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Leibniz Institute identifies smoke from Canadian wildfires over Germany

04 Jul 2023

Advances in lidar allow better analysis of aerosols and improved climate monitoring.

Since May 2023 a team at the Leibniz Institute for Tropospheric Research (TROPOS) has been recording thin layers of smoke at altitudes between 3 and 12 kilometers above Leipzig, and identifying their point of origin.

Using lidar to analyze particulates in the smoke has allowed TROPOS to confirm that it originated from wildfires, clearly distinguishable from other particles such as volcanic particles or Saharan dust.

Mapping of the prevailing air currents has confirmed that in this case the smoke layers originated from North America, and from the wildfires currently burning across areas of Canada.

"It is impressive and frightening at the same time to see the dimensions these wildfires have reached," said Benedikt Gast from TROPOS. "When forests burn for weeks in Canada and the USA, it is not only the people there who suffer from this disaster. The atmosphere over Europe is also affected."

The capabilities of lidar platforms as tools for measuring atmospheric aerosols and particulates make them key instruments for both the topical monitoring of smoke from wildfires, and also for longer term atmosphere analysis and climate monitoring.

Fluorescence lidar platforms in particular have become increasingly sophisticated at detecting smoke content in the upper troposphere and lower stratosphere, sometimes in tandem with other techniques such as Mie-Raman lidar, in which light is scattered elastically by particles of similar diameter to the wavelength.

TROPOS operates multi-wavelength polarization lidars at various locations for the detection and classification of aerosols, including the Leipzig-based MARTHA (Multiwavelength Atmospheric Raman Lidar for Temperature, Humidity, and Aerosol Profiling), a platform recently equipped with a new channel to measure fluorescence backscatter in the range of 444 to 488 nanometers.

These instruments can also monitor parameters such as the lidar ratio, or relationship between signal backscatter and extinction; the depolarization of the optical signal; and the Angstrom exponent, relating to the optical thickness of an aerosol at particular wavelengths.

The Institute has now published DeLiAn, a collection of lidar-derived aerosol-intensive optical properties for several aerosol types based on these spectral parameters, intended to serve as a basis for future measurements from both ground- and space-based lidar instruments.

Worrying trend for climate change and public health

Recent studies have shown that fluorescence lidar has the potential to improve aerosol classification because it provides data about the fluorescence capacity, or ratio of fluorescence backscatter to elastic backscatter coefficients, which the latest modification to MARTHA is designed to monitor.

"Since the new MARTHA channel is only sensitive to particle scattering, it is perfectly suited for aerosol profiling," said Cristofer Jimenez from TROPOS. "A fluorescence channel in the lidar is like a having a loupe magnifier for aerosol layers. Especially at low particle concentrations, the new approach could provide interesting and completely new results. There is much to explore and expect from the technique."

A more powerful laser, allowing the study of even higher layers of the atmosphere and lower concentrations of aerosol, is expected to be incorporated in the TROPOS measurements soon, a further contribution to the international network of lidar systems studying aerosols, clouds and trace gases.

"Since the start of the 2023 wildfire season in the northern hemisphere, we have seen smoke in almost every layer of the atmosphere, including the lower stratosphere," commented TROPOS researcher Albert Ansmann. "From an atmospheric science perspective, this is a worrying trend. In addition to global warming making large fires around the Arctic Circle more severe, there is new evidence suggesting that the smoke is disrupting the ozone layer and thus posing a health risk to millions of people."

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