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A new study reveals that springtime variation in Arctic black carbon mist abundance is closely related to biomass burning in mid-latitudes.

The research was published in the journal Atmospheric Chemistry and Physics, and the research warns that current models underestimate the black carbon contribution from biomass burning by threefold.

In recent decades, the average annual temperature in the Arctic has risen at twice the rate of the rest of the world. Although the main driver of this warming is the global increase in carbon dioxide concentration, there are other elements that amplify this warming, among them black carbon aerosols.

The black carbon emitted into the atmosphere from burning fossil fuels and burning biomass effectively absorbs solar radiation and heats the atmosphere. In addition, black carbon deposited on snow and ice can reduce its reflection and accelerate its melting.

Most of the black carbon in the Arctic is believed to be from regions outside the Arctic. However, estimates of the relative contribution of various sources to Arctic black carbon and thus its impact on climate still involve a great deal of uncertainty.

The research group measured vertical profiles of black carbon mass concentrations up to 5 km high in the Arctic in March and April 2018, during the Arctic Regional Climate Model Simulation and Polar Airborne Measurements (PAMARCMiP) project led by the Alfred Wegener Institute (AWI) in Germany.

Observations were made using the AWI Polar 5 research aircraft, Nord Station (81.6°N, 16.7°W) as the base of operations. The observed mass concentrations of black carbon were compared with those obtained in previous arctic air spring experiments (ARCTAS in 2008, HIPPO in 2010 and NETCARE in 2015) in order to identify the factors responsible for the interannual variation in abundance. carbon black.

Mass concentrations of black carbon in 2018 ranged between 7 and 23 nanograms per cubic meter (ng per cubic meter), compared to 2010. On the other hand, in 2008 and 2015, higher values ​​were observed systematically at all altitudes. up to 5 km. Although all jet measurements were made in a limited area and time duration, these results reveal a large interannual variation in black carbon mass concentrations in the Arctic spring.

The research group found that relative changes in the annual variation of “vertically integrated mass concentrations of black carbon” – that is, the amount of black carbon in columns between 0 and 5 km in height – were generally consistent with biomass. Combustion activities were estimated using satellite-derived fire counts. MODIS detected at latitudes north of 50°N.

Atmospheric transport affected by biomass burning in regions between 45-60°N latitudes and 30-50°E and 100-130°E longitudes (Western and Eastern Eurasia, respectively) was likely responsible for the observed increase in black carbon levels during spring in the North Pole.

During PAMARCMiP in 2018, a layer of pollution, the sources of which are likely to be burning biomass in mid-latitudes, was occasionally visible through the windows of the research aircraft. They likely see that there was a more frequent transfer of pollution from biomass burning to the Arctic during the 2008 and 2015 observation periods.

The research group also examined the ability of current numerical model simulations to reproduce the observed year-to-year variation in vertical amounts of black carbon.

Numerical models can estimate the contributions of anthropogenic sources of black carbon and those from biomass burning separately and reproduce the observations relatively well in 2010 and 2018, when biomass burning activity was low, while showing much lower values ​​than the observations in 2008 and 2015, When biomass burning activity was high.

These results indicate that current numerical models generally reproduce well the contribution of anthropogenic black carbon, while significantly underestimating (by a factor of three) the contribution of black carbon from biomass burning.

The global warming effects (positive radiative forcing) of black carbon in the Arctic are greatest in spring, when the mass concentration of black carbon is higher and incoming solar radiation increases.

Black carbon is also important in spring because small changes in the timing of snow/ice melt can affect the radiation balance in the Arctic.

The observations presented in this study provide a useful basis for the improvement and evaluation of numerical model simulations that assess the radiative forcing of black carbon in the Arctic. Moreover, global warming has the potential to increase biomass burning in the middle and high latitudes.

This study indicates that these future changes in carbon emissions could affect the amount of black carbon in the Arctic and its radiative effects more than estimates from previous studies.