Ultrafine particles in wildfire smoke change weather patterns

Ultrafine particles (UFPs) in wildfire smoke can significantly impact air quality, human health, and the environment, extending far beyond the immediate vicinity of the fires. These tiny particles can travel long distances, spreading their effects over vast regions.

While larger particles from fires are known to affect weather patterns and climate by altering cloud formation and the reflection or absorption of the sun’s energy, the specific role of ultrafine particles has often been overlooked due to their elusive and transient nature.

Overlooked impact of ultrafine particles

The minuscule particles, measuring less than 100 nanometers in diameter, were thought to be quickly “scavenged” by larger particles, thus minimizing their influence on atmospheric processes and reducing their potential to linger in the atmosphere.

However, emerging research indicates that ultrafine particles are more resilient and influential than previously thought, suggesting their impact on climate and weather patterns might be far more significant than earlier assumptions.

This challenges traditional views on how wildfire smoke interacts with the atmosphere and calls for a deeper investigation into the role of ultrafine particles in environmental processes.

Abundant ultrafine particles in smoke

A team of researchers from the Pacific Northwest National Laboratory (PNNL), in collaboration with their partners using the specialized G-1 research aircraft, conducted comprehensive measurements and advanced model simulations to analyze ultrafine particles in detail.

The study revealed that UFPs were not only present but also highly abundant in smoke from vegetation fires in the Amazon rainforest, with specific atmospheric conditions favoring their formation, persistence, and survival.

The team’s high-resolution modeling further demonstrated that these UFPs have the potential to intensify storm clouds, leading to increased occurrences of heavy rainfall.

The research significantly enhances our understanding of how aerosols produced by vegetation fires can influence weather patterns, cloud dynamics, and long-term climate change, underscoring the need to incorporate ultrafine particles into climate models.

Limitations in Earth system models

Previously, Earth system models did not account for secondary UFPs formed through nucleation and the growth of atmospheric constituents resulting from chemical oxidation in smoke from burning biomass. Earlier assumptions suggested significant losses of nucleating species to primary smoke particles.

However, the team identified efficient nucleation and growth mechanisms for secondary UFPs, highlighting how nucleating species in smoke could overcome these losses and maintain the presence of many ultrafine particles.

The study, published in the journal One Earth, fills a significant gap in our understanding of ultrafine particle processes. It opens new research opportunities by showcasing the potential impacts of ultrafine particles formed in biomass smoke on cloud formation, rain development, and both short-term weather and long-term climate conditions.

Advanced modeling techniques

Detailed analysis using the G-1 aircraft measurements of smoke tracer gas acetonitrile and particle size distributions over the Amazon rainforest revealed a large amount of ultrafine particles in smoke from fresh vegetation fires.

The multi-institutional team used the Weather Research and Forecasting Model coupled to chemistry (WRF-Chem) for regional modeling. The analysis identified key mechanisms explaining the formation of ultrafine particles in biomass smoke.

The researchers found that the inclusion of biomass burning emissions of dimethyl amines (DMA) in the model was necessary to maintain observed ultrafine particle concentrations and overcome the large losses of nucleating species to primary biomass burning aerosols.

Ultrafine particles and storm intensity

The researchers also proposed adjustments to the model, such as increasing the emission rates of dimethyl amines (DMA), sulfuric acid, and extremely low volatility organic compounds to better reflect the particle size distributions observed in wildfire smoke.

To understand how both ultrafine and larger particles influence cloud formation and precipitation, the team employed particle size data and hygroscopicity profiles generated by the WRF-Chem model, combined with a sophisticated cloud microphysics framework known as WRF with spectral bin cloud microphysics.

The simulations revealed that while ultrafine particles have the potential to strengthen storms, enlarge storm anvils, and lead to more intense rainfall, the presence of larger particles from fires tends to delay precipitation onset and reduce rainfall intensity.

The study is published in the journal One Earth.

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