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| Titel |
Sample drying to improve HCHO measurements by PTR-MS instruments: laboratory and field measurements |
| VerfasserIn |
B. T. Jobson, J. K. McCoskey |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 4 ; Nr. 10, no. 4 (2010-02-17), S.1821-1835 |
| Datensatznummer |
250008118
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| Publikation (Nr.) |
 copernicus.org/acp-10-1821-2010.pdf |
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| Zusammenfassung |
| A significant improvement in the PTR-MS instrument sensitivity to
formaldehyde was obtained by drying the air sample to a dew point of
−30 °C using a cold trap to condense and freeze water
vapour. At warmer trap temperatures there was significant uptake of
formaldehyde and other water soluble organics, suggesting the
presence of a quasi-liquid layer on the ice surface. By removing
water vapour to a low constant dew point, the PTR-MS can be operated
at low E/N ratios, significantly increasing normalized
sensitivities for all organics and removing their humidity
dependence due to reactions with H+(H2O)2. At an
E/N ratio of 80 Td, the formaldehyde normalized
sensitivity was 25 Hz/ppbv per MHz H3O+ with an estimated
detection limit of 78 pptv. Field testing demonstrated good
agreement between HCHO measurements made at ambient humidity and
corrected for water vapour effects compared to dehumidified sampling
at −30 °C. Field testing also revealed that at an
E/N ratio of 100 Td or lower there was a significant ion
signal at m/z=49, likely CH3OOH. Sampling drying and
operation at low E/N ratios enables sensitive measurements
of HCHO and potentially CH3OOH, both important tropospheric
photoproducts. |
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