Key drivers of cloud response to surface-active organics

• Published in: Nature communications Vol. 10; no. 1; p. 5214
• Main Authors: Lowe, S. J., Partridge, D. G., Davies, J. F., Wilson, K. R., Topping, D., Riipinen, I.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 18.11.2019; Nature Publishing Group; Nature Portfolio
• Subjects: 704/106/35/823; 704/106/35/824; Aerosols; Applied Environmental Science; Atmospheric models; Climate models; Clouds; Droplets; Empirical analysis; ENVIRONMENTAL SCIENCES; Humanities and Social Sciences; Microphysics; multidisciplinary; Optical properties; Particle size distribution; Radiative forcing; Science; Science (multidisciplinary); Sensitivity analysis; Short wave radiation; Size distribution; Surface tension; tillämpad miljövetenskap; Ultrafines; Water availability
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-12982-0

Aerosol-cloud interactions constitute the largest source of uncertainty in global radiative forcing estimates, hampering our understanding of climate evolution. Recent empirical evidence suggests surface tension depression by organic aerosol to significantly influence the formation of cloud droplets, and hence cloud optical properties. In climate models, however, surface tension of water is generally assumed when predicting cloud droplet concentrations. Here we show that the sensitivity of cloud microphysics, optical properties and shortwave radiative effects to the surface phase are dictated by an interplay between the aerosol particle size distribution, composition, water availability and atmospheric dynamics. We demonstrate that accounting for the surface phase becomes essential in clean environments in which ultrafine particle sources are present. Through detailed sensitivity analysis, quantitative constraints on the key drivers – aerosol particle number concentrations, organic fraction and fixed updraft velocity – are derived for instances of significant cloud microphysical susceptibilities to the surface phase. Aerosol-cloud interactions are a large source of uncertainty in radiative forcing estimates. Here, the authors show that the radiative effects of clouds are influenced by a combination of aerosol particle distribution, environmental conditions and atmosphere dynamics.