Oxygenated volatile organic compounds (OVOCs) are formed during the oxidation of gas-phase hydrocarbons in the atmosphere. However, analytical challenges have hampered ambient measurements for many of these species, leaving unanswered questions regarding their atmospheric fate. We present the development of an in situ gas chromatography (GC) technique that, when combined with the sensitive and specific detection of chemical ionization mass spectrometry (CIMS), is capable of the isomer-resolved detection of a wide range of OVOCs. The instrument addresses many of the issues typically associated with chromatographic separation of such compounds (e.g., analyte degradation). The performance of the instrumentation is assessed through data obtained in the laboratory and during two field studies. We show that this instrument is able to successfully measure otherwise difficult-to-quantify compounds (e.g., organic hydroperoxides and organic nitrates) and observe the diurnal variations in a number of their isomers.

This study investigates the rain-initiated mixing and variability in the mixing ratio of selected trace gases in the atmosphere over the central Amazon rain forest. It builds on comprehensive data from the Amazon Tall Tower Observatory (ATTO), spanning from 2013 to 2020 and comprising the greenhouse gases (GHGs) carbon dioxide (CO₂) and methane (CH4); the reactive trace gases carbon monoxide (CO), ozone (O₃), nitric oxide (NO), and nitrogen dioxide (NO₂); and selected volatile organic compounds (VOCs). Based on more than 1000 analyzed rainfall events, the study resolves the trace gas mixing ratio patterns before, during, and after the rain events, along with vertical mixing ratio gradients across the forest canopy. The assessment of the rainfall events was conducted independently for daytime and nighttime periods, which allows us to elucidate the influence of solar radiation. The mixing ratios of CO₂, CO, and CH₄ clearly declined during rainfall, which can be attributed to the downdraft-related entrainment of pristine air from higher altitudes into the boundary layer, a reduction of the photosynthetic activity under increased cloud cover, and changes in the surface fluxes. Notably, CO showed a faster reduction than CO₂, and the vertical gradient of CO₂ and CO is steeper than for CH₄. Conversely, the O₃ mixing ratio increased across all measurement heights in the course of the rain-related downdrafts. Following the O₃ enhancement by up to a factor of 2, NO, NO₂, and isoprene mixing ratios decreased. The temporal and vertical variability of the trace gases is intricately linked to the diverse sink and source processes, surface fluxes, and free-troposphere transport. Within the canopy, several interactions unfold among soil, atmosphere, and plants, shaping the overall dynamics. Also, the mixing ratio of biogenic VOCs (BVOCs) clearly varied with rainfall, driven by factors such as light, temperature, physical transport, and soil processes. Our results disentangle the patterns in the trace gas mixing ratio in the course of sudden and vigorous atmospheric mixing during rainfall events. By selectively uncovering processes that are not clearly detectable under undisturbed conditions, our results contribute to a better understanding of the trace gas life cycle and its interplay with meteorology, cloud dynamics, and rainfall in the Amazon.

The photooxidation of volatile organic compounds (VOCs) in the troposphere has important implications for air quality, weather, and climate. A deeper understanding of the underlying mechanisms can be achieved by studying these reactions under controlled conditions and analysing the emerging photooxidation products. This requires dedicated laboratory infrastructure as well as sensitive and selective analytical techniques. Here, we constructed a new 300 L indoor Teflon atmospheric simulation chamber as part of the Bayreuth ATmospheric simulation CHambers (BATCH) infrastructure. The chamber was irradiated by a bandpass-filtered solar simulator that enabled experiments with realistic photon fluxes and OH radical concentrations. It was coupled to a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) and a solid-phase microextraction–gas chromatography–mass spectrometry (SPME-GC-MS) system for the on-line analysis of the precursor VOC and its oxidation products in the gas phase. As part of the SPME-GC-MS method, multifunctional oxygenated compounds (carbonyls, alcohols, carboxylic acids) were derivatized with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) and N-trimethylsilyl-N-methyltrifluoroacetamide (MSTFA). We designed a permeation source for the on-line addition of internal standards to improve method reproducibility. The joint setup was tested and validated by studying the OH-radical-induced photooxidation of toluene, one of the most abundant aromatic hydrocarbons in the atmosphere. For chamber characterization, we first derived the photolysis rates for several typical toluene products in the irradiated BATCH Teflon chamber (1.77 × 10⁻⁸–3.02 × 10⁻⁴ s⁻¹). Additionally, wall loss rates were determined empirically (4.54 × 10⁻⁶–8.53 × 10⁻⁵ s⁻¹) and then parameterized according to fundamental molecular properties. For the cresols, we compiled a weighted calibration factor for the PTR-ToF-MS, taking into account isomer-specific sensitivities as well as the relative distribution as determined by the SPME-GC-MS. The weighted calibration improved the instrumental agreement to 14 %, whereas the PTR-ToF-MS overestimated the sum of the isomers by 31 % compared to the SPME-GC-MS concentrations when using the averaged calibration factor. Thus, the combined data set offered insight into both temporal trends and the isomeric composition. Finally, we conducted six toluene photooxidation experiments to evaluate the ring-retaining first-generation products. Based on the loss-corrected concentrations, we derived formation yields for o-cresol (8.0 ± 1.8 %), m-cresol (0.4 ± 0.1 %), p-cresol (2.4 ± 0.6 %), benzyl alcohol (0.5 ± 0.1 %), and benzaldehyde (4.6 ± 1.7 %) under NO_x-free conditions at T = 298 ± 1 K. These yields are consistent with previous studies and therefore serve as proof of concept for our applied methods.

Particles originating from tire wear and road interactions, tire and road wear particles (TRWP), are an emerging class of nonexhaust emissions with growing environmental concern. Yet, little is known about their atmospheric abundance and variability due to emissions, transport and transformation processes. This study addressed this gap by quantifying six tire additives that serve as markers for the indirect detection of TRWP in complex environmental samples. Using a newly developed analytical workflow based on high-performance liquid chromatography-mass spectrometry (HPLC-MS), we traced three antiozonants, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and N,N'-diphenyl-p-phenylenediamine (DPPD), their oxidation products (6PPD quinone and IPPD quinone), and the vulcanization accelerator 1,3-diphenylguanidine (DPG) across a wide range of sample types. This single-method framework enabled us to observe marker variabilities, from pristine tire material to abrasion-related emissions from the testbed and road, airborne ultrafine particles (UFPs), and total atmospheric deposition. Marker composition varied strongly with source, emission conditions, and environmental exposure. During abrasion, 6PPD decreased by ∼90%, while 6PPD quinone increased along the emission pathway. In ambient UFP from six Bavarian (Germany) sites, mean 6PPD concentrations ranged from <0.01 to 0.55 ng m^-3. In the particulate fraction in total deposition from an urban, semi-industrial site, the ratio of oxygenated and parent PPD varied seasonally, revealing a higher degree of oxidation during summer. 6PPD dominated in the autumn and winter with an average of 6.6 ± 0.91 ng m^-2 day^-1, while 6PPDq was highest in spring and summer with average concentrations of 5.6 ± 5.91 ng m^-2 day^-1 and reaching an estimated annual deposition of 1.7 ± 0.5 μg m^-2 year^-1. By linking source materials to atmospheric samples, this study demonstrated the traceability of TRWP along their emission pathway for the first time and highlighted the importance of accounting for the chemical transformation of dedicated marker components in assessing their environmental fate.