To what extent affect three key uncertainties (emission factor, injection parameterisation and tracer lifetime) the top-down estimates on total carbon emissions released by fires?

Constraining carbon emissions from fire based on CO observations are to date subject to three major sources of uncertainties: assumptions on 1) emission factors, 2) dynamics of the emission process in the atmosphere and 3) tracer lifetime.

Firstly, uncertainties in emission factors to date are in the order 10- 30% for CO, and larger for other trace gases such as CH4, NO2, HCHO and other VOC’s (Andreae, 2019), in turn adding to uncertainties in estimated carbon emissions (Bauwens et al., 2016; Huijnen et al., 2016b). This can be understood as emission factors strongly depend on fire characteristics, which in turn is largely governed by vegetation characteristics, in combination with meteorological factors influencing the evolution of the fire (Questions 1 and 2).

Secondly, the parameterisation of the altitude of tracer emission in the atmosphere is particularly important for the interpretation of the evaluation of short-lived tracers such as NO2 and HCHO against satellite observations whose sensitivity depends on the altitude (Bauwens et al., 2016; Schreier et al., 2015).

Finally, assumptions on the local tracer evolution, in particular governed by its lifetime, may considerably affect the estimation of the emission strength that is needed to match to the observations (Huijnen et al., 2016b, 2019). Here we propose to provide a quantitative assessment of these uncertainties, exploiting Sentinel-5p observations together with a state-of-the-art atmospheric composition-modelling framework as developed in CAMS. Combining Sentinel observations of CO, HCHO and NO2 will provide constraints on emission factors, while Aerosol Layer Height (ALH) and Absorbing Aerosol Index (AAI) observations will be used to constrain the altitude of the fire plume and evolution. Finally, various chemistry schemes as available in the CAMS modelling system can provide constraints on tracer lifetime effects.