Sink, Source or Something In-Between? Net Effects of Precipitation on Aerosol Particle Populations

Interactions between atmospheric aerosols, clouds, and precipitation impact Earth's radiative balance and air quality, yet remain poorly constrained. Precipitating clouds serve as major sinks for particulate matter, but recent studies suggest that precipitation may also act as a particle source. The magnitude of the sources versus sinks, particularly for cloud condensation nuclei (CCN) numbers, remain unquantified. This study analyzes multi-year in situ observations from tropical and boreal forests, as well as Arctic marine environment, showing links between recent precipitation and enhanced particle concentrations, including CCN-sized particles. In some cases, the magnitude of precipitation-related source equals or surpasses corresponding removal effect. Our findings highlight the importance of cloud-processed material in determining near-surface particle concentrations and the value of long-term in situ observations for understanding aerosol particle life cycle. Robust patterns emerge from sufficiently long data series, allowing for quantitative assessment of the large-scale significance of new phenomena observed in case studies. Atmospheric aerosols, clouds, and precipitation play a significant role in Earth's temperature regulation and air quality. However, understanding their interactions is still a challenge. While clouds and precipitation help remove particles from the atmosphere, recent research suggests rain could also introduce new particles. The extent of this particle source and its impact on climate are still unknown. In this study, we analyzed years of observational data from clean environments, including tropical and boreal forests and the Arctic marine boundary layer. We discovered that after precipitation, new particles were sometimes added to the surface atmosphere. In some cases, rain introduced as many or even more particles than it removed. Our findings highlight the importance of considering how clouds and rain recycle particles when studying air quality and climate. Long-term, real-world observations help us understand atmospheric particle life cycles and identify consistent patterns, ultimately improving our knowledge of the complex interactions between aerosols, clouds, and precipitation. Precipitation can act as a source for particles of varying sizes depending on the environment, reflecting diverse underlying mechanismsRecycling cloud-processed material influences near-surface particle concentrations, emphasizing its relevance for climate model implementationStudying the time-dependent instead of total accumulated precipitation elucidates direct versus indirect effects on aerosol populations

Automated summary

Interactions between atmospheric aerosols, clouds, and precipitation have significant impacts on Earth's radiative balance and air quality, but their effects are still poorly constrained. Precipitation can serve as both a source and a sink for particles, but the magnitude of these sources and sinks remains uncertain. In this study, multi-year in situ observations from various environments were analyzed, revealing links between recent precipitation and increased particle concentrations, including cloud condensation nuclei (CCN)-sized particles. In some cases, the particle source introduced by precipitation was equal to or even greater than the corresponding removal effect. These findings emphasize the importance of considering cloud-processed material in determining surface-level particle concentrations and the value of long-term observational data for understanding aerosol particle life cycles. Quantitative assessment of large-scale significance can be achieved through robust patterns identified in sufficiently long data series.