Wildfire plumes detection from Sentinel-5P TROPOMI

Air quality
Increasingly devastating wildfires have recently raised international concerns about their impacts on air quality and climate. The “UV-visible observations” group is exploiting the high resolution Sentinel-5P TROPOMI instrument which holds the potential to provide valuable insights into trace gas emissions from fires. For the first time, nitrous acid (HONO) from fires was detected from space. Research focuses also on formaldehyde (HCHO) and glyoxal (CHOCHO), important indicators of biomass burning hydrocarbons emissions.

Biomass burning is one of the major contributors of trace gases and aerosols to the atmosphere, significantly affecting its chemistry and radiative balance. As a result of climate change and human activity, the intensity and frequency of wildfires dramatically increase, as evidenced from recent huge fires in the US, Australia and Amazonia.

Instruments such as TROPOMI onboard Sentinel-5p are essential for studying the impact of fires on the atmospheric composition and air quality. Its small pixels and improved spectral characteristics and coverage allow for unprecedentedly detailed observations of fire plumes for a suite of trace gases, such as:

  • NO2
  • HONO
  • HCHO
  • CHOCHO
  • CO
  • aerosols

The “UV-visible observations” team pursues the development and scientific exploitation of some of these products as they provide valuable insights on burning processes, atmospheric chemistry interactions, and long-range impact of fire emissions.

First satellite mapping of nitrous acid in wildfire plumes

With its improved spatial resolution, TROPOMI allows to better detect short-lived trace gas for which pixel-averaged concentrations are significantly lower for coarse resolution satellites. For the first time, it was possible to detect nitrous acid (HONO) from space. It consistently reveals the existence of enhanced HONO over wildfires for major ecosystems.

The importance of HONO in atmospheric chemistry stems from its role as precursor of the OH radical. The latter is among the most important oxidizing molecules and controls the degradation of pollutants and greenhouse gases, and contributes to ozone formation and photochemical smog. Pyrogenic HONO emission assessments have been significantly underestimated. HONO emissions may account for about two-thirds of OH production in fresh wildfire plumes and can have a significant impact on atmospheric composition at regional level.

Satellite monitoring of formaldehyde and glyoxal from biomass burning

Emissions of hydrocarbons by fires produce oxygenated volatile organic compounds (OVOCs) either directly or through secondary reactions. OVOCs are involved in fast oxidation chemical processes, which in turn contributes to the formation of ozone and secondary aerosols. Important OVOCs are formaldehyde (HCHO) and glyoxal (CHOCHO) which are both measurable by TROPOMI, and provide complementary information on the underlying chemical mechanisms in fire plumes.

High-quality long-term products based on recently developed or refined algorithms can be used to study HCHO and CHOCHO from biomass burning. In particular, the recent mega fires in the USA, Australia and Amazonia are unprecedented in magnitude in the satellite data records. As an illustration, the inset figure below indicates that the 2020 fires in California emitted at least half as much HCHO as ever been observed during the entire OMI lifetime at that season.

California fires 2020 HCHO emission
Animation of CHOCHO column measurements from wildfires in California (USA) observed by TROPOMI in September 2020.

Further reading:

 
Fires in Victoria and New South Wales HONO emissions
HONO emissions by fires in Victoria and New South Wales (Australia) as observed by TROPOMI on 4 Jan 2020.
Map HCHO emissions from wildfires in California (USA)
HCHO emissions from wildfires in California (USA) observed by TROPOMI (10-12 September 2020). Inset figure shows long-term time series of averaged HCHO columns over San Francisco from OMI (in red) and TROPOMI (in black)