Source identification of atmospheric organic vapors in two European pine forests: Results from Vocus PTR-TOF observations

Abstract

Abstract. Atmospheric organic vapors play essential roles in the formation of secondary organic aerosol. Source identification of these vapors is thus fundamental to understand their emission sources and chemical evolution in the atmosphere and their further impact on air quality and climate change. In this study, a Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF) was deployed in two forested environments, the Landes forest in southern France and the boreal forest in southern Finland, to measure atmospheric organic vapors, including both volatile organic compounds (VOCs) and their oxidation products. For the first time, we performed binned positive matrix factorization (binPMF) analysis on the complex mass spectra acquired with the Vocus PTR-TOF and identified various emission sources as well as oxidation processes in the atmosphere. Based on separate analysis of low- and high-mass ranges, fifteen PMF factors in the Landes forest and nine PMF factors in the Finnish boreal forest were resolved, showing a high similarity between the two sites. Factors representing monoterpenes dominate the biogenic VOCs in both forests, with less contributions from the isoprene factors and sesquiterpene factors. Particularly, various terpene reaction products were separated into individual PMF factors with varying oxidation degrees, such as lightly oxidized compounds from both monoterpene and sesquiterpene oxidations, monoterpene-derived organic nitrates, and monoterpene more oxidized compounds. These factors display similar mass profiles and diurnal variations between the two sites, revealing similar terpene reaction pathways in these forests. With the distinct characteristics of VOCs and oxygenated VOCs measured by the Vocus PTR-TOF, this study identified various primary emission sources and secondary oxidation processes of atmospheric organic vapors in the European pine forests, providing a more comprehensive understanding of gas-phase atmospheric chemistry.

Field Detection of Highly Oxygenated Organic Molecules in Shanghai by Chemical Ionization–Orbitrap

“…One aromatic oxidation factor (ARO), an alkane/alkene oxidation factor (ALK), two nighttime terpene factors (Night_MT dominated by NO 3 chemistry and MT dominant by O 3 + NO x ), and an NPF-related factor were also distinguished from individual ranges. The results in this study agreed well with previous research on OOM factorization, measured by CI–APi–TOF in foresty or suburban environments. ,,, Note that this good agreement should not be interpreted as indicating that the Orbitrap technology is not advantageous compared to traditional techniques but rather a validation for the results in our study. On the one hand, the Orbitrap reduced significantly the efforts in peak fitting while offering an unprecedented accuracy in the identification of the analytes, which provided the crucial chemical/molecular information needed to understand the atmospheric processes.…”

“…To our knowledge, only a few studies have been conducted to understand ambient VOC oxidation by PMF analysis, ,,, most of which have substantial influence from biogenic sources. Different from previous studies, anthropogenic-originated contribution in our study was absolutely dominant in the Shanghai urban environment, 94% on average (sum of the factors, excluding Night_MT and MT).…”

Atmospheric reactivity of biogenic volatile organic compounds in a maritime pine forest during the LANDEX episode 1 field campaign

“…Considering this unusual observation, it was decided to validate -a posteriori -the NO 3 concentration calculation methodology used in the present study, by applying it to other datasets from previous campaigns carried out in a similar environment. Our choice focused on a boreal forested site, at the SMEAR II station, Hyytiälä, southern Finland, with one dataset from the HUMMPA-COPEC-10 campaign, performed in summer 2010 (Yassaa et al, 2012;Hens et al, 2014;Mogensen et al, 2015) and one gathering some ambient measurements monitored in summer 2019 (Li et al, 2020a)). In both cases, NO 3 concentrations were found to be maximum at nighttime, as usually observed.…”

Observations of biogenic volatile organic compounds over a mixed temperate forest during the summer to autumn transition

“…Forest found the diel profile of MT to be consistent with C10H17O + , with an average evening [C10H16O]:[ΣMT] of 0.03, compared to 0.08 in this study. The authors suggested that C10H16O was partially sourced from directly-emitted camphor or a MT oxidation product (Li et al, 2020(Li et al, , 2021, although at the CNNF site there are few species that directly emit camphor and those that do (north white cedar, white spruce), emit camphor in low amounts . Figure 3 (Atkinson and Arey, 2003).…”