Ice Nucleation Activity of Laboratory Generated Soil Organic Particles

Description

Soil organic particles and other aerosol particles are emitted to the atmosphere through land-atmosphere interactions (e.g., raindrop impaction on soil surface). Soil organic particles can play a significant role in heterogeneous ice nucleation under mixed-phase and cirrus cloud conditions. Our previous study showed that sub-micrometer solid airborne soil organic particles (ASOP) contribute substantially to the total number of atmospheric particles following intensive rain events in the Southern Great Plains (ARM site), Oklahoma. In this study we collected aliquots of ‘soil organic matter brine’ from a puddle created by the rain events to generate spherical solid ASOP-like particles under laboratory conditions. Furthermore, we developed a laboratory set-up to generate raindrop impact particles. Preliminary results show significant amount of particles are generated upon impingement of rain droplets on soil surface. Chemical imaging and micro-spectroscopy analysis of soil organic particles are performed to characterize their physico-chemical properties. A single particle mass spectrometer, miniSPLAT was used to characterize in real-time the size, shape, density, and composition, of individual particles. Furthermore, molecular characterization and elemental composition analysis of particle constituents are performed by high-resolution mass spectrometry. Ice nucleation experiments are performed using a continuous flow diffusion chamber, simulating immersion freezing under mixed-phase cloud conditions and using a custom-built ice nucleation cell, interfaced with an environmental scanning electron microscope operated at temperature and relative humidity relevant for cirrus cloud formation. We show dynamic microscopic observations of ice nucleation events on individual submicron size soil organic particles. Overall, our results show that soil organic particles promote ice formation under mixed-phase and cirrus cloud conditions.