Understanding how thin organic films affect the Earth’s climate
24 Jul 2026 - Rohini Gupta
Atmospheric aerosols are tiny particles suspended in the air that can influence earth's climate by scattering and absorbing sunlight. Many of these particles are coated with extremely thin organic films, but scientists do not fully understand how these films affect the particles' optical properties and climate impacts.
Furthermore, current climate models do not fully account for the effects of thin organic coatings on aerosol particles. Since aerosols play an important role in regulating earth’s temperature, understanding these coatings can help improve predictions of climate change and atmospheric processes.
Here, researchers from Royal Holloway, University of London – Professor Martin King, and Edward Stuckey (previous ISIS part-funded student), as well as ISIS Instrument Scientist Becky Welbourn, investigated how organic films at the mineral–water interface of aerosol particles change when exposed to ozone and how these changes influence light scattering.
Method
To investigate this, these researchers used model organic films using three lipid molecules: DPPC, POPC, and DOPC. These molecules were selected because they contain different numbers of carbon–carbon double bonds, allowing the team to investigate how chemical structure influences oxidation over an aerosol particle’s lifetime. These films were deposited onto a silica-water surface that represented a mineral aerosol particle coated in water, such as a cloud or fog-droplet. The films were then exposed to ozone dissolved in water to simulate atmospheric oxidation. The scientists measured changes in the thickness and structure of the films before and after oxidation. However, a key challenge was that the mineral–water interface is a buried interface that cannot easily be observed using conventional techniques – a challenge that was overcome by the use of neutrons.
Result
Using the Inter beamline at the ISIS neutron and Muon Source, their experiment is one of the first investigations of atmospheric processes occurring at the mineral–water interface using neutron reflectometry. As neutrons can penetrate through materials and reveal the structure of extremely thin films only a few nanometres thick, the researchers could observe, in real time, how ozone altered the organic films.
Their neutron measurements showed that all three lipids initially formed films approximately 4 nm thick (about 20,000 times smaller than a human hair!). However, their response to ozone depended strongly on their chemistry. DPPC, which contains no carbon–carbon double bonds, remained largely unchanged. In contrast, POPC and DOPC underwent substantial oxidation, with film thicknesses decreasing to approximately 1.6 nm and 0.4 nm, respectively. The greater the number of double bonds present, the greater the extent of film degradation. Importantly, some organic material remained at the interface even after prolonged oxidation, suggesting that these films may persist throughout much of an aerosol particle’s atmospheric lifetime.
To understand the climatic significance of these observations, the experimentally measured film thicknesses were incorporated into computational scattering models. These simulations revealed that even nanometre-thick organic films can alter how aerosol particles interact with sunlight. Increasing film thickness caused the particles to scatter more sunlight forward and changed how strongly they influenced earth’s energy balance (the amount of warming or cooling they produce). Oxidation reduced these effects by thinning the films but did not eliminate them entirely.
The results demonstrate that the chemical ageing of organic films can influence aerosol radiative properties and potentially affect Earth's climate.Their research shows that that tiny organic coatings on atmospheric particles can affect climate-relevant processes. Their findings highlight the importance of including organic films and their oxidation chemistry in future aerosol and climate models, leading to more accurate predictions of atmospheric behaviour and climate change.
This work was led by Edward Stuckey, in collaboration with Martin King (RHUL), Rebecca Welbourn (ORNL), Tobias Robson (Forest Research UK), Philipp Gutfruend (ILL), Katherine Thompson (Birkbeck University) and Adrian Rennie (Uppsala University).
