Variation in Global Chemical Composition of PM <sub>2.5</sub> : Emerging Results from SPARTAN
Bibliographic record
Abstract
Abstract. The Surface PARTiculate mAtter Network (SPARTAN) is a long-term project designed to maximize the chemical and physical information obtained from filter samples collected worldwide. This manuscript discusses the ongoing efforts of SPARTAN to define and quantify major ions and trace metals found in aerosols. Our methods infer the spatial and temporal variability of PM2.5 in a cost-effective manner; single filters represent multi-day averaged fine particulate matter (PM2.5), while an adjacent nephelometer samples air continuously. SPARTAN instruments are collocated with AERONET to better understand the relationship between ground-level PM2.5 and columnar aerosol optical depth (AOD). We have examined the chemical composition of PM2.5 at 12 globally dispersed, densely populated urban locations and a site at Mammoth Cave (US) National Park used as a baseline comparison. Each SPARTAN location has so far been active between the years 2013 and 2015 over 2 to 22 month periods. These sites have collectively gathered over 10 years of quality aerosol data. The major PM2.5 constituents across all sites (relative contribution ± SD) were ammonium sulfate (20 % ± 10 %), crustal material (12 % ± 6.2 %), black carbon (11 % ± 8.4 %), ammonium nitrate (4.0 % ± 2.8 %), sea salt (2.2 % ± 1.5 %), trace element oxides (0.9 % ± 0.6 %), water (7.2 % ± 3.1 %) and residue materials (43 % ± 25 %). Analysis of filter samples revealed that several PM2.5 chemical components varied by more than an order of magnitude between sites. Ammonium sulfate ranged from 1.1 μg m−3 (Buenos Aires, Argentina) to 17 μg m−3 (Kanpur, India [dry season]). Ammonium nitrate ranged from 0.2 μg m−3 (Mammoth Cave, in summer) to 6.7 μg m−3 (Kanpur, dry season). Equivalent black carbon ranged from 0.7 μg m−3 (Mammoth Cave) to 8 μg m−3 (Dhaka, Bangladesh and Kanpur). Comparison with coincident measurements from the IMPROVE network at Mammoth Cave yielded a high degree of consistency for daily PM2.5 (r2 = 0.76, slope = 1.12), daily sulfate (r2 = 0.86, slope = 1.03) and mean fractions of all major PM2.5 components (within 6 %). Major ions generally agree well with previous studies at the same urban locations (e.g. sulfate fractions agree within 4 % for eight out of 11 collocation comparisons). Enhanced anthropogenic dust fractions in large urban areas (e.g. Singapore, Kanpur, Hanoi and Dhaka) were apparent from high Zn : Al ratios. The expected water contribution to aerosols was calculated via the hygroscopicity parameter κv for each filter. Mean aggregate values ranged from 0.15 (Manila and Ilorin) to 0.31 (Rehovot); with the latter included a major sulfate event. The all-site parameter mean is 0.19. Chemical composition and water retention in each filter measurement allowed inference of hourly PM2.5 at 35 % relative humidity by merging with nephelometer measurements. These hourly PM2.5 estimates compare favorably with a beta attenuation monitor (MetOne) at the nearby US embassy in Beijing, with a coefficient of variation r2 = 0.67 (n = 3167), compared to r2 = 0.62 when κv was not considered. SPARTAN continues to provide an open-access database of PM2.5 compositional filter information and hourly mass collected from a global federation of instruments.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| 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 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".