Atmospheric Aerosols and Climate

[energyepsilon]

New Publications:

 

"Spatial and temporal variability in aerosol properties over the Mediterranean basin based on 6-year (2000-2006) MODIS data"

Papadimas et al., 2008 JGR (JOURNAL OF GEOPHYSICAL RESEARCH-Atmospheres), VOL. 113, D11205, doi:10.1029/2007JD009189, 2008

 

http://www.agu.org/pubs/crossref/2008/2007JD009189.shtml

 

Abstract

 

The temporal variability of aerosol optical properties is investigated over the broader Mediterranean basin, with emphasis on aerosol optical depth (AOD) that is an effective measure of aerosol load. The study is performed using Collection 005 Level-3 mean daily spectral aerosol data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument on board the Terra and Aqua satellites, which cover the 6-year period from 2000 to 2006. The results of our analysis reveal a significant interannual variability of AOD in the study region. Specifically, the regional mean visible AOD over land and ocean has decreased over the period 2000–2006 by 20% in relative percentage terms (or by 0.04 in absolute terms). This tendency is statistically significant according to the Man-Kendall test. However, the decreasing tendency of AOD is not uniform over the whole basin. It appears mainly in the western parts of Iberian, Italian, and Balkan peninsulas (and coastal areas), as well as in the southern Anatolian peninsula. The analysis for summer (June to September) and winter (November to March) seasons revealed different tendencies in both AOD and precipitation. The summer-period AOD has decreased by 0.04 (or by 14%) probably due to decreased emission rates of anthropogenic pollution. In contrast, the winter AOD has increased by 0.03 (or 19%) mainly related to decreased precipitation (associated with an increasing tendency in the NAO index). The decreasing tendency in MODIS AOD is in good agreement with corresponding AOD tendencies based on data from Aerobot Robotic Network (AERONET) stations in the study region and ground based PM10 measurements at selected stations.

[JohnB]

And?

[energyepsilon]

...Atmospheric aerosols can cause climate change through their direct, indirect and semi-direct effects on the radiative energy budget of the Earth-Atmosphere system. However, the quantification of these effects is very difficult because the aerosol physical, chemical and optical properties are highly variable in space and time, due to their short atmospheric lifetime and to inhomogeneous emission (e.g. Kaufman et al., 2002). Therefore, continuous monitoring of aerosol properties is essential, especially for climatically sensitive regions such as the Mediterranean basin, parts of which are threatened by desertification processes (IPCC, 2007). This region is of special importance because it is a crossroad where aerosols from different sources are superimposed and mixtures of different kind of particles converge (e.g. Lelieveld et al., 2002) such as fine anthropogenic aerosols from Europe, desert dust from North Africa and maritime aerosols from the Mediterranean Sea. The Mediterranean basin is an important study region for aerosols, which exert a strong climatic effect especially in summer, due to cloud-free conditions and high solar radiation intensity. Moreover, the Mediterranean Sea is one of the ocean areas with the highest aerosol optical depths in the world (Husar et al., 1997) related to an aerosol concentration that is typically of 2 to 10 factors higher than that over the North Pacific Ocean, considered to be the least polluted environment at low northern latitudes (Lelieveld et al., 2002). Moreover, some land regions surrounding to the Mediterranean Sea (e.g. west Sahara) have even larger aerosol optical depths similar to those in downwind regions of Asia (India, China).

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Assessment of the MODIS Collections C005 and C004 aerosol optical depth products over the Mediterranean basin

Atmos. Chem. Phys., 9, 2987-2999, 2009

 

http://www.atmos-chem-phys.net/9/2987/2009/acp-9-2987-2009.html

 

C. D. Papadimas, N. Hatzianastassiou, N. Mihalopoulos, M. Kanakidou, B. D. Katsoulis, and I. Vardavas

 

Abstract

The second generation Collection 005 (C005) MODIS operational algorithm for retrieval of aerosol properties was evaluated and validated for the greater Mediterranean basin (29.5° N–46.5° N and 10.5° W–38.5° E), a region with an atmosphere under siege by air pollution and diminishing water resources that are exacerbated by high aerosol loads and climatic change. The present study aims to quantify the differences between the C005 and the previous (C004) MODIS collections, and re-assess the results of previous studies that have been performed for the region using MODIS C004 aerosol optical depth (AOD) products. Daily data of AOD from EOS-Terra covering the 6-year period 2000–2006 were taken from both C005 and C004 Level-3 datasets, and were inter-compared and validated against ground-based measurements from 29 AERONET stations. The C005 data were found to significantly better agree with the AERONET data than those of C004. The correlation coefficient between MODIS and AERONET was found to increase from 0.66 to 0.76 and the slope of linear regression MODIS/AERONET from 0.79 to 0.85. The MODIS C005 data still overestimate/underestimate the AERONET AOD values smaller/larger than 0.25, but to a much smaller extent than C004 data. The better agreement of C005 with AERONET data arises from the generally lower C005 values, with regional mean AOD values equal to 0.27 and 0.22 for C004 and C005, respectively. This decrease, however, is not uniform over the region and involves a significant decrease over land and a small increase over the ocean for AOD values greater than 0.1 (opposite changes were found under aerosol-clean conditions). Both data sets indicate a decrease in the regional mean AOD over the period 2000–2006, equal to 20% based on C005 and 17% based on C004 datasets, though the intra-annual and inter-annual variation did not change significantly, thus indicating a systematic correction to C004 values.