Global top-down smoke-aerosol emissions estimation using satellite fire radiative power measurements

摘要

Fire emissions estimates have long been based on bottom-up approaches that are not only complex, but also fraught with compounding uncertainties. We present the development of a global gridded (1° ×1°) emission coefficients (C_e) product for smoke total particulate matter (TPM) based on a top-down approach using coincident measurements of fire radiative power (FRP) and aerosol optical thickness (AOT) from the Moderate-resolution Imaging Spectroradiometer (MODIS) sensors aboard the Terra and Aqua satellites. This new Fire Energetics and Emissions Research version 1.0 (FEER.v1) C_e product has now been released to the community and can be obtained from http://feer.gsfc. nasa.gov/, along with the corresponding 1-to-1 mapping of their quality assurance (QA) flags that will enable the C_e values to be filtered by quality for use in various applications. The regional averages of C_e values for different ecosystem types were found to be in the ranges of 16–21 g MJ~(?1) for savanna and grasslands, 15–32 g MJ~(?1) for tropical forest, 9–12 g MJ~(?1) for North American boreal forest, and 18– 26 g MJ~(?1) for Russian boreal forest, croplands and natural vegetation. The FEER.v1 C_e product was multiplied by time-integrated FRP data to calculate regional smoke TPM emissions, which were compared with equivalent emissions products from three existing inventories. FEER.v1 showed higher and more reasonable smoke TPM estimates than two other emissions inventories that are based on bottom-up approaches and already reported in the literature to be too low, but portrayed an overall reasonable agreement with another top-down approach. This suggests that top-down approaches may hold better promise and need to be further developed to accelerate the reduction of uncertainty associated with fire emissions estimation in air-quality and climate research and applications. Results of the analysis of FEER.v1 data for 2004–2011 show that 65–85 Tg yr~(?1) of TPM is emitted globally from open biomass burning, with a generally decreasing trend over this short time period. The FEER.v1 C_e product is the first global gridded product in the family of "emission factors", that is based essentially on satellite measurements, and requires only direct satellite FRP measurements of an actively burning fire anywhere to evaluate its emission rate in near-real time, which is essential for operational activities, such as the monitoring and forecasting of smoke emission impacts on air quality.