Modeling atmospheric particles and climate change
Anthropogenic activities have greatly increased the number of atmsopheric particles since the Industrial Revolution. Particles tend to cool the Earth’s climate by reflecting sunlight back to space and changing the optical properties of clouds. It is estimated that these cooling effects have offset between 10-80% of greenhouse warming. General circulation models (GCMs) are mathematical models of the climate system, but representing the interactions between particulate pollution, clouds and climate is a major challenge in modeling climate change.
Over the last decade, my research group has focused on enhancing how GCMs model the tropospheric CCN cycle. Cloud condensation nuclei (CCN) are a subset of atmospheric particles that nucleate cloud droplets in supersaturated conditions. Understanding their sources and formation processes at the global scale is still in its infancy. This requires representing tropospheric particulate matter in much more detail than typical for GCMs with special attention to the particle size distribution and composition. Our model includes the following processes: emissions of particles, new particle formation (aerosol nucleation), growth of particles by condensation of sulfuric acid and secondary organic aerosol (SOA), in-cloud sulfur chemistry, and size-resolved coagulation and deposition. This model has allowed us to estimate the potential impact of a hypothesized link between cosmic rays, clouds, and climate. It also allows us to inform policy-makers about the climate impacts of reducing black carbon (soot) emissions. A physically based approach such as this allows the model to estimate a budget for tropospheric CCN number concentrations. We can also use the model to estimate the importance of various processes to the atmospheric CCN budget: new particle formation, SOA chemistry, combustion and other sources of particle and gaseous emissions.
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