Abstract
Abstract. Five years (July 2007 to June 2012) of CO tropospheric columns derived from the hyperspectral Infrared Atmospheric Sounding Interferometer (IASI) on-board Metop-A are used to study the impact of fires on the concentrations of CO in the troposphere. Following Chédin et al. (2005, 2008), who found a quantitative relation between the daily tropospheric excess of CO2 and fire emissions, we show that tropospheric CO also displays a diurnal signal with a seasonality that agrees well with the seasonal evolution of fires given by Global Fire Emission Database version 3 (GFED3.1) and Global Fire Assimilation System version 1 (GFAS1.0) emissions and Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 5 burned area product. Unlike day- or night-time CO fields, which mix local emissions with nearby emissions transported to the region of study, the day–night difference of CO allows to highlight the CO signal due to local fire emissions. A linear relationship between CO fire emissions from the GFED3.1 and GFAS1.0 inventories and the diurnal difference of IASI CO was found over various regions in the tropics, with a better agreement with GFAS1.0 (correlation coefficient of R2 ∼ 0.7) than GFED3.1 (R2 ∼ 0.6). Based on the specificity of the two main phases of the combustion (flaming vs. smoldering) and on the vertical sensitivity of the sounder to CO, the following mechanism is proposed to explain such a CO diurnal signal: at night, after the passing of IASI at 21:30 local time (LT), a large amount of CO emissions from the smoldering phase is trapped in the boundary layer before being uplifted the next morning by natural and pyroconvection up to the free troposphere, where it is seen by IASI at 09:30 LT. The results presented here highlight the need to take into account the specificity of both the flaming and smoldering phases of fire emissions in order to fully take advantage of CO observations.
Highlights
Biomass burning plays an important and singular role in the global carbon cycle, with a combination of human and natural drivers
Similar conclusions have been obtained with even more strongly polluted profile. This experiment is an approximation of the influence of the variations of the vertical sensitivity between night and day, these results strongly suggest that the diurnal tropospheric excess of carbon monoxide (CO) retrieved from Infrared Atmospheric Sounding Interferometer (IASI) is mostly due to the diurnal cycle of fire emissions
The relation between tropical biomass burning emissions and CO has been analysed by interpreting 5 years (2007–2012) of tropospheric CO column retrieved from IASI observations by day and by night (09:30/21:30 local time (LT)) and temporal series of burned areas (MODIS) and fire emissions (GFED3.1 and GFAS1.0)
Summary
Biomass burning plays an important and singular role in the global carbon cycle, with a combination of human and natural drivers. An approach developed by Chédin et al (2005, 2008) allows the isolatation of CO2 fire emissions from space by calculating the difference between CO2 retrieved by night and CO2 retrieved by day that results from the diurnal cycle of fires (Giglio, 2007) This difference is calculated from the observations of TIROS-N Operational Vertical Sounder (TOVS) on-board NOAA10 and is called daily tropospheric excess (DTE). The mechanism explaining the observation of such a signal is as follows: (i) in the afternoon, during the period of high fire activity, large quantities of CO2 are emitted into the free troposphere; (ii) CO2 accumulates under the tropopause and is seen by the satellite at 19:30; (iii) CO2 is diluted by large-scale transport during the 12 h preceding the pass of the satellite, at 07:30, before fires start again This result was theoretically confirmed with a pyro-thermal plume model (Rio et al, 2010).
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