Unprecedented wildfire smoke in the Siberian Arctic in August 2021

Long-range transport to the Arctic carries tracers of anthropogenic activities and wildfires, among other aerosol constituents. Black carbon (BC) shows a contribution of fossil fuels combustion and natural biomass burning (BB) to the Arctic atmosphere chemistry and aerosol pollution.  Fossil sources mostly prevail during winter-spring season while BB sources dominate during low BC concentration periods in summer. Spectral dependence of the light absorption described by the absorption Ångström exponent (AAE) is used to differentiate between different aerosol types (BC, BrC) and indicate the impact of BB.

Long-term airborne observations of BC in Northern Siberia have revealed a strong impact of forest fires in summer (Kozlov et al., 2016; Paris et al., 2009;Popovicheva et al., 2020). Particulate brown carbon (BrC) has been reported to be emitted by intense wildfires and measured in plumes transported over two days  (Forrister et al., 2015). Due to the mixing with background aerosol and ageing processes, the air masses influenced by BB events is expected to have increased AAE as compared to the BC produced by fossil fuel.

Yamalo-Nenets Autonomous Okrug (YNAO) is located in the Far North of Western Siberia, more than 50% of its area takes place beyond the Polar Circle. On August 4 of 2021, strong smoke enveloped Salehard, Noyabrsk, Tarko-Sale and other municipalities of the district. The air mass transportation from the southeastern directions brought smoke from forest fires located on the territory of the Republic of Sakha (Yakutia). According to the operational data of “Avialesokhrana”, 105 wildfires were active over an area of ​​about 1.2 million hectares there.

A dense haze covered a city Nadym, located around 100 km to the south the Polar Circle, as well. Smoke sampling performed from 5 to 12 August 2021 was correlated with the haze day duration and showed the variation of AAE up to 2.5, the feature of strong BB impact. Unprecedented high BC is observed on Bely island taking place in the Kara sea, above Yamal Peninsula. Unprecedented high pollution for the Siberian Arctic was recorded by research polar aerosol station “Island Bely”. An extreme increase of BC concentration was observed on August 5, reaching 4000 ng per m³. The Arctic summer background was exceeded 40 times!  It was found 8 times higher than the highest arctic haze concentrations observed in December 2019. AAE approached 1.4, very high value for area such remoted from wildfires (more than 1000 km). It indicated the long-range transportation from Yakutia of aged air masses influenced by BB events. Basic research in the Siberian Arctic is supported by Russia Geographical Society №17-2021И.