Satellite data is providing researchers with a new way to estimate the amount of emissions from wildfires. While new technology is being utilized, this research also stresses the value of improving the accuracy of spaceborne sounders.
Simply stated, what is your paper about?
Wildfires emit gases and aerosols into the atmosphere and impact Earth's climate. In turn,the global climate influences wildfires.Estimating these emissions quantitatively is not an easy task. To date, most estimates have used inventories of emissions, the so-called "bottom-up" approach. Satellite data provides the opportunity for breakthroughsin this research by giving us the ability to make "top-down" assessments.
During combustion, the main product is carbon dioxide while a by-product is carbon monoxide. Carbon monoxide also happens to be one of the most convenient gases to be measured from space. For example, total column carbon monoxide over fires may exceed its normal values by up to 4-5 times, while detected levels of other greenhouse gases are typically no higher than several percent or hardly visible at all. So far, the accuracy of carbon monoxide retrievals estimated in validation campaigns in remote clean areas have been found to be better than plus or minus 10%. However, sounders that use the carbon monoxide band near 4.6 micrometers have low sensitivity at the bottom atmospheric level. In other words, satellites "do not see" extremely high carbon monoxide concentrations near the surface. Validation experiments in areas surrounded by severe wildfires have not been carried out so far.
Wild forest and peat fires occurred in the European part of Russia throughout July and August of 2010. Contrary to other severe wildfires in the boreal belt of the Northern hemisphere, such as those that occurred in Siberia in 2002 and 2003 and in Alaska in 2004, the Russian fires happened in a densely populated area. Less than 100 miles away, Moscow and its environs were covered by the fire plume. As a result, numerous local experimental facilities were able to gather valuable pollution data. For our case, the most valuable data came from two identical sun-tracking spectrometers that were sensitive to the entire troposphere and supplied accurate data for total column carbon monoxide. These data could be directly compared to the satellite data. In addition, surface and tower-based in-situ measurements were available.
What did your research reveal?
During the days of maximum pollution (up to 10 parts per million carbon monoxide in the surface layer), ground-based spectrometers reported the total column carbon monoxide over Moscow to be about 2.5 to 3 times greater than the mid-tropospheric amounts measured by the AIRS and MOPITT satellite instruments. The mid-tropospheric observations from the more sensitive IASI/Metop-A satellite instrument were found to be slightly larger, but still missing about ~ 80% of the total carbon monoxide. We extrapolated these ratios over Moscow onto the entire plume which covered up to 6 million square kilometers, and estimated that the Russian fires emitted between 34 to 40 megatons of carbon monoxide. These ground-based modifications of the satellite observations indicated a maximum daily emitted carbon monoxide of 2.2 megatons per day.
What part of your research do you consider to be the most significant?
We hope our paper will attract attention to the case of using Russian fires for the validation of satellite-based remote sensing of atmospheric composition. We used only 1% of available ground-based measurements in Moscow and other Russian cities impacted by the fires, and the estimate of emitted carbon monoxide that we considered to be reasonable should be verified using more complicated modeling. We also believe that our results for Russian fires could be extended to other severe fires, and top-down satellite-based estimates of emissions should be significantly re-evaluated. Finally, the necessity of improving the accuracy of satellite sounders for carbon monoxide should be stressed.
