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Development of a sensitive long pathlength absorbance photometer to quantify peroxides in aerosol particles (Peroxide-LOPAP)

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Author(s): P. Mertes | L. Pfaffenberger | J. Dommen | M. Kalberer | U. Baltensperger

Journal: Atmospheric Measurement Techniques Discussions
ISSN 1867-8610

Volume: 5;
Issue: 1;
Start page: 1431;
Date: 2012;
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ABSTRACT
A new off-line instrument to quantify peroxides in aerosol particles using iodometry in long pathlength absorption spectroscopy has been developed and is called peroxide long pathlength absorbance photometer (Peroxide-LOPAP). The new analytical setup features important technical innovations compared to hitherto published iodometric peroxide measurements. Firstly, the extraction, chemical conversion and measurement of the aerosol samples are performed in a closed oxygen-free (∼1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 μM peroxide in solution or 0.25 nmol m−3 with respect to an aerosol sample volume of 1000 l. The test reaction was done at a constant elevated temperature of 40 °C and the reaction time was 60 min. Calibration experiments showed that the test reaction with all reactive peroxides, i.e. hydrogen peroxide (H2O2), peracids and peroxides with vicinal carbonyl groups (e.g. lauroyl peroxide) goes to completion and their sensitivity (slope of calibration curve) varies by only ±5%. However, very stable peroxides have a lower sensitivity. For example tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1h. A kinetic study revealed that even after 5 h only 85% of this stable compound had reacted. The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of α-pinene in smog chamber experiments were measured. The highest amount of peroxides with 34% (assuming a MW of 300 g mol−1) was found in freshly generated SOA from α-pinene ozonolysis. Contents decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was observed with aging of the aerosol indicating a decomposition of peroxides in the particles.

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Tangokurs Rapperswil-Jona

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