Amazon fires produce rain-promoting particles

September 2 () –

Characteristic ultrafine particles, emitted by vegetation fires in the Amazon regionare capable of intensifying storm clouds and heavy rains, a new study reveals.

Smoke particles from wildfires can reduce air quality and harm human health. Smoke aerosols can also influence weather and climate by modifying cloud formation. and changing the amount of solar energy that is reflected or absorbed in the atmosphere.

Compared to larger particles emitted directly by fires, the formation and presence of ultrafine particles (UFP) has previously been overlooked, as they were thought to be quickly “cleaned” by larger particles.

By analyzing aircraft measurements and performing detailed model simulations, a team of researchers found that ultrafine particles were abundant in smoke from vegetation fires in the Amazon region, and that their formation and survival were favored. Furthermore, high-resolution modeling showed that these ultrafine particles may intensify storm clouds and heavy rains. This research deepens our understanding of how vegetation fires produce aerosols that can affect the weather and climate change.

Earth system models have not considered secondary UFPs formed by the nucleation and growth of atmospheric components that form by chemical oxidation in biomass burning smoke, because prior knowledge suggested that there were large losses of nucleating species in the primary smoke particles.

Against this idea, a team of researchers identified efficient nucleation and growth mechanisms for secondary UFPs which produced nucleating species in smoke that could overcome their losses in primary smoke particles and thus maintain nucleation and the long-term presence of many UFPs in smoke, informs in a statement the Environmental Molecular Sciences Laboratory.

This work is expected to fill a major gap in the understanding of the UFP process and open new frontiers of research by highlighting the large potential impacts of UFPs formed in biomass burning smoke on cloud formation, rainfall development, short-term weather conditions, and long-term climate conditions that have been previously overlooked. The study It is published in One Earth magazine.

The formation of new particles in smoke from vegetation fires is thought to be unlikely due to large condensation and coagulation sinks that remove newly nucleated molecular groups in smoke. By analyzing measurements of the smoke tracer gas acetonitrile and particle size distributions from the G-1 aircraft collected in the Amazon rainforest, a multi-institutional team of researchers identified abundant UFPs present in smoke from recent vegetation fires.

Using detailed regional modeling with the Weather Research and Forecasting Model-Chem (WRF-Chem), They elucidated the key mechanisms that explain the formation of UFP in biomass smokeTheir analyses suggest that to maintain the observed UFP concentrations and overcome the large losses of nucleating species in aerosols from primary biomass burning, biomass burning emissions of dimethylamines (DMA) should be included in the model.

Furthermore, DMA emission rates, along with chemical production rates of sulfuric acid and extremely low volatility organic gases in smoke, should be increased proportionally to the particle size distributions observed in smoke.

To simulate the impacts of UFPs and larger particles in smoke on clouds and precipitation, the team used the particle size distributions and hygroscopicity profiles simulated by WRF-Chem and fed them into a detailed cloud microphysics model, called WRF with Spectral Bin Cloud Microphysics. The fine resolution of the WRF with Spectral Bin Cloud Microphysics simulations showed that UFPs can cause a stronger storm with a larger anvil and heavier rainfall, while larger particles emitted directly by fires delay and suppress rainfall.