Aerosol Direct Radiative Effects under Cloud-Free Conditions over Highly-Polluted Areas in Europe and Mediterranean: A Ten-Years Analysis (2007–2016)

Tony Landi,Jared Marquis,Michele Brunetti,Paolo Di Girolamo,Simone Lolli,James Campbell,Paolo Bonasoni

doi:10.3390/rs13152933

Abstract

This study investigates changes in aerosol radiative effects on two highly urbanized regions across the Euro-Mediterranean basin with respect to a natural desert region as Sahara over a decade through space-based lidar observations. The research is based on the monthly-averaged vertically-resolved aerosol optical depth (AOD) atmospheric profiles along a 1∘×1∘ horizontal grid, obtained from the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) instrument measurements aboard the Cloud-Aerosol lidar and Infrared Pathfinder Satellite Observation (CALIPSO). To assess the variability of the anthropogenic aerosols on climate, we compared the aerosol vertical profile observations to a one-dimensional radiative transfer model in two metropolitan climate sensible hot-spots in Europe, namely the Po Valley and Benelux, to investigate the variability of the aerosol radiative effects over ten years. The same analysis is carried out as reference on the Sahara desert region, considered subject just to natural local emission. Our findings show the efficacy of emission reduction policies implemented at government level in strongly urbanized regions. The total atmospheric column aerosol load reduction (not observed in Sahara desert region) in Po Valley and Benelux can be associated with: (i) an increase of the energy flux at the surface via direct effects confirmed also by long term surface temperature observations, (ii) a general decrease of the atmospheric column, and likely (iii) an increase in surface temperatures during a ten-year period. Summarizing, the analysis, based on the decade 2007–2016, clearly show an increase of solar irradiation under cloud-free conditions at the surface of +3.6 % and +16.6% for the Po Valley and Benelux, respectively, and a reduction of −9.0% for the Sahara Desert.

Highlights

From Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) data analysis on highly urbanized sites, among the eighteen aerosol species parameterized into the FLG RT model from the OPAC catalog, we considered only the main four species that match the Cloud-Aerosol lidar and Infrared Pathfinder Satellite Observation (CALIPSO) classification: transported dust (CALIPSO: “dust”), urban (CALIPSO: “polluted continental/smoke”), 50% dust, and
Where Pλ (r )r2 is the range corrected received power, Cλ is related to the system calibration coefficient, and Tλ2 (r ) is the total two-way signal transmission containing the integration of αtot (r ) the total extinction coefficient. β mol (r ) and β aer (r ) are the molecular and aerosol backscattering coefficients, respectively
We give quantitative evidence to the changes in direct radiative effect under cloud-free conditions associated with anthropogenic aerosol emissions over a decade (2007–2016) in two highly-urbanized Euro-Mediterranean areas, i.e., the

Summary

Introduction

The so-called old continent, includes the Western part of the Eurasia. Marked by cultural diversity and origins, some of European regions are historically related to social and economical progress, e.g., the industrial revolution in the XVII century that led to an unavoidable increase in anthropogenic emissions. Air-quality and climate related research activities identified some European regions as climate hot-spots. In these areas, resulting climate changes happen faster respect to other areas [1,2,3]. We can count the Mediterranean basin, the cradle of western civilization that developed its culture and historical background with

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