Estimating the impact of fires on the atmosphere
European scientists globally monitor wildfires with the help of satellites. The emission data are important for globally and regionally forecasting air quality.
Wherever fires occur, they strongly affect the air we breathe. They even affect the composition of the atmosphere on a global scale. As part of the EU-funded project MACC II, scientists now implement a service that provides daily data on the emissions from wildfires. These data are based on satellite observations. They serve as an input to global and regional model forecasts of atmospheric composition and air quality. Here, sub-project leader Johannes Kaiser, researcher at the department of geography of King's College London, UK, and the department of atmospheric chemistry at the Max Planck Institute for Chemistry in Mainz, Germany, talks to youris.com about the challenges of estimating fire emissions from satellite data.
Which emissions from wild fires are most important?
The most prominent components are aerosols and carbon monoxide. Open fires contribute about 40% to the global carbon monoxide budget. This strongly affects the reactive gas chemistry of the atmosphere. Black carbon and organic matter are important aerosols on a global scale. In the regional air quality forecasts for Europe, aerosols are represented as so-called particulate matter, such as respirable particles smaller than 2.5 micrometer. These aerosols have very strong health effects. For example, last year Singapore experienced the worst air quality on record because of fires in Sumatra.
Black carbon is also relevant for climate studies. According to a review published last year, black carbon might be the second strongest climate-forcing agent from human sources, such as diesel engines, after carbon dioxide. But in smoke from fires organic matter compensates the effect of black carbon. Black smoke absorbs radiation and thus leads to heating while white smoke reflects radiation and thus cools the atmosphere. But the partitioning between these two is not well known.
How do you estimate the emissions from satellite data?
We look at the thermal radiation emitted from forest fires, savannah fires and agricultural burning. They can be quantitatively observed through the infrared channel of satellites. We use these observations to calculate the amount of biomass burning, as satellites pass over these fires. Then we convert this to the emission fluxes of different smoke constituents such as carbon dioxide, carbon monoxide, black carbon, organic matter or particulate matter. We rely on published emission factors that are derived from observations in the field.
What are the challenges of the approach?
Fires are diverse and their occurrence also varies. Currently, we use data from the two MODIS instruments of NASA. We get four observations per day. But fires are often shorter than six hours. We therefore want to include observations from geostationary weather satellites, for example EUMETSAT's Meteosat satellites. These provide data every 15 minutes. This would allow us to observe the whole diurnal fire cycle.
Another difficulty is to characterise the fire type correctly and adapt the emission estimates accordingly. For example, flaming fires emit more black carbon than smouldering fires. But they emit less carbon monoxide. Capturing all this variability is the most challenging bit. We also work on including data from new satellites into the system. This is to maintain the accuracy when older satellites die and to improve the accuracy by including more observations.
Who benefits from the data?
The data are used in the project's global forecasts for aerosols, for the reactive gases and for the greenhouse gases. The regional air quality forecasts will include these emissions later this year. But we also have a number of other users. For example, the research branch of the Japan Meteorological Agency gets our data in real-time to run their own aerosol forecasting system. Recently, the Meteorological Service Singapore requested access to our data. They want to forecast smoke and air quality over Singapore. And we had a request from NASA. We also provide data to people modelling fires within climate models. The Joint Research Centre of the European Commission uses the data to look at the current fire situation in the Mediterranean and to inform the emergency response infrastructure.
Who else has access to the data?
People can freely access the data via the project's website with minimal registration. The data is also included in public emission inventories, such as the one compiled by GEIA/ECCAD. This data is about one month behind real-time. But if you ask, you can also get the data in real-time, more specifically every morning at 7am for the previous day.