Technology development grants awarded
1 Dec 2009
Scientists from the Centre for Atmospheric Science have recently been awarded four grants in the NERC Technology Proof of Concept directed programme. The grants awarded have a combined value of over £600,000.
The projects funded include development of novel instrumentation for atmospheric and laboratory measurements and software development for modelling studies. Details of the individual projects are listed below.
A Novel Controlled Thermal Desorption Technique for Evaluation of Organic Aerosol Component Volatility and Absorptive Partitioning (G. McFiggans, M. Alfarra, M. Flynn)
Particulate material in the atmosphere has a major effect on both climate and human health; specifically the finer particulate material (below around one micron in diameter) being responsible for the majority of the radiative and air quality impacts. Whilst inorganic components are readily quantified, organic components comprise a large fraction of the particulate material, normally greater than 50% of the total mass. This fraction is very poorly quantified or described. Some of the organic material is known to be emitted directly into the atmosphere and is therefore known as primary material. This is normally a minority of the total organic aerosol mass, the rest comprising "secondary" components (aerosol being the sum of the particulate and gaseous components). Secondary components may be defined in a number of ways, but a useful working definition is that they are the components that have entered the particles from the gas phase or have been formed in the particle from components that have entered the particles from the gas phase. The absorptive partitioning model of secondary organic aerosol (SOA) component formation has been widely applied and found to provide a useful framework for explanation of the process of gas to particle conversion. More recently there has been a postulation of significant pathways for condensed phase reaction and potential formation of these secondary components by reactive uptake which would impact on the reversibility of SOA formation and the ability to explain SOA formation by the absorptive partitioning alone. In the Manchester aerosol chamber, we have recently noticed some interesting results on dilution of SOA samples. Because of the predictions of absorptive partitioning, it would be expected that SOA mass would reduce more than the amount by which it has been diluted owing to evaporation of more volatile components. This has not been observed in our experiments in several biogenic precursor systems and has very significant atmospheric implications. If absorptive partitioning is demonstrably incapable of explaining the chamber results, then many models of atmospheric organic aerosol behaviour based on chamber yield data will have problems. Previous experiments have used thermal denuders to probe the SOA volatility and loosely infer reversibility of SOA formation. It is proposed to design and construct a novel thermal denuder system to probe, in combination with controlled dilution, the volatility of secondary organic aerosol components formed in the chamber photo-oxidation of biogenic and anthropogenic organic precursors. The denuder system will be characterised using particles of known composition and properties generated in the laboratory prior to coupling it to the Manchester aerosol chamber to establish the validity of the widely accepted absorptive partitioning model of aerosol formation. The anticipated superior performance of the denuder system will be suitable for quantifying component volatility and, by coupling it to the chamber in dilution experiments, for assessing the reversibility predicted by absorptive partitioning theory.
Novel informatic software for automated aerosol component property predictions and ensemble predictions for direct model - measurement comparison (D. Topping, G. McFiggans)
Atmospheric aerosol particles, or particulate matter suspended in the atmosphere, are highly important yet highly uncertain components of the earths climate system and key determinants of air quality. Properties which determine these highly uncertain impacts are linked at the most fundamental level to the chemical components which may reside in the particle. Both inorganic and organic material can transfer between the gas and particle phase. Inorganic material is restricted to a few well-understood compounds. However, organic material can comprise many thousands, as yet largely unidentified, compounds with a vast range of properties. Owing to the complexity and diversity of atmospheric aerosol components, quantification of the properties that determine their highly uncertain climatic and human health impacts requires the development and application of novel technological applications such as the informatic software proposed here. Firstly, we must be able to predict how ever many thousands of components can exist in particulate matter. Specifically, predicting the evolution of aerosol requires calculation of the distribution of all components between the gas and particle phases which in turn requires knowledge of all component vapour pressures and other thermodynamic properties. Furthermore, the physical properties of the aerosol determining their climatic impacts require detailed knowledge of fundamental properties of all components. The many thousands of individual aerosol components ensure that explicit manual calculation of these properties is laborious, time-consuming and often impossible. Thus, automation is necessary. Secondly, to identify key components and resolve their environmental impacts we must be able to replicate chemical characteristics measured in real/simulated atmospheres. A comprehensive experimental determination of individual organic components of atmospheric aerosols is not available, leading to indirect measurements on 'chemical signatures' of mixtures. Through automation of component property estimation, combined with a gas/aerosol transfer model, these 'chemical sigmatures' as determined by state-of-the-science atmospheric sampling instrumentation will be predicted. This will be achieved by calculating instrument response functions with the predicted abundance of all components. Again, the prediction (and combination) of instrument response functions for each individual component lends itself to automation due to the vast numbers involved. The informatics suite will be built using a flexible high-level portable programming language and an open source chemical informatics package that is designed to allow extraction of appropriate sub-molecular information relevant for each property estimation method.
The development of a Lithium-attachment chemical ionization mass spectrometer for studies in the atmosphere (C. Percival, M. Alfarra, M. Benyezzar, D. Topping)
This research project will develop a state-of-the-art ionization source that can be used for laboratory studies and as a field instrument for the detection and quantification of both gas-phase and aerosol-phase analytes. A novel adaptation of Li+-attachment chemical ionization mass spectrometry will be used as a detection system for various species present in the atmosphere. By realizing the innovations within this project, Li+-attachment has the potential to be a universal detection system that can ionize practically any component of the air and is therefore diverse with respect to the chemical systems that it can monitor as well as the conditions in which it can be employed. This project will demonstrate the capability of this ionization scheme via three proof-of-principle projects, namely the detection of BVOCs, detection and speciation of organic aerosols and the development of Knudsen effusion mass spectrometry to determine organic activity coefficients.
A miniature Atmospheric Particle Classifier (APC) (M. Gallagher joint with University of Hertforshire)
The single greatest source of uncertainty in the estimates of climate sensitivity to either natural or man-made changes continues to be clouds (IPCC 2001, 2007). Much of this uncertainty arises from the lack of information relating to the properties of smaller cloud particles (droplets, ice crystals) and aerosol. These particles directly and indirectly affect how much sunlight the clouds reflect back into space (ie: cooling the Earth) and how much infrared or heat radiation from the Earth's is trapped (ie: warming the Earth). Climate scientists therefore need accurate information on the sizes, shape, and abundance of these different types of atmospheric particle so that the effect of cloud properties on our future climate can be predicted. Cloud microphysicists have at their disposal several types of in-situ instrument for counting and sizing atmospheric particles down to sub-micrometre sizes, whilst other instruments can capture real images of larger individual particles. Such images are especially valuable as they provide detailed particle shape data, but instrument optical aberrations and depth of field limitations result in image blurring, restricting such imaging techniques to particles greater than ~25um in size. The greatest lack of knowledge, and therefore potentially the greatest source of uncertainty, surrounds smaller particles, such as ice crystals down to a micrometre in size, well below the resolution limits of cloud particle imaging probes. An alternative approach that can provide detailed information on these smaller cloud particles is that of spatial light scattering, in which the unique patterns of light scattered by individual particles passing through a laser beam is recorded and analysed. In the past, the University of Hertfordshire has developed several types of aircraft instrument based on spatial light scattering (so called SID probes) and these have been procured by meteorological research organisations in the USA, UK, and Europe. However, SID probes are large (each requiring a 'PMS' wing-mounted canister) and expensive (>£80k). This limits their deployment to the relatively small numbers of research aircraft that carry PMS canisters (and where competition for such canisters is normally intense). This Proof-of-Concept proposal therefore seeks to address this by developing a small, low-cost (<£3k) and light-weight (<1kg) 'miniature SID' sensor, referred to as the Atmospheric particle Classifier. The APC would exploit recent major technological advances in diode laser and detector array technologies developed for mass consumer markets (such as DVD R/RW players, security systems, etc.) to achieve similar performance to the predecessor SID probes but at a small fraction of the cost, size and weight. The APC would count, size and classify atmospheric particles down to micrometre sizes at rates of several thousand per second, differentiating droplets, solid aerosol, and ice crystals on the basis of shape and determining the extinction coefficient of each particle (an important parameter in understanding cloud radiative properties). The sensor would be small enough to be borne by balloon or UAV, or to be part of a combination probe in a single PMS canister (potentially freeing other PMS mountings). It could potentially be carried by civilian passenger aircraft, thus generating a huge source of cloud data. Beyond this, the APC could also find wider application in general aerosol monitoring (see 'Beneficiaries') in areas of environmental health, pollution monitoring, etc., where a knowledge of the aerosol's constituent particle types is essential. The APC sensor would built and tested at UH, with performance validation and calibration being carried out by the University of Manchester in their cloud simulation chamber. The finished APC would become available for use by all of the UK science community through NERC's Facility for Ground-based Atmospheric Measurement (FGAM).