OHB-SGP

OH Burst in Cloud Droplets at SGP

1 March 2022 - 30 September 2022

Lead Scientist: Suzanne Paulson

Observatory: SGP

Aerosol particles (tiny liquid or solid particles in the atmosphere, ranging in size from a few nanometers to several micrometers in diameter) and aerosol-cloud interactions are the most uncertain aspect of the climate system. Aerosol particles are at the heart of cloud droplets—each droplet forms on an aerosol particle. The particle partly dissolves in the cloud water, and the water takes up organic and acidic gasses from the air. Chemical reactions take place, and when the cloud evaporates the aerosol particles left behind have altered sizes, chemical composition, and radiative properties, although the process is not well understood.

We recently found a new, substantial source of hydroxyl radicals (OH) in cloud droplets. Hydroxyl radicals (water molecules minus one hydrogen atom) are one of the main drivers of chemical reactions in cloud droplets. During the first few minutes following cloud droplet formation, in daylight, material in aerosols produces a burst of hydroxyl radicals. The estimated contribution of the ‘OH burst’ to total OH in droplets ranges from ~100% to up to around a factor of 10 larger than other known sources, significantly enhancing the ability of cloud droplets to process organics present in the particles that served as cloud condensation nuclei. However, these estimates are based on measurements of urban particles