Browsing by Author "Ferracci, Valerio"
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Item Open Access Atmospheric isoprene measurements reveal larger-than-expected Southern Ocean emissions(Springer Nature, 2024-03-22) Ferracci, Valerio; Weber, James; Bolas, Conor G.; Robinson, Andrew D.; Tummon, Fiona; Rodríguez-Ros, Pablo; Cortés-Greus, Pau; Baccarini, Andrea; Jones, Roderic L.; Galí, Martí; Simó, Rafel; Schmale, Julia; Harris, NeilIsoprene is a key trace component of the atmosphere emitted by vegetation and other organisms. It is highly reactive and can impact atmospheric composition and climate by affecting the greenhouse gases ozone and methane and secondary organic aerosol formation. Marine fluxes are poorly constrained due to the paucity of long-term measurements; this in turn limits our understanding of isoprene cycling in the ocean. Here we present the analysis of isoprene concentrations in the atmosphere measured across the Southern Ocean over 4 months in the summertime. Some of the highest concentrations ( >500 ppt) originated from the marginal ice zone in the Ross and Amundsen seas, indicating the marginal ice zone is a significant source of isoprene at high latitudes. Using the United Kingdom Earth System Model we show that current estimates of sea-to-air isoprene fluxes underestimate observed isoprene by a factor >20. A daytime source of isoprene is required to reconcile models with observations. The model presented here suggests such an increase in isoprene emissions would lead to >8% decrease in the hydroxyl radical in regions of the Southern Ocean, with implications for our understanding of atmospheric oxidation and composition in remote environments, often used as proxies for the pre-industrial atmosphere.Item Open Access CCQM-K90, formaldehyde in nitrogen, 2 μmol mol− 1 Final report(IOP, 2017-09-26) Viallon, Joële; Flores, Edgar; Idrees, Faraz; Moussay, Philippe; Wielgosz, Robert Ian; Kim, D.; Kim, Y. D.; Lee, S.; Persijn, S.; Konopelko, L. A.; Kustikov, Y. A.; Malginov, A. V.; Chubchenko, I. K.; Klimov, A. Y.; Efremova, O. V.; Zhou, Z.; Possolo, A.; Shimosaka, T.; Brewer, P.; Macé, T.; Ferracci, Valerio; Brown, Richard J. C.; Aoki, AokiThe CCQM-K90 comparison is designed to evaluate the level of comparability of national metrology institutes (NMI) or designated institutes (DI) measurement capabilities for formaldehyde in nitrogen at a nominal mole fraction of 2 μmol mol−1. The comparison was organised by the BIPM using a suite of gas mixtures prepared by a producer of specialty calibration gases. The BIPM assigned the formaldehyde mole fraction in the mixtures by comparison with primary mixtures generated dynamically by permeation coupled with continuous weighing in a magnetic suspension balance. The BIPM developed two dynamic sources of formaldehyde in nitrogen that provide two independent values of the formaldehyde mole fraction: the first one based on diffusion of trioxane followed by thermal conversion to formaldehyde, the second one based on permeation of formaldehyde from paraformaldehyde contained in a permeation tube. Two independent analytical methods, based on cavity ring down spectroscopy (CRDS) and Fourier transform infrared spectroscopy (FTIR) were used for the assignment procedure. Each participating institute was provided with one transfer standard and value assigned the formaldehyde mole fraction in the standard based on its own measurement capabilities. The stability of the formaldehyde mole fraction in transfer standards was deduced from repeated measurements performed at the BIPM before and after measurements performed at participating institutes. In addition, 5 control standards were kept at the BIPM for regular measurements during the course of the comparison. Temporal trends that approximately describe the linear decrease of the amount-of-substance fraction of formaldehyde in nitrogen in the transfer standards over time were estimated by two different mathematical treatments, the outcomes of which were proposed to participants. The two treatments also differed in the way measurement uncertainties arising from measurements performed at the BIPM were propagated to the uncertainty of the trend parameters, as well as how the dispersion of the dates when measurements were made by the participants was taken into account. Upon decision of the participants, the Key Comparison Reference Values were assigned by the BIPM using the largest uncertainty for measurements performed at the BIPM, linear regression without weight to calculate the trend parameters, and not taking into account the dispersion of dates for measurements made by the participant. Each transfer standard was assigned its own reference value and associated expanded uncertainty. An expression for the degree of equivalence between each participating institute and the KCRV was calculated from the comparison results and measurement uncertainties submitted by participating laboratories. Results of the alternative mathematical treatment are presented in annex of this report.Item Open Access Characterization of Fourier transform infrared, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy instruments for the analysis of ammonia in biogas and biomethane(American Chemical Society, 2022-10-27) Culleton, Lucy P.; di Meane, Elena Amico; Ward, Michael K. M.; Ferracci, Valerio; Persijn, Stefan; Holmqvist, Albin; Arrhenius, Karine; Murugan, Arul; Brewer, Paul J.Novel traceable analytical methods and reference gas standards were developed for the detection of trace-level ammonia in biogas and biomethane. This work focused on an ammonia amount fraction at an upper limit level of 10 mg m–3 (corresponding to approximately 14 μmol mol–1) specified in EN 16723-1:2016. The application of spectroscopic analytical methods, such as Fourier transform infrared spectroscopy, cavity ring-down spectroscopy, and optical feedback cavity-enhanced absorption spectroscopy, was investigated. These techniques all exhibited the necessary ammonia sensitivity at the required 14 μmol mol–1 amount fraction. A 29-month stability study of reference gas mixtures of 10 μmol mol–1 ammonia in methane and synthetic biogas is also reported.Item Open Access Continuous isoprene measurements in a UK temperate forest for a whole growing season: effects of drought stress during the 2018 heatwave(American Geophysical Union (AGU), 2020-07-08) Ferracci, Valerio; Bolas, Conor G.; Freshwater, Ray A.; Staniaszek, Zosia; King, Thomas; Jaars, Kerneels; Otu‐Larbi, Frederick; Beale, John; Malhi, Yadvinder; Waine, Toby William; Jones, Roderic L.; Ashworth, Kirsti; Harris, NeilIsoprene concentrations were measured at four heights below, within and above the forest canopy in Wytham Woods (UK) throughout the summer of 2018 using custom-built gas chromatographs (the iDirac). These observations were complemented with selected ancillary variables, including air temperature, photosynthetically active radiation (PAR), occasional leaf gas exchange measurements and satellite retrievals of normalized difference vegetation and water indices (NDVI and NDWI). The campaign overlapped with a long and uninterrupted heatwave accompanied by moderate drought. Peak isoprene concentrations during the heatwave-drought were up to a factor of 4 higher than those before or after. Higher temperatures during the heatwave could not account for all the observed isoprene; the enhanced abundances correlated with drought stress. Leaf-level emissions confirmed this and also included compounds associated with ecosystem stress. This work highlights that a more in-depth understanding of the effects of drought stress is required to better characterize isoprene emissions.Item Open Access Development of an urban greenhouse gas modelling system to support a London monitoring network(Wiley, 2020-09-07) Hoare, D.; Jones, R. L.; Harris, Neil; Ferracci, Valerio; Carruthers, D.; Stidworthy, A.; Forsyth, E.; Rigby, M.A greenhouse gas monitoring network is being developed across London that will allow independent evaluation of reported emissions based on atmospheric data. The first site is operational at the Thames Barrier, and in this work, two atmospheric dispersion models (NAME and ADMS‐URBAN) are compared to observed methane concentrations between 5 May 2018 and 31 July 2018. We find that the models simulate some of the major features in the data, with consistent data–model discrepancies suggesting errors in the emissions inventory.Item Open Access Exploring the coupled ocean and atmosphere system with a data science approach applied to observations from the Antarctic Circumnavigation Expedition(EGU: European Geophysical Union, 2021-11-30) Landwehr, Sebastian; Volpi, Michele; Haumann, F. Alexander; Robinson, Charlotte M.; Thurnherr, Iris; Ferracci, Valerio; Baccarini, Andrea; Thomas, Jenny; Gorodetskaya, Irina; Tatzelt, Christian; Henning, Silvia; Modini, Rob L.; Forrer, Heather J.; Lin, Yajuan; Cassar, Nicolas; Simó, Rafel; Hassler, Christel; Moallemi, Alireza; Fawcett, Sarah E.; Harris, Neil; Airs, Ruth; Derkani, Marzieh H.; Alberello, Alberto; Toffoli, Alessandro; Chen, Gang; Rodríguez-Ros, Pablo; Zamanillo, Marina; Cortés-Greus, Pau; Xue, Lei; Bolas, Conor G.; Leonard, Katherine C.; Perez-Cruz, Fernando; Walton, David; Schmale, JuliaThe Southern Ocean is a critical component of Earth's climate system, but its remoteness makes it challenging to develop a holistic understanding of its processes from the small scale to the large scale. As a result, our knowledge of this vast region remains largely incomplete. The Antarctic Circumnavigation Expedition (ACE, austral summer 2016/2017) surveyed a large number of variables describing the state of the ocean and the atmosphere, the freshwater cycle, atmospheric chemistry, and ocean biogeochemistry and microbiology. This circumpolar cruise included visits to 12 remote islands, the marginal ice zone, and the Antarctic coast. Here, we use 111 of the observed variables to study the latitudinal gradients, seasonality, shorter-term variations, geographic setting of environmental processes, and interactions between them over the duration of 90 d. To reduce the dimensionality and complexity of the dataset and make the relations between variables interpretable we applied an unsupervised machine learning method, the sparse principal component analysis (sPCA), which describes environmental processes through 14 latent variables. To derive a robust statistical perspective on these processes and to estimate the uncertainty in the sPCA decomposition, we have developed a bootstrap approach. Our results provide a proof of concept that sPCA with uncertainty analysis is able to identify temporal patterns from diurnal to seasonal cycles, as well as geographical gradients and “hotspots” of interaction between environmental compartments. While confirming many well known processes, our analysis provides novel insights into the Southern Ocean water cycle (freshwater fluxes), trace gases (interplay between seasonality, sources, and sinks), and microbial communities (nutrient limitation and island mass effects at the largest scale ever reported). More specifically, we identify the important role of the oceanic circulations, frontal zones, and islands in shaping the nutrient availability that controls biological community composition and productivity; the fact that sea ice controls sea water salinity, dampens the wave field, and is associated with increased phytoplankton growth and net community productivity possibly due to iron fertilisation and reduced light limitation; and the clear regional patterns of aerosol characteristics that have emerged, stressing the role of the sea state, atmospheric chemical processing, and source processes near hotspots for the availability of cloud condensation nuclei and hence cloud formation. A set of key variables and their combinations, such as the difference between the air and sea surface temperature, atmospheric pressure, sea surface height, geostrophic currents, upper-ocean layer light intensity, surface wind speed and relative humidity played an important role in our analysis, highlighting the necessity for Earth system models to represent them adequately. In conclusion, our study highlights the use of sPCA to identify key ocean–atmosphere interactions across physical, chemical, and biological processes and their associated spatio-temporal scales. It thereby fills an important gap between simple correlation analyses and complex Earth system models. The sPCA processing code is available as open-access from the following link: https://renkulab.io/gitlab/ACE-ASAID/spca-decomposition (last access: 29 March 2021). As we show here, it can be used for an exploration of environmental data that is less prone to cognitive biases (and confirmation biases in particular) compared to traditional regression analysis that might be affected by the underlying research question.Item Open Access Formic acid in hydrogen: is it stable in a gas container?(MDPI, 2023-06-07) Bacquart, Thomas; Morris, Abigail S. O.; Hookham, Mathew; Ward, Michael K. M.; Underwood, Robin; Hristova, Yoana; Perkins, Mark; Ferracci, Valerio; Murugan, ArulFormic acid is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687, the amount fraction level of formic acid present in the hydrogen supplied to fuel cell electric vehicles must not exceed 200 nmol·mol−1. The development of formic acid standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the fuel cell electric vehicles industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 4 to 100 µmol·mol−1, with a shelf-life of 1 year (stability uncertainty < 7%; k = 2). Stability was not affected over 1 year or by low temperature or pressure. At sub-µmol·mol−1 level, formic acid amount fraction was found to decrease due to adsorption on the gas cylinder surface; however, it is possible to certify the formic acid amount fraction after a period of 20 days and ensure the certified value validity for 1 year with an uncertainty below 7% (k = 1) confirmed by thermodynamic investigation. This study demonstrated that formic acid in hydrogen gas reference materials can be prepared with reasonable uncertainty (>7%, k = 1) and shelf life (>1 year). Potential applications include the calibration of analysers and for studying the impact of formic acid on future application with relevant traceability and accuracy.Item Open Access Global modelling of the total OH reactivity: investigations on the “missing” OH sink and its atmospheric implications(European Geosciences Union (EGU) / Copernicus Publications, 2018-05-24) Ferracci, Valerio; Heimann, Ines; Abraham, N. Luke; Pyle, John A.; Archibald, Alexander T.The hydroxyl radical (OH) plays a crucial role in the chemistry of the atmosphere as it initiates the removal of most trace gases. A number of field campaigns have observed the presence of a “missing” OH sink in a variety of regions across the planet. A comparison of direct measurements of the OH loss frequency, also known as total OH reactivity (kOH), with the sum of individual known OH sinks (obtained via the simultaneous detection of species such as volatile organic compounds and nitrogen oxides) indicates that, in some cases, up to 80 % of kOH is unaccounted for. In this work, the UM-UKCA chemistry-climate model was used to investigate the wider implications of the missing reactivity on the oxidising capacity of the atmosphere. Simulations of the present-day atmosphere were performed and the model was evaluated against an array of field measurements to verify that the known OH sinks were reproduced well, with a resulting good agreement found for most species. Following this, an additional sink was introduced to simulate the missing OH reactivity as an emission of a hypothetical molecule, X, which undergoes rapid reaction with OH. The magnitude and spatial distribution of this sink were underpinned by observations of the missing reactivity. Model runs showed that the missing reactivity accounted for on average 6 % of the total OH loss flux at the surface and up to 50 % in regions where emissions of the additional sink were high. The lifetime of the hydroxyl radical was reduced by 3 % in the boundary layer, whilst tropospheric methane lifetime increased by 2 % when the additional OH sink was included. As no OH recycling was introduced following the initial oxidation of X, these results can be interpreted as an upper limit of the effects of the missing reactivity on the oxidising capacity of the troposphere. The UM-UKCA simulations also allowed us to establish the atmospheric implications of the newly characterised reactions of peroxy radicals (RO2) with OH. Whilst the effects of this chemistry on kOH were minor, the reaction of the simplest peroxy radical, CH3O2, with OH was found to be a major sink for CH3O2 and source of HO2 over remote regions at the surface and in the free troposphere. Inclusion of this reaction in the model increased tropospheric methane lifetime by up to 3 %, depending on its product branching. Simulations based on the latest kinetic and product information showed that this reaction cannot reconcile models with observations of atmospheric methanol, in contrast to recent suggestions.Item Open Access iDirac: a field-portable instrument for long-term autonomous measurements of isoprene and selected VOCs(European Geosciences Union, 2020-02-19) Bolas, Conor G.; Ferracci, Valerio; Robinson, Andrew D.; Mead, Mohammed Iqbal; Nadzir, Mohd Shahrul Mohd; Pyle, John A.; Jones, Roderic L.; Harris, NeilThe iDirac is a new instrument to measure selected hydrocarbons in the remote atmosphere. A robust design is central to its specifications, with portability, power efficiency, low gas consumption and autonomy as the other driving factors in the instrument development. The iDirac is a dual-column isothermal oven gas chromatograph with photoionisation detection (GC-PID). The instrument is designed and built in-house. It features a modular design, with the novel use of open-source technology for accurate instrument control. Currently configured to measure biogenic isoprene, the system is suitable for a range of compounds. For isoprene measurements in the field, the instrument precision (relative standard deviation) is ±10 %, with a limit of detection down to 38 pmol mol−1 (or ppt). The instrument was first tested in the field in 2015 during a ground-based campaign, and has since shown itself suitable for deployment in a variety of environments and platforms. This paper describes the instrument design, operation and performance based on laboratory tests in a controlled environment as well as during deployments in forests in Malaysian Borneo and central England.Item Open Access Inferring London’s methane emissions from atmospheric measurements(EGU: European Geophysical Union, 2021-04-30) Hoare, Daniel; Jones, Rod L.; Fan, Shiwei; Harris, Neil; Ferracci, Valerio; Carruthers, David; Stidworthy, Amy; Forsyth, Ella; Rigby, MattItem Open Access Investigation of cylinder pre-treatments for the stability of ammonia gas reference materials(Springer, 2022-07-14) di Meane, Elena Amico; Brown, Richard J. C.; Brewer, Paul J.; Ferracci, Valerio; van Wijk, Janneke I. T.This report describes work to evaluate the performance of different commercial and proprietary cylinder treatments in improving the stability of ammonia reference materials in high pressure cylinders. Gas mixtures of 100 µmol/mol and 10 µmol/mol ammonia in nitrogen were prepared gravimetrically at both NPL and VSL. Comparative measurements at each amount-of-substance fraction were used to assess which passivation technique minimised the loss of ammonia upon preparation. The results indicate little difference between the commercial treatments, except at lower amount-of-substance fractions (10 μmol/mol). The variation observed in performance might be explained by the different abilities of the various treatments to prevent the adsorption of ammonia molecules on the internal surfaces of the cylinder, although the role of residual water on the cylinder surface in reacting with ammonia is unclear.Item Open Access Modelling the effect of the 2018 summer heatwave and drought on isoprene emissions in a UK woodland(Wiley, 2019-12-13) Otu‐Larbi, Frederick; Bolas, Conor G.; Ferracci, Valerio; Staniaszek, Zosia; Jones, Roderic L.; Malhi, Yadvinder; Harris, Neil R. P.; Wild, Oliver; Ashworth, KirstiProjected future climatic extremes such as heatwaves and droughts are expected to have major impacts on emissions and concentrations of biogenic volatile organic compounds (bVOCs) with potential implications for air quality, climate and human health. While the effects of changing temperature and photosynthetically active radiation (PAR) on the synthesis and emission of isoprene, the most abundant of these bVOCs, are well known, the role of other environmental factors such as soil moisture stress are not fully understood and are therefore poorly represented in land surface models. As part of the Wytham Isoprene iDirac Oak Tree Measurements campaign, continuous measurements of isoprene mixing ratio were made throughout the summer of 2018 in Wytham Woods, a mixed deciduous woodland in southern England. During this time, the United Kingdom experienced a prolonged heatwave and drought, and isoprene mixing ratios were observed to increase by more than 400% at Wytham Woods under these conditions. We applied the state‐of‐the‐art FORest Canopy‐Atmosphere Transfer canopy exchange model to investigate the processes leading to these elevated concentrations. We found that although current isoprene emissions algorithms reproduced observed mixing ratios in the canopy before and after the heatwave, the model underestimated observations by ~40% during the heatwave–drought period implying that models may substantially underestimate the release of isoprene to the atmosphere in future cases of mild or moderate drought. Stress‐induced emissions of isoprene based on leaf temperature and soil water content (SWC) were incorporated into current emissions algorithms leading to significant improvements in model output. A combination of SWC, leaf temperature and rewetting emission bursts provided the best model‐measurement fit with a 50% improvement compared to the baseline model. Our results highlight the need for more long‐term ecosystem‐scale observations to enable improved model representation of atmosphere–biosphere interactions in a changing global climate.Item Open Access Optimizing the isoprene emission model MEGAN with satellite and ground-based observational constraints(American Geophysical Union (AGU) - Wiley, 2023-02-02) DiMaria, Christian A.; Jones, Dylan B. A.; Worden, Helen; Bloom, A. Anthony; Bowman, Kevin; Stavrakou, Trissevgeni; Miyazaki, Kazuyuki; Worden, John; Guenther, Alex; Sarkar, Chinmoy; Seco, Roger; Park, Jeong-Hoo; Tota, Julio; Gomes Alves, Eliane; Ferracci, ValerioIsoprene is a hydrocarbon emitted in large quantities by terrestrial vegetation. It is a precursor to several air quality and climate pollutants including ozone. Emission rates vary with plant species and environmental conditions. This variability can be modeled using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). MEGAN parameterizes isoprene emission rates as a vegetation-specific standard rate which is modulated by scaling factors that depend on meteorological and environmental driving variables. Recent experiments have identified large uncertainties in the MEGAN temperature response parameterization, while the emission rates under standard conditions are poorly constrained in some regions due to a lack of representative measurements and uncertainties in landcover. In this study, we use Bayesian model-data fusion to optimize the MEGAN temperature response and standard emission rates using satellite- and ground-based observational constraints. Optimization of the standard emission rate with satellite constraints reduced model biases but was highly sensitive to model input errors and drought stress and was found to be inconsistent with ground-based constraints at an Amazonian field site, reflecting large uncertainties in the satellite-based emissions. Optimization of the temperature response with ground-based constraints increased the temperature sensitivity of the model by a factor of five at an Amazonian field site but had no impact at a UK field site, demonstrating significant ecosystem-dependent variability of the isoprene emission temperature sensitivity. Ground-based measurements of isoprene across a wide range of ecosystems will be key for obtaining an accurate representation of isoprene emission temperature sensitivity in global biogeochemical models.Item Open Access Production and stability of low amount fraction of formaldehyde in hydrogen gas standards(Elsevier, 2018-03-03) Bacquart, Thomas; Perkins, Mark; Ferracci, Valerio; Martin, Nicholas A.; Resner, Kate; Ward, Michael K. M.; Cassidy, Nathan; Hook, Joshua B.; Brewer, Paul J.; Irvine, John T. C.; Connor, Paul A.; Murugan, ArulFormaldehyde is an intermediate of the steam methane reforming process for hydrogen production. According to International Standard ISO 14687-2 the amount fraction level of formaldehyde present in hydrogen supplied to fuel cell electric vehicles (FCEV) must not exceed 10 nmol mol−1. The development of formaldehyde standards in hydrogen is crucial to validate the analytical results and ensure measurement reliability for the FCEV industry. NPL demonstrated that these standards can be gravimetrically prepared and validated at 10 μmol mol−1 with a shelf-life of 8 weeks (stability uncertainty <10%; k = 1), but that formaldehyde degrades into methanol and dimethoxymethane, as measured by FTIR, GC-MS and SIFT-MS. The degradation kinetics is more rapid than predicted by thermodynamics, this may be due to the internal gas cylinder surface acting as a catalyst. The identification of by-products (methanol and dimethoxymethane) requires further investigation to establish any potential undesirable impacts to the FCEV.Item Open Access Revisiting the concentration observations and source apportionment of atmospheric ammonia(Springer, 2020-08-13) Pan, Yuepeng; Gu, Mengna; He, Yuexin; Wu, Dianming; Liu, Chunyan; Song, Linlin; Tian, Shili; Lü, Xuemei; Sun, Yang; Song, Tao; Walters, Wendell W.; Liu, Xuejun; Martin, Nicholas A.; Zhang, Qianqian; Fang, Yunting; Ferracci, Valerio; Wang, YuesiWhile China’s Air Pollution Prevention and Control Action Plan on particulate matter since 2013 has reduced sulfate significantly, aerosol ammonium nitrate remains high in East China. As the high nitrate abundances are strongly linked with ammonia, reducing ammonia emissions is becoming increasingly important to improve the air quality of China. Although satellite data provide evidence of substantial increases in atmospheric ammonia concentrations over major agricultural regions, long-term surface observation of ammonia concentrations are sparse. In addition, there is still no consensus on whether agricultural or non-agricultural emissions dominate the urban ammonia budget. Identifying the ammonia source by nitrogen isotope helps in designing a mitigation strategy for policymakers, but existing methods have not been well validated. Revisiting the concentration measurements and identifying source apportionment of atmospheric ammonia is thus an essential step towards reducing ammonia emissions.Item Open Access ROOOH: the missing piece of the puzzle for OH measurements in low NO environments(European Geosciences Union (EGU) / Copernicus Publications, 2019-01-10) Fittschen, Christa; Al Ajami, Mohamad; Batut, Sebastien; Ferracci, Valerio; Archer-Nicholls, Scott; Archibald, Alexander T.; Schoemaecker, CoralieField campaigns have been carried out with the FAGE (fluorescence assay by gas expansion) technique in remote biogenic environments in the last decade to quantify the in situ concentrations of OH, the main oxidant in the atmosphere. These data have revealed concentrations of OH radicals up to a factor of 10 higher than predicted by models, whereby the disagreement increases with decreasing NO concentration. This was interpreted as a major lack in our understanding of the chemistry of biogenic VOCs (volatile organic compounds), particularly isoprene, which are dominant in remote pristine conditions. But interferences in these measurements of unknown origin have also been discovered for some FAGE instruments: using a pre-injector, all ambient OH is removed by fast reaction before entering the FAGE cell, and any remaining OH signal can be attributed to an interference. This technique is now systematically used for FAGE measurements, allowing the reliable quantification of ambient OH concentrations along with the signal due to interference OH. However, the disagreement between modelled and measured high OH concentrations of earlier field campaigns as well as the origin of the now-quantifiable background OH is still not understood. We present in this paper the compelling idea that this interference, and thus the disagreement between model and measurement in earlier field campaigns, might be at least partially due to the unexpected decomposition of a new class of molecule, ROOOH, within the FAGE instruments. This idea is based on experiments, obtained with the FAGE set-up of the University of Lille, and supported by a modelling study. Even though the occurrence of this interference will be highly dependent on the design and measurement conditions of different FAGE instruments, including ROOOH in atmospheric chemistry models might reflect a missing piece of the puzzle in our understanding of OH in clean atmospheres.Item Open Access Understanding sources and drivers of size-resolved aerosol in the High Arctic islands of Svalbard using a receptor model coupled with machine learning(American Chemical Society, 2022-07-25) Song, Congbo; Becagli, Silvia; Beddows, David C. S.; Brean, James; Browse, Jo; Dai, Qili; Dall'Osto, Manuel; Ferracci, Valerio; Harrison, Roy M.; Harris, Neil; Li, Weijun; Jones, Anna E.; Kirchgäßner, Amelie; Kramawijaya, Agung Ghani; Kurganskiy, Alexander; Lupi, Angelo; Mazzola, Mauro; Severi, Mirko; Traversi, Rita; Shi, ZongboAtmospheric aerosols are important drivers of Arctic climate change through aerosol–cloud–climate interactions. However, large uncertainties remain on the sources and processes controlling particle numbers in both fine and coarse modes. Here, we applied a receptor model and an explainable machine learning technique to understand the sources and drivers of particle numbers from 10 nm to 20 μm in Svalbard. Nucleation, biogenic, secondary, anthropogenic, mineral dust, sea salt and blowing snow aerosols and their major environmental drivers were identified. Our results show that the monthly variations in particles are highly size/source dependent and regulated by meteorology. Secondary and nucleation aerosols are the largest contributors to potential cloud condensation nuclei (CCN, particle number with a diameter larger than 40 nm as a proxy) in the Arctic. Nonlinear responses to temperature were found for biogenic, local dust particles and potential CCN, highlighting the importance of melting sea ice and snow. These results indicate that the aerosol factors will respond to rapid Arctic warming differently and in a nonlinear fashion.