An Evaluation of three methods for measuring black carbon at Alert, Canada
Bibliographic record
Abstract
Abstract. Absorption of sunlight by black carbon (BC) warms the atmosphere, which may be important for Arctic climate. The measurement of BC is complicated by the lack of a simple definition of BC and the absence of techniques that are uniquely sensitive to BC (e.g. Petzold et al., 2013). At the Global Atmosphere Watch baseline observatory at Alert, Nunavut (82.5 °N), BC mass is estimated in three ways, none of which fully represent BC: conversion of light absorption measured with an Aethalometer to give equivalent black carbon (EBC), thermal desorption of elemental carbon from weekly-integrated filter samples to give elemental carbon (EC), and measurement of incandescence from the refractory black carbon (rBC) component of individual particles using a Single Particle Soot Photometer (SP2). Based on measurements between March 2011 and December 2013, EBC and EC are 2.7 and 3.1 times higher than rBC respectively. The EBC and EC measurements are influenced by factors other than just BC, and higher estimates of BC are expected from these techniques. Some bias in the rBC measurement may result from calibration uncertainties that is difficult to estimate here. Considering a number of factors, our best estimate of BC mass at Alert, which may be useful for evaluation of chemical transport models, is an average of the rBC and EC measurements with a range bounded by the rBC and EC combined with the respective measurement uncertainties. Winter, spring, summer, and fall averaged (± atmospheric variability) estimates of BC mass at Alert for this study period are 49 ± 28 ng m−3, 30 ± 26 ng m−3, 22 ± 13 ng m−3, and 29 ± 9 ng m−3, respectively. Average coating thicknesses estimated from the SP2 are 25 % to 40 % of the 160–180 nm diameter rBC core sizes. For particles of approximately 200–400 nm optical diameter, the fraction containing rBC cores is estimated to be between 10 % and 16 %, but the possibility of smaller undetectable rBC cores in some of the particles cannot be excluded. Mass absorption coefficients (MAC) ± uncertainty at 550 nm wavelength, calculated from light absorption measurements divided by the best estimates of BC mass concentrations, are 8 ± 4, 8 ± 4, 5 ± 2.5 and 9 ± 4.5 m2 g−1, for winter, spring, summer and fall respectively. Adjusted to better estimate absorption by BC only, the winter and spring values of MAC are 7.6 ± 3.8 and 7.7 ± 3.8 m2 g−1. There is evidence that the MAC values increase with coating thickness.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.008 | 0.012 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.006 | 0.006 |
| Science and technology studies | 0.006 | 0.001 |
| Scholarly communication | 0.003 | 0.001 |
| Open science | 0.004 | 0.002 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
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 source (direct Gemma or distilled Codex), 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".