Transcript Slide 1
Using satellite observations to investigate natural aerosol loading Colette L. Heald David A. Ridley, Kateryna Lapina EGU April 5, 2011 DUST FROM NORTH AFRICA: IMPACTING AQ AND THE BIOSPHERE DOWN-WIND More than half of dust emitted globally from N. Africa TOMS: June 13-21, 2001 summer winter/spring French Guiana (1978-1979) Miami (1989-1997) [Prospero et al., 1981] [Prospero et al., 1999] SATELLITE CONSTRAINTS ON DUST SOURCE & TRANSPORT GEOS-Chem overestimates observed AOD in source region, underestimates summertime export Dave Ridley REALISTIC APPORTIONMENT OF SUB-MICRON DUST MASS Observed Saharan dust size distribution Simulated decrease in AOD [Haywood et al., 2003] OLD NEW Shifted mass to larger sub-micron sizes (less optically efficient). Reduces AOD in better agreement with satellite & AERONET observations DUST TRANSPORT FROM NORTH AFRICA Annual Mean AOD CALIOP WINTER GEOS-Chem SUMMER CALIOP GEOS-Chem Good model simulation of dust transport and removal in winter/spring. Underestimate in dust in the SAL in summertime. [Ridley et al., in prep] CAN SATELLITE OBSERVATIONS SHED ANY LIGHT ON THE BUDGET OF OA? Bottom-up calculations suggest that SOA source may be anywhere from 140-910 TgC/yr [Goldstein and Galbally, 2007]. z top SATELLITE AOD AOD= α RH z M z dz 0 Assumptions: Optical Properties Size Distributions Aerosol Distributions AEROSOL SPECIATED MASS CONCENTRATIONS Organic aerosol Soot Dust Sulfate Nitrate SURFACE REFLECTANCE Sea Salt ATTRIBUTE ENTIRE MODEL UNDERESTIMATE OF AOD TO ORGANICS DJF JJA MISR Estimate that ~150 TgC/yr source is required to close the MISR-GEOS-Chem* discrepancy. GEOS-Chem* MISRGEOS-Chem* *excluding OA UNCERTAINTY ANALYSIS (boring but important!) Estimated uncertainty on OA budget due to: Aerosol optical properties Size parameters Refractive indices Aerosol water uptake (growth factor) Relative humidity (assuming 5% uncertainty in GEOS-5 fields) Conversion from burden to source Aerosol lifetime (including effects of vertical profile and export fraction) Global budget of “other” aerosols simulated in GEOS-Chem MISR AOD measurements Total Error (added in quadrature) Uncertainty on OA optical properties 50% 20% 10% 6%* 50% 25% 10% 80% * Except over high RH regions Assumed optical properties based on GADS database and log-normal size distribution recently evaluated by Drury et al. [2010] Uncertainty on estimated OA source = 80% HAVE WE REDUCED THE UNCERTAINTY ON THE OA BUDGET? 910 Range estimated by: Goldstein and Galbally [2007] This is more than THREE TIMES what is currently included in global models…. BUT at the low end of Goldstein & Gallbally [2007] range. 140 150 47 Our satellite top-down estimate Existing GEOS-Chem sources All units in TgCyr-1 [Heald et al., 2010] ANNUAL MEAN AOD OVER THE REMOTE OCEANS MODIS % Difference GEOS-Chem GEOS-Chem Sea Salt Gong [2003] sea salt scheme updated to include SST dependence & validated against observations [Jaeglé et al., 2010] GEOS-Chem underestimates (~30%) marine AOD observed by MODIS (and Maritime Aerosol Network). Likely fine aerosol [Jaegle et al., 2010], but does not match simulated sea salt. OTHER POSSIBLE FINE MARINE PARTICLE SOURCES Comparison of simulated sulfate to recent cruise observations (AMS) Observed aerosol composition at Mace Head SeaWIFS [O’Dowd et al., 2004] GEOS-Chem simulation of sulfate relatively unbiased not the problem. BUT under biologically active conditions, OA dominates sub-micron aerosol mass. IS THE OCEAN AN IMPORTANT SOURCE OF OA? Previous estimates range from 2.3 to 75 TgC/yr No marine OA With marine OA OA Emissions Observations from 5 ship cruises show that marine OA from 2 schemes [Spracklen et al., 2008; Langmann et al., 2008] of ~8 TgC/yr are more than sufficient to reproduce sub-micron OA. Makes very little contribution to AOD (0.003). [Lapina et al., ACPD, 2011] Acknowledgments: Dominick Spracklen, Steve Arnold, James Allan, Hugh Coe and Gordon McFiggans, Soeren Zorn, Frank Drewnick, Tim Bates, Lelia Hawkins, Lynn Russell, Sasha Smirnov, Colin O’Dowd, Andy Hind, Easan Drury, Sonia Kreidenweis, and MISR, MODIS & CALIOP retrieval teams