Improving the accuracy of black carbon measurements for air quality and climate change
File(s)
Author(s)
Ciupek, Krzysztof
Type
Thesis or dissertation
Abstract
Black carbon (BC) and elemental carbon (EC) are widely used parameters to quantify carbonaceous particles in ambient air. They are important for climate modelling, source apportionment of air pollutants and formulating and evaluating air quality policy. This thesis investigates both practical and fundamental aspects of these measurements.
UK air monitoring network data over the period 2014 2019 showed that BC concentrations from Aethalometer instruments decreased at all sites (-12.5% y^-1 at the traffic site), whereas the EC concentrations changed less, and increased at the rural site. Despite these differences, the trends in the mass absorption cross section (MAC) parameter of the particles decreased at all sites with rates from -5.5% y^-1 to -10.1% y^-1. Interpretation of these results is difficult, because any changes in the properties of the aerosol particles will affect measurements of BC and EC in different ways, so that separating real changes from method artefacts is challenging.
Instrumental upgrades within the unstandardised method for BC could lead to uncertainty in long term trends, impacting policy evaluation. Comparison campaigns in London showed that the results from different models of collocated Aethalometer (AE22 and AE33) had consistent differences of up to 40%; most likely due to inappropriate internal correction factors. This highlights the need to calibrate Aethalometers with defined synthetic aerosols.
A facility for generating synthetic aerosols containing different particle types was developed and characterised at the National Physical Laboratory (NPL). This facility demonstrated the ability to generate uncoated soot particles and oxidised, coated soot particles (similar to “fresh” and “aged” soot in the atmosphere) in a consistent and controllable way. Differences in BC concentrations measured by the AE22 and AE33 Aethalometer in field tests were reproduced in the new test facility at NPL. Data analysis from field and laboratory experiments are presented and discussed, together with suggestions for future work.
UK air monitoring network data over the period 2014 2019 showed that BC concentrations from Aethalometer instruments decreased at all sites (-12.5% y^-1 at the traffic site), whereas the EC concentrations changed less, and increased at the rural site. Despite these differences, the trends in the mass absorption cross section (MAC) parameter of the particles decreased at all sites with rates from -5.5% y^-1 to -10.1% y^-1. Interpretation of these results is difficult, because any changes in the properties of the aerosol particles will affect measurements of BC and EC in different ways, so that separating real changes from method artefacts is challenging.
Instrumental upgrades within the unstandardised method for BC could lead to uncertainty in long term trends, impacting policy evaluation. Comparison campaigns in London showed that the results from different models of collocated Aethalometer (AE22 and AE33) had consistent differences of up to 40%; most likely due to inappropriate internal correction factors. This highlights the need to calibrate Aethalometers with defined synthetic aerosols.
A facility for generating synthetic aerosols containing different particle types was developed and characterised at the National Physical Laboratory (NPL). This facility demonstrated the ability to generate uncoated soot particles and oxidised, coated soot particles (similar to “fresh” and “aged” soot in the atmosphere) in a consistent and controllable way. Differences in BC concentrations measured by the AE22 and AE33 Aethalometer in field tests were reproduced in the new test facility at NPL. Data analysis from field and laboratory experiments are presented and discussed, together with suggestions for future work.
Version
Open Access
Date Issued
2023-01
Date Awarded
2023-06
Copyright Statement
Creative Commons Attribution NonCommercial Licence
Advisor
Fuller, Gary W.
Butterfield, David
Quincey, Paul
Publisher Department
School of Public Health
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)