Title: Aerosol Direct Radiative Effect in the Po Valley Region Derived from AERONET Measurements
Citation: ATMOSPHERIC CHEMISTRY AND PHYSICS vol. 8 no. 16 p. 4925-4946
Publication Year: 2008
JRC Publication N°: JRC43000
ISSN: 1680-7316
URI: http://www.atmos-chem-phys.net/8/4925/2008/acp-8-4925-2008.html
Type: Articles in Journals
Abstract: The aerosol direct radiative effect (ADRE) affecting the Po Valley and the adjacent North Adriatic Sea is studied using 10-year series of measurements collected at two AERONET sites located in the western part of the Valley (Ispra), and on a platform (AAOT) offshore Venice. This region is characterized by a high, mostly continental, aerosol load with comparable average aerosol optical thickness (AOT) at both locations (0.21 at 500 nm) and more absorbing aerosols at Ispra. A dynamic aerosol model accounting for the changes in scattering phase function with AOT is used for radiative transfer calculations, together with boundary conditions representative of terrestrial and marine surfaces. A sensitivity analysis allows the construction of an error budget for the daily ADRE estimates, found to be of the order of 20% and mostly due to uncertainties on aerosol single scattering albedo and AOT. The daily radiative efficiencies, normalized by AOT at 500 nm, increase from December to June, from -17 to -24 W m-2 AOT-1 at top-of-atmosphere (TOA) and -33 to -72 W m-2 AOT-1 at surface for the Po Valley, and from -15 to -32 (TOA) and -35 to -65 W W m-2 AOT-1 (surface) for the AAOT site. The average of log-transformed ADRE for TOA, surface and atmosphere are -5.2, -12.2 and +6.8 W m-2 for the Po Valley case, and -6.5, -13.0 and +6.5 W m-2 for the AAOT site but these values can be much higher for individual days. Concurrent clear-sky days give indications on the regional atmospheric heating spatial gradients. Differences between the atmospheric ADRE at the two locations average 6.3 W m-2 with a gradient positive towards the inner valley in 65% of the cases. This study confirms the importance of duly considering the radiative impact of aerosols on the regional climate.
JRC Institute:Institute for Environment and Sustainability

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