Stable carbon isotope composition of ambient VOC and its use in the determination of photochemical ages of air masses
Notice bibliographique
Résumé
Stable Carbon Isotopic Composition measurements can provide valuable information about the processing of trace gases in the atmosphere. Not only can it be used to distinguish physical processes such as dilution and mixing from photochemical ageing, but it can also be an important tool in identification of sources, in calculating the photochemical age and qualitatively and quantitatively connecting precursors with their atmospheric products. \n\nEven though isotopic composition analysis is a valuable technique, its use is hindered by the low concentrations of compounds in the atmosphere, complexity of the samples and complex measuring instrumentation. The intention of this research project was to develop and validate sampling and instrumental analysis techniques that can be used to perform isotopic composition measurements of volatile organic compounds (VOC) and to apply these methods to analysis of ambient samples. \n\nSince most VOC are present in the atmosphere in sub-ppbv to ppbv levels and more than 1 ng of carbon is required for isotopic analysis, collection of large volumes of air is required. A method based on sampling onto cartridges filled with an adsorbent (Carboxene-569) for VOC collection in the field has been developed. VOC are selectively collected by passing large volumes (up to 100 L) of air through the cartridges. Thermal desorption of VOC from the cartridges is followed by two step cryogenic trapping and separation by gas chromatography. Once separated, all VOC are oxidized in a combustion interface. The isotopic composition of resulting carbon dioxide is then determined on-line by isotope ratio mass spectrometry. Various validation tests were performed in order to test accuracy and precision of both the preconcentration system and sampling-desorption procedure. \n\nThe newly developed sampling and analysis techniques were applied in field studies: Border air quality study (BAQS) (2007) and Environment Canada-York University campaign (EC-YU) (2009-2010). Ambient samples were collected over various time periods and the isotopic composition of individual compounds was analyzed. Determined mixing ratios were in pptv to low ppbv ranges and isotope composition varied from -30%0 to -20%0 for most of the compounds. Analysis of mixing ratios and isotope composition, their distribution and trends indicated that sampling locations can be qualitatively classified as rural (Ridgetown), semi-rural (Harrow and Egbert) and semi-urban (Toronto) areas, with strong local vehicle emission sources. Quantitative analysis of the photochemical ages (PCA) determined using hydrocarbon and isotope hydrocarbon clocks (Egbert and Toronto samples) resulted in similar values, suggesting that both of these methods are valid and are applicable. However, while both PCA methods indicated that local sources have larger impact on the air quality in these two locations, PCA from isotope composition analysis has demonstrated that different VOC in photochemically processed air masses differ in their PCA depending on VOC reactivity.
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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,001 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,001 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,001 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».