Observational constraints on particle acidity using measurements and modelling of particles and gases
Bibliographic record
Abstract
In many parts of the world, the implementation of air quality regulations has led to significant decreases in SO 2 emissions with minimal impact on NH 3 emissions. In Canada and the United States, the molar ratio of NH 3 : SO 2 emissions has increased dramatically between 1990 and 2014. In many regions of North America, this will lead the molar ratio of NH x : SO 4 , where NH x is the sum of particle phase NH 4 + and gas phase NH 3 , and SO 4 is the sum of particle phase HSO 4 − and SO 4 2− , to exceed 2. A thermodynamic model (E-AIM model II) is used to investigate the sensitivity of particle pH, and the gas-particle partitioning of NH x and inorganic nitrate, to the atmospheric NH x : SO 4 ratio. Steep increases in pH and the gas fraction of NH x are found as NH x : SO 4 varies from below 1 to above 2. The sensitivity of the gas fraction of nitrate also depends strongly on temperature. The results show that if NH x : SO 4 exceeds 2, and the gas and particle phase NH x are in equilibrium, the particle pH will be above 2. Observations of the composition of particulate matter and gas phase NH 3 from two field campaigns in southern Canada in 2007 and 2012 have median NH x : SO 4 ratios of 3.8 and 25, respectively. These campaigns exhibited similar amounts of NH 3 , but very different particle phase loadings. Under these conditions, the pH values calculated using the observations as input to the E-AIM model were in the range of 1–4. The pH values were typically higher at night because the higher relative humidity increased the particle water content, diluting the acidity. The assumption of equilibration between the gas and particle phase NH x was evaluated by comparing the observed and modelled gas fraction of NH x . In general, E-AIM was able to reproduce the partitioning well, suggesting that the dominant constituents contributing to particle acidity were measured, and that the estimated pH values were realistic. These results suggest that regions of the world where the ratio of NH 3 : SO 2 emissions is beginning to exceed 2 on a molar basis may be experiencing rapid increases in aerosol pH of 1–3 pH units. This could have important consequences for the rates of condensed phase reactions that are acid-catalyzed.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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 | 0.002 | 0.006 |
| Meta-epidemiology (narrow) | 0.001 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.002 | 0.001 |
| Research integrity | 0.002 | 0.001 |
| 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".