Regional aerosol optical properties and radiative impact of the extreme smoke event in the European Arctic in spring 2006

[摘要] In spring 2006 a special meteorological situation occurred in the EuropeanArctic region giving record high levels of air pollution. The synopticsituation resulted in extensive transport of pollution predominantly fromagricultural fires in Eastern Europe into the Arctic region and record highair-pollution levels were measured at the Zeppelin observatory atNy-Ålesund (78°54' N, 11°53' E) in the period from 25 April to12 May. In the present study we investigate the optical properties of theaerosols from this extreme event and we estimate the radiative forcing ofthis episode.

We examine the aerosol optical properties from the source region and intothe European Arctic and explore the evolution of the episode and the changesin the optical properties. A number of sites in Eastern Europe, NorthernScandinavia and Svalbard are included in the study. The observations showthat the maximum AOD was from 2–3 May at all sites and varies from 0.52 to0.87, and the corresponding Ångstrøm exponent was relatively large.Lidar measurements from Minsk, ALOMAR (Arctic Lidar Observatory for MiddleAtmosphere Research at Andenes) and Ny-Ålesund show that the aerosollayer was below 3 km at all sites the height is decreasing from the sourceregion and into the Arctic. For the AERONET sites included (Minsk, Toravere,Hornsund) we have further studied the evolution of the aerosol size. Thesingle scattering albedo at Svalbard is provided for two sites;Ny-Ålesund and Hornsund. Importantly the calculated single scatteringalbedo based on the aerosol chemical composition and size distribution fromNy-Ålesund and the AERONET measurements at Hornsund are consistent. Wehave found strong agreement between the satellite daily MODIS AOD and theground-based AOD observations. This agreement is crucial for accurateradiative forcing calculations. We calculate a strong negative radiativeforcing for the most polluted days employing the analysed ground based data,MODIS AOD and a multi-stream model for radiative transfer of solarradiation. During this specific pollution event the forcing reached valuesas low as −35 W m⁻² in the region. For comparison, the direct forcing ofa corresponding aerosol layer with a typical AOD of 0.05 for the season isaround −5 W m⁻².

[学科分类] 大气科学