Soot Aerodynamic Size Selection for Optical properties (SASSO)
Lead Research Organisation:
University of Manchester
Department Name: Earth Atmospheric and Env Sciences
Abstract
Atmospheric soot is a pollutant that contains black carbon (BC) and potentially also brown carbon (BrC) and is produced from combustion sources such as diesel engines, wildfires, agricultural waste burning and the burning of solid fuels such as wood and coal. Because BC and BrC absorb sunlight, they can have a warming effect on climate, in particular on local scales; there is evidence to suggest that the increase in absorbing aerosols associated with pollution has been responsible for the weakening of the South Asian Monsoon. However, while BC and BrC are very important for climate, they are currently very poorly represented in the models used to study and predict these effects. Comparison exercises between the various models in use around the world tend to highlight strong disagreements and comparisons against observations of absorbing aerosols are consistently very poor. This indicates a strong need to improve the treatment of soot and its processes within models, however this has so far been limited by deficiencies in the instrumentation and laboratory techniques available. SASSO will capitalise on the timely development of new methodologies, facilities and instruments at the Universities of Manchester and Exeter to use a novel and unique combination of tools to study soot on a level of detail previously not possible. This data will be used to develop and test new models of soot optical properties and this will be implemented in the UK's main climate model (hadGEM3), to test what effects this new, improved understanding has on predictions of climate responses to changes in soot emissions.
The microphysical properties of soot are complex and traditionally extremely difficult to constrain and quantify on the level of detail desired to generate the detailed models and parameterisations needed. A particular complication is caused when BC co-exists with another substance (a 'coating') in a particle, which is the usual configuration in the atmosphere. The presence of a coating can increase the per-mass absorption of the BC through a phenomenon known as 'lensing', although data on this has so far proved inconsistent. There are also technical difficulties in the study of soot particles, such as the need to be able to strictly isolate particles of a single size while remaining aerosolised and the need to be able to separate the BC from the BrC in biomass burning emissions. The new technical developments at the Universities of Manchester and Exeter that will finally address these are as follows:
1. The Aerodynamic Aerosol Classifier, a centrifuge-based instrument capable of selecting particles by size and free of the charging artefacts that affect previous techniques
2. A new experimental technique for temporally separating the BC and BrC emissions from a burning wood sample using commercial fire testing equipment
3. The new EXSCALABAR aerosol optical instrument developed by the Met Office
4. The new Exeter wildFIRE facility for combustion studies
5. The Manchester Aerosol Chamber coupled to a light-duty diesel engine rig.
The combination of these will be used to generate data capable of probing BC and BrC components on a level of detail not previously possible. We will authoritatively quantify fundamental parameters of their physical properties (primarily their refractive indexes) and objectively test approaches to modelling lensing and other microphysical effects, suitable for use in climate models. The new modelling framework and parameters will be tested against ambient data (in situ and remote sensing) and implemented within hadGEM3. The effects of this improved scheme will be thoroughly tested on various levels including radiative transfer, climate forcing and local climate trends. The modifications will also be incorporated into the core hadGEM3 model for future work using this tool
The microphysical properties of soot are complex and traditionally extremely difficult to constrain and quantify on the level of detail desired to generate the detailed models and parameterisations needed. A particular complication is caused when BC co-exists with another substance (a 'coating') in a particle, which is the usual configuration in the atmosphere. The presence of a coating can increase the per-mass absorption of the BC through a phenomenon known as 'lensing', although data on this has so far proved inconsistent. There are also technical difficulties in the study of soot particles, such as the need to be able to strictly isolate particles of a single size while remaining aerosolised and the need to be able to separate the BC from the BrC in biomass burning emissions. The new technical developments at the Universities of Manchester and Exeter that will finally address these are as follows:
1. The Aerodynamic Aerosol Classifier, a centrifuge-based instrument capable of selecting particles by size and free of the charging artefacts that affect previous techniques
2. A new experimental technique for temporally separating the BC and BrC emissions from a burning wood sample using commercial fire testing equipment
3. The new EXSCALABAR aerosol optical instrument developed by the Met Office
4. The new Exeter wildFIRE facility for combustion studies
5. The Manchester Aerosol Chamber coupled to a light-duty diesel engine rig.
The combination of these will be used to generate data capable of probing BC and BrC components on a level of detail not previously possible. We will authoritatively quantify fundamental parameters of their physical properties (primarily their refractive indexes) and objectively test approaches to modelling lensing and other microphysical effects, suitable for use in climate models. The new modelling framework and parameters will be tested against ambient data (in situ and remote sensing) and implemented within hadGEM3. The effects of this improved scheme will be thoroughly tested on various levels including radiative transfer, climate forcing and local climate trends. The modifications will also be incorporated into the core hadGEM3 model for future work using this tool
Planned Impact
The insights into the climate responses to soot will also have impacts beyond purely academic sector and into national and international policymaking. Because hadGEM3 is one of the main models in use internationally, the results of the studies looking at the effect of model improvement and the generally improved outputs will feed directly into activities such as CMIP and AEROCOM, and in turn the IPCC and international policymaking. Domestically, hadGEM3 represents the backbone of the UK's main climate and earth system modelling capability, so the work here will serve the national interests that this feeds into government decision-making relating to energy strategy, climate resilience (including extreme weather events) and the response to other global impacts of climate change.
There may be additional benefits from the technical development aspects, in terms of the novel applications of new, UK-developed instruments (the AAC and EXSCALABAR) and developments of methodologies of studying combustion processes. This may have further impacts within the instrumentation field.
There will be further benefits to the UK skills base through the training of PDRAs in the use of equipment and models that they would not otherwise have used, e.g. through Manchester staff using the facilities at Exeter. The general cross-disciplinary nature of the work will mean that scientists will be exposed to new facilities, instruments and ways of working.
In terms of outreach and public engagement, we believe that there is much scope, given the interest in climate change and also the very visible forms that soot and smoke can take. We will see to exploit various outreach channels available at both universities and the Met Office, such as science fairs, blogs, press releases, school visits and social media.
There may be additional benefits from the technical development aspects, in terms of the novel applications of new, UK-developed instruments (the AAC and EXSCALABAR) and developments of methodologies of studying combustion processes. This may have further impacts within the instrumentation field.
There will be further benefits to the UK skills base through the training of PDRAs in the use of equipment and models that they would not otherwise have used, e.g. through Manchester staff using the facilities at Exeter. The general cross-disciplinary nature of the work will mean that scientists will be exposed to new facilities, instruments and ways of working.
In terms of outreach and public engagement, we believe that there is much scope, given the interest in climate change and also the very visible forms that soot and smoke can take. We will see to exploit various outreach channels available at both universities and the Met Office, such as science fairs, blogs, press releases, school visits and social media.
Publications
Cotterell M
(2020)
Sensitivity and accuracy of refractive index retrievals from measured extinction and absorption cross sections for mobility-selected internally mixed light absorbing aerosols
in Aerosol Science and Technology
Damany-Pearce L
(2022)
Australian wildfires cause the largest stratospheric warming since Pinatubo and extends the lifetime of the Antarctic ozone hole.
in Scientific reports
Damany-Pearce L
(2022)
Australian Wildfires cause the largest stratospheric warming since Pinatubo.
Fang C
(2023)
Impacts of reducing scattering and absorbing aerosols on the temporal extent and intensity of South Asian summer monsoon and East Asian summer monsoon
in Atmospheric Chemistry and Physics
Hu D
(2023)
Refractive Index of Engine-Emitted Black Carbon and the Influence of Organic Coatings on Optical Properties
in Journal of Geophysical Research: Atmospheres
Hu D
(2021)
Physical and chemical properties of black carbon and organic matter from different combustion and photochemical sources using aerodynamic aerosol classification
in Atmospheric Chemistry and Physics
Johnson B
(2023)
Assessing the Impact of Self-Lofting on Increasing the Altitude of Black Carbon in a Global Climate Model
in Journal of Geophysical Research: Atmospheres
Liang J
(2023)
Future changes in atmospheric rivers over East Asia under stratospheric aerosol intervention
in Atmospheric Chemistry and Physics
Wells A
(2023)
Including ash in UKESM1 model simulations of the Raikoke volcanic eruption reveals improved agreement with observations
in Atmospheric Chemistry and Physics
Title | Data for the manuscript entitled "Refractive index of engine-emitted black carbon and the influence of organic coatings on optical properties" submitted to the Journal of Geophysical Research-Atmospheres. |
Description | Black carbon (BC) and brown carbon (BrC) aerosols are extensively investigated components of atmospheric aerosol due to their ability to absorb solar radiation and contribute to atmospheric heating, resulting in a positive radiative forcing on climate. Although BC and BrC are very important for climate, they are poorly represented in atmospheric models. This is in part due to the lack of accurate refractive index (RI) descriptions for both BC and BrC. Previous studies have used mobility selection approaches to select BC/BrC particles upstream of optical spectroscopy instruments to allow RI characterisations, but these retrievals suffer from issues caused by multiple charging. We solved this issue by using a new aerosol classification technique, enabling optical measurements for an aerosol sample classified according to a single physical size without multiple charge artefacts, which improves the subsequent RI retrieval. In addition, non-absorbing and weakly absorbing organic materials were condensed onto BC to form coated soot particles, allowing different optical models for mixed particles to be evaluated. We found that the absorption of coated BC particles may not be predicted with sufficient accuracy from knowledge of only the equivalent diameter, coating composition, and RI, and considering additional factors such as morphology may be necessary for accurate predictions. |
Type Of Art | Film/Video/Animation |
Year Produced | 2023 |
Impact | Figure for publication |
URL | https://figshare.manchester.ac.uk/articles/figure/Data_for_the_manuscript_entitled_strong_Refractive... |
Title | Data for the manuscript entitled "Refractive index of engine-emitted black carbon and the influence of organic coatings on optical properties" submitted to the Journal of Geophysical Research-Atmospheres. |
Description | Black carbon (BC) and brown carbon (BrC) aerosols are extensively investigated components of atmospheric aerosol due to their ability to absorb solar radiation and contribute to atmospheric heating, resulting in a positive radiative forcing on climate. Although BC and BrC are very important for climate, they are poorly represented in atmospheric models. This is in part due to the lack of accurate refractive index (RI) descriptions for both BC and BrC. Previous studies have used mobility selection approaches to select BC/BrC particles upstream of optical spectroscopy instruments to allow RI characterisations, but these retrievals suffer from issues caused by multiple charging. We solved this issue by using a new aerosol classification technique, enabling optical measurements for an aerosol sample classified according to a single physical size without multiple charge artefacts, which improves the subsequent RI retrieval. In addition, non-absorbing and weakly absorbing organic materials were condensed onto BC to form coated soot particles, allowing different optical models for mixed particles to be evaluated. We found that the absorption of coated BC particles may not be predicted with sufficient accuracy from knowledge of only the equivalent diameter, coating composition, and RI, and considering additional factors such as morphology may be necessary for accurate predictions. |
Type Of Art | Film/Video/Animation |
Year Produced | 2023 |
Impact | Figure for publication |
URL | https://figshare.manchester.ac.uk/articles/figure/Data_for_the_manuscript_entitled_strong_Refractive... |
Description | The research developed new methods for quantitatively analysing the properties of soot produced from various sources including wood burning, a diesel engine and an inverted gas flame device. By using various combinations of instruments, we were able to accurately probe properties such as the size, shape, density and refractive index of the black and organic carbon produced during combustion. By operating these experiments under controlled conditions we were able to study these as we varied things such as fuel type and combustion phase. We were also able to artificially age the soot particles by coating the particles with secondary organic aerosol in a reaction chamber. The parameters derived (including refractive indexes) can be used parametrically within climate models. We also studied the effect of absorbing aerosols within the earth's system, focusing on the effect of these on the atmospheric chemistry and circulation. One particular case study showed the profound effects Australian wildfires had on stratospheric temperature and the ozone layer. |
Exploitation Route | Optical model parameters derived in WP2 usable for climate model development and application. Aerosol properties (chemical composition, shape, size) determined during WP1 useful for aerosol and emissions research. Method development performed in WP1 and WP2 and datasets can be used for further studies and instrument development Aerosol-climate interaction studies in WP3 will be use for further studies on wildfire impacts on the earth system |
Sectors | Energy Environment |
Description | Light Absorption for Volatile Aerosol Particles: A New Measurement Approach |
Amount | £285,168 (GBP) |
Funding ID | NE/X000036/1 |
Organisation | Natural Environment Research Council |
Sector | Public |
Country | United Kingdom |
Start | 03/2023 |
End | 04/2025 |
Title | SASSO experimental dataset |
Description | Data produced during the SASSO campaign |
Type Of Material | Database/Collection of data |
Year Produced | 2023 |
Provided To Others? | Yes |
Impact | Data used in publications and development of optical parameterisations |
URL | https://catalogue.ceda.ac.uk/uuid/7a4feaf0fd624dacaf34a0129f074fcc |
Description | EUROCHAMP BC experiment |
Organisation | Catalytic Instruments GmbH & Co.KG |
Country | Germany |
Sector | Private |
PI Contribution | A separate experiment was funded through the Horizon 2020 EUROCHAMP network to perform a series of experiments at the Manchester facility to develop methods for standardised soot generation (inverted propane flame), monitors used for compliance purposes and catalytic devices used to study soot particles. This was timed to occur immediately prior to the SASSO IOP2 and SASSO provided additional instruments such as EXSCALABAR, SP2 and sizing instruments to supplement their science. |
Collaborator Contribution | The use of the soot generators during the EUROCHAMP work served as additional data points for the purposes of calibrating the SP2 and also provided an additional soot source for optical characterisation by EXSCALABAR that will supplement the SASSO scientific output. Catalytic Instruments also loaned one of their catalytic stripper devices for the SASSO IOP2, which facilitated the production of pure black carbon from the diesel engine. |
Impact | Contributed to publications |
Start Year | 2019 |
Description | EUROCHAMP BC experiment |
Organisation | NRC Canada |
Country | Canada |
Sector | Public |
PI Contribution | A separate experiment was funded through the Horizon 2020 EUROCHAMP network to perform a series of experiments at the Manchester facility to develop methods for standardised soot generation (inverted propane flame), monitors used for compliance purposes and catalytic devices used to study soot particles. This was timed to occur immediately prior to the SASSO IOP2 and SASSO provided additional instruments such as EXSCALABAR, SP2 and sizing instruments to supplement their science. |
Collaborator Contribution | The use of the soot generators during the EUROCHAMP work served as additional data points for the purposes of calibrating the SP2 and also provided an additional soot source for optical characterisation by EXSCALABAR that will supplement the SASSO scientific output. Catalytic Instruments also loaned one of their catalytic stripper devices for the SASSO IOP2, which facilitated the production of pure black carbon from the diesel engine. |
Impact | Contributed to publications |
Start Year | 2019 |
Description | EXSCALABAR collaboration |
Organisation | Meteorological Office UK |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Our work involving EXSCALABAR instrument has helped to further develop the instrument and set the scene for follow on experiments at the University of Bristol, also using Aerodynamic Sizing |
Collaborator Contribution | The Met Office provided support for the operation and data analysis of the instrument beyond what was envisaged in the original proposal. Michael Cotterell at the University of Bristol provided further input to the data analysis and interpretation. |
Impact | Enhanced the output of the EXSCALABAR dataset for this project. Further developed the EXSCALABAR data retrieval methods. |
Start Year | 2019 |
Description | EXSCALABAR collaboration |
Organisation | University of Bristol |
Country | United Kingdom |
Sector | Academic/University |
PI Contribution | Our work involving EXSCALABAR instrument has helped to further develop the instrument and set the scene for follow on experiments at the University of Bristol, also using Aerodynamic Sizing |
Collaborator Contribution | The Met Office provided support for the operation and data analysis of the instrument beyond what was envisaged in the original proposal. Michael Cotterell at the University of Bristol provided further input to the data analysis and interpretation. |
Impact | Enhanced the output of the EXSCALABAR dataset for this project. Further developed the EXSCALABAR data retrieval methods. |
Start Year | 2019 |