Long term (2002 2014) evolution and trend in Collection 5.1 Level 2 aerosol products derived from the MODIS and MISR sensors over the Chinese Yangtze River Delta
Abstract The present study aims to investigate spatio temporal evolution and trend in the aerosol optical properties (aerosol optical depth, AOD; Angstrom exponent, AE) qualitatively identify different types and origin of aerosols over an urban city, Nanjing in the Yangtze River Delta, East China. For this purpose, the Collection 5.1 Level 2 data obtained from the Moderate resolution Imaging Spectroradiometer (MODIS) sensor onboard Terra and Aqua satellites and the Multi angle Imaging Spectroradiometer (MISR) instrument for the period between 2002 and 2014 have been analyzed. An inter comparison and validation of AOD were performed against the AOD measurements obtained from the ground based Aerosol Robotic Network (AERONET) sunphotometer. The MODIS AOD 550 exhibited wide spatial and temporal distributions over East China, while MISR AOD 555 was consistently lower than that of Terra and Aqua AOD 550 values. The temporal variations (monthly and seasonal mean) of MODIS (Terra and Aqua) and MISR AOD values exhibited a similar pattern. The seasonal mean AOD 550 (AE 470 660 was found to be maximum with 0.97 0.48 during summer (1.16 0.33 in summer) and a minimum of 0.61 0.28 during the winter season (0.80 0.28 in spring) The annual mean Terra AOD 550 at Nanjing showed a strong decreasing trend 0.70% year 1 while the Aqua exhibited a slight increasing trend 0.01 year 1 during the study period. Seasonal air mass back trajectories obtained from the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model were also computed to infer on the transport component over the study region. Different aerosol types were identified via the relationship between AOD 550 and fine mode fraction, which reveals that the biomass burning/urban industrial type aerosols (desert dust) are abundant over the region in summer (spring) apart from the mixed aerosol type.