Environmental Chamber Experiments Research Articles

Advancing characterization of VOC diffusion in indoor fabrics: A dual-porosity modeling approach

Volatile organic compounds (VOCs) are major chemical pollutants in indoor air. Indoor fabrics, such as curtains, carpets, sofas, and clothes, strongly adsorb VOCs due to their high loading rates and large specific surface areas. The desorption of VOCs from these fabrics can act as a secondary source, worsening indoor air pollution and prolonging its effects. The diffusion coefficient is a key parameter that determines the source-sink properties of fabrics. In this study, the VOC diffusion characteristics in fabrics were investigated through microstructural examination, mass transfer analysis, and environmental chamber experiments. Yarn and fiber gaps were identified as dual mass transfer channels within the fabrics and were represented using two distinct fractal models. A dual-porosity medium (DPM) model, based on these fractal representations, was developed to predict the VOC diffusion coefficients in indoor fabrics and was validated via experiments under various environmental conditions and fabric-VOC combinations. The results highlight the significant impact of fabric structure and composition on VOC adsorption and emission dynamics. The validated DPM model provides a comprehensive approach to predicting VOC diffusion in fabrics, providing a more accurate method for assessing indoor air quality and fabric-mediated human exposure.

Can we achieve atmospheric chemical environments in the laboratory? An integrated model-measurement approach to chamber SOA studies.

Secondary organic aerosol (SOA), atmospheric particulate matter formed from low-volatility products of volatile organic compound (VOC) oxidation, affects both air quality and climate. Current 3D models, however, cannot reproduce the observed variability in atmospheric organic aerosol. Because many SOA model descriptions are derived from environmental chamber experiments, our ability to represent atmospheric conditions in chambers directly affects our ability to assess the air quality and climate impacts of SOA. Here, we develop an approach that leverages global modeling and detailed mechanisms to design chamber experiments that mimic the atmospheric chemistry of organic peroxy radicals (RO2), a key intermediate in VOC oxidation. Drawing on decades of laboratory experiments, we develop a framework for quantitatively describing RO2 chemistry and show that no previous experimental approaches to studying SOA formation have accessed the relevant atmospheric RO2 fate distribution. We show proof-of-concept experiments that demonstrate how SOA experiments can access a range of atmospheric chemical environments and propose several directions for future studies.

Molecular analysis of secondary organic aerosol and brown carbon from the oxidation of indole

Abstract. Indole (ind) is a nitrogen-containing heterocyclic volatile organic compound commonly emitted from animal husbandry and from different plants like maize with global emissions of 0.1 Tg yr−1. The chemical composition and optical properties of indole secondary organic aerosol (SOA) and brown carbon (BrC) are still not well understood. To address this, environmental chamber experiments were conducted to investigate the oxidation of indole at atmospherically relevant concentrations of selected oxidants (OH radicals and O3) with or without NO2. In the presence of NO2, the SOA yields decreased by more than a factor of 2, but the mass absorption coefficient at 365 nm (MAC365) of ind-SOA was 4.3 ± 0.4 m2 g−1, which was 5 times higher than that in experiments without NO2. In the presence of NO2, C8H6N2O2 (identified as 3-nitroindole) contributed 76 % to all organic compounds detected by a chemical ionization mass spectrometer, contributing ∼ 50 % of the light absorption at 365 nm (Abs365). In the absence of NO2, the dominating chromophore was C8H7O3N, contributing to 20 %–30 % of Abs365. Indole contributes substantially to the formation of secondary BrC and its potential impact on the atmospheric radiative transfer is further enhanced in the presence of NO2, as it significantly increases the specific light absorption of ind-SOA by facilitating the formation of 3-nitroindole. This work provides new insights into an important process of brown carbon formation by interaction of two pollutants, NO2 and indole, mainly emitted by anthropogenic activities.

Chemical Composition and Optical Properties of Secondary Organic Aerosol from Photooxidation of Volatile Organic Compound Mixtures.

The chemical and optical properties of secondary organic aerosols (SOA) have been widely studied through environmental chamber experiments, and some of the results have been parametrized in atmospheric models to help understand their radiative effects and climate influence. While most chamber studies investigate the aerosol formed from a single volatile organic compound (VOC), the potential interactions between reactive intermediates derived from VOC mixtures are not well understood. In this study, we investigated the SOA formed from pure and mixtures of anthropogenic (phenol and 1-methylnaphthalene) and/or biogenic (longifolene) VOCs using continuous-flow, high-NOx photooxidation chamber experiments to better mimic ambient conditions. SOA optical properties, including single scattering albedo (SSA), mass absorption coefficient (MAC), and refractive index (RI) at 375 nm, and chemical composition, including the formation of oxygenated organic compounds, organic-nitrogen compounds (including organonitrates and nitro-organics), and the molecular structure of the major chromophores, were explored. Additionally, the imaginary refractive index values of SOA in the multi-VOC system were predicted using a linear-combination assumption and compared with the measured values. When two VOCs were oxidized simultaneously, we found evidence for changes in SOA chemical composition compared to SOA formed from single-VOC systems, and this change led to nonlinear effects on SOA optical properties. The nonlinear effects were found to vary between different systems.

Improvements of a low-cost CO2 commercial nondispersive near-infrared (NDIR) sensor for unmanned aerial vehicle (UAV) atmospheric mapping applications

Abstract. Unmanned aerial vehicles (UAVs) provide a cost-effective way to fill in gaps between surface in situ observations and remotely sensed data from space. In this study, a novel portable CO2 measuring system suitable for operations on board small-sized UAVs has been developed and validated. It is based on a low-cost commercial nondispersive near-infrared (NDIR) CO2 sensor (Senseair AB, Sweden), with a total weight of 1058 g, including batteries. The system performs in situ measurements autonomously, allowing for its integration into various platforms. Accuracy and linearity tests in the lab showed that the precision remains within ± 1 ppm (1σ) at 1 Hz. Corrections due to temperature and pressure changes were applied following environmental chamber experiments. The accuracy of the system in the field was validated against a reference instrument (Picarro, USA) on board a piloted aircraft and it was found to be ± 2 ppm (1σ) at 1 Hz and ± 1 ppm (1σ) at 1 min. Due to its fast response, the system has the capacity to measure CO2 mole fraction changes at 1 Hz, thus allowing the monitoring of CO2 emission plumes and of the characteristics of their spatial and temporal distribution. Details of the measurement system and field implementations are described to support future UAV platform applications for atmospheric trace gas measurements.

Fragment ion–functional group relationships in organic aerosols using aerosol mass spectrometry and mid-infrared spectroscopy

Abstract. Aerosol mass spectrometry (AMS) and mid-infrared spectroscopy (MIR) are two analytical methods for characterizing the chemical composition of organic matter (OM). While AMS provides high-temporal-resolution bulk measurements, the extensive fragmentation during the electron ionization makes the characterization of OM components limited. The analysis of aerosols collected on polytetrafluoroethylene (PTFE) filters using MIR, on the other hand, provides functional group information with reduced sample alteration but results in a relatively low temporal resolution. In this work, we compared and combined MIR and AMS measurements for several environmental chamber experiments of combustion-related aerosols to achieve a better understanding of the AMS spectra and the OM chemical evolution with aging. Fresh emissions of wood and coal burning were injected into an environmental simulation chamber and aged with hydroxyl and nitrate radicals. A high-resolution time-of-flight AMS measured the bulk chemical composition of fine OM. Fine aerosols were also sampled on PTFE filters before and after aging for the offline MIR analysis. After comparing AMS and MIR bulk measurements, we used multivariate statistics to identify the functional groups associated the most with the AMS OM for different aerosol sources and oxidants. We also identified the key fragment ions resulting from molecules containing each functional group for the complex OM generated from biomass and fossil fuel combustion. Finally, we developed a statistical model that enables the estimation of the high-time-resolution functional group composition of OM using collocated AMS and MIR measurements. AMS spectra can be used to interpolate the functional group measurements by MIR using this approach. The latter allows us to better understand the evolution of OM during the aging process.

Fine Ash‐Bearing Particles as a Major Aerosol Component in Biomass Burning Smoke

AbstractBiomass burning (BB) events are occurring globally with increasing frequency, and their emissions are having more impacts on human health and climate. Large ash particles are recognized as a BB product with major influences on soil and water environments. However, fine‐ash particles, which have diameters smaller than several microns and characteristic morphologies and compositions (mainly Ca and Mg carbonates), have not yet been explicitly considered as a major BB aerosol component either in field observations or climate models. This study measured BB aerosol samples using transmission electron microscopy (TEM) and ion chromatography during the Fire Influence on Regional to Global Environments and Air Quality (FIREX‐AQ) campaign. We show that significant amounts of fine ash‐bearing particles are transported >100 km from their fire sources. Our environmental chamber experiments suggest that they can act as cloud condensation and ice nuclei. We also found considerable amounts of fine ash‐bearing particles in the TEM samples collected during previous campaigns (Biomass Burning Observation Project and Megacity Initiative: Local and Global Research Observations). These ash particles are commonly mixed with organic matter and make up ∼8% and 5% of BB smoke by number and mass, respectively, in samples collected during the FIREX‐AQ campaign. The measured ash‐mass concentrations are approximately five times and six times greater than those of BB black carbon and potassium, respectively, scaling to an estimated global emission of 11.6 Tg yr−1with a range of 8.8–16.3 Tg yr−1. Better characterization and constraints on these fine ash‐bearing particles will improve BB aerosol measurements and strengthen assessments of BB impacts on human health and climate.

Wide range continuously tunable and fast thermal switching based on compressible graphene composite foams

Thermal switches have gained intense interest recently for enabling dynamic thermal management of electronic devices and batteries that need to function at dramatically varied ambient or operating conditions. However, current approaches have limitations such as the lack of continuous tunability, low switching ratio, low speed, and not being scalable. Here, a continuously tunable, wide-range, and fast thermal switching approach is proposed and demonstrated using compressible graphene composite foams. Large (~8x) continuous tuning of the thermal resistance is achieved from the uncompressed to the fully compressed state. Environmental chamber experiments show that our variable thermal resistor can precisely stabilize the operating temperature of a heat generating device while the ambient temperature varies continuously by ~10 °C or the heat generation rate varies by a factor of 2.7. This thermal device is promising for dynamic control of operating temperatures in battery thermal management, space conditioning, vehicle thermal comfort, and thermal energy storage.

Gas-Phase Chlorine Radical Oxidation of Alkanes: Effects of Structural Branching, NOx, and Relative Humidity Observed during Environmental Chamber Experiments

Chlorine-initiated oxidation of alkanes has been shown to rapidly form secondary organic aerosol (SOA) at higher yields than OH-alkane reactions. However, the effects of alkane volatile organic compound precursor structure and the reasons for the differences in SOA yield from OH-alkane reactions remain unclear. In this work, we investigated the effects of alkane molecular structure on oxidation by chlorine radical (Cl) and resulting formation of SOA through a series of laboratory chamber experiments, utilizing data from an iodide chemical ionization mass spectrometer and an aerosol chemical speciation monitor. Experiments were conducted with linear, branched, and branched cyclic C10 alkane precursors under different NOx and RH conditions. Observed product fragmentation patterns during the oxidation of branched alkanes demonstrate the abstraction of primary hydrogens by Cl, confirming a key difference between OH- and Cl-initiated oxidation of alkanes and providing a possible explanation for higher SOA production from Cl-initiated oxidation. Low-NOx conditions led to higher SOA production. SOA formed from butylcyclohexane under low NOx conditions contained higher fractions of organic acids and lower volatility molecules that were less prone to oligomerization relative to decane SOA. Branched alkanes produced less SOA, and branched cycloalkanes produced more SOA than linear n-alkanes, consistent with past work on OH-initiated reactions. Overall, our work provides insights into the differences between Cl- and OH-initiated oxidation of alkanes of different structures and the potential significance of Cl as an atmospheric oxidant.

Ecological niches of an introduced species Typha laxmannii and native Typha species in Austria

We studied fruit morphology, germination and growth of juvenile plants and clonal ramets of the non-native species Typha laxmannii and the two common native species Typha angustifolia and Typha latifolia in Lower Austria by means of morphological measurements, germination tests in an environmental test chamber and garden experiments with different water and nutrient levels. The ecological niche of T. laxmannii was close to the niches of the native species T. latifolia and T. angustifolia. All species were light-dependent and quick germinating under suitable conditions. Fruit morphology of T. laxmannii was very similar to that of T. angustifolia, but viability and germination of T. laxmannii were comparable to that of T. latifolia. All three species were profiting from higher water and nutrient levels in the experiments. Only minor advantages or disadvantages of T. laxmannii compared to the native species were detected, hence a direct replacement of them is not expectable. Additional factors like the availability of diaspores in the study area of the Tullnerfeld and Danube valley could be more crucial for the present distribution of T. laxmannii than differences in ecological niches of species themselves.

Comprehensive Analysis of Products and the Development of a Quantitative Mechanism for the OH Radical-Initiated Oxidation of 1-Alkenes in the Presence of NOx.

The reactions of 1-tetradecene and 1-pentadecene, the C14 and C15 linear 1-alkenes, with OH radicals in the presence of NOx were investigated in a series of environmental chamber experiments. Particle-phase β-hydroxynitrates, dihydroxynitrates, dihydroxycarbonyls, and 1,4-hydroxynitrates and gas-phase aldehydes were sampled and then identified and quantified using a suite of offline analytical techniques that included derivatization, gas and liquid chromatography, and multiple types of mass spectrometry. Measured molar yields of products formed by OH radical addition to the C═C double bond, including β-hydroxynitrates, dihydroxynitrates, dihydroxycarbonyls (which have not been previously directly quantified with high accuracy), and aldehydes were 0.125 ± 0.01, 0.048 ± 0.005, 0.240 ± 0.04, and 0.268 ± 0.03 (0.264 ± 0.02 and 0.271 ± 0.04 for the formaldehyde and tridecanal/tetradecanal co-products of β-hydroxyalkoxy radical decomposition), respectively. These values give a total molar yield of 0.681 ± 0.05, which agrees very well with the results of kinetics measurements that indicate that the fraction of reaction that occurs by OH radical addition is 0.70. The yields were used to calculate branching ratios for all OH radical addition pathways, including a value of 0.18 for the formation of dihydroxynitrates from the reaction of dihydroxyperoxy radicals with NO and values of 0.47 and 0.53 for β-hydroxyalkoxy radical decomposition and isomerization. The results were used with literature data on the yields of aldehydes measured for similar reactions of smaller alkenes, a model for the effect of carbon number on branching ratios for organic nitrate formation, and a mechanism for H atom abstraction derived from studies of linear alkanes to achieve a complete, quantitative gas-phase reaction mechanism for 1-alkenes. The results should also be useful for constructing mechanisms for more complex reactions of volatile organic compounds.

A multi-objective optimization method for under-the-hood thermal management of vehicles

This study proposes a systematic multi-objective optimization method for thermal management of passenger vehicles. We address the problems of the battery surface temperature and the engine outlet water temperature exceeding the allowable values. First, the causes of excessive temperature were studied through 1D/3D collaborative simulation analysis, and the key influencing factors of the optimization objectives were determined: radiator core thickness (l1), radiator band pitch (λ1), the blocking percentage (θ) between the cooling module and mounting frame, and the grille opening ratio (α). Second, a training set of key influencing factors was created, and a prediction model between key influencing factors and optimization objectives was developed. Third, the prediction model was applied as a fitness evaluation model for particle swarm optimization (PSO), and the Pareto front of the optimization objectives was calculated. Finally, the optimal point of the Pareto front was selected for simulation and environmental chamber experiments to verify the proposed method. The experimental results indicated that when α = 27%, l1 = 27.9 mm, λ1 = 3.4 mm, and θ = 80%, the battery surface temperature and the engine outlet water temperature reduced promptly; the experimental results revealed that this method alleviated the battery surface temperature and the engine outlet water temperature promptly, and the decreasing amplitude was 9.6% and 5.9%, respectively, both met the experimental requirements. This method can effectively minimize the thermal risk of vehicles.

Kinetic modeling of formation and evaporation of secondary organic aerosol from NO<sub>3</sub> oxidation of pure and mixed monoterpenes

Abstract. Organic aerosol constitutes a major fraction of the global aerosol burden and is predominantly formed as secondary organic aerosol (SOA). Environmental chambers have been used extensively to study aerosol formation and evolution under controlled conditions similar to the atmosphere, but quantitative prediction of the outcome of these experiments is generally not achieved, which signifies our lack in understanding of these results and limits their portability to large-scale models. In general, kinetic models employing state-of-the-art explicit chemical mechanisms fail to describe the mass concentration and composition of SOA obtained from chamber experiments. Specifically, chemical reactions including the nitrate radical (NO3) are a source of major uncertainty for assessing the chemical and physical properties of oxidation products. Here, we introduce a kinetic model that treats gas-phase chemistry, gas–particle partitioning, particle-phase oligomerization, and chamber vapor wall loss and use it to describe the oxidation of the monoterpenes α-pinene and limonene with NO3. The model can reproduce aerosol mass and nitration degrees in experiments using either pure precursors or their mixtures and infers volatility distributions of products, branching ratios of reactive intermediates and particle-phase reaction rates. The gas-phase chemistry in the model is based on the Master Chemical Mechanism (MCM) but trades speciation of single compounds for the overall ability of quantitatively describing SOA formation by using a lumped chemical mechanism. The complex branching into a multitude of individual products in MCM is replaced in this model with product volatility distributions and detailed peroxy (RO2) and alkoxy (RO) radical chemistry as well as amended by a particle-phase oligomerization scheme. The kinetic parameters obtained in this study are constrained by a set of SOA formation and evaporation experiments conducted in the Georgia Tech Environmental Chamber (GTEC) facility. For both precursors, we present volatility distributions of nitrated and non-nitrated reaction products that are obtained by fitting the kinetic model systematically to the experimental data using a global optimization method, the Monte Carlo genetic algorithm (MCGA). The results presented here provide new mechanistic insight into the processes leading to formation and evaporation of SOA. Most notably, the model suggests that the observed slow evaporation of SOA could be due to reversible oligomerization reactions in the particle phase. However, the observed non-linear behavior of precursor mixtures points towards a complex interplay of reversible oligomerization and kinetic limitations of mass transport in the particle phase, which is explored in a model sensitivity study. The methodologies described in this work provide a basis for quantitative analysis of multi-source data from environmental chamber experiments but also show that a large data pool is needed to fully resolve uncertainties in model parameters.

Resistance among selected wild soybean and associated soybean accessions against two virulent colonies of Aphis glycines (Hemiptera: Aphididae)

The soybean aphid (Aphis glycines) is an important pest of soybean (Glycine max). Wild soybean (Glycine soja; also known as ‘soja’) has many useful traits, including some accessions with aphid resistance that may be incorporated into modern soybean cultivars. The objective of this work was to evaluate 76 selected soja accessions and 14 associated soybean accessions for resistance against two virulent colonies of soybean aphid in environmental-chamber experiments. In free-choice tests, soja accessions PI 407175, PI 407190, PI 407206, PI 407240, PI 507624 and PI 562558 were resistant against the Accrue colony, and PI 407191wf and PI 597458 C were resistant against the Volga16 colony. None of the soybean test accessions except the resistant check, PI 437696, showed resistance against either colony in free-choice tests. In no-choice tests, soja accession PI 507624 showed strong resistance against the Accrue colony; whereas PI 407240 and PI 407190 had intermediate aphid levels; PI 597458 C showed strong resistance to Volga16 aphids, and PI 407191wf had an intermediate level of resistance. Based on results from both sets of tests, soja accessions PI 507624 and PI 597458 C may be strong candidates in breeding programs to develop aphid-resistant soybean cultivars.

Evaluating Organic Aerosol Sources and Evolution with a Combined Molecular Composition and Volatility Framework Using the Filter Inlet for Gases and Aerosols (FIGAERO).

ConspectusThe complex array of sources and transformations of organic carbonaceous material that comprises an important fraction of atmospheric fine particle mass, known as organic aerosol, has presented a long running challenge for accurate predictions of its abundance, distribution, and sensitivity to anthropogenic activities. Uncertainties about changes in atmospheric aerosol particle sources and abundance over time translate to uncertainties in their impact on Earth's climate and their response to changes in air quality policy. One limitation in our understanding of organic aerosol has been a lack of comprehensive measurements of its molecular composition and volatility, which can elucidate sources and processes affecting its abundance. Herein we describe advances in the development and application of the Filter Inlet for Gases and Aerosols (FIGAERO) coupled to field-deployable High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometers (HRToF-CIMS). The FIGAERO HRToFCIMS combination broadly probes gas and particulate OA molecular composition by using programmed thermal desorption of particles collected on a Teflon filter with subsequent detection and speciation of desorbed vapors using inherently quantitative selected-ion chemical ionization. The thermal desorption provides a means to obtain quantitative insights into the volatility of particle components and thus the physicochemical nature of the organic material that will govern its evolution in the atmosphere.In this Account, we discuss the design and operation of the FIGAERO, when coupled to the HRToF-CIMS, for quantitative characterization of the molecular-level composition and effective volatility of organic aerosol in the laboratory and field. We provide example insights gleaned from its deployment, which improve our understanding of organic aerosol sources and evolution. Specifically, we connect thermal desorption profiles to the effective equilibrium saturation vapor concentration and enthalpy of vaporization of detected components. We also show how application of the FIGAERO HRToF-CIMS to environmental simulation chamber experiments and the field provide new insights and constraints on the chemical mechanisms governing secondary organic aerosol formation and dynamic evolution. We discuss the associated challenges of thermal decomposition during desorption and calibration of both the volatility axis and signal. We also illustrate how the FIGAERO HRToF-CIMS can provide additional insights into organic aerosol through isothermal evaporation experiments as well as for detection of ultrafine particulate composition. We conclude with a description of future opportunities and needs for its ability to further organic aerosol science.

Oxygenated Aromatic Compounds are Important Precursors of Secondary Organic Aerosol in Biomass-Burning Emissions.

Biomass burning is the largest combustion-related source of volatile organic compounds (VOCs) to the atmosphere. We describe the development of a state-of-the-science model to simulate the photochemical formation of secondary organic aerosol (SOA) from biomass-burning emissions observed in dry (RH <20%) environmental chamber experiments. The modeling is supported by (i) new oxidation chamber measurements, (ii) detailed concurrent measurements of SOA precursors in biomass-burning emissions, and (iii) development of SOA parameters for heterocyclic and oxygenated aromatic compounds based on historical chamber experiments. We find that oxygenated aromatic compounds, including phenols and methoxyphenols, account for slightly less than 60% of the SOA formed and help our model explain the variability in the organic aerosol mass (R2 = 0.68) and O/C (R2 = 0.69) enhancement ratios observed across 11 chamber experiments. Despite abundant emissions, heterocyclic compounds that included furans contribute to ∼20% of the total SOA. The use of pyrolysis-temperature-based or averaged emission profiles to represent SOA precursors, rather than those specific to each fire, provide similar results to within 20%. Our findings demonstrate the necessity of accounting for oxygenated aromatics from biomass-burning emissions and their SOA formation in chemical mechanisms.

Photolysis Controls Atmospheric Budgets of Biogenic Secondary Organic Aerosol.

Secondary organic aerosol (SOA) accounts for a large fraction of the tropospheric particulate matter. Although SOA production rates and mechanisms have been extensively investigated, loss pathways remain uncertain. Most large-scale chemistry and transport models account for mechanical deposition of SOA but not chemical losses such as photolysis. There is also a paucity of laboratory measurements of SOA photolysis, which limits how well photolytic losses can be modeled. Here, we show, through a combined experimental and modeling approach, that photolytic loss of SOA mass significantly alters SOA budget predictions. Using environmental chamber experiments at variable relative humidity between 0 and 60%, we find that SOA produced from several biogenic volatile organic compounds undergoes photolysis-induced mass loss at rates between 0 and 2.2 ± 0.4% of nitrogen dioxide (NO2) photolysis, equivalent to average atmospheric lifetimes as short as 10 h. We incorporate our photolysis rates into a regional chemical transport model to test the sensitivity of predicted SOA mass concentrations to photolytic losses. The addition of photolysis causes a ∼50% reduction in biogenic SOA loadings over the Amazon, indicating that photolysis exerts a substantial control over the atmospheric SOA lifetime, with a likely dependence upon the SOA molecular composition and thus production mechanisms.

AtChem (version 1), an open-source box model for the Master Chemical Mechanism

Abstract. AtChem is an open-source zero-dimensional box model for atmospheric chemistry. Any general set of chemical reactions can be used with AtChem, but the model was designed specifically for use with the Master Chemical Mechanism (MCM, http://mcm.york.ac.uk/, last access: 16 January 2020). AtChem was initially developed within the EUROCHAMP project as a web application (AtChem-online, https://atchem.leeds.ac.uk/webapp/, last access: 16 January 2020) for modelling environmental chamber experiments; it was recently upgraded and further developed into a stand-alone offline version (AtChem2), which allows the user to run complex and long simulations, such as those needed for modelling of intensive field campaigns, as well as to perform batch model runs for sensitivity studies. AtChem is installed, set up and configured using semi-automated scripts and simple text configuration files, making it easy to use even for inexperienced users. A key feature of AtChem is that it can easily be constrained to observational data which may have different timescales, thus retaining all the information contained in the observations. Implementation of a continuous integration workflow, coupled with a comprehensive suite of tests and version control software, makes the AtChem code base robust, reliable and traceable. The AtChem2 code and documentation are available at https://github.com/AtChem/ (last access: 16 January 2020) under the open-source MIT License.

Solar air collector with the solar absorber plate containing a PCM – Environmental chamber experiments and computer simulations

The influence of latent heat thermal energy storage integrated with the solar absorber plate was investigated through lab experiments and computer simulations. Two experimental solar air collectors were built. One collector had the solar absorber plate made of sheet metal while that of the other collector consisted of nine aluminium panels containing a paraffin-based PCM. The square-wave variation of the solar radiation intensity was considered, and a good agreement was observed between the computer simulations and experimental data. The peak-to-peak amplitudes of the outlet air temperature were reduced from 11 K (the collector with the metal sheet absorber) to 5 K (the collector with the absorber plate containing the PCM). The main contribution of the study consists in the experimental approach and in the validated model of the solar air collector for TRNSYS simulation tool. The experiments were conducted in an environmental chamber fitted with a solar simulator under both the quasi steady-state and the transient boundary conditions. In comparison to other studies with experiments conducted outdoors, the controlled environment of the climatic chamber allowed for the reduction of the uncertainty on the side of the boundary conditions, e.g. the influence of wind speed, wind direction, and cloudiness.

Formation of oxidized organic compounds from Cl-initiated oxidation of toluene

The formation of secondary organic aerosol (SOA) from toluene can impact urban air quality and therefore human health. Most SOA studies have focused on OH chemistry; however recent work suggests that chlorine atoms (Cl) may affect tropospheric chemistry more than previously assumed. This work focuses on SOA formation from Cl-initiated oxidation of toluene under different conditions. The fast reaction between Cl and toluene enabled complete consumption of toluene in environmental chamber experiments and aging of the toluene SOA. A high resolution time-of-flight chemical ionization mass spectrometer was used to observe several generations of gas-phase products. The presence of nitric oxides (NOx) appears to delay the formation of later generation products. Data from an aerosol chemical speciation monitor suggest that all SOA formed had high oxidation state, and that the bulk organic composition was different for SOA from Cl-dominated reactions compared to SOA from OH-dominated reactions. Addition of oxidant after all toluene had been consumed did not result in a significant change in the organic aerosol oxidation state, suggesting that the system may have reached an oxidative end-point in the particle phase.