Andes Stations Monitor Record Smoke Pollution Events
Biomass burning in the Amazonian region over the last two years has been more intense and longer lasting than usual
Biomass burning in the Amazonian region over the last two years has been more intense and longer lasting than usual. This year, the intense biomass burning season has produced exceptionally strong smoke pollution events and large amounts of smoke and gases that have been transported towards the Andes mountains’ region. Satellite imagery shows extended areas of South America covered in smoke, especially the Plurinational State of Bolivia, where many fires have been reported since August. The Global Atmosphere Watch (GAW) Chacaltaya (CHC) station, located 5 240 metres (m) above sea level (asl) (16.35 ºS, 68.13 ºW), and other Bolivian stations have monitored the transport of smoke, recording almost 10 times higher increases in aerosols.
The CHC station, as well as two other auxiliary sites in the metropolitan area of La Paz (LP, 3 420 m asl, 16.54 ºS, 68.06 ºW) and El Alto (EA, 4 025 m asl, 16.51 ºS, 18.20 ºW), have different types of instruments monitoring atmospheric composition. In particular, data from two aethalometers (at both CHC and EA), two sunphotometers (at CHC and LP), and a gas concentration analyser (at CHC) are used here to report the transport of biomass burning smoke to those locations.
Aerosol Optical Depth (AOD), a measure of the extinction of solar light by the presence of aerosol particles in the atmosphere, measured in LP by sunphotometers, shows a maximum value of 0.7 when measured at a wavelength of 500 nm (~0.08 under clean conditions) on 12 September. Correspondingly, at CHC on the same day, a maximum AOD value of 0.25 (~0.02 under clean conditions) was observed. This suggests that the aerosol loading could have increased by almost a factor of 10 with respect to the cleanest periods of the year.
At the same time, Extinction Angstrom Exponent (EAE), which gives an indication of the size of the aerosols, as well as equivalent black carbon (eBC), a short-lived climate pollutant, measured at two channels by the aetahalometers, indicate that the same type of particles arrived at LP and CHC. Mean values computed for the first half of September show that eBC values increased about 2.5 times compared to the mean values calculated from 2016 to 2023. The same type of calculation for concentrations of carbon monoxide (CO) shows that in 2024 this value increased by a factor of two.
The monitored values were compared to values that were already high because September is the month with the highest number of fires in the region, which historically produce large amounts of smoke in the lowlands. All these measurements confirm that the transport of products from biomass burning to the Central Andes region in 2024 has been one of the most intense of the last decade (box-and-whiskers plot).
