Comparison of normalized export efficiencies for BC, SOx,
HNO3T in Asian outflow indicates that BC is scavenged in wet
updrafts but not to the extent of sulfate or nitrate.
The current model parameterizations, based on direct
emission of hydrophobic BC and conversion to hydrophilic
BC on a time scale of τ days, are consistent with vertical
profiles observed in Asian outflow if τ = 1±1 days.
The export efficiency of BC is 50% at 4 km altitude,
the atmospheric lifetime is 5.8±1.8 days, the global burden
is 0.11±0.03 Tg using Bond et al. [2004] inventory, and the
decrease in Arctic snow albedo due to BC is 3.1±2.5%.