MODIS derived fine mode fraction characteristics of marine, dust, and anthropogenic aerosols over the ocean, constrained by GOCART, MOPITT, and TOMS

[1] One year (December 2003 to November 2004) of Terra Moderate Resolution Imaging Spectroradiometer (MODIS), Total Ozone Mapping Spectrometer (TOMS), and Measurement of Pollution in the Troposphere (MOPITT) data over the open ocean are used in conjunction with the Goddard Chemistry Transport Model (GOCART) to characterize differing aerosol types as a function of satellite observable parameters. GOCART model output is used to select regions that are dominated (at least 80% of the total aerosol optical thickness from a single aerosol species) by anthropogenic (black carbon + organic carbon + sulfate), dust (DU) and sea salt regions (SS). Aerosol optical thickness (AOT) and fine mode fraction (FMF) retrieved from MODIS are averaged for each aerosol species region at 1 month intervals to examine the observational differences among each aerosol species. Anthropogenic (AN) aerosols are further separated into those produced primarily from biomass burning (BB) versus those from combustion and industrial pollution (PO). TOMS ultraviolet absorbing aerosol index (AI) in conjunction with MOPITT carbon monoxide (CO) data sets on Terra are used to contrast the differences between BB and PO aerosol properties. Annually averaged estimates for SS, DU, and AN MODIS FMF are 0.25 ± 0.07, 0.45 ± 0.05, and 0.84 ± 0.04, respectively, in agreement with or slightly lower than previous estimates. However, FMF values were observed to change substantially as a function of space and time as regions dominated by single aerosol types shrink, expand, and move around from month to month. The greatest variability in FMF was observed for SS and DU aerosols. SS are associated with regions of high near-surface wind speeds in the Southern Hemisphere, which have large temporal and spatial variations. Dust transport off of the Saharan Desert is maximized in the Northern Hemisphere summer, increasing the area of predominately dust aerosols. MODIS aerosol effective radius for each aerosol type also showed a similar trend with SS, DU, and AN values of 1.03, 0.68, and 0.32 mm. TOMS-AI values for DU exceeded SS and AN values up to 100% between April and October 2004 in association with the greatest dust concentrations in the North Atlantic. For BB and PO components of AN aerosols, no significant difference in MODIS FMF were observed; however, substantial differences in TOMS-AI and MOPITT values were observed between BB and PO aerosols, especially between June and November. For both TOMS-AI and MOPITT CO, BB aerosols are generally associated with higher values than are PO aerosols. The use of GOCART to constrain regions where a dominant aerosol species exists has allowed a comprehensive analysis of the satellite observed properties of various aerosol species.