In-situ measurements of trace gases, PM, and aerosol optical properties during the 2017 NW US wildfire smoke event
Bibliographic record
Abstract
Abstract. In mid-August through mid-September of 2017 a major wildfire smoke/haze episode strongly impacted most of the NW US and SW Canada. During this period our ground-based site in Missoula, MT experienced heavy smoke impacts for ~ 500 hours (up to 471 µg m−3 hourly average PM2.5). We measured wildfire trace gases, PM2.5, and black carbon and sub-micron aerosol scattering and absorption at 870 and 401 nm. This may be the most extensive real-time data for these wildfire smoke properties to date. Our range of trace gas ratios for ΔNH3/ΔCO and ΔC2H4/ΔCO confirmed that the smoke from mixed, multiple sources varied in age from ~ 2–3 hours to ~ 1–2 days. Our study-average ΔCH4/ΔCO ratio (0.166 ± 0.088) indicated a large contribution to the regional burden from inefficient “smoldering” combustion. Our ΔBC/ΔCO ratio (0.0012 ± 0.0005) for our ground site was moderately lower than observed in aircraft studies (~ 0.0015) to date, also consistent with a relatively larger contribution from smoldering combustion. Our ΔBC/ΔPM2.5 ratio (0.0095 ± 0.0003) was consistent with the overwhelmingly non-BC, mostly organic nature of the smoke observed in airborne studies of wildfire smoke to date. Smoldering combustion is usually associated with enhanced PM emissions, but our ΔPM2.5/ΔCO ratio (0.126 ± 0.002) was about half the ΔPM1.0/ΔCO measured in fresh wildfire smoke from aircraft (~ 0.266). Assuming PM2.5 is dominated by PM1, this suggests that aerosol evaporation, at least near the surface, can often reduce PM loading and its atmospheric/air-quality impacts on the time scale of several days. Much of the smoke was emitted late in the day suggesting that nighttime processing would be important in the early evolution of smoke. The diurnal trends show BrC, PM2.5, and CO peaking in early morning and BC peaking in early evening. Over the course of one month, the average single scattering albedo for individual smoke peaks at 870 nm increased from ~ 0.9 to ~ 0.96. Bscat401/Bscat870 was used as a proxy for the size and “photochemical age” of the smoke particles with this interpretation being supported by the simultaneously-observed ratios of reactive trace gases to CO. The size/age proxy implied that the Ångström absorption exponent decreased significantly after about ten hours of daytime smoke aging, consistent with the only airborne measurement of the brown carbon (BrC) lifetime in an isolated plume. However, our results clearly show that non-BC absorption can be important in “typical” regional haze/moderately-aged plumes with BrC ostensibly accounting for about half the absorption at 401 nm on average for our entire data set.
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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 | 0.000 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".