Organic aerosols represent a subset of atmospheric particles able to act as cloud condensation nuclei (CCN) and, as more recently found, ice nucleating particles (INPs). CCN and INPs affect the ratio of water and ice in mixed-phase clouds, leading to an impact on Earth’s radiative balance. In the work to be presented, we use dissolved organic matter (DOM) as a proxy for organic aerosols and lake spray aerosols in ice nucleation experiments. As the dominant IN mechanism in mixed-phase clouds is immersion freezing, we investigated the ability of DOM to act as INPs, using our homebuilt DRop freezing Ice Nucleation Counter (DRINC). We use field collected DOM, purchased DOM standards and DOM subcomponents such as lignin, sugars and proteins as potential INP. We find that DOM, despite coming from different sources, shows consistent ice nucleating abilities in immersion freezing as warm as –10 °C (50% activated fraction), with a spread we are currently attempting to parameterize using organic carbon properties. To address the effect of atmospheric processing on the ability of DOM to nucleate ice, we submitted the different DOM samples to photochemistry using a photochemical reactor. We find that indirect photochemistry leads to a decrease in INP concentrations. We are also interested in determining the ice-active subcomponent of DOM, and have investigated the ice nucleation ability of natural polymeric material such as lignin in more depth. We find that lignin is also ice-active and that atmospheric processing such as exposure to ozone and sunlight decreases the ability of lignin to act as an ice nucleating particle. In sum, we will present a laboratory-based chemical perspective on the ability of organic material present in the atmosphere to nucleate ice.

Molecular insight on organic matter’s atmospheric ice nucleating ability

2019 Fall National Meeting

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