Aerosol processes relevant to the indoor environment simulated in a detailed chemistry and aerosol microphysics model:S.P. O’Meara1,2, G. McFiggans2 and N. Carslaw3 1National Centre for Atmospheric Science, UK 2Department of Earth and Environmental Sciences, University of Manchester, Manchester, M13 9PL, UK 3Department of Environment and Geography, University of York, York, YO10 5NG, UK Keywords: model, aerosol, indoor air quality, indoor environment, HOMs. Associated conference topics: 4.1, 5.6 Presenting author email: [email protected]

A mathematical model (CHemistry with Aerosol Microphysics (PyCHAM)) is extended from including detailed gas-phase chemistry with dynamic gas-particle and gas-single surface (e.g. wall) partitioning to also including surface reactions, partitioning to multiple surfaces and wavelength-dependent transmission of natural light. The improved PyCHAM can simulate physicochemical processes occurring indoors. The combination of processes now simulated in PyCHAM alongside relatively detailed chemistry is novel compared to alternative models. Furthermore, PyCHAM is open-source and includes a user-friendly interface and manual (PyCHAM (2023)). Here we present the ability of PyCHAM to reproduce observations from indoor environments and provide additional insight. In particular, we compare against observations in homes that target processes affecting indoor air quality: gas-surface partitioning (e.g. Figure 1), surface reactions, light transmission through windows, particle deposition to surfaces, indoor emission of gases and particles, indoor-outdoor exchange of gases and particles. In Figure 1 of this abstract is an example of PyCHAM reproducing observations: when semi-volatile organic components (SVOC) are present on indoor surfaces and allowed to partition into the gas-phase and then the particle-phase, indoor particle concentrations of organics (separated by alkane-equivalent volatility bins (carbon number (C) 24-31)) increases as the mass concentration of particles with diameter less than 2.5 μm (PM2.5) increases. The same trend, with comparable gradient (m), is reported in observations from a recently occupied household (Lunderberg et al (2020)). As an example of the detail available from PyCHAM, we report the role of Highly Oxygenated Molecules (HOMs) on particle loading and oxidation state, since chamber studies indicate HOMs can significantly affect these properties (Kruza et al (2020)). The role of HOMs is investigated over several cases in which the following variables are changed within published ranges: surface deposition of ozone; surface reactions affecting ozone, nitrogen oxides and nitrous acid; source strength of indoor and outdoor particulates; source strength of indoor and outdoor gases

The characterisation of the interaction between atmospheric aerosol and water vapour

Understanding the interaction between atmospheric aerosol and water vapour is key in assessing the impacts of anthropogenic influences on the earth's radiative budget, both directly through scattering and absorbing incident solar radiation, and indirectly through changing cloud properties, with considerable uncertainty in the magnitude of the estimated forcings of the latter. Although aerosol particle water uptake is well defined for inorganic compounds, the effects of the aerosol organic fraction on cloud droplet formation and cloud condensation nuclei (CCN) properties are relatively poorly characterised, due to the large number of organic compounds present in atmosphere and their highly complex influences on properties such as water solubility and surface tension.This thesis presents extensive field measurements of CCN/aerosol hygroscopicity from three different environments, together with a novel error model, which has been developed to propagate instrumental uncertainties from measurements in the sub- and supersaturated regimes through to commonly used data products used in large-scale models. This study illustrates that a single hygroscopicity framework is not able to reconcile the measurements within errors, for different measurement environments. The sensitivity of this type of reconciliation study was assessed using several different scenarios, making different assumptions in each case; sensitivity tests using a 'typical' regional aerosol particle water uptake or number-size distribution, demonstrate that it is not possible to apply a constant correction to data to guarantee reconciliation, that the best reconciliation was achieved for size-resolved high-temporal water uptake and aerosol number-size distribution data, and that the application of single-parameter hygroscopicity models requires further examination. It is concluded that high-temporal size-resolved measurements of sub- and supersaturated particle water uptake are fundamental to providing a thorough characterisation of the interaction between atmospheric aerosol and water vapour, and are essential in order to achieve the best possible predictive capability from large-scale models.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

UManSysProp: an online facility for molecular property prediction and atmospheric aerosol calculations

Abstract. In this paper we describe the development and application of a new web based facility, UManSysProp (http://umansysprop.seaes.manchester.ac.uk), for automating predictions of molecular and atmospheric aerosol properties. Current facilities include: pure component vapour pressures, critical properties and sub-cooled densities of organic molecules; activity coefficient predictions for mixed inorganic–organic liquid systems; hygroscopic growth factors and CCN activation potential of mixed inorganic/organic aerosol particles; absorptive partitioning calculations with/without a treatment of non-ideality. The aim of this new facility is to provide a single point of reference for all properties relevant to atmospheric aerosol that have been checked for applicability to atmospheric compounds where possible. The group contribution approach allows users to upload molecular information in the form of SMILES strings and UManSysProp will automatically extract the relevant information for calculations. Built using open source chemical informatics, and hosted at the University of Manchester, the facilities are provided via a browser and device-friendly web-interface, or can be accessed using the user's own code via a JSON API. In this paper we demonstrate its use with specific examples that can be simulated using the web-browser interface. </jats:p

HIPTox—Hazard Identification Platform to Assess the Health Impacts from Indoor and Outdoor Air Pollutant Exposures, through Mechanistic Toxicology:A Single-Centre Double-Blind Human Exposure Trial Protocol

Over the past decade, our understanding of the impact of air pollution on short- and long-term population health has advanced considerably, focusing on adverse effects on cardiovascular and respiratory systems. There is, however, increasing evidence that air pollution exposures affect cognitive function, particularly in susceptible groups. Our study seeks to assess and hazard rank the cognitive effects of prevalent indoor and outdoor pollutants through a single-centre investigation on the cognitive functioning of healthy human volunteers aged 50 and above with a familial predisposition to dementia. Participants will all undertake five sequential controlled exposures. The sources of the air pollution exposures are wood smoke, diesel exhaust, cleaning products, and cooking emissions, with clean air serving as the control. Pre- and post-exposure spirometry, nasal lavage, blood sampling, and cognitive assessments will be performed. Repeated testing pre and post exposure to controlled levels of pollutants will allow for the identification of acute changes in functioning as well as the detection of peripheral markers of neuroinflammation and neuronal toxicity. This comprehensive approach enables the identification of the most hazardous components in indoor and outdoor air pollutants and further understanding of the pathways contributing to neurodegenerative diseases. The results of this project have the potential to facilitate greater refinement in policy, emphasizing health-relevant pollutants and providing details to aid mitigation against pollutant-associated health risks

The Influence of Algal Exudate on the Hygroscopicity of Sea Spray Particles

We examined the effect of organic matter released by four different algal species on the hygroscopic growth and droplet activation behaviour of laboratory-generated marine aerosol particles. Hygroscopic growth factors and dry diameters for activation were reduced by less than 10%, compared to that of sodium chloride or of artificial seawater that was devoid of marine surfactants. Concentration-dependent nonideal behaviour was observed for the artificial seawater. But within measurement uncertainty, the measured hygroscopic growth and droplet activation behaviour for the samples that contained organic matter were consistent with a hygroscopicity parameter that was constant between the sub- and supersaturated measurement points. Also, the hygroscopic growth measured for hydrated particles after 3 and after 10 seconds was similar, which implies that in this time range no kinetic effects were detected

The influence of the addition of isoprene on the volatility of particles formed from the photo-oxidation of anthropogenic–biogenic mixtures

In this study, we investigate the influence of isoprene on the volatility of secondary organic aerosol (SOA) formed during the photo-oxidation of mixtures of anthropogenic and biogenic precursors. The SOA particle volatility was quantified using two independent experimental techniques (using a thermal denuder and the Filter Inlet for Gas and Aerosols iodide high-resolution time-of-flight Chemical Ionisation Mass Spectrometer – FIGAERO-CIMS) in mixtures of α-pinene/isoprene, o-cresol/isoprene, and α-pinene/o-cresol/isoprene. Single-precursor experiments at various initial concentrations and results from previous α-pinene/o-cresol experiments were used as a reference. The oxidation of isoprene did not result in the formation of detectable SOA particle mass in single-precursor experiments. However, isoprene-derived products were identified in the mixed systems, likely due to the increase in the total absorptive mass. The addition of isoprene resulted in mixture-dependent influence on the SOA particle volatility. Isoprene made no major change to the volatility of α-pinene SOA particles, though changes in the SOA particle composition were observed and the volatility was reasonably predicted based on the additivity. Isoprene addition increased o-cresol SOA particle volatility by ∼5/15 % of the total mass/signal, respectively, indicating a potential to increase the overall volatility that cannot be predicted based on the additivity. The addition of isoprene to the α-pinene/o-cresol system (i.e. α-pinene/o-cresol/isoprene) resulted in slightly fewer volatile particles than those measured in the α-pinene/o-cresol systems. The measured volatility in the α-pinene/o-cresol/isoprene system had an ∼6 % higher low volatile organic compound (LVOC) mass/signal compared to that predicted assuming additivity with a correspondingly lower semi-volatile organic compound (SVOC) fraction. This suggests that any effects that could increase the SOA volatility from the addition of isoprene are likely outweighed by the formation of lower-volatility compounds in more complex anthropogenic–biogenic precursor mixtures. Detailed chemical composition measurements support the measured volatility distribution changes and showed an abundance of unique-to-the-mixture products appearing in all the mixed systems accounting for around 30 %–40 % of the total particle-phase signal. Our results demonstrate that the SOA particle volatility and its prediction can be affected by the interactions of the oxidized products in mixed-precursor systems, and further mechanistic understanding is required to improve their representation in chemical transport models.</p

Emissions of biogenic volatile organic compounds and subsequent photochemical production of secondary organic aerosol in mesocosm studies of temperate and tropical plant species

Silver birch (Betula pendula) and three Southeast Asian tropical plant species (Ficus cyathistipula, Ficus benjamina and Caryota millis) from the pantropical fig and palm genera were grown in a purpose-built and environment-controlled whole-tree chamber. The volatile organic compounds emitted from these trees were characterised and fed into a linked photochemical reaction chamber where they underwent photo-oxidation under a range of controlled conditions (relative humidity or RH ~65–89%, volatile organic compound-to-NOx or VOC / NOx ~3–9 and NOx ~2 ppbV). Both the gas phase and the aerosol phase of the reaction chamber were monitored in detail using a comprehensive suite of on-line and off-line chemical and physical measurement techniques. Silver birch was found to be a high monoterpene and sesquiterpene but low isoprene emitter, and its emissions were observed to produce measurable amounts of secondary organic aerosol (SOA) via both nucleation and condensation onto pre-existing seed aerosol (YSOA 26–39%). In contrast, all three tropical species were found to be high isoprene emitters with trace emissions of monoterpenes and sesquiterpenes. In tropical plant experiments without seed aerosol there was no measurable SOA nucleation, but aerosol mass was shown to increase when seed aerosol was present. Although principally isoprene emitting, the aerosol mass produced from tropical fig was mostly consistent (i.e. in 78 out of 120 aerosol mass calculations using plausible parameter sets of various precursor specific yields) with condensation of photo-oxidation products of the minor volatile organic compounds (VOCs) co-emitted; no significant aerosol yield from condensation of isoprene oxidation products was required in the interpretations of the experimental results. This finding is in line with previous reports of organic aerosol loadings consistent with production from minor biogenic VOCs co-emitted with isoprene in principally isoprene-emitting landscapes in Southeast Asia. Moreover, in general the amount of aerosol mass produced from the emissions of the principally isoprene-emitting plants was less than would be expected from published single-VOC experiments, if co-emitted species were solely responsible for the final SOA mass. Interpretation of the results obtained from the fig data sets leaves room for a potential role for isoprene in inhibiting SOA formation under certain ambient atmospheric conditions, although instrumental and experimental constraints impose a level of caution in the interpretation of the results. Concomitant gas- and aerosol-phase composition measurements also provide a detailed overview of numerous key oxidation mechanisms at work within the systems studied, and their combined analysis provides insight into the nature of the SOA formed

The Effect of Varying Engine Conditions on Unregulated VOC Diesel Exhaust Emissions

Abstract. An extensive set of measurements were performed to investigate the effect of different engine conditions (i.e. load, speed, temperature, "driving scenarios") and emission control devices (with/without diesel oxidative catalyst, DOC) on the composition and abundance of unregulated exhaust gas emissions from a light-duty diesel engine. Exhaust emissions were introduced into an atmospheric chamber and measured using thermal desorption comprehensive two-dimensional gas chromatography coupled to a flame ionisation detector (TD-GC×GC-FID). In total, 16 individual and 8 groups of volatile organic compounds (VOCs) were measured in the exhaust gas, ranging from volatile to intermediate volatility. The total speciated VOC (∑SpVOC) emission rates varied significantly with different engine conditions, ranging from 70 to 9268 milligrams of VOC mass per kilogram of fuel burnt (mg kg-1). ∑SpVOC emission rates generally decreased with increasing engine load and temperature, and to a lesser degree, engine speed. The exhaust gas composition changed as a result of two main influencing factors, the DOC hydrocarbon (HC) removal efficiency and engine combustion efficiency. Increased DOC HC removal efficiency and engine combustion efficiency resulted in a greater percentage contribution of the C7 to C12 branched aliphatics and C7 to C12 n-alkanes, respectively, to the ∑SpVOC emission rate. The investigated DOC removed 46 ± 10 % of the ∑SpVOC emissions, with removal efficiencies of 83 ± 3 % for the single-ring aromatics and 39 ± 12 % for the aliphatics (branched and straight-chain). The DOC aliphatic removal efficiency generally decreased with increasing carbon chain length. The emission factors of n-nonane to n-tridecane were compared with on-road diesel emissions from a highway tunnel in Oakland California. Comparable emission factors were from experiments with relatively high engine loads and speeds, engine conditions which are consistent with the driving conditions of the on-road diesel vehicles. Emission factors from low engine loads and speeds (e.g. cold-start) showed no agreement with the on-road diesel emissions as expected, with the emission factors observed to be 2 to 8 times greater. To our knowledge, this is the first study which has explicitly discussed the effect of the DOC HC removal efficiency and combustion efficiency on the exhaust gas composition. With further work, compositional differences in exhaust gas emissions as a function of engine temperature, could be implemented into air-quality models, resulting in improved refinement and better understanding of diesel exhaust emissions on local air quality. </jats:p