Vertical transport of surface fire emissions observed from space

We use optimal estimation to infer the vertical distribution of surface emissions lofted from boreal and tropical biomass burning during June–October (JJASO) 2006. We use satellite observations of CO, a tracer of incomplete combustion, at thermal infrared and microwave wavelengths from Aura Tropospheric Emission Spectrometer (TES) and Microwave Limb Sounder (MLS), respectively. TES and MLS together typically provide two to three pieces of information. We use a maximum a posteriori (MAP) methodology to estimate emitted CO mass in five vertical regions spanning the troposphere and lower stratosphere, equivalent to estimating surface emissions. Correlations between neighboring vertical regions, due to vigorous mixing induced by surface heating, reduce the inversion to the information content provided by the data. We use a total of 1785 TES profile measurements, of which 672 are colocated with MLS. We define an injection height based on MAP statistics. We find that 10%–20% of boreal and tropical fire emissions, depending on the region, reach the free and upper troposphere during JJASO 2006. Our injection height estimates during two key pyroconvective events, Siberia (July) and Indonesia (October), qualitatively agree with measurements of aerosol index and attenuated backscatter from Aura Ozone Monitoring Instrument (OMI) and CALIPSO, respectively. Surface emissions inferred from our mass estimates agree with the Global Fire Emission Database biomass burning emission inventory to within ±10%. The small percentage of emissions injected above the boundary layer result in disproportionate changes in CO concentrations of more than 2–25 ppb and 15–160 ppb over boreal and tropical regions, respectively.