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Oxygenated organic molecules (OOMs) play an important role in the formation of atmospheric aerosols. Due to various analytical challenges with respect to measuring organic vapors, uncertainties remain regarding the formation and fate of OOMs. The chemical ionization Orbitrap (CI-Orbitrap) mass spectrometer has recently been shown to be a powerful technique that is able to accurately identify gaseous organic compounds due to its greater mass resolution. Here, we present the ammonium-ion-based CI-Orbitrap (NH4+ -Orbitrap) as a technique capable of measuring a wide range of gaseous OOMs. The performance of the NH4+ -Orbitrap is compared with that of state-of-the-art mass spectrometers, including a nitrate-ion-based chemical ionization atmospheric pressure interface coupled to a time-of-flight mass spectrometer (NO3- -LTOF), a new generation of proton transfer reaction-TOF mass spectrometer (PTR3-TOF), and an iodide-based CI-TOF mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (I- -CIMS). The instruments were deployed simultaneously in the Cosmic Leaving OUtdoors Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN) during the CLOUD14 campaign in 2019. Products generated from α -pinene ozonolysis under various experimental conditions were simultaneously measured by the mass spectrometers. The NH4+ -Orbitrap was able to identify the widest range of OOMs (i.e., O ≥ 2), from less-oxidized species to highly oxygenated organic molecules (HOMs). Excellent agreement was found between the NH4+ -Orbitrap and the NO3- -LTOF with respect to characterizing HOMs and with the PTR3-TOF for the less-oxidized monomeric species. OOM concentrations measured by NH4+ -Orbitrap were estimated using calibration factors derived from the OOMs with high time-series correlations during the side-by-side measurements. As with the other mass spectrometry techniques used during this campaign, the detection sensitivity of the NH4+ -Orbitrap to OOMs is greatly affected by relative humidity, which may be related to changes in ionization efficiency and/or multiphase chemistry. Overall, this study shows that NH4+ -ion-based chemistry associated with the high mass resolution of the Orbitrap mass analyzer can measure almost all inclusive compounds. As a result, it is now possible to cover the entire range of compounds, which can lead to a better understanding of the oxidation processes. [ABSTRACT FROM AUTHOR]

Oxygenated organic molecules (OOMs) play an important role in the formation of atmospheric aerosols. Due to various analytical challenges in measuring organic vapors, uncertainties remain in the formation and fate of OOMs. The chemical ionization Orbitrap mass spectrometer (CI-Orbitrap) has recently been shown to be a powerful technique able to accurately identify gaseous organic compounds due to its great mass resolving power. Here we present the ammonium ion (NH4+) based CI-Orbitrap as a technique capable of measuring a wide range of gaseous OOMs. The performance of the CI-(NH4+)-Orbitrap was compared with that of state-of-the-art mass spectrometers, including a nitrate ion (NO3-) based CI coupled to an atmospheric pressure interfaced to long time-of-flight mass spectrometer (APi-LTOF), a new generation of proton transfer reaction-TOF mass spectrometer (PTR3-TOF), and an iodide (I-) based CI-TOF mass spectrometer equipped with a Filter Inlet for Gases and AEROsols (FIGAERO-CIMS). The instruments were deployed simultaneously in the Cosmic Leaving OUtdoors Droplets (CLOUD) chamber at the European Organization for Nuclear Research (CERN) during the CLOUD14 campaign in 2019. Products generated from α-pinene ozonolysis across multiple experimental conditions were simultaneously measured by the mass spectrometers. NH4+-Orbitrap was able to identify the widest range of OOMs (i.e., O = 2), from low oxidized species to highly oxygenated volatile organic compounds (HOM). Excellent agreements were found between the NH4+-Orbitrap and the NO3--LTOF for characterizing HOMs and with the PTR3- TOF for the less oxidized monomeric species. A semi-quantitative information was retrieved for OOMs measured by NH4+-Orbitrap using calibration factors derived from this side-by-side comparison. As other mass spectrometry techniques used during this campaign, the detection sensitivity of NH4+-Orbitrap to OOMs is greatly affected by relative humidity, which may be related to changes in ionization efficiency and/or multiphase chemistry. Overall, this study shows that NH4+ ion46 based chemistry associated with the high mass resolving power of the Orbitrap mass analyzer can measure almost all-inclusive compounds. As a result, it is now possible to cover the entire range of compounds, which can lead to a better understanding of the oxidation processes. [ABSTRACT FROM AUTHOR]

Terpenes, a class of hydrocarbons including isoprene (C5H8), monoterpenes (MTs; C10H16), sesquiterpenes (SQTs; C15H24), and diterpenes (DTs; C20H32), are highly reactive to atmospheric oxidants and can form highly oxidized organic molecules (HOMs), leading to new particle formation (NPF), and secondary pollutants like tropospheric ozone and secondary organic aerosols (SOA). Wetlands are primarily found in the boreal and tundra regions of the Northern hemisphere and are well-known for their high methane emissions. However, their VOC emissions were investigated by relatively few studies, showing them to be high isoprene emitters. Terpene emissions have an exponential temperature dependence, while boreal wetlands are experiencing above two times the average global warming, and recent enclosure studies show a substantial increase in terpene emissions. In this study, we present ecosystem-scale eddy covariance (EC) fluxes of terpenes (up to DTs) from Siikaneva, a boreal fen in southern Finland, from the start to the peak of the growing season of 2021 (19 May 2021 to 28 June 2021). These are the first EC fluxes reported using the novel state-of-the-art Vocus- proton transfer reaction mass spectrometer (Vocus-PTR) and the first-ever fluxes reported for DTs from a wetland. Isoprene was the dominant terpene emitted by the wetland, followed by MTs, SQTs, and DTs. All terpenes exhibited distinct diurnal patterns with maxima around noon and a strong exponential dependence on temperature. The Q10 values, the factor by which terpene emissions increases for every 10 °C rise in temperature, were up to 5 times higher than those used in most BVOC models. During the campaign, the air temperature peaked above 31 °C on 21–22 June 2021, which is abnormally high for boreal environments, and the maximum flux for all terpenes coincided with this period. We observed that terpene emissions were elevated after this abnormally “high-temperature stress period,” indicating that past temperatures alter emissions significantly. The standardized emission factor (EF) of the fen for isoprene (EFiso) was 11.1 ± 0.3 nmol m-2 s-1, which is at least two times higher than in previous studies and as high as the emission factors typical for broadleaf and other forests in the lower latitudes. We observed EFMT of 2.4 ± 0.1 nmol m-2 s-1, EFSQT of 1.3 ± 0.03 nmol m-2 s-1, higher than typical for needle leaf and broadleaf tree functional types, and EFDT of 0.011 ± 0.001 nmol m-2 s-1. We also compared the landscape average emissions to the Model of Emissions of Gases and Aerosols from Nature (MEGAN) v2.1, specifically using EF for the “C3 Arctic grass” plant functional type, and found that the emissions were underestimated by over 9 times for isoprene, over 300 times for MTs, and 800 times for SQTs. Our results show that due to very high EFs and high sensitivity to increasing temperatures, these high latitude ecosystems can be a large source of terpenes to the atmosphere, and anthropogenic global warming could induce much higher BVOC emissions from wetlands in the future. [ABSTRACT FROM AUTHOR]

We evaluate monoterpene-derived peroxy radical (MT-RO2) unimolecular autoxidation and self and cross reactions with other RO2 in the GEOS-Chem global chemical transport model. Formation of associated highly oxygenated organic molecule (HOM) and accretion products are tracked in competition with other bimolecular reactions. Autoxidation is the dominant fate up to 6-8 km for first-generation MT-RO2 which can undergo unimolecular H-shifts. Reaction with NO can be a more common fate for H-shift rate constants < 0.1 s-1 or at altitudes higher than 8 km due to the imposed Arrhenius temperature dependence of unimolecular H-shifts. For MT-derived HOM-RO2, generated by multi-step autoxidation of first-generation MT-RO2, reaction with other RO2 is predicted to be the major fate throughout most of the boreal and tropical forested regions, while reaction with NO dominates in temperate and subtropical forests of the Northern Hemisphere. The newly added reactions result in ~4 % global average decrease of HO2 and RO2 mainly due to faster self-/cross-reactions of MT-RO2, but the impact upon HO2/OH/NOx abundances is only important in the planetary boundary layer (PBL) over portions of tropical forests. Within the bounds of formation kinetics and HOM photochemical lifetime constraints from laboratory studies, predicted HOM concentrations in MT-rich regions and seasons reach 10 % or even exceed total organic aerosol as predicted by the standard GEOS-Chem model. Comparisons to observations reveal large uncertainties remain for key reaction parameters and processes, especially the photochemical lifetime of HOM and associated accretion products. Using the highest reported yields and H-shift rate constants of MT-RO2 that undergo autoxidation, HOM concentrations tend to exceed the limited set of observations. Similarly, we infer that RO2 cross reactions rate constants near the gas-kinetic limit with accretion product branching greater than ~0.25 are inconsistent with total organic aerosol unless there is rapid decomposition of accretion products, the accretion products have saturation vapor concentrations > > 1 μg m-3, or modeled MT emission rates are overestimated. This work suggests further observations and laboratory studies related to MT-RO2 derived HOM and gas-phase accretion product formation kinetics, and especially their atmospheric fate, such as gas-particle partitioning, multi-phase chemistry, and net SOA formation, are needed. [ABSTRACT FROM AUTHOR]

Metallurgical industry in Kola peninsula, North-West Russia, form a second largest source of air pollution in the Arctic and sub-Arctic domain. Sulphur dioxide emissions from the ore smelters are transported to wide areas including Finnish Lapland. We performed investigations on concentrations of SO2 and aerosol precursor vapours, aerosol and ion cluster size distributions together with chemical composition measurements of freshly formed clusters at SMEAR I station in Finnish Lapland relatively close (~300 km) to Kola peninsula industrial sites during winter 2019-2020. We show that highly concentrated SO2 from smelter emissions is converted to sulphuric acid (H2SO4) with sufficient concentrations to drive new particle formation hundreds of kilometres downwind of the emission sources even with very low solar radiation intensities. Observed new particle formation is primarily initiated by H2SO4 - ammonia (negative-) ion induced nucleation. Particle growth to cloud condensation nuclei (CCN) sizes was concluded to result from sulphuric acid condensation. However, airmass advection had a large role in modifying aerosol size distributions and other growth mechanisms cannot be fully excluded. Our results demonstrate the dominance of SO2 emissions in controlling winter-time aerosol and CCN concentrations in the subarctic region with heavily polluting industry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]