Doppler lidar observations of Russian forest fire plumes over Helsinki

In August 2006, forest fires in north-western Russia led to elevated concentrations of fine particles reducing air quality in southern Finland over a number of weeks. Predominately easterly and south-easterly winds resulted in smoke plumes extending over the Gulf of Finland and affecting eastern and southern Finland during 7–14 August 2006 and 21–23 August 2006. This article describes observations using Doppler lidar of two episodes where smoke plumes from the Russian forest fires were evident over the Helsinki area on 7 and 9 August 2006. The observations were made during a convective field campaign, part of the Helsinki Testbed, an international mesoscale meteorology research project running from January 2005 until September 2007 (Dabberdt et al., 2005). During the 2006 fire season, a total of 23 046 fires were recorded, affecting 999 080 hectares of forested lands and 579 234 hectares of non-forested lands with most fires reported in the Kareliya, Leningradskaya and Murmanskaya regions of north-western and western Russia (Global Fire Monitoring Center, 2006). Emissions from boreal fires are important because of their location at climatically sensitive northern latitudes. The main pollutants released during vegetation fires are aerosols, carbon monoxide and dioxide, nitrogen oxides and non-methane hydrocarbons. These emissions play an important role in the atmospheric chemistry and radiative properties of the atmosphere (Damoah et al., 2004). Smoke and aerosol particles scatter sunlight and reflect it directly back to space thereby having a cooling effect on the atmosphere by increasing cloud reflectance (Kaufman and Fraser, 1997). Smoke particles are also a major source of cloud condensation nuclei (CCN) and increases in CCN affect the microphysics of clouds, thereby altering cloud albedo, affecting the way clouds absorb and reflect sunlight. Emissions from forest fires also have a warming effect on the atmosphere, as greenhouse gases are emitted contributing to the greenhouse effect. Biomass burning is thought to account for as much as 25% of the total global emission of greenhouse gases (Rebelo, 2006). Changes in the concentration of carbon monoxide and aerosols affect ozone, which plays an important role in the global climate system (Daniel and Solomon, 1998). In 1998, global boreal forest regions experienced some 17.9 million hectares of fire and it has been estimated from models that global fire emissions contribute 8.9% of total carbon emissions, 13.8% of carbon monoxide emissions and 12.4% of methane emissions (Kasischke and Bruhwiler, 2003). Occurrence of smoke plumes over southern Finland