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Title: Primary versus secondary contributions to particle number concentrations in the European boundary layer
Author: Reddington, Carly Lauren
ISNI:       0000 0004 2748 0470
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2012
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It is important to understand the relative contribution of primary and secondary particles to regional and global aerosol so that models can attribute aerosol radiative forcing to different sources. This thesis is concerned with quantifying how primary particle emissions and secondary particle formation influence total and cloud condensation nuclei (CCN)- sized particle number concentrations over Europe, using a global aerosol microphysics model (GLOMAP) together with aerosol measurements from the European Integrated Project on Aerosol Cloud Climate and Air Quality Interactions (EUCAARI). Analysis of surface aerosol measurements at 15 European sites under polluted anticy- clonic conditions shows that the dominant source of uncertainty in CCN-sized particle concentrations is the emitted size of primary carbonaceous particles. For particle number concentrations with Dp>50nm (N50) and Dp>100nm (NlOO), this uncertainty exceeds that associated with treatments of particle formation (nucleation) in the boundary layer (BL). Within the uncertainty of the observations and accounting for the uncertainty in the emitted size of carbonaceous particles, BL nucleation makes a statistically significant contribution to CCN-sized particles at less than 27% of the measurement sites. The model agrees well with aircraft measurements of CCN-sized particles in the BL but underpredicts particle concentrations between Dp =10~ 160 nm, which can be only partly explained by BL nucleation. Comparisons with observed non-volatile particle number concentrations in the BL show that the underprediction is partly due to a missing fraction of non-volatile cores, most likely from combustion sources. An intercomparison of four large-scale models shows that inter-model structural differ- ences are more important for CCN-sized particles than uncertainties in BL nucleation. To capture seasonal and diurnal variations in NlOo, it is more important to correctly simulate processes such as transport, deposition, emissions, and BL dynamics. Results also show that a model's ability to capture the seasonal cycle in total particle number concentrations does not necessarily imply an ability to capture N50 and NlOO. Analysis of the size distribution of refractory black carbon (BC) from airborne measure- ments of the Single Particle Soot Photometer shows good agreement with modelled BC mass in the range DBC =90~400 nm, but large differences in the distribution of BC across the particle size distribution. More than 90% of the model particles with Dp ;(,260nm are predicted to contain BC, while the observations suggest only 21 % + j- 35 % 14 %. The results suggest that the size distribution of the BC component of the emitted carbonaceous particles is incorrect. Thus, models that assume uniform mixing ratios of BC across the particle distribution may incorrectly calculate direct radiative forcing due to BC.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available