Multiyear MODIS observation of global aerosols from EOS Terra/Aqua satellites: validation, variability, and application

The multiyear MODIS (Moderate Resolution Imaging Spectroradiometer) measurements are full of exciting aerosol events, such as the well-known Asian/Saharan dust outbreaks, biomass burning in South Africa, Southeast Asia, Central America, and Southern Africa, and air pollution all over the world. The MODIS aerosol optical depths (τ_a) are validated against AERONET (aerosol robotic network) and other radiometer/sunphotometer (e.g., airborne sunphotometer, shadowband radiometer, microtops, etc.) measurements within the expected retrieval errors of Δτ_a = ±0.05±0.2 τ_a (e.g., 25% fir τ_a = 1) over land and Δτ_a = ±0.03±0.05τ_a (e.g., 8% for τ_a = 1) over ocean. The comparisons of monthly MODIS V4 (version 4) and GACP (global aerosol climatology project) AVHRRR (advanced very high resolution radiometer) aerosol optical depths with AVHRR show that the difference of aerosol loading are generally larger in the northern hemisphere than in the southern hemisphere form March to August 2000 and February 2001 in both hemispheres. Similar conclusions can also be drawn from regional analysis, except in pristine oceans in the northern hemisphere where MODIS and AVHRR aerosol retrievals are in agreement throughout the year. The preliminary results of correlating MODIS aerosol optical depths with PM_2.5 (particular matter with diameter < 2.5 μm) mass concentrations measured at surface are promising with the correlation coefficients found as high as 0.8-0.9 in many metropolitan areas. MODIS ability to provide the pseudosynoptic movement of aerosol-laden air mass can greatly improve air quality assessment and forecast.