A new simplified approach for simultaneous retrieval of SO2 and ash content of tropospheric volcanic clouds: an application to the Mt Etna volcano

A new procedure is presented for simultaneous estimation of SO2 and ash abundance in a volcanic plume, using thermal infrared (TIR) MODIS data. Plume altitude and temperature are the only two input parameters required to run the procedure, while surface emissivity, temperature, atmospheric profiles, ash optical properties, and radiative transfer models are not necessary to perform the atmospheric corrections. The procedure gives the most reliable results when the surface under the plume is uniform, for example above the ocean, but still produces fairly good estimates in more challenging and not easily modelled conditions, such as above land or meteorological cloud layers. The developed approach was tested on the Etna volcano. By linearly interpolating the radiances surrounding a detected volcanic plume, the volcanic plume removal (VPR) procedure described here computes the radiances that would have been measured by the sensor in the absence of a plume, and reconstructs a new image without plume. The new image and the original data allow computation of plume transmittance in the TIR-MODIS bands 29, 31, and 32 (8.6, 11.0 and 12.0 μm) by applying a simplified model consisting of a uniform plume at a fixed altitude and temperature. The transmittances are then refined with a polynomial relationship obtained by means of MODTRAN simulations adapted for the geographical region, ash type, and atmospheric profiles. Bands 31 and 32 are SO2 transparent and, from their transmittances, the effective ash particle radius (Re), and aerosol optical depth at 550 nm (AOD550) are computed. A simple relation between the ash transmittances of bands 31 and 29 is demonstrated and used for SO2 columnar content (cs) estimation. Comparing the results of the VPR procedure with MODTRAN simulations for more than 200 000 different cases, the frequency distribution of the differences shows the following: the Re error is less than ±0.5 μm in more than 60% of cases; the AOD550 error is less than ±0.125 in 80% of cases; the cs error is less than ±0.5 gm−2 in more than 60% of considered cases. The VPR procedure was applied in two case studies of recent eruptions occurring at the Mt Etna volcano, Italy, and successfully compared with the results obtained from the established SO2 and ash assessments based on look-up tables (LUTs). Assessment of the sensitivity to the plume altitude uncertainty is also made. The VPR procedure is simple, extremely fast, and can be adapted to other ash types and different volcanoes

Implementation of IMAPP/IDEA-I over the Po Valley region, northern Italy, for air quality monitoring and forecasting

Satellite Earth Observations (EO) represent a powerful tool for environmental applications such as air quality monitoring and forecasting; new sensors and image processing methodologies allow for better spatial resolution. Air pollution is an important concern in the Po valley (northern Italy), one of the main industrialized and populated areas of the country, and, for this reason, intensely studied. In this work we focus on the applicability of satellite Aerosol Optical Depth (AOD) retrievals in support of air quality monitoring and assessment in urban environments within the Po valley by using the implementation of the International MODIS/AIRS Processing Package (IMAPP) Air Quality Applications software, IDEA-I (Infusing satellite Data into Environmental Applications-International) over the area. For our specific analyses, IDEA-I was installed at University of Modena and Reggio Emilia, (Italy) using a large European domain, and a smaller domain over the Po valley. One year (2012) of MOD04 AOD retrievals from MODIS on board NASA’s Terra satellite was considered using IDEA-I in a retrospective study. We needed to develop tools to adapt IDEA-I using MODIS AOD data archived at the NASA Level 1 and Atmosphere Archive and Distribution System (LAADS). This was required because IDEA- I is setup for near-real time use of MODIS Direct Broadcast retrievals by default. The Level 2 Aerosol Products, collection 5.1 have been used, which returns AOD data at 0.55 µm with a spatial resolution of 10X10 km 2 retrieved from MODIS (MOD04). These retrieved data were compared with PM 10 mass concentration measurements from the Italian Agency for Environmental Protection (ARPA) network. Correspondence between AOD and PM 10 data suggests that satellite AOD values could be a good substitute for monitoring air quality over the Po valley domain. Moreover, the integration of the use of IDEA-I over the Po valley could give the opportunity to monitor and forecast air pollution and understand particular polluted situations in the past with a retrospective use of IDEA- I. Because of the limited domain of analyses, it is useful to refine the spatial resolution of MODIS AOD maps. This will be accomplished by introducing the use of a recently developed AOD algorithm, MAIAC (Multi-angle Implementation of Atmospheric Correction), which provides MODIS AOD maps at a high spatial resolution of 1 km. This new application will permit us to obtain high resolution AOD maps for the year 2012 over the Po valley domain

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

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) algorithm from MODIS is investigated in this work. We focus on evaluating the ability of these two products to characterize the spatial distribution of aerosols within urban areas. This is done through the comparison with PM10 measurements from 126 of the Italian Regional Agency for Environmental Protection (ARPA) ground monitoring stations 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. Population and industrial activities are located within a large number of urban areas within the valley. We find that the annual correlations between PM10 and AOD are R2 = 0.90 and R2 = 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 to capture the seasonal cycle of the observed PM10 over the Po valley and significantly improves the PM vs. AOD relationship, leading to a correlation of R2 = 0.98 for both retrievals when they are normalized by the PBL depth. The results show that the normalized 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 retrieval for the same days and locations

Application of MAIAC high spatial resolution aerosol retrievals over Po Valley (Italy)

The Moderate Resolution Imaging Spectroradiometer (MODIS) Aerosol Optical Depth (AOD) data retrieved at 0:55 μm with spatial resolutions of 10 km and 1 km AOD have been considered in this work. The 10 km resolution of MODIS AOD product is from the MODIS Collection 5:1 dark target retrieval and the 1 km resolution retrieval is from the new Multi-Angle Implementation of Atmospheric Correction (MAIAC) algorithm. We evaluate ability of these two products to characterize the spatial distribution of aerosols in urban areas through comparison with surface PM10 measurements. The Po Valley area (northern Italy) is considered in this study since urban air pollution is an important concern. Population and industrial activities are located in a large number of urban areas distributed within the valley. The 10 km spatial resolution of MODIS AOD product is considered too large for air quality studies at the urban scale. Using MAIAC data at 1 km, we examine the relationship between PM10 concentrations, AOD, and AOD normalized by Planetary Boundary Layer (PBL) depths obtained from NCEP global analysis, for year 2012 over the Po Valley. Results show that the MAIAC retrieval provides a high resolution depiction of the AOD within the Po Valley and performs nearly as well in a statistical sense as the standard MODIS retrieval during the time period considered. Results also show that normalization by the analyzed PBL depth to obtain an estimate of the mean boundary layer extinction is needed to capture the seasonal cycle of the observed PM10 over the Po Valley