Massive wildfires in Canada have destroyed millions of hectares of forest, displacing over 100,000 people and impacting air quality for millions in North America. The ecological disaster’s effects have even been observed in the atmosphere over Germany.

Researchers at the Leibniz Institute for Tropospheric Research (TROPOS) have been detecting thin layers of smoke at altitudes of 3 to 12 kilometers above Leipzig since mid-May. They used a new technique for identifying smoke particles of biological origin to confirm that these were indeed from the wildfires. When illuminated with UV light from a laser, smoke particles glow and can be distinguished from other particles, such as volcanic particulates or Sahara dust. The smoke layers were traced back to North America using air currents.

Benedikt Gast from TROPOS noted:

“It is impressive and frightening at the same time to see the dimensions these wildfires have reached in the meantime: 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: In the high, normally cloud-free air layers, thin veil clouds appear to form due to the smoke particles.”

Not a health risk but still poses a threat

In comparison to North America, where cities on the East Coast experienced smoke for days in June and a fine dust alarm was issued, the smoke from North America does not pose a health risk in Europe. While the smoke layers are present at high altitudes and are highly diluted, it still affects the atmosphere and climate. The smoke particles scatter solar radiation, leading to a slight dimming of light. This can cause the sky to appear slightly cloudy, similar to the effect of Saharan dust. Furthermore, the smoke can impact cloud formation in the upper layers of the atmosphere. During the MOSAiC expedition in the Arctic in 2020, researchers discovered an unusually large amount of smoke around the North Pole and observed the formation of cirrus clouds.

A study from Cyprus also shows that smoke particles can act as nucleation nuclei for the formation of ice crystals under certain conditions. Researchers from the Eratosthenes Centre of Excellence, Cyprus University of Technology, and TROPOS analyzed data from Limassol in autumn 2020, when smoke from severe wildfires in North America was transported to the Mediterranean region from Portugal to Cyprus. The measurements provided clear evidence that aged smoke particles at around -50°C triggered ice formation at the transition between the humid troposphere and the dry stratosphere, leading to the formation of ice clouds.

“Our current observations over Leipzig also show indications of such connection. During several measurements in the last few weeks, we were able to observe smoke layers, and ice clouds (also known as cirrus clouds) in its surroundings at altitudes from 10 to 12 km. Such smoke layers in the strong presence of cirrus clouds were observed not only in Leipzig but also in various stations in Europe: From the southwest in Evora (Portugal), through Warsaw (Poland) to Kuopio (Finland) in the northeast. The smoke causing more clouds, could open a new impact-pathway in the context of climate change, since clouds can have a cooling or warming effect, depending on their optical thickness, phase, and microphysical properties. The more intense and more frequent wildfires are potentially affecting atmospheric radiation budget at a still unknown extent. This potential motivates us to further investigate the interplay of forest-fire smoke and cloud formation.”

Climate change causes more wildfires which releases aerosols into atmosphere

Climate change is causing more wildfires, which release large amounts of aerosol into the atmosphere. These aerosol particles can spread throughout the troposphere and even the stratosphere, affecting the Earth’s radiation budget and cloud cover over long periods and large areas. This is a concerning trend, as global warming is causing more severe and frequent fires, especially in large forests around the Arctic Circle. The resulting changes to the atmosphere are significant and can influence the climate. Recent evidence shows that the smoke from these fires is also harming the ozone layer, putting millions of people at risk.

Accurate aerosol typing is crucial for understanding and quantifying the effects of aerosols on climate. Multi-wavelength polarisation lidars, like those used by TROPOS at various locations, are effective tools for detecting and classifying aerosols using parameters such as the lidar ratio, depolarisation ratio, and Ångström exponent. However, it is difficult to distinguish stratospheric smoke from volcanic sulfate aerosol.

Recent studies indicate that fluorescence lidar has the potential to improve aerosol classification by introducing an additional parameter: fluorescence capacity (the ratio of fluorescence backscatter to elastic backscatter coefficients). To investigate this potential, researchers have expanded MARTHA, the large, stationary atmospheric lidar at TROPOS in Leipzig by adding a receiving channel that can measure fluorescence backscatter in the 444-488 nanometer spectral range.

Experience gained from fluorescence observations at TROPOS indicates that this technique has great potential not only for aerosol typing but also for detecting smoke layers. According to Dr. Cristofer Jimenez from TROPOS, “since the new channel is only sensitive to particle scattering, it is ideally suited for aerosol profiling. A fluorescence channel in the lidar is like a magnifying glass 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.”

In the coming months, a more powerful laser will be available to study even higher layers of the atmosphere and lower concentrations. Both the station in Leipzig and the one in Limassol belong to PollyNet, a network of lidar systems that use laser beams to study the atmosphere from the ground. PollyNet is part of the European research infrastructure ACTRIS, which studies aerosols, clouds, and trace gases.

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Canadian wildfire smoke analysis. via Eureka News with usage type - News Release Media
Canadian wildfire smoke analysis. via Eureka News with usage type - News Release Media