A12A-01
Comparison of Airborne Sunphotometer and Satellite Retrievals of Aerosol Optical Depth during MILAGRO/INTEX-B
In March 2006 the 14-channel Ames Airborne Tracking Sunphotometer (AATS) was operated on a Jetstream 31 (J31) aircraft based in Veracruz, Mexico during MILAGRO/INTEX-B (Megacity Initiative-Local And Global Research Observations /Phase B of the Intercontinental Chemical Transport Experiment). AATS measured total extinction aerosol optical depth (AOD) at 13 wavelengths (354-2139 nm) and water vapor column content in 13 flights that sampled clean and polluted airmasses over the Gulf of Mexico and Mexico City. Vertical differentiation of AOD and columnar water vapor data obtained during J31 vertical profiles yields vertical profiles of multiwavelength aerosol extinction and water vapor density, respectively. J31 flights were coordinated with overflights of several satellites, including Aqua, Aura, Terra, and Parasol, plus other aircraft, including the NASA DC-8 and King Air and the NCAR C-130. Data obtained by the Ozone Monitoring Instrument (OMI) aboard Aura are routinely inverted using two different inversion schemes, a near UV algorithm and a multiwavelength (MW) algorithm, to yield retrievals of AOD and absorption AOD (AAOD). We have identified four Aura overpasses for which OMI retrievals have been performed and AATS AOD spectra have been calculated at coincident or near-coincident times and locations. Three of these (3, 10 and 17 March) were over the Gulf of Mexico, and one (19 March) was over the Mexico City area. In this presentation we will compare the AATS and OMI AOD retrievals. For the 10 and 17 March comparisons, MODIS (aboard Aqua) AOD retrievals are available, and these agree well with the AATS AOD spectra. AOD values resulting from application of both the OMI UV and MW retrieval algorithms on 3, 10, and 17 March significantly overestimate the AATS and MODIS values. The suborbital data set for the 19 March comparison is particularly rich, including ground-based AERONET retrievals of aerosol properties from the T2 site NNE of Mexico City and the T0 site in the heart of the city, additional aerosol retrievals from radiometers on the J31, and lidar and in situ measurements from the DC-8. AERONET data at T0 yield AOD spectra that are consistent with AATS AOD spectra calculated from measurements acquired ~ 450 m above the T0 site. OMI UV and MW AOD retrievals significantly exceed the AATS and AERONET values. However, when the comparison is performed in AAOD after conversion of AATS AOD to AAOD using realistic single scattering albedos obtained from other measurements during previous field campaigns, the OMI UV AAOD retrievals (which are less sensitive to surface albedo uncertainties than the OMI MW retrievals) agree well with the corresponding AATS values. We intend to examine possible reasons for these observed differences and explore plausible approaches to bring the retrievals into agreement. In particular we will explore using different assumptions about the nature of the absorbing particles.
A12A-02
Understanding The Correlation of San Joaquin Air Quality Monitoring With Aerosol Optical Thickness Satellite Measurements
Air quality in the San Joaquin Valley (SJV) has failed to meet state and federal attainment standards for Particulate Matter (PM) for several years. Air quality agencies currently use ground monitoring sites to monitor air quality in the San Joaquin Valley. This method provides accurate information at specific points but does not provide a clear indication of what is occurring over large regions. Using measurements from satellite imagery has the potential to provide valuable air quality information in a timely manner across large regions. While previous studies show good correlations between satellite derived Aerosol Optical Thickness (AOT) and surface PM measurements on the East Coast of the United States, the data do not correlate well in the SJV. This paper compares PM2.5 ground data from the California Air Resources Board (CARB) and the Interagency Monitoring of Protected Environments (IMPROVE) sites with satellite data in an effort to understand this discrepancy. To verify satellite AOT value accuracy, ground AOT values were collected from the Aerosol Robotic Network (AERONET) and from measurements using the hand-held MicroTops II Sun Photometer field instrument. We found good correlation of the AOT values between MODIS, MISR and AERONET. However, we found poor correlations between satellite- based AOT values and PM2.5 values, and consideration of aerosol speciation did not improve the correlations. Further investigation is needed to determine the causes of the poor correlation. Acquiring detailed information on the meteorological conditions and vertical profiles of the atmosphere using ground-based LIDAR or data from CALIPSO may provide better results.
A12A-03
Fusion of MODIS, TOMS, MOPITT and GOCART for aerosol studies
Two years [January 2003-December 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 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 one 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) vs. 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. Preliminary estimates for SS, DU, and AN MODIS FMF are 0.25¡Ó0.07, 0.45¡Ó0.05, and 0.84¡Ó0.04 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. Dust transport off of the Saharan Desert is maximized in the northern hemisphere summer respectively, 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 ƒÝm. 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. http://vortex.nsstc.uah.edu/~sundar/papers/2007/submit-final-jgr2007-FMF.pdf
A12A-04
Utilization of NASA MODerate Resolution Imaging Spectroradiometer (MODIS) Derived Aerosol Optical Depth (AOD) for Trends Analysis Over the United States-Canada Border Region
A systematic and comprehensive method of air pollutant trends analysis is critical in benchmarking change in air quality conditions and informing policy makers (EPA, 2007; Environment Canada, 2006; NARSTO, 2004). AOD derived from the MODIS instrument aboard the NASA Terra and Aqua satellites is correlated with the ground- based AErosol RObotic NETwork (AERONET, AEROCAN in Canada) AOD and compared to trends in ambient fine particulate matter (PM2.5) in the United States-Canada border region from May-September, 2000-2006. Trends are calculated using the change in AOD or PM2.5 over the given time period, determined from simple linear regression at each point in a standard grid. The method enables robust comparison of AERONET AOD and regridded MODIS AOD, as well as comparison of trends in MODIS AOD and ambient PM2.5, between ground site, month of study, and satellite. Results were tabulated for comparison at each of these levels (i.e. For the month of July, Aqua MODIS AOD correlated well with PM2.5 at one site, R2 = 0.78). The research results convey the utility of MODIS AOD to assess air quality trends in international regions with spatially sparse or variable ground PM2.5 monitors, and to address the impacts of policy implementation and inform decision-making. Disclaimer Although this work was reviewed by Environmental Protection Agency and approved for publication, it may not necessarily reflect official Agency policy.
A12A-05
Combined use of MODIS, MISR, CERES, and a data assimilation method for estimating aerosol climate forcing over Saharan regions
Advanced satellite aerosol optical depth retrievals and datasets now allow the scientific community an unprecedented volume of observations of the global aerosol distribution. Each algorithm has advantages and disadvantages, and no single dataset can boast top performance everywhere over the globe. Furthermore, satellite aerosol retrievals, to varying degree, are limited to cloud free skies, and thus are subject to clear-sky bias and other contextual biases. For this study, we developed a multi-sensor aerosol optical depth analysis over Saharan regions by assimilating MODIS and MISR aerosol products into NRL Aerosol Analysis and Prediction System (NAAPS) using a recently developed aerosol data assimilation package (NAVDAS-AP). Studies showed that the new aerosol data assimilation system allows for very accurate modeling of larger aerosol features. Using the aerosol optical depth analysis developed from this study, we estimated aerosol climate forcing over Saharan regions. The aerosol climate forcing values derived from this study were compared with measurement- based aerosol forcing estimates. Contextual and clear sky biases that are associated with the measurement- based forcing estimates are also examined.
A12A-06
Long-term global comparisons of aerosol optical depth from MISR, MODIS and AERONET using AMAPS (the Aerosol Measurement and Processing System)
NASA's Terra satellite has been in orbit for nearly eight years. Both the MODIS (the Moderate Resolution Imaging Spectroradiometer) and MISR (Multi-angle Imaging SpectroRadiometer) instruments have produced validated data sets of optical depth which are now ripe for comprehensive comparison against AERONET (the Aerosol Robotic Network) over the entire life of the mission. We compare both MODIS and MISR to AERONET as follows. First, we stratify AERONET locations by climatological zone and season. Second, we reduce each AERONET time series corresponding to a Terra overpass to a single value, and associate each such value with one MISR and one MODIS value. Note that various methods to reduce and associate measurements are possible at this stage of the analysis. Third, we regress MISR and MODIS on AERONET separately and record the intercept, slope, and coefficient of determination. Fourth, we evaluate and compare these statistics as functions of location, time, and instrument, paying special attention to the effects of different data reduction and association strategies on our conclusions. We use the Aerosol Measurement and Processing System (AMAPS) to conduct this analysis because it provides streamlined access to and manipulation of large volumes of Level 2 data. This allows us to efficiently repeat our analysis under a variety of assumptions and methodologies. Finally, we comment on how our results, derived using the same methodology to compare both MISR and MODIS to AERONET, differs from earlier validation results in which different methodologies were used by the MISR and MODIS teams.
A12A-07
Aerosol properties from OMI using the multi-wavelength algorithm in combination with CALIPSO lidar data
The Ozone Monitoring Instrument (OMI) is an imaging UV-VIS solar backscatter spectrometer. It is a Dutch- Finnish instrument onboard the NASA satellite EOS-Aura which has been launched in July 2004. The OMI mission has yielded more than 3 years of science data including global data sets of various atmospheric parameters with high spatial resolution on a daily basis. The multi-wavelength algorithm is used to retrieve aerosol parameters from OMI spectra in 14 wavelength bands between 342.5 nm and 483.5 nm. The space borne lidar CALIOP on the CALIPSO platform provides the height of aerosol layers. In this contribution we present mineral dust aerosol parameters retrieved using the multi- wavelength retrieval algorithm in combination with CALIPSO height data. The multi-wavelength algorithm is capable to distinguish between absorbing aerosol types, such as desert dust and biomass burning, and weakly absorbing aerosols like sea-salt and sulfates. We show the impact of using additional height information on the retrieved absorption properties.
A12A-08
A Future "Global Atmospheric Composition Mission" (GACM) Concept.
Resolution of important outstanding questions in air quality, climate change and ozone layer stability demands global observations of multiple chemical species with high horizontal and vertical resolution from the boundary layer to the stratopause. We present a mission concept that delivers the needed atmospheric composition observations, along with cloud ice and water vapor data needed for improvements in climate and weather forecasting models. The mission comprises ultraviolet and infrared nadir and microwave limb viewing instruments observing wide swaths each orbit. We review the scientific goals of the mission and the measurement capabilities this concept will deliver. We describe how precessing orbits offer significant improvements in temporal resolution and diurnal coverage compared to sun-synchronous orbits. Such improvements are needed to quantify the impact of critical "fast processes" such as deep convection on the composition and radiative properties of the upper troposphere, a region where water vapor and ozone are strong but poorly understood greenhouse gases. This concept can serve as the "Global Atmospheric Composition Mission" (GACM) recently recommended by the National Academy of Sciences decadal survey as one of 17 priority earth science missions for the coming decade.