Reducing the Uncertainties in Aerosol Hygroscopic Growth

Lead Research Organisation: University of Bristol
Department Name: Chemistry

Abstract

Aerosols and clouds are important components of the Earth's atmosphere, influencing the radiation budget and chemical composition, and impacting on human health. Indeed, the impact of aerosols and clouds on global climate remains one of the largest single uncertainties in understanding previous climate observations and in predicting future climate change. Aerosols and clouds can scatter and absorb sunlight and terrestrial radiation, having a direct effect on climate by altering the balance of incoming solar radiation and outgoing infrared light. Aerosols have an indirect effect on climate, influencing the albedo and lifetime of clouds. All cloud droplets form from the much smaller aerosol particle seeds on which water can condense. Changes in the number of aerosol particles in the Earth's atmosphere and their size distribution can lead to changes in the number of cloud droplets that form. In addition, some aerosols (such as inorganic salts) are considerably more hygroscopic than others (such as water insoluble organic compounds) and therefore have different affinities for water, changing the conditions under which cloud droplet formation can occur. This indirect effect of aerosols on climate is poorly constrained and generally counteracts the warming induced by increased levels of greenhouse gases in the atmosphere, exerting a cooling effect on the Earth's climate.

In this project we will examine some of the factors that control the affinity of aerosol for water and their ability to act as cloud condensation nuclei. We will simulate aerosol processes on single particles trapped by either light or electrical fields, measuring their evolving size with high time-resolution (better than 10 ms) and high accuracy (better than +/- 0.5 %). More specifically, the research will be divided into three smaller work packages.

In the first work package, we will assess and refine the current thermodynamic models for quantifying the affinity of aerosol particles for water. Measurements will allow us to determine the change in particle size with relative humidity with considerably better accuracy than has previously been possible even up to the conditions under which cloud droplets form. Recorded from aerosol particles containing a wide range of organic and inorganic solutes typical of components found in the atmosphere, these new data will provide greater constraints for modelling the growth of aerosol particles into cloud droplets.

In a second work package, we will investigate the factors that control the equilibrium and time-dependent composition of the surface of a growing cloud droplet. The surface composition, which differs from the bulk, is crucial in determining how facile it is for aerosol particles to become cloud droplets. Current models of surface composition (tension) are based on very little data and will be refined as a consequence of the measurements made in this project.

In a final work package, we will simulate and measure the kinetics of cloud droplet growth, specifically examining the condensation of organic compounds on a growing water droplet that can accompany the condensation of water. This has been highlighted very recently as a significant effect that has been largely ignored. Improved quantification of the condensation kinetics of organic compounds will allow the cloud droplet number to be better predicted, the sensitivity of which will be tested through cloud parcel models.

In summary, this project will seek to reduce some of the uncertainties in quantifying the microphysical processes that occur on atmospheric aerosol particles and their impact on clouds.

Planned Impact

Climate change is recognised as presenting one of the most significant challenges faced by humanity over the coming century. The project described here will address some of the remaining challenges in understanding and quantifying the microphysical properties and processes that control the formation of cloud droplets from aerosol particles. Indeed, such indirect effects of aerosols on climate are recognised as representing one of the single largest uncertainties in quantifying climate change. Preciously estimated as having a cloud albedo forcing of -0.7 W/m2, there remain significant uncertainties in aerosol effects. Most notably, it has recently been shown that including the microphysical process of the co-condensation of organic components during aerosol activation and cloud droplet growth could change cloud droplet numbers by as much as 40 % and the cloud albedo forcing to -1.8 W/m2. The work packages in this project will seek to reduce some of the underlying process uncertainties in quantifying the role of aerosol, thereby reducing the uncertainty in quantifying the indirect effect of aerosols on climate. This would contribute to an improved level of certainty in aerosol forcings and, thus, climate models. The consequences of improved models for climate are clear and are wide ranging, with political and societal impacts.

The specific impact of improving our understanding of the role of atmospheric aerosol and water partitioning to clouds will most directly benefit academic researchers working in atmospheric science, as described under Academic Beneficiaries. Beyond this, a better understanding of aerosol is crucial and arises when integrated over the research efforts of the larger atmospheric aerosol science community. Notably beyond climate change, improvements in our understanding will lead to improvements in predicting air quality through better understanding the properties of secondary organic aerosol, and a better understanding of atmospheric composition. Further, understanding water transport kinetics is important for better quantifying the deposition patterns of aerosol particles in the respiratory tract. Such an improvement would be beneficial for researchers working in the area of drug delivery to the lungs and in the impact of environmental pollution on human morbidity and mortality.

Publications

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Rovelli G (2017) Hygroscopic properties of aminium sulfate aerosols in Atmospheric Chemistry and Physics

 
Description The following key discoveries and developments are reported:
(1) We have undertaken a wide range of measurements of aerosol hygroscopicity of benchmark organic aerosol components designed to improve the quantification of the uptake of water of atmospheric particles (Work Package 1). (2) Following from (1), a number of papers have been published or are currently in preparation for publication. These have been used to test existing models of hygroscopic growth of aerosols (E-AIM, UManSysProp and IOMFAC) implemented by collaborators (Clegg, UEA; Topping, Manchester; Zeund, McGill) (Work Package 1). (3) We have made measurements of droplet surface tension and compared with model predictions from collaborators to validate existing models of surface tension (Dutcher, U. of Minnesota) (Work Package 2) . (4)We have measured the evaporation coefficient of various organic molecules from organic aerosol (Work Package 3) and published the data in a paper appearing in Journal of Geophysical Research in 2017.
Exploitation Route In the refinement of models for predicting the hygroscopic growth of atmospheric aerosol for use in global climate and air pollution models.
Sectors Environment

 
Title Evaporation kinetics of polyol droplets: determination of evaporation coefficients and diffusion constants (JGR 2017) 
Description In order to quantify the kinetics of mass transfer between the gas and condensed phases in aerosol, physicochemical properties of the gas and condensed phases as well as kinetic parameters (mass/thermal accommodation coefficient) are crucial for estimating mass fluxes over a wide size range from the free-molecule to continuum regimes. In this study, we report measurements of the evaporation kinetics of droplets of 1-butanol, ethylene glycol (EG), diethylene glycol (DEG) and glycerol under well-controlled conditions (gas flow rates, temperature) using the previously-developed cylindrical electrode Electrodynamic Balance (EDB) technique. Measurements are compared with a model that captures the heat and mass transfer occurring at the evaporating droplet surface. The aim of these measurements is to clarify the discrepancy in the reported values of mass accommodation coefficient (aM, equals to evaporation coefficient based on microscopic reversibility) for 1-butanol, EG and DEG, and improve the accuracy of the value of the diffusion coefficient for glycerol in gaseous nitrogen. The uncertainties in the thermophysical and experimental parameters are carefully assessed, the literature values of the vapour pressures of these components are evaluated and the plausible ranges of the evaporation coefficients for 1-butanol, EG and DEG as well as uncertainty in diffusion coefficient for glycerol are reported. Results show that aM should be greater than 0.4, 0.2 and 0.4 for EG, DEG and 1-butanol, respectively. The refined values are helpful for accurate prediction of the evaporation / condensation rates. This work was undertaken as part of the NERC grant NE/L006901/1 
Type Of Material Database/Collection of data 
Year Produced 2017 
Provided To Others? Yes  
 
Description Collaboration with Prof. Cari Dutcher on development of hygroscopicity prediction models 
Organisation University of Minnesota
Department Department of Mechanical Engineering
Country United States 
Sector Academic/University 
PI Contribution We have provided Prof. Dutcher with experimental data to model for hygroscopic growth and surface tension of aerosol particles.
Collaborator Contribution Prof. Dutcher's group have developed thermodynamic models for predicting the hygroscopic growth of aerosols and surface tension. We have worked with them to simulate our experimental data and they have provide refined model outputs for comparison in manuscript under review.
Impact Publications: Marsh, A., Miles, R. E. H., Rovelli, G., Cowling, A. G., Nandy, L., Dutcher, C. S., & Reid, J. P. (2016). Influence of Organic Compound Functionality on Aerosol Hygroscopicity: Dicarboxylic Acids, Alkyl-Substituents, Sugars and Amino Acids. Atmospheric Chemistry and Physics Discussions, (December), 1-30. https://doi.org/10.5194/acp-2016-1051 Boyer, H. C., Bzdek, B. R., Reid, J. P., & Dutcher, C. S. (2017). A Statistical Thermodynamic Model for Surface Tension of Organic and Inorganic Aqueous Mixtures. The Journal of Physical Chemistry A, 121, 198-205. https://doi.org/10.1021/acs.jpca.6b10057 Cai, C., Stewart, D. J., Reid, J. P., Zhang, Y., Ohm, P., Dutcher, C. S., & Clegg, S. L. (2015). Organic Component Vapor Pressures and Hygroscopicities of Aqueous Aerosol Measured by Optical Tweezers. Journal of Physical Chemistry A, 119, 704-718. https://doi.org/10.1021/jp510525r Marshall, F. H., Miles, R. E. H., Song, Y.-C., Ohm, P. B., Power, R. M., Reid, J. P., & Dutcher, C. S. (2016). Diffusion and Reactivity in Ultraviscous Aerosol and the Correlation with Particle Viscosity. Chem. Sci., 7, 1298-1308. https://doi.org/10.1039/C5SC03223G
Start Year 2015
 
Description Collaboration with Prof. Markus Petters, North Carolina State University 
Organisation North Carolina State University
Department Marine, Earth and Atmospheric Science
Country United States 
Sector Academic/University 
PI Contribution Research visits by students each direction, one to NCSU from Bristol and one from Bristol to NCSU. During extended visits of 3 weeks each, the students undertook collaborative measurements and these will lead to two publications (currently in preparation)
Collaborator Contribution Research visits by students each direction, one to NCSU from Bristol and one from Bristol to NCSU. During extended visits of 3 weeks each, the students undertook collaborative measurements and these will lead to two publications (currently in preparation)
Impact Publications in preparation
Start Year 2016
 
Description American Chemical Society Fall conference 2017 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk at American Chemical Society Fall conference in environmental impacts of aerosol chemistry symposium
Year(s) Of Engagement Activity 2017
 
Description Contributed talk by Dr. Rachael Miles at the European Aerosol Conference 2015 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Contributed conference talk
Year(s) Of Engagement Activity 2015
 
Description Gordon Research Conference on Molecular Interactions and Dynamics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Gordon Research Conference on Molecular Interactions and Dynamics at Stonehill College, Mass, US.
Year(s) Of Engagement Activity 2018
 
Description Invited talk at Pittcon on aerosol droplet spectroscopy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at Pittcon on aerosol droplet spectroscopy in Orlando, Florida, US
Year(s) Of Engagement Activity 2018
 
Description Invited talk at Respiratory Drug Delivery in Arizona, US, April 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited plenary talk at Respiratory Drug Delivery in Arizona, US, April 2018
Year(s) Of Engagement Activity 2018
 
Description Invited talk at XXIst Symposium on Atomic, Cluster and Surface Physics, Obergurgl, Austria, 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at XXIst Symposium on Atomic, Cluster and Surface Physics, Obergurgl, Austria, 2018
Year(s) Of Engagement Activity 2018
 
Description Invited talk at annual Electromagnetic Light Scattering Conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at the annual conference on Electromagnetic Light Scattering at University of Maryland, US
Year(s) Of Engagement Activity 2017
 
Description Pittcon Conference, Orlando, Florida 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at the annual Pittcon Conference, Orlando, Florida, February 2018.
Year(s) Of Engagement Activity 2018
 
Description Plenary talk at Drug Delivery to the Lungs conference 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Plenary talk to all attendees at the annual drug delivery to the lungs conference at the Edinburgh International Convention Centre
Year(s) Of Engagement Activity 2017
 
Description Postgraduate course in aerosol science, Beijing Institute of Technology, China 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A taught course I delivered as a visiting professor
Year(s) Of Engagement Activity 2015
 
Description Presentation of paper and talk at Faraday Discussion on Chemistry of the Anthropocene 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation of paper and talk at Royal Society of Chemistry Faraday Discussion on Chemistry of the Anthropocene at University of York
Year(s) Of Engagement Activity 2017
 
Description Research talk at University of Alberta, California 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research talk at University
Year(s) Of Engagement Activity 2016
 
Description Seminars at ETH-Zurich (Switzerland), University of Kyoto (Japan), and York (UK) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talks
Year(s) Of Engagement Activity 2013
 
Description Seminars at Universities of Manchester and Cambridge 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Invited talks
Year(s) Of Engagement Activity 2015
 
Description Talk at CECAM workshop on Crystallisation 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact CECAM workshop in Lausanne on crystallisation and nucleation.
Year(s) Of Engagement Activity 2017
 
Description Talk at European Aerosol Conference 2016 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research talk at international conference
Year(s) Of Engagement Activity 2016
 
Description Talk at Future of Chemical Physics conference in Oxford 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research talk at international conference
Year(s) Of Engagement Activity 2016
 
Description Talk at Inhalation and Respiratory Drug Delivery Congress 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Industry/Business
Results and Impact Talk at the Inhalation and Respiratory Drug Delivery Congress in London
Year(s) Of Engagement Activity 2017
 
Description Talk at Spring meeting of the American Chemical Society 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Research talk at international conference
Year(s) Of Engagement Activity 2016
 
Description Talk at University of Warwick 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact Research talk at university
Year(s) Of Engagement Activity 2016
 
Description Talk at Workshop Entitled "Towards a Molecular Understanding of Atmospheric Aerosols" in Cologne, Germany 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk at Workshop Entitled "Towards a Molecular Understanding of Atmospheric Aerosols" in Cologne, Germany. This was a workshop attended by ~100 participants (academics, students and researchers) working in the field of atmospheric aerosols.
Year(s) Of Engagement Activity 2018
 
Description Talk at XXIst Symposium on Atomic, Cluster and Surface Physics 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Invited talk at XXIst Symposium on Atomic, Cluster and Surface Physics 2018, Obergurgl, Austria (2018).
Year(s) Of Engagement Activity 2018
 
Description Talk to local interest group 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Talk about atmospheric science and climate change at public engagement event held by A Rocha UK at Little Dewchurch, Herefordshire
Year(s) Of Engagement Activity 2017
 
Description Workshop on aerosol hygroscopicity 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Workshop on aerosol hygroscopicity hosted at North Carolina State University in collaboration with Prof. Markus Petters and Prof. Simon Clegg. This will lead to a publication on atmospheric aerosol hygroscopicity.
Year(s) Of Engagement Activity 2017