Measurement of atmospheric sesquiterpenes by proton transfer reaction-mass spectrometry (PTR-MS)

Considerable fragmentation of bicyclic sesquiterpenes, i.e. β-caryophyllene and α-humulene, cause the accuracy to be reduced to 50% if only the parent ion (m/z 205⁺) is considered. These findings were applied to a field dataset collected above a deciduous forest at the PROPHET (Program for Research on Oxidants: Photochemistry, Emissions, and Transport) research station in 2005. Inferred average daytime ecosystem scale mixing ratios (fluxes) of isoprene, sum of monoterpenes (MT), and sum of SQT exhibited values of 15 μg m⁻³ (4.5 mg m⁻² h⁻¹), 1.2 μg m⁻³ (0.21 mg m⁻² h⁻¹), and 0.0016 μg m⁻³ (0.10 mg m⁻² h⁻¹), respectively.

A range of MT and SQT reactivities with respect to the OH radical was calculated and compared to an earlier study inferring significantly underestimated OH reactivities due to unknown terpenes above this deciduous forest. The results indicate that incorporating these MT and SQT results can resolve ~30% of missing OH reactivity reported for this site.