A comparison of new measurements of total monoterpene flux with improved measurements of speciated monoterpene flux

Abstract

Abstract. Many monoterpenes have been identified in forest emissions using gas chromatography (GC). Until now, it has been impossible to determine whether all monoterpenes are appropriately measured using GC techniques. We used a proton transfer reaction mass spectrometer (PTR-MS) coupled with the eddy covariance (EC) technique to measure mixing ratios and fluxes of total monoterpenes above a ponderosa pine plantation. We compared PTR-MS-EC results with simultaneous measurements of eight speciated monoterpenes, β-pinene, α-pinene, 3-carene, d-limonene, β-phellandrene, α-terpinene, camphene, and terpinolene, made with an automated, in situ gas chromatograph with flame ionization detectors (GC-FID), coupled to a relaxed eddy accumulation system (REA). Monoterpene mixing ratios and fluxes measured by PTR-MS averaged 30±2.3% and 31±9.2% larger than by GC-FID, with larger mixing ratio discrepancies between the two techniques at night than during the day. Two unidentified peaks that correlated with β-pinene were resolved in the chromatograms and completely accounted for the daytime difference and reduced the nighttime mixing ratio difference to 20±2.9%. Measurements of total monoterpenes by PTR-MS-EC indicated that GC-FID-REA measured the common, longer-lived monoterpenes well, but that additional terpenes were emitted from the ecosystem that represented an important contribution to the total mixing ratio above the forest at night.

Emissions and ambient distributions of Biogenic Volatile Organic Compounds (BVOC) in a ponderosa pine ecosystem: interpretation of PTR-MS mass spectra

“…MBO and MT are the dominant BVOCs emitted from ponderosa pine as observed in earlier studies (Baker et al, 2001). The emission strength of MT that was measured by GC-MS is ∼ 72% of that measured by PTR-MS, a result consistent with the findings of Lee et al (2005), who suggested the existence of reactive MT that can only be measured by PTR-MS. Less than 5% of the discrepancy can be explained by the contributions of oxygenated MT, such as linalool and bornyl acetate, which were detected on m/z 81 + and 137 + . In addition, the GC-MS detected elevated levels of toluene from the branch enclosure (∼ 4 times higher than ambient concentration).…”

Known and Unexplored Organic Constituents in the Earth's Atmosphere

“…PTR-MS was used to observe the sum of all individual monoterpenes in a forest environment; 30% more terpenes were revealed than could be measured by preconcentration followed by GC separation (18). PTR-MS has also been used to scan the atmosphere for known and potentially unknown compounds in a variety of environments, including forested areas in Surinam (19) and California (20).…”

BVOC ecosystem flux measurements at a high latitude wetland site

“…The coefficients of determination (R 2 ) were very high, irrespective of the BVOC. Spirig et al (2005) found an underestimation of turbulent fluxes due to neglecting high frequency transport of 10.7%, and Lee et al (2005) assumed the error for sensible heat flux due to the spectral response to be within 10%. Both had measurement systems placed 5 to 7 m above forest canopies, with stand heights of 7 and more than 30 m, respectively.…”

“…Typical integration times, which are BVOC dependent, are 0.2 and 0.5 s (e.g. Schade and Custer, 2004;Spirig et al, 2005;Lee et al, 2005;Brunner et al, 2007), and might cause underestimation of the high frequency part of the turbulence spectrum. Second, masses are determined sequentially in the PTR-MS and a number of masses, depending on the BVOCs of interest, are analyzed in a continuously repeating sequence.…”