Aerosol-Cloud Interaction - A Directed Programme to Reduce Uncertainty in Forcing through a Targeted Laboratory and Modelling Programme

Lead Research Organisation: University of York
Department Name: Chemistry

Abstract

Aerosol particles act as sites for cloud droplet and ice particle formation. Cloud properties can be perturbed through the addition of aerosol particles into the atmosphere from anthropogenic and natural processes. This addition influences cloud microphysical properties, and subsequently affects cloud dynamics and thermodynamics, and the way the cloud interacts with radiation. The Earth's radiation budget is very greatly affected by clouds, and human-induced changes to the particle loading affecting them, known as indirect effects, are large and highly uncertain. A large part of this uncertainty is the result of poor knowledge of the fundamental aerosol and cloud properties and processes, leading to their poor representation in models. A programme of research is proposed here to i) directly investigate these processes in the laboratory, ii) evaluate the sensitivity of climate relevant parameters to the studied processes, iii) interpret the laboratory studies with detailed model investigations and iv) to incorporate and test new descriptions of the studied processes in cloud-scale and, where possible, global scale models. The programme will thereby reduce the uncertainty in estimates of radiative forcing and climate feedbacks relating to aerosol and cloud processes. The studies are split into those affecting warm clouds (those containing only liquid droplets) and those affecting clouds containing ice particles. The programme brings together an interdisciplinary team of researchers with expertise in 'warm' and 'cold' cloud and aerosol processes combining laboratory and multiscale modelling activities to deliver the improved predictive capability. The 'warm' laboratory work focuses on two major aspects i) the rate at which water is taken up by growing aerosol particles as they become cloud droplets (or 'activate) and ii) the ability of aerosol particles of various compositions to act as seeds for cloud droplets. These studies use a number of techniques including single particle optical levitation and investigations in a large photochemical chamber coupled to a large number of chemical and physical probes of ensembles of particles formed in simulated atmospheric chemical processes. The 'cold' work uses a similar coupling of a large, well-instrumented cloud chamber experiments and single particle levitation studies. The chambers used in both aspects will be coupled to investigate the impacts of aerosol transformation conditions on warm and cold cloud formation, using the instrumental payload from both chambers. A range of detailed models will be used to explicitly describe the processes by which aerosol particles interact with increasing relative humidity and reducing temperature to form cloud droplet and ice crystals and to their properties. The processes and properties will be represented in dynamical frameworks to predict the interactions between aerosols and clouds and their radiative effects at cloud resolving scales and radiative forcing of some of the investigated properties on global radiative forcing and feedbacks. The sensitivity of climate relevant parameters to the fundamental parameters investigated in the laboratory programme and their improved quantification will be evaluated using a simplified model 'emulator'.
 
Description The aim of this grant was to reduce the uncertainty in the aerosol indirect effect. Secondary organic aerosol formation leads to increases in the number and mass of particles in the atmosphere but the formation mechanisms are unclear. One issue is that the chemical species formed during oxidation are not commercially available. In this project we designed a new aerosol flow reactor to create large amounts of SOA. We then separated this complex mixture and isolated individual chemicals. Using these, we could quantify a large proportion of SOA for the first time. This method has the potential to allow us to probe the effects of atmospheric aerosol composition on physical properties such as water uptake with much greater certainty. The methods developed in this project have now been used to study the formation of SOA in Beijing as part of the NERC funded APHH program.
Exploitation Route The method developed is simple and so could be used easily by other groups. It has been used in a upcoming NERC project to study aerosol hygroscopicity and diffusion at the single particle level.
Sectors Environment

URL http://pubs.acs.org/doi/abs/10.1021/ac5028512
 
Description A review of the state-of-the-science relating to secondary particulate matter of relevance to the composition of the UK atmosphere: Full technical report to Defra, project AQ0732. McFiggans, G. B., Alfarra, M. R., Allan, J., Coe, H., Hamilton, J., Harrison, R., Jenkin, M. E., Lewis, A., Moller, S. J. & Williams, P. I. 26 Nov 2015 Defra. 206 p.
Sector Government, Democracy and Justice
Impact Types Policy & public services

 
Description NERC Capital
Amount £300,000 (GBP)
Funding ID cc090 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2015 
End 06/2015
 
Description NERC stnandard grant
Amount £594,000 (GBP)
Funding ID NE/M002411/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 01/2015 
End 01/2018
 
Description RSC Analytical Summer Studentship
Amount £1,140 (GBP)
Organisation Royal Society of Chemistry 
Sector Learned Society
Country United Kingdom
Start 07/2014 
End 08/2014