Single-particle characterisation of black carbon in urban and biomass burning plumes and impacts on optical properties
Bibliographic record
Abstract
Black carbon (BC) is the light-absorbing component of soot, a combustion-generated aerosol that warms the climate by absorbing solar radiation. Its impacts on climate depend on its microphysical properties, which are modified by atmospheric processes including condensation, coagulation and wet removal. State of the art climate models consider soot in a concentric core/shell configuration, with a BC core coated by nonrefractory material such as organics or sulphate. Within this model, thicker coatings enhance visible light absorption, but also wet removal efficiency, and these have opposing effects on the total amount of light absorbed over BC?s lifetime. How well the core/shell model can calculate Mass Absorption Coefficient (MAC, the ratio of absorption to BC mass) is uncertain, as real soot forms more complex (often fractal) shapes, and detailed optical models using these morphologies predict the core/shell model may under- or over-estimate MAC depending on the precise properties of the particles.Few reliable measurements of variations in ambient MAC are available, as most older measurement techniques suffer from systematic uncertainties. In this work, a Single Particle Soot Photometer (SP2) and PhotoAcoustic Soot Spectrometer (PASS) were used to measure BC mass concentration and absorption, and these instruments do not suffer from such uncertainties. The SP2 was also used to report core size and coating thickness distributions that are required to test state of the art climate models.Firstly, a method was developed to minimise bias in the measured coating thicknesses related to the limited detection range of the SP2. The sensitivity of this technique to the assumed density and refractive index of the BC core was also explored, and the most appropriate parameters to use with ambient measurements were determined.Core and shell distributions were measured in Pasadena, California under a range of different photochemical ages. These were then used to calculate MAC, which was compared to that measured using the SP2 and PASS. The measured and modelled MAC agreed within 10% at 532 nm, though this was dependent on the assumed refractive index of the BC core. Overall MAC increased by 15 ?25% in around one third of a day of photochemical ageing. This is quite modest compared to some climate models, but not compared to the previous best estimate, which predicted MAC may increase by a factor of ~1.5 over BC?s lifetime.Core and coating distributions were also measured in Canadian boreal biomass burning plumes. A case study was presented comparing the properties of BC in three plumes, one of which had passed through a precipitating cloud. It was demonstrated that larger and more coated BC-containing particles were removed more efficiently, in agreement with previous thermodynamic theory. By calculating MAC using the measured core/shell distributions and comparing to measured scattering, it was demonstrated that the MAC and single-scattering albedo in the plumes were likely not significantly affected by the wet removal, as greater differences were observed between the two plumes not affected by precipitation.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".