 |
| Titel |
Importance of relative humidity in the oxidative ageing of organic aerosols: case study of the ozonolysis of maleic acid aerosol |
| VerfasserIn |
P. J. Gallimore, P. Achakulwisut, F. D. Pope, J. F. Davies, D. R. Spring, M. Kalberer |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 11, no. 23 ; Nr. 11, no. 23 (2011-12-07), S.12181-12195 |
| Datensatznummer |
250010244
|
| Publikation (Nr.) |
 copernicus.org/acp-11-12181-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| Many important atmospheric aerosol processes depend on the chemical
composition of the aerosol, e.g. water uptake and particle cloud
interactions. Atmospheric ageing processes, such as oxidation reactions,
significantly and continuously change the chemical composition of aerosol
particles throughout their lifetime. These ageing processes are often poorly
understood. In this study we utilize an aerosol flow tube set up and an
ultra-high resolution mass spectrometer to explore the effect of relative
humidity (RH) in the range of <5–90% on the ozonolysis of maleic acid
aerosol which is employed as model organic aerosol system. Due to the slow
reaction kinetics relatively high ozone concentrations of 160–200 ppm were
used to achieve an appreciable degree of oxidation of maleic acid. The
effect of oxidative ageing on the hygroscopicity of maleic acid particles is
also investigated using an electrodynamic balance and thermodynamic
modelling. RH has a profound effect on the oxidation of maleic acid
particles. Very little oxidation is observed at RH < 50% and the only
observed reaction products are glyoxylic acid and formic acid. In
comparison, when RH > 50% there are about 15 oxidation products
identified. This increased oxidation was observed even when the particles
were exposed to high humidities long after a low RH ozonolysis reaction.
This result might have negative implications for the use of water as an
extraction solvent for the analysis of oxidized organic aerosols. These
humidity-dependent differences in the composition of the ozonolyzed aerosol
demonstrate that water is both a key reactant in the oxidation scheme and a
determinant of particle phase and hence diffusivity. The measured chemical
composition of the processed aerosol is used to model the hygroscopic
growth, which compares favourably with water uptake results from the
electrodynamic balance measurements. A reaction mechanism is presented which
takes into account the RH dependent observations. This study emphasises the
importance of studying the combined effects of several atmospheric
parameters such as oxidants and RH to accurately describe the complex
oxidation scheme of organic aerosols. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|