Abstract
Abstract. Airborne lidar and in-situ measurements of the aerosol properties were conducted between Svalbard Island and Scandinavia in April 2008. Evidence of aerosol transport from Europe and Asia is given. The analysis of the aerosol optical properties based on a multiwavelength lidar (355, 532, 1064 nm) including volume depolarization at 355 nm aims at distinguishing the role of the different aerosol sources (Siberian wild fires, Eastern Asia and European anthropogenic emissions). Combining, first aircraft measurements, second FLEXPART simulations with a calculation of the PBL air fraction originating from the three different mid-latitude source regions, and third level-2 CALIPSO data products (i.e. backscatter coefficient 532 nm,volume depolarization and color ratio between 1064 and 532 nm in aerosol layers) along the transport pathways, appears a valuable approach to identify the role of the different aerosol sources even after a transport time larger than 4 days. Optical depth of the aerosol layers are always rather small (<4%) while transported over the Arctic and ratio of the total attenuated backscatter (i.e. including molecular contribution) provide more stable result than conventional aerosol backscatter ratio. Above Asia, CALIPSO data indicate more depolarization (up to 15%) and largest color ratio (>0.5) for the northeastern Asia emissions (i.e. an expected mixture of Asian pollution and dust), while low depolarization together with smaller and quasi constant color ratio (≈0.3) are observed for the Siberian biomass burning emissions. A similar difference is visible between two layers observed by the aircraft above Scandinavia. The analysis of the time evolution of the aerosol optical properties revealed by CALIPSO between Asia and Scandinavia shows a gradual decrease of the aerosol backscatter, depolarization ratio and color ratio which suggests the removal of the largest particles in the accumulation mode. A similar study conducted for a European plume has shown aerosol optical properties intermediate between the two Asian sources with color ratio never exceeding 0.4 and moderate depolarization ratio being always less than 8%, i.e. less aerosol from the accumulation mode.
Highlights
Radiative effects of aerosols can be quite different in the Arctic compared to elsewhere (Quinn et al, 2008)
To discuss the methodology developed in the paper, we will focus on the results of 11 April 2008, because they include the two kinds of aerosol layers encountered during the POLARCAT spring campaign
We used mainly the pseudo volume depolarization at 355 nm and pseudo color ratio between 1064 and 532 to distinguish both layers because they are more stable quantities when looking at relative variations of the optical properties of layers with low aerosol optical depths (
Summary
Radiative effects of aerosols can be quite different in the Arctic compared to elsewhere (Quinn et al, 2008). Considering the crucial role of European and Asian emission suggested by the model studies and a significant altitude dependence of the occurrence of aerosol layers, new aircraft observations were conducted in 2008 at the same time over the European Arctic and North American sector to clarify questions raised during the previous campaigns (Jacob et al, 2009). The purpose of this paper is to discuss how a backscatter lidar, in-situ aerosol and CO observations obtained over the European Arctic sector can be combined with a transport model and spaceborne measurements by the CALIOP lidar in order to get a better understanding of the aerosol source attribution in this region This kind of methodology is very useful for studying the aerosol evolution during the long range transport. This work contributes to check how meaningful the CALIOP operational aerosol layer products are
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