The results of sensing of the gas and aerosol composition of the atmosphere with the Optik Tu‐134 aircraft laboratory in the period from 31 July to 1 August 2012 are presented. The measurements were conducted along the flight route Novosibirsk‐Tomsk‐Mirny‐Yakutsk‐Bratsk‐Novosibirsk. A significant part of the Siberian territory during this period was covered by numerous forest fires. The synoptic situation during the measurements was characterized by the presence of low‐gradient field. This fact determined the low rate of transport and diffusion of pollutants and their accumulation in the region under study. The maximal concentrations of CO2, CH4, and CO over fire zones achieved 432 ppm, 2367 ppb, and 4036 ppb, respectively. The aerosol particle number density in emission plumes achieved 4400 cm−3. Outside emission plumes, the concentration ranged within 400–1000 cm−3 depending on the region. The mass concentration of aerosol in plumes increased approximately 7 times (6.9). The enrichment of the concentration of some elements and ions in the plume with respect to the background varied from 1.3 to 9.1 times. The generation of ozone from biomass burning products was observed at plume boundaries. Two versions of this process are possible: ozone generation under and above the plume.