High spatial resolution aerosol retrievals used for daily particulate matter monitoring over Po valley, northern Italy

Abstract

The Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5.1 Aerosol Optical Depth (AOD) data retrieved at 0.55 µm with spatial resolution of 10 km (MYD04) and the new 1 km Multi-Angle Implementation of Atmospheric Correction (MAIAC) al-gorithm from MODIS is investigated in this work. We focus on evaluating the ability 5 of these two products to characterize the spatial distribution of aerosols within urban areas. This is done through the comparison with PM 10 measurements from 126 of the Italian Regional Agency for Environmental Protection (ARPA) ground monitoring sta-tions during 2012. The Po Valley area (northern Italy) was chosen as the study domain since urban air pollution is one of the most important concerns in this region. Popu-10 lation and industrial activities are located within a large number of urban areas within the valley. We find that the annual correlations between PM 10 and AOD are R 2 = 0.90 and R 2 = 0.62 for MYD04 and for MAIAC respectively. When the depth of the planetary boundary layer (PBL) is used to normalize the AOD, we find a significant improvement in the PM–AOD correlation. The introduction of the PBL information is needed for AOD 15 to capture the seasonal cycle of the observed PM 10 over the Po valley and significantly improves the PM vs. AOD relationship, leading to a correlation of R 2 = 0.98 for both retrievals when they are normalized by the PBL depth. The results show that the nor-malized MAIAC retrieval provides a higher resolution depiction of the AOD within the Po Valley and performs as well in a statistical sense as the normalized standard MODIS 20 retrieval for the same days and locations.