Abstract
Abstract. We characterise the vertical distribution of biomass-burning emissions across the Amazon during the biomass-burning season (July–November) with an extensive climatology of smoke plumes derived from MISR and MODIS (2005–2012) and CALIOP (2006–2012) observations. Smoke plume heights exhibit substantial variability, spanning a few hundred metres up to 6 km above the terrain. However, the majority of the smoke is located at altitudes below 2.5 km. About 60 % of smoke plumes are observed in drought years, 40 %–50 % at the peak month of the burning season (September) and 94 % over tropical forest and savanna regions, with respect to the total number of smoke plume observations. At the time of the MISR observations (10:00–11:00 LT), the highest plumes are detected over grassland fires (with an averaged maximum plume height of ∼1100 m) and the lowest plumes occur over tropical forest fires (∼800 m). A similar pattern is found later in the day (14:00–15:00 LT) with CALIOP, although at higher altitudes (2300 m grassland vs. 2000 m tropical forest), as CALIOP typically detects smoke at higher altitudes due to its later overpass time, associated with a deeper planetary boundary layer, possibly more energetic fires, and greater sensitivity to thin aerosol layers. On average, 3 %–20 % of the fires inject smoke into the free troposphere; this percentage tends to increase toward the end of the burning season (November: 15 %–40 %). We find a well-defined seasonal cycle between MISR plume heights, MODIS fire radiative power and atmospheric stability across the main biomes of the Amazon, with higher smoke plumes, more intense fires and reduced atmospheric stability conditions toward the end of the burning season. Lower smoke plume heights are detected during drought (800 m) compared to non-drought (1100 m) conditions, in particular over tropical forest and savanna fires. Drought conditions favour understory fires over tropical forest, which tend to produce smouldering combustion and low smoke injection heights. Droughts also seem to favour deeper boundary layers and the percentage of smoke plumes that reach the free troposphere is lower during these dry conditions. Consistent with previous studies, the MISR mid-visible aerosol optical depth demonstrates that smoke makes a significant contribution to the total aerosol loading over the Amazon, which in combination with lower injection heights in drought periods has important implications for air quality. This work highlights the importance of biome type, fire properties and atmospheric and drought conditions for plume dynamics and smoke loading. In addition, our study demonstrates the value of combining observations of MISR and CALIOP constraints on the vertical distribution of smoke from biomass burning over the Amazon.
Highlights
Fires burn across the Amazon region every year, releasing large amounts of trace gases and aerosols into the atmosphere (e.g. Andreae and Merlet, 2001)
We explore the relationship between smoke plume height, fire characteristics (i.e. Moderate Resolution Imaging Spectroradiometer (MODIS) fire radiative power (FRP) and aerosol optical depth (AOD)) and atmospheric conditions derived in the vicinity of the fires throughout the burning season, across the major biomes in the Amazon except cropland
Consistent with previous studies that have shown significant positive relationships between drought conditions and aerosol loading (e.g. Reddington et al, 2015; Tang and Arellano, 2017), we find a significant relationship between Multi-angle Imaging SpectroRadiometer (MISR) AOD and MODIS drought severity index (DSI) on an annual basis in tropical forest and savanna fires (r = −0.7 and p < 0.01; Fig. 8)
Summary
Fires burn across the Amazon region every year, releasing large amounts of trace gases and aerosols into the atmosphere (e.g. Andreae and Merlet, 2001). Amazon fires can contribute up to about 15 % of the total global biomass-burning emissions (Van der Werf et al, 2010). These emissions have important implications for air quality, atmospheric composition, climate and ecosystem health Air pollution from deforestation fires is estimated to cause on average about 3000 premature deaths per year across South America (Reddington et al, 2015) and may decrease the net primary productivity in the Amazon forest as a result of increases in surface ozone (Pacifico et al, 2015)
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