Technical Note: Quantitative long-term measurements of VOC concentrations by PTR-MS ? measurement, calibration, and volume mixing ratio calculation methods

International audienceProton transfer reaction mass spectrometry (PTR-MS) is a technique for online measurements of atmospheric concentrations, or volume mixing ratios, of volatile organic compounds (VOCs). The aim of this paper is to give a detailed description of our measurement, calibration, and volume mixing ratio calculation methods, which have been designed for long-term stand-alone field measurements by PTR-MS. We also show how the information obtained from a calibration can be used to determine the instrument specific relative transmission curve, which enables quantitative mixing ratio calculation for VOCs which are not present in a calibration gas standard. To illustrate the functionality of our measurement, calibration, and calculation methods, we present a one-month period of ambient mixing ratio data measured in a boreal forest ecosystem at the SMEAR II station in southern Finland. During the measurement period 27 March?26 April 2007, the hourly averages of mixing ratios were 0.1?0.5 ppbv for formaldehyde, 0.2?3.0 ppbv for methanol, 0.04?0.39 ppbv for benzene, and 0.03?1.25 ppbv for monoterpenes

Hydrocarbon fluxes above a Scots pine forest canopy: Measurements and modeling

International audienceWe measured the fluxes of several hydrocarbon species above a Scots pine (Pinus sylvestris) stand using disjunct eddy covariance technique with proton transfer reaction ? mass spectrometry. The measurements were conducted during four days in July at SMEAR II research station in Hyytiälä, Finland. Compounds which showed significant emission fluxes were methanol, acetaldehyde, acetone, and monoterpenes. A stochastic Lagrangian transport model with simple chemical degradation was applied to assess the sensitivity of the above canopy fluxes to chemistry. According to the model, the chemical degradation had a minor effect on the fluxes measured in this study but has a major effect on the vertical flux profiles of more reactive compounds, such as sesquiterpenes. The monoterpene fluxes followed the traditional exponential temperature dependent emission algorithm but were considerably higher than the fluxes measured before at the same site. The normalized emission potential (30°C) was 2.5 ?g gdw?1 h?1 obtained using the temperature dependence coefficient of 0.09°C?1

Continuous flux measurements of VOCs using PTR-MS — reliability and feasibility of disjunct-eddy-covariance, surface-layer-gradient, and surface-layer-profile methods

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Winter to spring transition and diurnal variation of VOCs in Finland at an urban background site and a rural site

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Future vegetation–climate interactions in Eastern Siberia: an assessment of the competing effects of CO2 and secondary organic aerosols

Disproportional warming in the northern high latitudes, and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur if increasing temperatures lead to e.g. a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOC) have been shown to contribute to the growth of secondary organic aerosol (SOA) which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC-SOA interactions, and discuss these changes in terms of possible climate effects. On global level, both are very small but when concentrating on Siberia and the northern hemisphere the negative forcing from changed aerosol direct and indirect effects become notable – even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC-SOA interplay used serves as an example of the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial feedbacks and highlights the importance of addressing ecosystem-climate feedbacks in consistent, process-based model frameworks

Terpenoid emissions from fully grown east Siberian Larix cajanderi trees

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Future vegetation-climate interactions in Eastern Siberia : an assessment of the competing effects of CO2 and secondary organic aerosols

Disproportional warming in the northern high latitudes and large carbon stocks in boreal and (sub)arctic ecosystems have raised concerns as to whether substantial positive climate feedbacks from biogeochemical process responses should be expected. Such feedbacks occur when increasing temperatures lead, for example, to a net release of CO2 or CH4. However, temperature-enhanced emissions of biogenic volatile organic compounds (BVOCs) have been shown to contribute to the growth of secondary organic aerosol (SOA), which is known to have a negative radiative climate effect. Combining measurements in Eastern Siberia with model-based estimates of vegetation and permafrost dynamics, BVOC emissions, and aerosol growth, we assess here possible future changes in ecosystem CO2 balance and BVOC-SOA interactions and discuss these changes in terms of possible climate effects. Globally, the effects of changes in Siberian ecosystem CO2 balance and SOA formation are small, but when concentrating on Siberia and the Northern Hemisphere the negative forcing from changed aerosol direct and indirect effects become notable - even though the associated temperature response would not necessarily follow a similar spatial pattern. While our analysis does not include other important processes that are of relevance for the climate system, the CO2 and BVOC-SOA interplay serves as an example for the complexity of the interactions between emissions and vegetation dynamics that underlie individual terrestrial processes and highlights the importance of addressing ecosystem-climate feedbacks in consistent, process-based model frameworks.Peer reviewe

Ambient measurements of aromatic and oxidized VOCs by PTR-MS and GC-MS : intercomparison between four instruments in a boreal forest in Finland

Proton transfer reaction mass spectrometry (PTR-MS) and gas chromatography mass spectrometry GC-MS) are commonly used methods for automated in situ measurements of various volatile organic compounds (VOCs) in the atmosphere. In order to investigate the reliability of such measurements, we operated four automated analyzers using their normal field measurement protocol side by side at a boreal forest site. We measured methanol, acetaldehyde, acetone, benzene and toluene by two PTR-MS and two GC-MS instruments. The measurements were conducted in southern Finland between 13 April and 14 May 2012. This paper presents correlations and biases between the concentrations measured using the four instruments. A very good correlation was found for benzene and acetone measurements between all instruments (the mean R value was 0.88 for both compounds), while for acetaldehyde and toluene the correlation was weaker (with a mean R value of 0.50 and 0.62, respectively). For some compounds, notably for methanol, there were considerable systematic differences in the mixing ratios measured by the different instruments, despite the very good correlation between the instruments (mean R = 0.90). The systematic difference manifests as a difference in the linear regression slope between measurements conducted between instruments, rather than as an offset. This mismatch indicates that the systematic uncertainty in the sensitivity of a given instrument can lead to an uncertainty of 50-100% in the methanol emissions measured by commonly used methods.Peer reviewe

Anthropogenic and biogenic influence on VOC fluxes at an urban background site in Helsinki, Finland

We measured volatile organic compounds (VOCs), carbon dioxide (CO2) and carbon monoxide (CO) at an urban background site near the city centre of Helsinki, Finland, northern Europe. The VOC and CO2 measurements were obtained between January 2013 and September 2014 whereas for CO a shorter measurement campaign in April-May 2014 was conducted. Both anthropogenic and biogenic sources were identified for VOCs in the study. Strong correlations between VOC fluxes and CO fluxes and traffic rates indicated anthropogenic source of many VOCs. The VOC with the highest emission rate to the atmosphere was methanol, which originated mostly from traffic and other anthropogenic sources. The traffic was also a major source for aromatic compounds in all seasons whereas isoprene was mostly emitted from biogenic sources during summer. Some amount of traffic-related isoprene emissions were detected during other seasons but this might have also been an instrumental contamination from cycloalkane products. Generally, the observed VOC fluxes were found to be small in comparison with previous urban VOC flux studies. However, the differences were probably caused by lower anthropogenic activities as the CO2 fluxes were also relatively small at the site.Peer reviewe