The aerosol optical depth (AOD) in the atmosphere has been retrieved from direct Sun (DS) measurements by the application of the Beer law (BL). On the other hand, the Langley method (LM), an offspring of the BL, is inappropriate to the retrieval of the AOD since it requires a stable atmosphere during DS measurements, a condition hardly achieved in typical turbulent scenes of biomass burning sites owing to the aerosol layer variability. In this work, some events of calmness of the aerosol layer during biomass burning episodes in the central area of Brazil are identified. Such a condition can be identified by low variability in the AOD values, and it makes the BL and the LM application yield similar results. Intervals of almost 2 hours have been identified, characterizing a state of calmness in the aerosol layer according to the chosen parameters. Measurement restrictions and statistical criteria for the retrieval of the AOD are used in the identification of the calmness states, and as a spin-off the retrieval of the irradiance at the top of the atmosphere (the extrapolated value Ioλ) from the LM has been improved, reducing its uncertainty from 0.5988 ¿ 107 to 0.1878 ¿ 107 photons/s (p/s) at 306.3 nm and from 0.4002 ¿ 107 to 0.1375 ¿ 107 p/s at 320.1 nm. Consequently, the AOD uncertainty has also been reduced by 47 and 56%, respectively, on average.