Aerosol advected from forest fires in Canada above Warsaw

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Intense influx of aerosols originating from forest fires in Canada observed over Poland by physicists from the University of Warsaw. The observations were made possible through continuous measurements conducted by the RS-Lab Remote Sensing Laboratory.

“The influx of aerosols from Canadian forest fires over the measurement station in Warsaw is interesting due to the intensity of transport—we observed layers of aerosols continuously for several days,” commented researchers from the Institute of Geophysics, Faculty of Physics at the University of Warsaw: Professor Iwona Stachlewska, who leads the RS-Lab research group, Dr. Łucja Janicka, an expert in biomass burning aerosol properties, and Dr. Dominika Szczepanik, who conducts lidar observations at the measurement station in Warsaw.

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The first aerosol layers were observed in the free troposphere over Warsaw as early as May 26th and remained present at various altitudes until June 12th. “Smoke was observed at different heights above the surface—ranging from 3 km to 8 km—and formed multiple layers of varying thickness in the vertical direction,” described Dr. Szczepanik.

This knowledge was obtained through lidar observations carried out under the direction of Prof. Iwona Stachlewska at the RS-Lab Remote Sensing Laboratory in the Institute of Geophysics at the University of Warsaw. The presence of this aerosol was confirmed by models such as the “HYSPLIT model, which provides backward trajectories of air mass movement, and the NAAPS model, which indicates the forecasted aerosol optical thickness caused by a given aerosol,” provided the atmospheric physicist.

Aerosols from biomass burning are characterized by small particle size and high solar radiation absorption capacity. “Therefore, their presence in the free troposphere has a dual effect. On the one hand, through scattering and absorption, they limit the amount of radiation reaching the Earth’s surface (cooling effect), while locally (where they are located), they heat the air due to strong radiation absorption,” explained Dr. Janicka.

“Their small size (and consequently, mass) results in slow gravitational settling of the aerosol, allowing it to remain in the atmosphere for a relatively long time—up to several days—and be transported by air masses over very large distances from the emission source. It is worth noting that this aerosol undergoes aging processes—its optical and microphysical properties change over time, so the aerosol observed over Warsaw will be different from the one observed close to the emission sources,” added the researcher.

As emphasized, the frequency of this phenomenon depends on various factors, primarily the intensity and location of the fires, the direction of air mass movement, and factors influencing the aging of the aerosol.

“Aerosols from biomass burning occur over the area of Poland every year, most frequently in spring when their source is steppe fires in Ukraine, as well as in summer when forests burn, both in Europe (Portugal, Spain) and faraway Canada (as is currently the case),” added Prof. Stachlewska.

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It also happens that aerosols emitted from locally occurring fires in Poland are transported in a direction where their presence is not observed over Warsaw. As an example, the physicist mentioned the tire landfill fire in Konin on April 22nd this year.

Wildfires are occurring more frequently and are becoming more intense due to prolonged periods of drought and rising temperatures. “In our opinion, this increase can be linked to climate change, but to confidently attribute such processes, long-term measurement series are needed,” summarized Prof. Stachlewska.

The RS-Lab lidar station has been operating continuously in automatic mode, 24/7 since July 2013. It is part of the European Research Infrastructure ACTRIS-ERIC and research networks EARLINET, PollyNET, and PolandAOD.

The long-range influx of aerosols from Canadian forest fires was also reported by Prof. Krzysztof Markowicz, who heads the SolarAOT Research Station in Strzyżów, Podkarpacie.

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