Abstract
Space monitoring of aerosol optical depth (AOD) trends over megacities can serve as a potential space indicator of global anthropogenic air-pollution changes. Three space aerosol sensors, MODIS-Terra, MODIS-Aqua and MISR, were used in order to study recent decadal trends of AOD over megacities around the world. Space monitoring of AOD trends has the advantage of global coverage and applies the same approach to detecting AOD trends over different sites. In spite of instrumental and time differences among the three sensors investigated, their global pictures of AOD trends over the 189 largest cities in the world are quite similar. The increasing AOD trends over the largest cities in the Indian subcontinent, the Middle East, and North China can be clearly seen. By contrast, megacities in Europe, the north-east of US, and South-East Asia show mainly declining AOD trends. In the cases where all three sensors show similar signs of AOD trends, the results can be considered as reliable. This is supported by the observed trends in surface solar radiation, obtained by using network pyranometer measurements in North and South China, India, and Europe. In the cases where the three sensors show differing signs of AOD trends (e.g. South America), additional research is required in order to verify the obtained AOD trends.
Highlights
In megacities, which are defined as metropolitan areas with population exceeding 10 million inhabitants, air quality is worsening as the population, traffic, industrialization and energy use are increasing [1,2]
Space monitoring of aerosol optical depth (AOD) trends over megacities can serve as a potential space indicator of global anthropogenic air-pollution changes
Space monitoring of AOD trends has the advantage of global coverage and applies the same approach to detecting AOD trends over different sites
Summary
In megacities, which are defined as metropolitan areas with population exceeding 10 million inhabitants, air quality is worsening as the population, traffic, industrialization and energy use are increasing [1,2]. Unlike ground-based measurements, satellite remote sensing of aerosols has the advantage of providing global coverage on a regular basis [10] This provides us with an opportunity to compare aerosol tendencies in different megacities using satellite data of the same sensors. The. current study was aimed at estimating aerosol optical depth (AOD) trends over the largest cities in the world in relation with the aerosol emission changes during the period 2002-2010. Global distribution of AOD tendencies over the largest cities in the world was verified by comparing the following three sensors: MODIS-Terra, MODIS-Aqua, and MISR. Comparisons between aerosol optical depth and its tendencies based on both MODIS and MISR data can help us expand our knowledge about aerosol tendencies over the largest cities in the world. For MODIS-Terra, a comparison between the ten-year AOD trends and the eightyear AOD trends have shown very similar results; we preferred to study the results for the three sensors during the aforementioned eight-year period
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