Abstract
Abstract. The emission and fate of reactive volatile organic compounds (VOCs) is of inherent interest to those studying chemical biosphere–atmosphere interactions. In-canopy VOC observations are obtainable using tower-based samplers, but the lack of suitable sampling systems for the full boundary layer has limited the availability of data characterizing the vertical structure of such gases above the canopy height and still in the boundary layer. This is an important region where many reactive VOCs are oxidized or otherwise removed. Here we describe an airborne sampling system designed to collect a vertical profile of air into a 3/8 in. OD (outer diameter) tube 150 m in length. The inlet ram air pressure is used to flow sampled air through the tube, which results in a varying flow rate based on aircraft speed and altitude. Since aircraft velocity decreases during ascent, it is necessary to account for the variable flow rate into the tube. This is accomplished using a reference gas that is pulsed into the air stream so that the precise altitude of the collected air can be reconstructed post-collection. The pulsed injections are also used to determine any significant effect from diffusion/mixing within the sampling tube, either during collection or subsequent extraction for gas analysis. This system has been successfully deployed, and we show some measured vertical profiles of isoprene and its oxidation products methacrolein and methyl vinyl ketone from a mixed canopy near Columbia, Missouri.
Highlights
Volatile organic compounds (VOCs) are emitted from almost all plant species (Fuentes et al, 2000; Kesselmeier and Staudt, 1999; Laothawornkitkul et al, 2009)
Direct flux measurements can be used, if one has a fast response trace gas measurement system. In this case an eddy covariance (EC) sampling line is used for realtime measurements of VOC concentrations that are correlated with vertical wind speed, w, as measured by a sonic anemometer located on the same tower (Müller et al, 2010; DiGangi et al, 2011)
The air sample inside the coiled tube is measured by using the PTR-TOFMS and the counts rate of the tracer gas as well as the VOC species are recorded simultaneously
Summary
Volatile organic compounds (VOCs) are emitted from almost all plant species (Fuentes et al, 2000; Kesselmeier and Staudt, 1999; Laothawornkitkul et al, 2009). Direct flux measurements can be used, if one has a fast response trace gas measurement system In this case an eddy covariance (EC) sampling line is used for realtime measurements of VOC concentrations that are correlated with vertical wind speed, w, as measured by a sonic anemometer located on the same tower (Müller et al, 2010; DiGangi et al, 2011). From this information, along with measurements of other atmospheric constituents, researchers can determine emissions rates and describe chemistry and transport within the forest canopy
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
