Global monitoring of air pollution over land from the Earth Observing System‐Terra Moderate Resolution Imaging Spectroradiometer (MODIS)

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Abstract
Moderate Resolution Imaging Spectroradiometer (MODIS) measurements (7 channels: 0.47–2.1 μm, 250–500 m resolutions) provide us with new insights into the characteristics of global aerosols. MODIS retrieves not only aerosol loading but also the fraction of fine mode particle. In this paper we demonstrate MODIS capability for use in monitoring global, regional, and local air pollution. Three case studies in northern Italy, Los Angeles, and Beijing showed the conclusive results of applying MODIS‐derived aerosol optical depths (τa) to regional and local air pollution in terms of accuracy (Δτa = ±0.05 ± 0.2τa) and spatial sensitivity of the retrievals. Under stagnant condition, accumulated aerosol abundance can reach τa > 1 (at 0.55 μm) before being removed by wind or precipitation. The correlation found between Aerosol Robotic Network (AERONET) daily averaged τa and 24‐hour PM10 (particulate matter with diameter 3) in northern Italy is encouraging with correlation coefficient ∼0.82. The derivation of PM concentration from satellite measurements may be possible once we know the detailed aerosol vertical distribution. To compare aerosol loading in different regions of the globe, we choose the two most populated regions (eastern China and India) and the two most industrialized regions (the eastern United States/Canada and western Europe). The time series of MODIS monthly mean τa from July 2000 to May 2001 depicts a strong seasonal variation with maxima in the spring/summer and minima in the winter. The clear separation between (1) the eastern United States/Canada and western Europe and (2) eastern China and India shows that the τa values in (2) are 50% to 2–3 times higher compared to those in (1). The enhancements of aerosol loading were due to smoke as originated from Montana/Idaho forest fires transported to the eastern United States in late August 2000 and dust outbreaks from Taklimakan and Gobi Deserts to eastern China as well as smoke from Southeast Asia to southern China in February–April 2001.

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