Aerosol optical properties

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This page describes the aerosol optical properties that are used as input to the FAST-J photolysis mechanism in GEOS-Chem.

Aerosol optical properties update for GEOS-Chem v8-03-01

Starting with GEOS-Chem v8-03-01, several of the aerosol optical properties for the FAST-J photolysis code (specified in the input file jv_spec.dat have been updated to take into account new observations from various datasets. Colette Heald has created an overview document which describes the implementation of the aerosol optics for FAST-J.

NOTE: For this update there are no modifications to the source code itself, just to the jv_spec.dat file.

Authors

Name Affiliation Date
Randall Martin Dalhousie University 19 November 2009
Colette Heald Colorado State University 29 January 2010

Overview

The updated jv_spec.dat file was created to reflect current information about aerosol size distributions for sulfate, organic carbon, black carbon and sea salt. The method follows Martin et al., [2003]. Refractive indices are based on GADS. The Mie code is from ftp://ftp.giss.nasa.gov/pub/crmim/spher.f and described in Mischenko et al. [1999]. The current calculation uses an geometric standard deviation (sigma_g) of 1.6 for sulfate, BC and OC following Wang et al. [2003ab] and Drury et al. [submitted]. The sigma_g was also reduced to 1.5 and 1.8 for fine and coarse sea salt respectively following Jaegle et al. [2010]. Specific geometric mean radii (r_g) for each species and relative humidity are in the headers of jv_spec.dat. Consistent aerosol optical properties at 550nm were also created for the file jv_spec_aod.dat.

Some illustrative differences between the "old" jv_spec.dat and the "current" one are given below for 70% relative humidity. The most important change is that organic carbon aerosols are larger in the current version, and that sea salt are substantially smaller.

Sulfate Old Value New Value
r_g (um) 0.07 0.11
sigma_g 2.0 1.6
r_eff (um) 0.24 0.19
Qext (at 300nm) 2.4 2.6
Qext (at 600nm) 1.3 0.93
Organic Carbon Old Value New Value
r_g (um) 0.03 0.09
sigma_g 2.0 1.6
r_eff (um) 0.095 0.15
Qext (at 300nm) 1.2 2.3
Qext (at 600nm) 0.34 0.75
Black Carbon Old value New value
r_g (um) 0.01 0.02
sigma_g 2.0 1.6
r_eff (um) 0.039 0.035
Qext (at 300nm) 1.06 0.95
Qext (at 600nm) 0.43 0.33
Sea salt (accumulation mode) Old value New value
r_g (um) 0.38 0.15
sigma_g 2.0 1.5
r_eff (um) 1.32 0.23
Qext (at 300nm) 2.33 3.04
Qext (at 600nm) 2.60 1.37
Sea salt (coarse mode) Old value New value
r_g (um) 3.2 0.73
sigma_g 2.0 1.8
r_eff (um) 10.1 1.7
Qext (at 300nm) 2.07 2.22
Qext (at 600nm) 2.11 2.43

The updated jv_spec.dat for v8-02-05 has the following top-of-file header:

jv_spec.dat:  FAST-J, FJX (jmao 4/09), Updated AOD's (rvm, clh, 3/10)

Issues

It is likely that organic aerosol at ultraviolet wavelengths is more absorbing than included here as based on GADS [Koepke et al., 1997].

Aerosols are often internally mixed, in contast with their implementation as an external mixture in jv_spec.dat.

--Bob Y. 11:02, 1 March 2010 (EST)

Download location

The updated jv_spec.dat file (and corresponding ratj.d file) are be located in the 1-month benchmark run directory for GEOS-Chem v8-02-05. You may also download them from the following location:

ftp ftp.as.harvard.edu
cd pub/geos-chem/data/aerosol_optics/v8-03-01-updates/

These files are now part of the standard GEOS-Chem run directory archive. You may download these with the Git version control software. Please see this wiki post for more information.

--Bob Y. 15:32, 15 November 2010 (EST)

Aerosol optical properties at high spectral resolution

Randall Martin has made available files containing aerosol optical properties at high spectral resolution. These files are not specifically for GEOS-Chem, but they may be useful for some satellite applications or radiative forcing calculations. The files are available from:

ftp ftp.as.harvard.edu
cd /pub/geos-chem/data/aerosol_optics/hi_spectral_res/

For more information about the data, please see this README file.

--Bob Y. 11:02, 1 March 2010 (EST)

References

  1. Drury, E., D.J. Jacob, R.J.D. Spurr, J. Wang, Y. Shinozuka, B.E. Anderson, A.D. Clarke, J. Dibb, C. McNaughton, and R. Weber, Synthesis of satellite (MODIS), aircraft (ICARTT), and surface (IMPROVE, EPA-AQS, AERONET) aerosol observations over North America to improve MODIS aerosol retrievals and constrain surface aerosol concentrations and sources , J. Geophys. Res., submitted.
  2. Jaegle et al. Global sea salt emissions: New constraints from in situ, AERONET, and MODIS observations, in preparation for submission to Atm. Chem. Phys. Discuss., 2010.
  3. Koepke, P., M. Hess, I. Schult, and E. P. Shettle, Global Aerosol Data Set, Report No. 243, Max-Planck-Institut fur Meteorologie, Hamburg, ISSN 0937-1060, 1997.
  4. Martin, R.V., D.J. Jacob, R.M. Yantosca, M. Chin, and P. Ginoux, Global and regional decreases in tropospheric oxidants from photochemical effects of aerosols, J. Geophys. Res., 108, 4097, doi:10.1029/2002JD002622, 2003.
  5. Mishchenko, M.I., J.M. Dlugach, E.G. Yanovitskij, and N.T. Zakharova, Bidirectional reflectance of flat optically thick particulate layers: an efficient radiative transfer solution and applications to snow and soil surfaces, J. Quant. Spectrosc. Radiat. Transfer, 63, 409-432, 1999.
  6. Wang, J., S.A. Christopher, F. Brechtel, J. Kim, B. Schmid, J. Redemann, P.B. Russell, P. Quinn, and B.N. Holben, Geostationary satellite rtrievals of aerosol optical thickness during ACE-Asia, J. Geophys. Res., 108, 8657, doi:10.1029/2003JD003580, 2003.
  7. Wang, J., S.A. Christopher, J.S. Reid, H. Maring, D. Savoie, B.H. Holben, J.M. Livingston, P.B. Russell, and S.K. Yang, GOES-8 retrieval of dust aerosol optical thickness over the Atlantic Ocean during PRIDE, J. Geophys. Res., 108, 8595, doi:10.1029/2002JD002494, 2003.

--Bob Y. 11:02, 1 March 2010 (EST)