The link between organic aerosol mass loading and degree of oxygenation: an α-pinene photooxidation study
| Autor: | J. Dommen, André S. H. Prévôt, Jay G. Slowik, Urs Baltensperger, L. Pfaffenberger, Arnaud P. Praplan, Peter Barmet |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2013 |
| Předmět: |
Atmospheric Science
Pinene 010504 meteorology & atmospheric sciences Analytical chemistry Oxygenation Particulates 010501 environmental sciences Mass spectrometry 01 natural sciences lcsh:QC1-999 Aerosol lcsh:Chemistry chemistry.chemical_compound chemistry lcsh:QD1-999 13. Climate action Environmental chemistry Mass spectrum Hydroxyl radical Volatility (chemistry) lcsh:Physics 0105 earth and related environmental sciences |
| Zdroj: | Atmospheric Chemistry and Physics, Vol 13, Iss 13, Pp 6493-6506 (2013) Atmospheric Chemistry and Physics |
| ISSN: | 1680-7324 1680-7316 |
| Popis: | A series of smog chamber (SC) experiments was conducted to identify factors responsible for the discrepancy between ambient and SC aerosol degree of oxygenation. An Aerodyne high-resolution time-of-flight aerosol mass spectrometer is used to compare mass spectra from α-pinene photooxidation with ambient aerosol. Composition is compared in terms of the fraction of particulate CO2+, a surrogate for carboxylic acids, vs. the fraction of C2H3O+, a surrogate for aldehydes, alcohols and ketones, as well as in the Van Krevelen space, where the evolution of the atomic hydrogen-to-carbon ratio (H : C) vs. the atomic oxygen-to-carbon ratio (O : C) is investigated. Low (near-ambient) organic mass concentrations were found to be necessary to obtain oxygenation levels similar to those of low-volatility oxygenated organic aerosol (LV-OOA) commonly identified in ambient measurements. The effects of organic mass loading and OH (hydroxyl radical) exposure were decoupled by inter-experiment comparisons at the same integrated OH concentration. An OH exposure between 3 and 25 × 107 cm−3 h is needed to increase O : C by 0.05 during aerosol aging. For the first time, LV-OOA-like aerosol from the abundant biogenic precursor α-pinene was produced in a smog chamber by oxidation at typical atmospheric OH concentrations. Significant correlation between measured secondary organic aerosol (SOA) and reference LV-OOA mass spectra is shown by Pearson's R2 values larger than 0.90 for experiments with low organic mass concentrations between 1.2 and 18 μg m−3 at an OH exposure of 4 × 107 cm−3 h, corresponding to about two days of oxidation time in the atmosphere, based on a global mean OH concentration of ~ 1 × 106 cm−3. α-Pinene SOA is more oxygenated at low organic mass loadings. Because the degree of oxygenation influences the chemical, volatility and hygroscopic properties of ambient aerosol, smog chamber studies must be performed at near-ambient concentrations to accurately simulate ambient aerosol properties. |
| Databáze: | OpenAIRE |
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