RESUMEN
Wildfires inject large amounts of black carbon (BC) particles into the atmosphere, which can reach the lowermost stratosphere (LMS) and cause strong radiative forcing. During a 14-month period of observations on board a passenger aircraft flying between Europe and North America, we found frequent and widespread biomass burning (BB) plumes, influencing 16 of 160 flight hours in the LMS. The average BC mass concentrations in these plumes (â¼140 ng·m-3, standard temperature and pressure) were over 20 times higher than the background concentration (â¼6 ng·m-3) with more than 100-fold enhanced peak values (up to â¼720 ng·m-3). In the LMS, nearly all BC particles were covered with a thick coating. The average mass equivalent diameter of the BC particle cores was â¼120 nm with a mean coating thickness of â¼150 nm in the BB plume and â¼90 nm with a coating of â¼125 nm in the background. In a BB plume that was encountered twice, we also found a high diameter growth rate of â¼1 nm·h-1 due to the BC particle coatings. The observed high concentrations and thick coatings of BC particles demonstrate that wildfires can induce strong local heating in the LMS and may have a significant influence on the regional radiative forcing of climate.