Global daily Aerosol Optical Depth measurements from Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Aqua and Terra satellites

This repository contains input MODIS AOD data prepared for “Subways and Urban Air Polution” by Gendron-Carrier, Gonzalez-Navarro, Polloni and Turner (American Economic Journal: Applied Economics, https://doi.org/10.1257/app.20180168). The main replication archive is available at https://doi.org/10.3886/E126401V1 .

Description of input MODIS AOD data

The Moderate Resolution Imaging Spectroradiometers aboard the Terra and Aqua earth-observing satellites provide daily measures of the aerosol optical depth of the atmosphere at a 3km spatial resolution everywhere in the world. Data is available in ‘granules’ which describe five minutes of satellite time. These granules are available, more or less continuously, from February 24, 2000 for the Terra satellite and from July 4, 2002 for Aqua. During September of 2018, we downloaded all available granules for Terra and Aqua until August 31, 2018 and subsequently consolidated them into daily rasters describing global AOD. In August 2020, we processed additional Terra data. This archive therefore contains daily rasters for Aqua (from 2002-07-04 to 2018-08-31) and Terra (from 2000-02-24 to 2020-07-31). We note that February 2005 data are missing for the Aqua satellite.

We use source products MOD04_3K (https://doi.org/10.5067/MODIS/MOD04_L2.006) and MYD04_3K (https://doi.org/10.5067/MODIS/MYD04_L2.006). The product files are stored in Hierarchical Data Format (HDF) and we use the "Optical Depth Land And Ocean" layer, which is stored as a Scientific Data Set (SDS) within the HDF file, as our measure of aerosol optical depth. The "Optical Depth Land And Ocean" dataset contains only the AOD retrievals of high quality. We convert all HDF formatted granules to GIS compatible formats using the HDF-EOS To GeoTIFF Conversion Tool (HEG) provided by NASA’s Earth Observing System Program. We consolidate GeoTIFF granules into a global raster for each day using ArcGIS. First, we keep only AOD values that do contain information. The missing value is -9999 in AOD retrievals. Second, we create a raster catalog with all the granules for a given day and calculate the average AOD value using the Raster Catalog to Raster Dataset tool. The code used to accomplish this is included for reference purposes in “dofiles/old_work” of the main replication archive at https://doi.org/10.3886/E126401V1.