EM – Black carbon aerosols heating the arctic: major contribution from mid-latitude biomass combustion


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November 4, 2021

from Nagoya University

Researcher around Dr. Sho Ohata from the Institute for Space-Earth-Environmental Research at Nagoya University, Japan, Dr. Makoto Koike from the University of Tokyo and Dr. Andreas Herber from the Alfred Wegener Institute, Germany, have shown that the year the spring fluctuation of the arctic soot aerosol frequency from year to year correlates strongly with the biomass combustion in the middle latitudes. In addition, current models underestimate the contribution of BC from the combustion of biomass by a factor of three.

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In the last few decades, the average annual temperature in the Arctic has risen almost twice as fast as anywhere else in the world. Although the main reason for this warming is the global increase in carbon dioxide concentrations, various climatic factors and feedback processes are exacerbating the warming of the Arctic. Black carbon (BC) aerosols in the Arctic have attracted attention as a climate driver accelerating this warming.

BC emitted into the atmosphere by burning fossil fuels and biomass efficiently absorbs solar radiation and warms the atmosphere. In addition, BC deposited on snow and ice can reduce their reflectivity and accelerate their melting. It is believed that most of Arctic BC was transported from regions outside the Arctic. Estimates of the relative contribution of various sources to Arctic BC and thus the climate impacts of BC are, however, still subject to considerable uncertainties.

In March-April 2018, the research group carried out a research project as part of the Polar Airborne Measurements and Arctic Regional Climate Model Simulation Project (PAMARCMiP) Under the direction of the Alfred Wegener Institute (AWI) in Germany, vertical profiles of BC mass concentrations up to 5 km in height in the Arctic were measured. The observations were carried out with the AWI research aircraft Polar 5 and the North Station (81.6 ° N, 16.7 ° W) as the base of operations. The observed BC mass concentrations were compared to those obtained in previous Arctic airplane experiments in the spring (ARCTAS in 2008, HIPPO in 2010, and NETCARE in 2015) to identify factors responsible for the annual variation in BC incidence are responsible. See Figure 1.

The mass concentrations of soot in 2018 were between 7 and 23 nanograms per cubic meter (ng m – 3) and were thus comparable to those in 2010 (Fig. 1 (left)). On the other hand, systematically higher values ​​were observed in 2008 and 2015 at all altitudes up to 5 km. Although each aircraft measurement was performed over a limited area and duration, these results show a significant variation in BC mass concentrations from year to year in the arctic spring.

The research group found that the relative changes in annual variation in ” vertically integrated BC mass concentrations “- d. H. the amount of BC in columns between 0 and 5 km altitude – generally consistent with the estimated biomass burning activities using MODIS satellite derived fire counts detected at latitudes north of 50º N (Fig. 1 (right)). Air transport influenced by biomass combustion in regions between latitudes 45–60 ° N and longitudes 30–50 ° E and 100–130 ° E (western and eastern Eurasia, respectively) was probably responsible for the observed increase in BC values ​​during the Arctic Feder.

During the PAMARCMiP in 2018, a layer of pollutants was occasionally visible through the windows of the research aircraft, the sources of which were probably biomass combustion in the middle latitudes (Fig. 2). It is likely that during the observation periods 2008 and 2015 there was more frequent transport of pollutants from the combustion of biomass to the Arctic. See Figure 2.

The research group also examined the extent to which current numerical model simulations can reproduce the observed variability of the BC pillars from year to year (Fig. 1 (right)). The numerical models can estimate contributions from anthropogenic BC sources and from biomass combustion separately. The numerical models reproduced the observations in 2010 and 2018 when the biomass burning activity was low relatively well, while they had significantly smaller values ​​than the observations in 2008 and 2015 when the biomass burning activity was high. These results suggest that current numerical models generally well reproduce the contribution of anthropogenic BC, while significantly underestimating the contribution of BC from biomass combustion (by a factor of three).

The atmospheric warming effects (positive radiative forcing) of BC in the Arctic are considered to be highest in the spring, when the BC mass concentration is highest and incident solar radiation increases. Spring BC is also important because minor changes in the timing of snow / ice melt can affect the radiation budget in the Arctic. The observations presented in this study provide useful foundations for improving and evaluating numerical model simulations that evaluate the BC radiation effect in the Arctic. In addition, global warming has the potential to increase biomass burning in mid and high latitudes. This study suggests that these future changes in BC emissions could affect the amount of Arctic BC and its radiation effects more than previously thought.

The paper “Arctic black carbon during PAMARCMiP 2018 and previous aircraft experiment in spring” was published online on November 4, 2021 in the journal Atmospheric Chemistry and Physics.

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Black carbon aerosols warming the Arctic: Large contribution from biomass combustion in mid-latitudes
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