Enviro-HIRLAM model estimates of elevated black carbon pollution over Ukraine resulted from forest fires

Abstract. Biomass burning is one of the biggest sources of
atmospheric black carbon (BC), which negatively impacts human health and
contributes to climate forcing. In this work, we explore the horizontal and
vertical variability of BC concentrations over Ukraine during wildfires in
August 2010. Using the Enviro-HIRLAM modelling framework, the BC atmospheric
transport was modelled for coarse, accumulation, and Aitken mode aerosol
particles emitted by the wildfire. Elevated pollution levels were observed
within the boundary layer. The influence of the BC emissions from the
wildfire was identified up to 550 hPa level for the coarse and accumulation
modes and at distances of about 2000 km from the fire areas. BC was mainly
transported in the lowest 3 km layer and mainly deposited at night and in
the morning hours due to the formation of strong surface temperature
inversions. As modelling is the only available source of BC data in Ukraine,
our results were compared with ground-level measurements of dust, which
showed an increase in concentration of up to 73 % during wildfires in
comparison to average values. The BC contribution was found to be 10 %–20 %
of the total aerosol mass near the wildfires in the lowest 2 km layer. At a
distance, BC contribution exceeded 10 % only in urban areas. In the areas
with a high BC content represented by both accumulation and coarse modes,
downwelling surface long-wave radiation increased up to 20 W m−2, and 2 m
air temperature increased by 1–4 ∘C during the midday hours. The
findings of this case study can help to understand the behaviour of BC
distribution and possible direct aerosol effects during anticyclonic
conditions, which are often observed in mid-latitudes in the summer and lead
to wildfire occurrences.
