Search

Biomass burning is a growing alternative to fossil fuels for power generation.

Complying with stricter emissions standards, a new generation of heavy-duty trucks (HDTs) has gradually increased its market share and now accounts for a large percentage of on-road mileage. The potential to improve air quality depends on an actual reduction in both emissions and subsequent formation of secondary pollutants. In this study, the emissions in real-world traffic from Euro VI-compliant HDTs were compared to those from older classes, represented by Euro V, using high-resolution time-of-flight chemical ionization mass spectrometry. Gas-phase primary emissions of several hundred species were observed for 70 HDTs. Furthermore, the particle phase and secondary pollutant formation (gas and particle phase) were evaluated for a number of HDTs. The reduction in primary emission factors (EFs) was evident (∼90%) and in line with a reduction of 28–97% for the typical regulated pollutants. Secondary production of most gas- and particle-phase compounds, for example, nitric acid, organic acids, and carbonyls, after photochemical aging in an oxidation flow reactor exceeded the primary emissions (EFAged/EFFresh ratio ≥2). Byproducts from urea-selective catalytic reduction systems had both primary and secondary sources. A non-negative matrix factorization analysis highlighted the issue of vehicle maintenance as a remaining concern. However, the adoption of Euro VI has a significant positive effect on emissions in real-world traffic and should be considered in, for example, urban air quality assessments., When more stringent Euro VI emission standards replaced Euro V standards, the emissions and secondary formation of both regulated and non-regulated air pollutants reduced significantly.

University student wellbeing is increasingly seen as a concern, and as demands on university staff time for research, teaching, leadership and pastoral support also increase, this is mirrored in concerns about staff wellbeing. Dominant sectoral narratives frame student and staff wellbeing as oppositional, with initiatives to support student wellbeing positioned as creating additional practical and emotional demands on staff time and resources. Using a large qualitative dataset collected in the UK, including staff and students, this paper argues that that this does not have to be the case. Instead, there is a need to look beyond the provision of reactive services or isolated individual interventions, to proactively and cohesively embed cultural and structural change across the whole institution to support positive wellbeing outcomes for the whole university community. We report on the intrinsic interconnection between staff and student wellbeing; the importance of formal institutional policies in supporting or impeding staff and student wellbeing; access to training interventions to support staff and student wellbeing as a practical manifestation of these policies; and the impact of workplace culture and the centrality of compassion and community. The paper finds that it is important that institutions within higher education acknowledge and respond proactively to both staff and student wellbeing issues. To do so, institutions should seek to foster a sustainable and effective academic environment with a whole university approach.

Aromatic hydrocarbons are a class of volatile organic compounds associated with anthropogenic activity and make up a significant fraction of urban volatile organic compound (VOC) emissions that contribute to the formation of secondary organic aerosol (SOA). Benzene is one of the most abundant species emitted from vehicles, biomass burning and industry. An iodide time-of-flight chemical ionisation mass spectrometer (ToF-CIMS) and nitrate ToF-CIMS were deployed at the Julich Plant Atmosphere Chamber as part of a series of experiments examining benzene oxidation by OH under high- and low-NO x conditions, where a range of organic oxidation products were detected. The nitrate scheme detects many oxidation products with high masses, ranging from intermediate volatile organic compounds (IVOCs) to extremely low volatile organic compounds (ELVOCs), including C 12 dimers. In comparison, very few species with C ≥6 and O ≥8 were detected with the iodide scheme, which detected many more IVOCs and semi-volatile organic compounds (SVOCs) but very few ELVOCs and low volatile organic compounds (LVOCs). A total of 132 and 195 CHO and CHON oxidation products are detected by the iodide ToF-CIMS in the low- and high-NO x experiments respectively. Ring-breaking products make up the dominant fraction of detected signal and 21 and 26 of the products listed in the Master Chemical Mechanism (MCM) were detected. The time series of highly oxidised (O ≥6 ) and ring-retaining oxidation products (C 6 and double-bond equivalent = 4) equilibrate quickly, characterised by a square form profile, compared to MCM and ring-breaking products which increase throughout oxidation, exhibiting sawtooth profiles. Under low-NO x conditions, all CHO formulae attributed to radical termination reactions of first-generation benzene products, and first-generation auto-oxidation products are observed. Several N-containing species that are either first-generation benzene products or first-generation auto-oxidation products are also observed under high-NO x conditions. Hierarchical cluster analysis finds four clusters, of which two describe photo-oxidation. Cluster 2 shows a negative dependency on the NO 2 / NO x ratio, indicating it is sensitive to NO concentration and thus likely to contain NO addition products and alkoxy-derived termination products. This cluster has the highest average carbon oxidation state ( OS C ‾ ) and the lowest average carbon number. Where nitrogen is present in a cluster member of cluster 2, the oxygen number is even, as expected for alkoxy-derived products. In contrast, cluster 1 shows no dependency on the NO 2 / NO x ratio and so is likely to contain more NO 2 addition and peroxy-derived termination products. This cluster contains fewer fragmented species, as the average carbon number is higher and OS C ‾ lower than cluster 2, and more species with an odd number of oxygen atoms. This suggests that clustering of time series which have features pertaining to distinct chemical regimes, for example, NO 2 / NO x perturbations, coupled with a priori knowledge, can provide insight into identification of potential functionality.

Organic aerosols, a major constituent of fine particulate mass in megacities, can be directly emitted or formed from secondary processing of biogenic and anthropogenic volatile organic compound emissions. The complexity of volatile organic compound emission sources, speciation and oxidation pathways leads to uncertainties in the key sources and chemistry leading to formation of organic aerosol in urban areas. Historically, online measurements of organic aerosol composition have been unable to resolve specific markers of volatile organic compound oxidation, while offline analysis of markers focus on a small proportion of organic aerosol and lack the time resolution to carry out detailed statistical analysis required to study the dynamic changes in aerosol sources and chemistry. Here we use data collected as part of the joint UK-China Air Pollution and Human Health (APHH-Beijing) collaboration during a field campaign in urban Beijing in the summer of 2017 alongside laboratory measurements of secondary organic aerosol from oxidation of key aromatic precursors (1,3,5-Trimethyl benzene, 1,2,4-Trimethyl benzene, propyl benzene, isopropyl benzene and 1-methyl naphthalene) to study the anthropogenic and biogenic contributions to organic aerosol. For the first time in Beijing, this study applies positive matrix factorisation to online measurements of organic aerosol composition from a time-of-flight iodide chemical ionisation mass spectrometer fitted with a filter inlet for gases and aerosols (FIGAERO-ToF-I-CIMS). This approach identifies the real-Time variations in sources and oxidation processes influencing aerosol composition at a near-molecular level. We identify eight factors with distinct temporal variability, highlighting episodic differences in OA composition attributed to regional influences and in situ formation. These have average carbon numbers ranging from C5-C9 and can be associated with oxidation of anthropogenic aromatic hydrocarbons alongside biogenic emissions of isoprene, α-pinene and sesquiterpenes. This journal is

A series of experiments of NO3 radical initiated oxidation of monoterpenes (C10H16) were conducted using an oxidation flow reactor (Go:PAM) combined with an iodide high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS). This study characterized the major organonitrate products from NO3 radical initiated oxidation of Δ‑3-Carene with various levels of oxidation, i.e. by increasing the concentration of NO3. C10 monomers (products with 10 carbons) are generally the dominant products of Δ‑3-carene (e.g. C10H15NO7 and C10H17NO5); but where higher oxidant levels enhance fragmentation. In comparison to α-pinene, the Δ‑3-carene oxidation has a higher propensity to create low volatile species, i.e. promote aerosol formation, mechanistically explained by difference in alkoxy radical (RO) bond scissions. A kinetic model (using FACSIMILE) was developed to simulate the formation of dominant products. The mechanism was based on analogue systems within the Master Chemical Mechanism (MCM) and recently available literature. The fate of RO2 under different chemical regimes was also investigated by comparing model runs and the experimental results.

Whilst existing evidence has demonstrated the imperative of social integration, inclusion, and belonging for student mental health, students often report relational challenges, barriers, and stressors at university. Drawing on thematic analysis of six student co-creation panels conducted during the Student Minds University Mental Health Charter consultations, this paper aims to elucidate student perspectives and proposals for promoting mental health at university by enhancing interpersonal interactions and social relationships. In particular, student panels identified existing challenges and opportunities to address social isolation, conflict, and exclusion in interactions with peers, academic staff, and the local community. The findings of this paper both echo and develop the principles of good practice propounded by the University Mental Health Charter, whilst the implications for university policy in the context of the Covid-19 pandemic are also discussed.

Oxidation of isoprene by nitrate radicals (NO3) or by hydroxyl radicals (OH) under high NOx conditions forms a substantial amount of organonitrates (ONs). ONs impact NOx concentrations and consequently ozone formation while also contributing to secondary organic aerosol. Here we show that the ONs with the chemical formula C4H7NO5 are a significant fraction of isoprene-derived ONs, based on chamber experiments and ambient measurements from different sites around the globe. From chamber experiments we found that C4H7NO5 isomers contribute 5%–17% of all measured ONs formed during nighttime and constitute more than 40% of the measured ONs after further daytime oxidation. In ambient measurements C4H7NO5 isomers usually dominate both nighttime and daytime, implying a long residence time compared to C5 ONs which are removed more rapidly. We propose potential nighttime sources and secondary formation pathways, and test them using a box model with an updated isoprene oxidation scheme.

Field experiments were undertaken in the summer of 2015 in Manchester, UK, to investigate the dispersion behaviour and infiltration into buildings of gas-phase pollutants over horizontal distances of 1–5 km. Inert cyclic perfluorocarbon tracers were released for 15 min at either one or three release points and samples taken in locations indoors and outdoors up to 2 km downwind. Background measurements of these cyclic perfluorocarbons range between 5.6 and 12.6 parts per quadrillion (ppq). On most occasions, tracer concentrations are higher on the sixth floor than at ground level. Tracer concentrations persist in the least well-ventilated rooms after concentrations return to background levels outdoors. The highest tracer concentrations, 329 ppq above background, occur at dawn on 23 July from a sixth-floor sampling position during thermally stable conditions. At low wind speeds, tracer is detected upwind of the prevailing wind direction; on 24 July, tracer is detected to the north-west of the release point for north-north-east wind direction. A simple street network model does not predict tracer concentrations at low wind speeds over the km scales in this investigation due to tracer likely escaping the urban canopy. Predictions from a simple correlation model overestimate concentrations originating from distant sources, which is believed to be due to infiltration into buildings along the journey from source to receptor. A Gaussian plume model predicts the highest tracer concentrations for most receptor points on 23 July when the lowest Obukhov length of – 26 m was measured, agreeing with tracer measurements.

Background:\ud Well-being is a multifaceted construct, and measuring well-being, both within particular groups and at a national level, is a priority for policy and practice. This national agenda on measuring well-being is mirrored in the Higher Education sector. This is the first conceptual review of how well-being is measured among university students in the UK.\ud \ud Aims:\ud The aims of the review were to identify (i) the definitions or conceptualisations of well-being guiding the selection of well-being indicators for research within this population and (ii) measures of well-being used in university students in the UK.\ud \ud Methods:\ud A scoping review method was used.\ud \ud Results:\ud Twenty-eight validated indicators used to measure well-being in UK students were identified. While many were direct measures of (primarily mental or psychological) well-being, indirect “proxy” indicators, including measures of mental health symptoms, were identified.\ud \ud Conclusions:\ud This review has highlighted that there are inconsistencies in defining and measuring university student well-being, and the measures that have been used in this population are focused on subjective experience. These findings are in line with reviews of well-being measures in the general population. Implications for further research are discussed.

Drawing on thematic analysis of six student co‐creation panels, conducted during the Student Minds University Mental Health Charter consultations, this paper elucidates students’ perspectives and proposals regarding the current issues and challenges around university student mental health and well‐being support services. In particular, panels identified existing challenges and opportunities to improve support service access, strategy, and delivery. The panels generated a series of recommendations aimed to establish a clear, coordinated, and strategic approach to delivering accessible and inclusive student mental health support services that are responsive to the diverse needs of the whole student population. Significantly, the student panels situated service reforms within a ‘whole university approach’ entailing holistic structural and cultural change to the university environment, in order to enrich student mental health and well‐being and reduce demand on services. The findings of this paper can both reaffirm and specify the principles of good practice propounded by the University Mental Health Charter from a student perspective.

This paper draws on staff and student consultations conducted during the development of Student Minds’ University Mental Health Charter to identify five key tensions which can arise in assessment design and strategy when seeking to balance the wellbeing of students with pedagogical, practical and policy considerations. It highlights the need to acknowledge the pressures of assessment on staff wellbeing as well as students. The particular tensions explored include the need to balance challenge against the psychological threats this can entail; the varying impacts of traditional and novel forms of assessment; the differing demands of collaborative and individual work; the tensions between ideal strategies and those which are practically feasible; and the ways in which feedback is given (as a constructive learning tool) and received (often as a psychological threat). These tensions can provide a valuable point of reflection for educators who need to critically and proactively navigate these conflicts within their own assessment design and practices, as part of a wider whole university approach to promoting student wellbeing.

Nitro-aromatic compounds (NACs) were measured hourly at a rural site in China during wintertime to monitor the changes due to local and regional impacts of biomass burning (BB). Concurrent and continuous measurements of the concentrations of 16 NACs in the gas and particle phases were performed with a time-of-flight chemical ionization mass spectrometer (CIMS) equipped with a Filter Inlet for Gases and AEROsols (FIGAERO) unit using iodide as the reagent ion. NACs accounted for <2 % of the mass concentration of organic matter (OM) and total particulate matter (PM), but the total particle mass concentrations of these compounds can reach as high as 1000 ng m−3 (299 ng m−3 avg), suggesting that they may contribute significantly to the radiative forcing effects of atmospheric particles. Levels of gas-phase NACs were highest during the daytime (15:00–16:00 local time, LT), with a smaller night-time peak around 20:00 LT. Box-model simulations showed that this occurred because the rate of NAC production from gas-phase sources exceeded the rate of loss, which occurred mainly via the OH reaction and to a lesser degree via photolysis. Data gathered during extended periods with high contributions from primary BB sources (resulting in 40 %–60 % increases in NAC concentrations) were used to characterize individual NACs with respect to gas–particle partitioning and the contributions of regional secondary processes (i.e. photochemical smog). On days without extensive BB, secondary formation was the dominant source of NACs, and NAC levels correlated strongly with the ambient ozone concentration. Analyses of individual NACs in the regionally aged plumes sampled on these days allowed precursors such as phenol and catechol to be linked to their NAC derivatives (i.e. nitrophenol and nitrocatechol). Correlation analysis using the high time resolution data and box-model simulation results constrained the relationships between these compounds and demonstrated the contribution of secondary formation processes. Furthermore, 13 of 16 NACS were classified according to primary or secondary formation process. Primary emission was the dominant source (accounting for 60 %–70 % of the measured concentrations) of 5 of the 16 studied NACs, but secondary formation was also a significant source. Photochemical smog thus has important effects on brown carbon levels even during wintertime periods dominated by primary air pollution in rural China.

Aromatic hydrocarbons are a class of volatile organic compounds associated with anthropogenic activity and make up a significant fraction of urban VOC emissions that contribute to the formation of secondary organic aerosol (SOA). Benzene is one of the most abundant species emitted from vehicles, biomass burning and industry. An iodide time of flight chemical ionisation mass spectrometer (ToF-CIMS) and nitrate ToF-CIMS were deployed at the Jülich plant chamber as part of a series of experiments examining benzene oxidation by OH under high and low NOx conditions, where a range of organic oxidation products were detected. The nitrate scheme detects many oxidation products with high masses ranging from intermediate volatile organic compounds (IVOC) to extremely low volatile organic compounds (ELVOC), including C12 dimers. In comparison, very few species with C≥6 and O≥8 were detected with the iodide scheme, which detected many more IVOC and semi volatile organic compounds (SVOC) but very few ELVOC and low volatile organic compounds (LVOC). 132 and 195 CHO and CHON oxidation products are detected by the iodide ToF-CIMS in the low and high NOx experiments respectively. Ring breaking products make up the dominant fraction of detected signal (89–91 %). 21 and 26 of the products listed in the master chemical mechanism (MCM) were detected and account for 6.4–7.3 % of total signal. The time series of highly oxidised (O≥6) and ring retaining oxidation products (C6 and double bond equivalent = 4) equilibrate quickly characterised by a square form profile, compared to MCM and ring breaking products which increase throughout oxidation exhibiting saw tooth profiles. Under low NOx conditions, all CHO formulae attributed to radical termination reactions of 1st generation benzene products and 1st generation autoxidation products are observed, and one exclusively 2nd generation autoxidation product is also measured (C6H8O8). Several N containing species that are either 1st generation benzene products or 1st generation autoxidation products are also observed under high NOx conditions. Hierarchical cluster analysis finds four cluster of which two describe photo-oxidation. Cluster 2 shows a negative dependency on the NO2/NOx ratio indicating it is sensitive to NO concentration thus likely to contain NO addition products and alkoxy derived termination products. This cluster has the highest average carbon oxidation state (OSc) and the lowest average carbon number and where nitrogen is present in cluster member, the oxygen number is even, as expected for alkoxy derived products. In contrast, cluster 1 shows no dependency on the NO2/NOx ratio and so is likely to contain more NO2 addition and peroxy derived termination products. This cluster contains less fragmented species, as the average carbon number is higher and OSc lower than cluster 2, and more species with an odd number of oxygen atoms. This suggests clustering of time series which have features pertaining to distinct chemical regimes e.g. NO2/NOx perturbations, coupled with a priori knowledge, can provide insight into identification of potential functionality.

Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene ‘scavenges’ hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production). Adding reactive gases such as isoprene to mixtures lowers the production of secondary organic aerosol in the atmosphere, thus reducing the atmospheric particulate burden, with implications for human health and climate.

Aromatic volatile organic compounds (VOC) are key anthropogenic pollutants emitted to the atmosphere and are important for both ozone and secondary organic aerosol (SOA) formation in urban areas. Recent studies have indicated that aromatic hydrocarbons may follow previously unknown oxidation chemistry pathways, including autoxidation that can lead to the formation of highly oxidised products. In this study we evaluate the gas and particle phase ions formed during the hydroxyl radical oxidation of substituted C9-aromatic isomers (1,3,5-trimethyl benzene, 1,2,4-trimethyl benzene, propyl benzene and isopropyl benzene) and a substituted polyaromatic hydrocarbon (1-methyl naphthalene) under low and medium NOx conditions. The majority of product signal in both gas and particle phases comes from ions which are common to all precursors, though signal distributions are distinct for different VOCs. Gas and particle phase composition are distinct from one another, and comparison with the near explicit gas phase Master Chemical Mechanism (MCMv3.3.1) highlights a range of missing highly oxidised products in the pathways. In the particle phase, the bulk of product signal from all precursors comes from ring scission ions, many of which have undergone further oxidation to form HOMs. Under perturbation of OH oxidation with increased NOx, the contribution of HOM ion signals to the particle phase signal remains elevated for more substituted aromatic precursors. Up to 25 % of product signal comes from ring-retaining ions including highly oxygenated organic molecules (HOMs); this is most important for the more substituted aromatics. Unique products are a minor component in these systems, and many of the dominant ions have ion formulae concurrent with other systems, highlighting the challenges in utilising marker ions for SOA.

Nitryl chloride (ClNO2) accumulation at night acts as a significant reservoir for active chlorine and impacts the following day's photochemistry when the chlorine atom is liberated at sunrise. Here, we report simultaneous measurements of N2O5 and a suite of inorganic halogens including ClNO2 and reactions of chloride with volatile organic compounds (Cl–VOCs) in the gas and particle phases utilising the Filter Inlet for Gas and AEROsols time-of-flight chemical ionisation mass spectrometer (FIGAERO-ToF-CIMS) during an intensive measurement campaign 40 km northwest of Beijing in May and June 2016. A maximum mixing ratio of 2900 ppt of ClNO2 was observed with a mean campaign nighttime mixing ratio of 487 ppt, appearing to have an anthropogenic source supported by correlation with SO2, CO and benzene, which often persisted at high levels after sunrise until midday. This was attributed to such high mixing ratios persisting after numerous e-folding times of the photolytic lifetime enabling the chlorine atom production to reach 2.3 × 105 molecules cm−3 from ClNO2 alone, peaking at 09:30 LT and up to 8.4 × 105 molecules cm−3 when including the supporting inorganic halogen measurements.Cl–VOCs were observed in the particle and gas phases for the first time at high time resolution and illustrate how the iodide ToF-CIMS can detect unique markers of chlorine atom chemistry in ambient air from both biogenic and anthropogenic sources. Their presence and abundance can be explained via time series of their measured and steady-state calculated precursors, enabling the assessment of competing OH and chlorine atom oxidation via measurements of products from both of these mechanisms and their relative contribution to secondary organic aerosol (SOA) formation.

The heterogeneous hydrolysis of dinitrogen pentoxide ( N2O5 ) has a significant impact on both nocturnal particulate nitrate formation and photochemistry on the following day through the photolysis of nitryl chloride ( ClNO2 ), yet these processes in highly polluted urban areas remain poorly understood. Here we present measurements of gas-phase N2O5 and ClNO2 by high-resolution time-of-flight chemical ionization mass spectrometer (ToF-CIMS) during summer in urban Beijing, China as part of the Air Pollution and Human Health (APHH) campaign. N2O5 and ClNO2 show large day-to-day variations with average ( ±1σ) mixing ratios of 79.2±157.1 and 174.3±262.0 pptv, respectively. High reactivity of N2O5 , with τ ( N2 O 5)−1 ranging from 0.20 × 10 −2 to 1.46 × 10 −2 s −1 , suggests active nocturnal chemistry and a large nocturnal nitrate formation potential via N2O5 heterogeneous uptake. The lifetime of N2O5 , τ ( N2O5 ), decreases rapidly with the increase in aerosol surface area, yet it varies differently as a function of relative humidity with the highest value peaking at ∼ 40 %. The N2O5 uptake coefficients estimated from the product formation rates of ClNO2 and particulate nitrate are in the range of 0.017–0.19, corresponding to direct N2O5 loss rates of 0.00044–0.0034 s −1 . Further analysis indicates that the fast N2O5 loss in the nocturnal boundary layer in urban Beijing is mainly attributed to its indirect loss via NO3 , for example through the reactions with volatile organic compounds and NO, while the contribution of the heterogeneous uptake of N2O5 is comparably small (7–33 %). High ClNO2 yields ranging from 0.10 to 0.35 were also observed, which might have important implications for air quality by affecting nitrate and ozone formation.

This paper outlines the structure and usage of the GenChem system, which includes a chemical pre-processor GenChem.py) and a simple box model (boxChem). GenChem provides scripts and input files for converting chemical equations into differential form for use in atmospheric chemical transport models (CTMs) and/or the boxChem system. Although GenChem is primarily intended for users of the Meteorological Synthesizing Centre – West of the European Monitoring and Evaluation Programme (EMEP MSC-W) CTM and related systems, boxChem can be run as a stand-alone chemical solver, enabling for example easy testing of chemical mechanisms against each other. This paper presents an outline of the usage of the GenChem system, explaining input and output files, and presents some examples of usage. The code needed to run GenChem is released as open-source code under the GNU license.

Recent studies have recognized highly oxygenated organic molecules (HOM) in the atmosphere as important in the formation of secondary organic aerosol (SOA). A large number of studies have focused on HOM formation from oxidation of biogenically emitted monoterpenes. However, HOM formation from anthropogenic vapours has so far received much less attention. Previous studies have identified the importance of aromatic volatile organic compounds (VOC) for SOA formation. In this study, we investigated several aromatic compounds, benzene (C6H6), toluene (C7H8), and naphthalene (C10H8), for their potential to form HOM upon reaction with hydroxyl radicals (OH). We performed flow tube experiments with all three VOC, and focused in detail on benzene HOM formation in the Jülich Plant Atmosphere Chamber (JPAC). In JPAC, we also investigated the response of HOM to NOx and seed aerosol. Using a nitrate-based chemical ionization mass spectrometer (CI-APi-TOF), we observed the formation of HOM in the flow reactor oxidation of benzene from the first OH attack. However, in the oxidation of toluene and naphthalene, which were injected at lower concentrations, multi-generation OH oxidation seemed to impact the HOM composition. We tested this in more detail for the benzene system in the JPAC, which allowed for studying longer residence times. The results showed that the apparent molar benzene HOM yield under our experimental conditions varied from 4.1 to 14.0 %, with a strong dependence on the OH concentration, indicating that the majority of observed HOM formed through multiple OH-oxidation steps. The composition of the identified HOM in the mass spectrum also supported this hypothesis. By injecting only phenol into the chamber, we found that phenol oxidation cannot be solely responsible for the observed HOM in benzene experiments. When NOx was added to the chamber, HOM composition changed and many oxygenated nitrogen-containing products were observed in CI-APi-TOF. Upon seed aerosol injection, the HOM loss rate was higher than predicted by irreversible condensation, suggesting that some undetected oxygenated intermediates also condensed onto seed aerosol, which is in line with the hypothesis of multi-generation HOM. Based on our results that HOM yield and composition in aromatic systems strongly depend on OH and VOC concentration, we conclude that atmospheric models should account for such dependency and the chemical regime when implementing the quantitative results of laboratory studies. We also suggest that the dependence of HOM yield on chamber conditions may explain part of the variability in SOA yields reported in the literature.

Knudsen Effusion Mass Spectrometry (KEMS) was used to find the solid state vapour pressures of a range of atmospherically relevant organic molecules from 298K to 333K. The selection of species analysed allowed for the effect of structural isomerism, specifically positional isomerism, and stereoisomerism, specifically geometric isomerism, on solid state vapour pressure to be investigated. In addition, the effect of varying the number of carboxylic acid groups present within a molecule’s structure, and of varying alkyl chain length was also assessed. The solid state vapour pressures were converted to subcooled liquid vapour pressures using experimental heat of fusion and melting point values. The resulting subcooled liquid vapour pressures were found to be up to 7 orders of magnitude lower than the vapour pressures estimated from models. Some of this variation between experimentally determined subcooled liquid vapour pressures and predicted vapour pressures, which use group contribution methods, can be attributed to the effects of isomerism which are largely not taken into account in models. Whilst these techniques might have both structural and parametric uncertainties, of the compound classes tested, a general inverse relationship between melting point and solid state vapour pressure was observed. Within each compound class the variations in vapour pressure can be attributed to the number and size of functional groups present and the relative positions of those functional groups to each other both positionally and geometrically. These two factors impact upon both the molecules’ dipole moments and upon their ability to interact both intramolecularly and intermolecularly via hydrogen bonding, thus explaining the differences in observed vapour pressure. Partitioning calculations using a range of condensed mass loadings show that whilst using vapour pressure values derived from models would put most of the compounds in the vapour phase, using the experimental values obtained here would mean a significant fraction of the organic molecules would be in the condensed phase. This could have a significant impact upon the formation and nature of atmospheric aerosol and comparisons with ambient data obtained from other mass spectrometry techniques during bonfire night in Manchester in 2016 are made in an attempt to assess this potential atmospheric importance.

Nitryl chloride (ClNO 2) acts as a source of highly reactive chlorine atoms as well as an important NO x reservoir. Measurements of ClNO 2 at an operational U.K. landfill site are reported here for the first time. A peak concentration of 4 ppb of ClNO 2 was found with a peak mean nighttime maximum of 0.9 ppb. Using models based upon the photolysis of observed ClNO 2 and atmospheric chlorine chemistry, chlorine atom concentrations reaching in excess of 1.20 × 10 5 molecules/cm 3 in the early morning following sunrise are calculated. These concentrations are approximately 10 times higher than previously reported in the United Kingdom, suggesting a significant impact on the oxidizing capacity around such sites. Given the ubiquity of landfill sites regionally and globally, and the large abundances of Cl atoms from the photolysis of ClNO 2, chlorine chemistry has a significant impact on ozone formation and volatile organic compounds oxidation as shown by WRF-Chem modeling.

A number of inorganic (nitryl chloride, ClNO2; chlorine, Cl2; and hypochlorous acid, HOCl) and chlorinated, oxygenated volatile organic compounds (ClOVOCs) have been measured in Manchester, UK during October and November 2014 using time-of-flight chemical ionisation mass spectrometry (ToF-CIMS) with the I− reagent ion. ClOVOCs appear to be mostly photochemical in origin, although direct emission from vehicles is also suggested. Peak concentrations of ClNO2, Cl2 and HOCl reach 506, 16 and 9 ppt respectively. The concentrations of ClNO2 are comparable to measurements made in London, but measurements of ClOVOCs, Cl2 and HOCl by this method are the first reported in the UK. Maximum HOCl and Cl2 concentrations are found during the day and ClNO2 concentrations remain elevated into the afternoon if photolysis rates are low. Cl2 exhibits a strong dependency on shortwave radiation, further adding to the growing body of evidence that it is a product of secondary chemistry. However, night-time emission is also observed. The contribution of ClNO2, Cl2 and ClOVOCs to the chlorine radical budget suggests that Cl2 can be a greater source of Cl than ClNO2, contributing 74 % of the Cl radicals produced on a high radiant-flux day. In contrast, on a low radiant-flux day, this drops to 14 %, as both Cl2 production and loss pathways are inhibited by reduced photolysis rates. This results in ClNO2 making up the dominant fraction (83 %) on low radiant-flux days, as its concentrations are still high. As most ClOVOCs appear to be formed photochemically, they exhibit a similar dependence on photolysis, contributing 3 % of the Cl radical budget observed here.