Investigation of oxygenated and intermediate volatility organic compounds (OVOCs/IVOCs) with a Proton Transfer Reaction - Time Of Flight - Mass Spectrometer (PTR-TOF-MS)
Loading...
Files
Date issued
Authors
Editors
Journal Title
Journal ISSN
Volume Title
Publisher
Reuse License
Abstract
Volatile organic compounds (VOCs) play an important role in chemical and physical processes of the atmosphere. They can influence the formation of secondary organic aerosol, change the oxidative capacity of the atmosphere or themselves be toxins, which impact air quality and human health.
For the measurement of VOCs a Proton Transfer Reaction-Time Of Flight-Mass Spectrometer (PTR-TOF-MS) is especially suitable, because it can monitor with high time and mass resolution. In this work various air chemistry applications for a PTR-TOF-MS are shown and the focus is placed on elucidating oxygenated VOCs (OVOCs) and intermediate-volatility VOCs (IVOCs).
To compare and improve the various measurement techniques an OVOC-inter-comparison between several Gas Chromatography (GC) and PTR-TOF-MS instruments was performed at the meteorological observatory in Hohenpeißenberg in 2013. This work concentrates on the results of the PTR-TOF-MS instruments. In general a very good agreement was found, only methanol and acetaldehyde showed, in part, significant discrepancies. The main reasons were the high polarity and therefore stickiness of methanol to surfaces as well as the production of acetaldehyde via the heterogeneous reaction between ozone and unsaturated compounds inside the tubing. Measures were taken to minimize these effects in the following studies.
A field campaign was conducted on the island of Cyprus in summer 2014 in order to investigate highly oxidized air advected from both Eastern and Western Europe. The most abundant VOC compounds measured there were methanol, acetone and acetic acid. Methanol and acetone did not show a diel cycle, but were mainly influenced by long distance transport. The mixing ratios of acetic acid, on the other hand, followed a distinct diel cycle during one part of the measurement campaign while its values were dominated by transport processes during the rest of the study. The analysis of these three long-lived compounds has given an insight into the role of the marine boundary layer (MBL) in transport phenomena.
A second application, in stark contrast to the clean air measured in Cyprus, was the analysis of exhaust gases directly emitted from a diesel and a gasoline vehicle. So far only the results of PTR-quadrupole-MS instruments, which have a lower mass resolution, have been found in the literature. It is shown that the PTR-TOF-MS represents a promising technique to monitor car emissions fast and efficiently, particularly as the higher transmission efficiencies at high masses reveal a poorly documented semivolatile fraction of VOCs. This complex mixture was dominated by alkanes, OVOCs and aromatic compounds. Clear differences in the chemical composition between gasoline and diesel vehicles were determined, e.g. diesel exhaust showed a higher amount of IVOCs.