Quantifying pyroconvective injection heights using observations of fire energy: sensitivity of spaceborne observations of carbon monoxide

Abstract

Abstract. We use observations of active fire area and fire radiative power (FRP) from the NASA Moderate Resolution Imaging Spectroradiometers (MODIS), together with a parameterized plume rise model, to estimate biomass burning injection heights during 2006. We use these injection heights in the GEOS-Chem (Goddard Earth Observing System Chemistry) atmospheric chemistry transport model to vertically distribute biomass burning emissions of carbon monoxide (CO) and to study the resulting atmospheric distribution. For 2006, we use over half a million FRP and fire area observations as input to the plume rise model. We find that convective heat fluxes and active fire area typically lie in the range of 1-100 kW m −2 and 0.001-100 ha, respectively, although in rare circumstances the convective heat flux can exceed 500 kW m −2 . The resulting injection heights have a skewed probability distribution with approximately 80 % of the injections remaining within the local boundary layer (BL), with occasional injection height exceeding 8 km. We do not find a strong correlation between the FRPinferred surface convective heat flux and the resulting injection height, with environmental conditions often acting as a barrier to rapid vertical mixing even where the convective heat flux and active fire area are large. We also do not find a robust relationship between the underlying burnt vegetation type and the injection height. We find that CO columns calculated using the MODIS-inferred injection height (MODIS-INJ) are typically −9 to +6 % different to the control calculation in which emissions are emitted into the BL, with differences typically largest over the point of emission. After applying MOPITT (Measurement of Pollution in the Troposphere) v5 scene-dependent averaging kernels we find that we are much less sensitive to our choice of injection height profile. The differences between the MOPITT and the model CO columns (max bias ≈ 50 %), due largely to uncertainties in emission inventories, are much larger than those introduced by the injection heights. We show that including a realistic diurnal variation in FRP (peaking in the afternoon) or accounting for subgrid-scale emission errors does not alter our main conclusions. Finally, we use a Bayesian maximum a posteriori approach constrained by MOPITT CO profiles to estimate the CO emissions but because of the inherent bias between model and MOPITT we find little impact on the resulting emission estimates. Studying the role of pyroconvection in the distribution of gases and particles in the atmosphere using global MOPITT CO observations (or any current spaceborne measurement of the atmosphere) is still associated with large errors, with the exception of a small subset of large fires and favourable environmental conditions, which will consequently lead to a bias in any analysis on a global scale.

Fire emission heights in the climate system – Part 2: Impact on transport, black carbon concentrations and radiation

“…The general CALIOP uncertainties in AOT profiles (e.g., Kacenelenbogen et al, 2011;Ma et al, 2013) exceed by far the uncertainties in emission heights. A minor general importance of emission heights compared to the large uncertainties in the emission inventories has also been found by Gonzi et al (2015) for CO emissions. net forcing net solar radiative forcing net thermal radiative forcing net forcing net solar radiative forcing net thermal radiative forcing Table 1.…”

“…For a study by Stein et al (2009), in one case PBL injections performed best, whereas in another case plume heights up to 3 km were necessary to reproduce observations. Gonzi et al (2015) applied a modified version of the 1-D plume model by Freitas et al (2007), Moderate Resolution Imaging Spectroradiometer (MODIS) fire radiative power (FRP) and fire size to simulate global CO concentrations in GEOS-Chem for the year 2006. The authors compared modeling results to MOPITT (Measurement of Pollution in the Troposphere) satellite data, but it turned out that the particular emission height impact on the overall bias was not quantifiable.…”

The importance of plume rise on the concentrations and atmospheric impacts of biomass burning aerosol

“…In this case, it can no longer be assumed that the aerosol above a location of the fire is vertically well mixed. Gonzi et al (2015) applied a one-dimensional plume rise model in global-scale GEOS-Chem simulations during the year 2006. They concluded that approximately 80 % of the injections of biomass burning aerosol occur below the boundary layer height.…”

A review of approaches to estimate wildfire plume injection height within large-scale atmospheric chemical transport models

“…However, for a more complete representation of the source fires, many CTMs can also make use of information on the altitude at which the bulk of the emitted species is injected into the wider atmosphere, where they can fully interact with ambient atmospheric circulation. In a recent study on fire emission transport Gonzi et al (2015) use the GEOS-Chem CTM with a horizontal resolution of 2 • × 2.5…”