Journal
ATMOSPHERIC MEASUREMENT TECHNIQUES
Volume 5, Issue 10, Pages 2339-2348Publisher
COPERNICUS GESELLSCHAFT MBH
DOI: 10.5194/amt-5-2339-2012
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Funding
- Swiss National Science Foundation
- FP7 project EUROCHAMP-2
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A new off-line instrument to quantify peroxides in aerosol particles using iodometry in long path absorption spectroscopy has been developed and is called peroxide long path absorption 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 (similar to 1 ppb) environment. Secondly, a 50-cm optical detection cell is used for an increased photometric sensitivity. The limit of detection was 0.1 mu M peroxide in solution or 0.25 nmol m(-3) with respect to an aerosol sample volume of 1m(3). The test reaction was done at a constant elevated temperature of 40 degrees 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 inert peroxides have a lower sensitivity. For example, tert-butyl hydroperoxide shows only 37% sensitivity compared to H2O2 after 1 h. A kinetic study revealed that even after 5 h only 85% of this inert compound had reacted. The time trends of the peroxide content in secondary organic aerosol (SOA) from the ozonolysis and photo-oxidation of alpha-pinene in smog chamber experiments were measured. The highest mass fraction of peroxides with 34% (assuming a molecular weight of 300 g mol(-1)) was found in freshly generated SOA from alpha-pinene ozonolysis. Mass fractions decreased with increasing NO levels in the photo-oxidation experiments. A decrease of the peroxide content was also observed with aging of the aerosol, indicating a decomposition of peroxides in the particles.
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