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Unsaturated triglycerides found in food and skin oils are reactive in ambient air. However, the chemical fate of such compounds has not been well characterized in genuine indoor environments. Here, we monitored the aging of oil coatings on glass surfaces over a range of environmental conditions, using mass spectrometry, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR) techniques. Upon room air exposure (up to 17 ppb ozone), the characteristic ozonolysis products, secondary ozonides, were observed on surfaces near the cooking area of a commercial kitchen, along with condensed-phase aldehydes. In an office setting, ozonolysis is also the dominant degradation pathway for oil films exposed to air. However, for indoor enclosed spaces such as drawers, the depleted air flow makes lipid autoxidation more favorable after an induction period of a few days. Forming hydroperoxides as the major primary products, this radical-mediated peroxidation behavior is accelerated by indoor direct sunlight, but the initiation step in dark settings is still unclear. These results are in accord with radical measurements, indicating that indoor photooxidation facilitates radical formation on surfaces. Overall, many intermediate and end products observed are reactive oxygen species (ROS) that may induce oxidative stress in human bodies. Given that these species can be widely found on both food and household surfaces, their toxicological properties are worth further attention.

Gas and particulate emissions from commercial kitchens are important contributors to urban air quality. Not only are these emissions important for occupational exposure of kitchen staff, but they can also be vented to outdoors, causing uncertain health and environmental impacts. In this study, we chemically speciated volatile organic compounds and measured particulate matter mass concentrations in a well-ventilated commercial kitchen for two weeks, including during typical cooking and cleaning operations. From cooking, we observed a complex mixture of volatile organic gases dominated by oxygenated compounds commonly associated with the thermal degradation of cooking oils. Gas-phase chemicals existed at concentrations 2-7 orders of magnitude lower than their exposure limits, due to the high ventilation in the room (mean air change rate of 28 h -1 during operating hours). During evening kitchen cleaning, we observed an increase in the signal of chlorinated gases from 1.1-9.0 times their values during daytime cooking. Particulate matter mass loadings tripled at these times. While exposure to cooking emissions in this indoor environment was reduced effectively by the high ventilation rate, exposure to particulate matter and chlorinated gases was elevated during evening cleaning periods. This emphasizes the need for careful consideration of ventilation rates and methods in commercial kitchen environments during all hours of kitchen operation.

Delhi, India, suffers from periods of very poor air quality, but little is known about the chemical production of secondary pollutants in this highly polluted environment. During the postmonsoon period in 2018, extremely high nighttime concentrations of NO x (NO and NO 2 ) and volatile organic compounds (VOCs) were observed, with median NO x mixing ratios of ∼200 ppbV (maximum of ∼700 ppbV). A detailed chemical box model constrained to a comprehensive suite of speciated VOC and NO x measurements revealed very low nighttime concentrations of oxidants, NO 3 , O 3 , and OH, driven by high nighttime NO concentrations. This results in an atypical NO 3 diel profile, not previously reported in other highly polluted urban environments, significantly perturbing nighttime radical oxidation chemistry. Low concentrations of oxidants and high nocturnal primary emissions coupled with a shallow boundary layer led to enhanced early morning photo-oxidation chemistry. This results in a temporal shift in peak O 3 concentrations when compared to the premonsoon period (12:00 and 15:00 local time, respectively). This shift will likely have important implications on local air quality, and effective urban air quality management should consider the impacts of nighttime emission sources during the postmonsoon period., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

Reactive nitrogen species (N r ), defined here as all N-containing compounds except N 2 and N 2 O, have been shown to be important drivers for indoor air quality. Key N r species include NO x (NO + NO 2 ), HONO and NH 3 , which are known to have detrimental health effects. In addition, other N r species that are not traditionally measured may be important chemical actors for indoor transformations ( e.g. amines). Cooking and cleaning are significant sources of N r , whose emission will vary depending on the type of activity and materials used. Here we present a novel instrument that measures the total gas-phase reactive nitrogen (tN r ) budget and key species NO x , HONO, and NH 3 to demonstrate its suitability for indoor air quality applications. The tN r levels were measured using a custom-built heated platinum (Pt) catalytic furnace to convert all N r species to NO x , called the tN r oven. The measurement approach was validated through a series of control experiments, such that quantitative measurement and speciation of the total N r budget are demonstrated. The optimum operating conditions of the tN r oven were found to be 800 °C with a sampling flow rate of 630 cubic centimetres per minute (ccm). Oxidized nitrogen species are known to be quantitatively converted under these conditions. Here, the efficiency of the tN r oven to convert reduced N r species to NO x was found to reach a maximum at 800 °C, with 103 ± 13% conversion for NH 3 and 79-106% for selected relevant amines. The observed variability in the conversion efficiency of reduced N r species demonstrates the importance of catalyst temperature characterization for the tN r oven. The instrument was deployed successfully in a commercial kitchen, a complex indoor environment with periods of rapidly changing levels, and shown to be able to reliably measure the tN r budget during periods of longer-lived oscillations (>20 min), typical of indoor spaces. The measured NO x , HONO and basic N r (NH 3 and amines) were unable to account for all the measured tN r , pointing to a substantial missing fraction (on average 18%) in the kitchen. Overall, the tN r instrument will allow for detailed survey(s) of the key gaseous N r species across multiple locations and may also identify missing N r fractions, making this platform capable of stimulating more in-depth analysis in indoor atmospheres.

Chloramines (NH 2 Cl, NHCl 2 , and NCl 3 ) are toxic compounds that can be created during the use of bleach-based disinfectants that contain hypochlorous acid (HOCl) and the hypochlorite ion (OCl - ) as their active ingredients. Chloramines can then readily transfer from the aqueous-phase to the gas-phase. Atmospheric chemical ionization mass spectrometry using iodide adduct chemistry (I-CIMS) made observations across two periods (2014 and 2016) at an urban background site on the University of Leicester campus (Leicester, UK). Both monochloramine (NH 2 Cl) and molecular chlorine (Cl 2 ) were detected and positively identified from calibrated mass spectra during both sampling periods and to our knowledge, this is the first detection of NH 2 Cl outdoors. Mixing ratios of NH 2 Cl reached up to 2.2 and 4.0 parts per billion by volume (ppbv), with median mixing ratios of 30 and 120 parts per trillion by volume (pptv) during the 2014 and 2016 sampling periods, respectively. Levels of Cl 2 were observed to reach up to 220 and 320 pptv. Analysis of the NH 2 Cl and Cl 2 data pointed to the same local source, a nearby indoor sports complex with a swimming pool and a cleaning product storage shed. No appreciable levels of NHCl 2 and NCl 3 were observed outdoors, suggesting the indoor pool was not likely to be the primary source of the observed ambient chloramines, as prior measurements made in indoor pool atmospheres indicate that NCl 3 would be expected to dominate. Instead, these observations point to indoor cleaning and/or cleaning product emissions as the probable source of NH 2 Cl and Cl 2 where the measured levels provide indirect evidence for substantial amounts transported from indoors to outdoors. Our upper estimate for total NH 2 Cl emissions from the University of Leicester indoor sports complexes scaled for similar sports complexes across the UK is 3.4 × 10 5 ± 1.1 × 10 5 μg h -1 and 0.0017 ± 0.00034 Gg yr -1 , respectively. The Cl-equivalent emissions in HCl are only an order of magnitude less to those from hazardous waste incineration and iron and steel sinter production in the UK National Atmospheric Emissions Inventory (NAEI).

Particulate nitrate ([Formula: see text]) has long been considered a permanent sink for NO x (NO and NO 2 ), removing a gaseous pollutant that is central to air quality and that influences the global self-cleansing capacity of the atmosphere. Evidence is emerging that photolysis of [Formula: see text] can recycle HONO and NO x back to the gas phase with potentially important implications for tropospheric ozone and OH budgets; however, there are substantial discrepancies in "renoxification" photolysis rate constants. Using aircraft and ground-based HONO observations in the remote Atlantic troposphere, we show evidence for renoxification occurring on mixed marine aerosols with an efficiency that increases with relative humidity and decreases with the concentration of [Formula: see text], thus largely reconciling the very large discrepancies in renoxification photolysis rate constants found across multiple laboratory and field studies. Active release of HONO from aerosol has important implications for atmospheric oxidants such as OH and O 3 in both polluted and clean environments.

Indian cities can experience severe air pollution, and the reduction in activity during the first national COVID-19 lockdown (2020) offered a natural experiment to study the contribution of local sources. The current work aimed to quantify the changes due to the lockdown in NO x , O 3 and PM 2.5 in two contrasting cities in India (Delhi and Hyderabad) using a boosted regression tree model to account for the influence of meteorology. The median NO x and PM 2.5 concentrations were observed to decrease after lockdown in both cities, up to 57% and 75% for PM 2.5 and NO x , respectively when compared to previous years. After normalization due to meteorology the calculated reduction after lockdown for PM 2.5 was small (<8%) in both cities, and was likely less attributable to changes in local emissions, but rather due changes in background levels ( i.e. regional source(s)). The reduction of NO x due to lockdown varied by site (on average 5-30%), likely reflecting differences in relative proximity of local sources to the monitoring site, demonstrating the key influence of meteorology on ambient levels post-lockdown. Ozone was observed to increase after lockdown at both sites in Delhi, likely due to changes in relative amounts of precursor concentrations promoting ozone production, suggesting a volatile organic compound (VOC)-limited regime in Delhi. Thus, the calculated reduction in air pollutants due to lockdown in the current work cannot be extrapolated to be solely from a reduction in emissions and instead reflects the overall change in ambient levels, as meteorology and atmospheric chemical processes also contributed.

People spend up to 90% of their time indoors, and yet our understanding of indoor air quality and the chemical processes driving it are poorly understood, despite levels of key pollutants typically being higher indoors compared to outdoors. Nitrous acid (HONO) is a species that drives these indoor chemical processes, with potentially detrimental health effects. In this work, a BODIPY-based probe was synthesized with the aim of developing the first selective passive sampler for atmospheric HONO. Our probe and its products are easily detected by UV-Vis spectroscopy with molar extinct coefficients of 37 863 and 33 787 M -1 cm -1 , respectively, and a detection limit of 14.8 ng mL -1 . When protonated, the probe fluoresces with a quantum yield of 33%, which is turned off upon reaction. The synthesized BODIPY probe was characterized using NMR and UV-Vis spectroscopy. Products were characterized by UV-Vis and ultra high-resolution mass spectrometry. The reaction kinetics of the probe with nitrite was studied using UV-Vis spectroscopy, which had a pseudo-first-order rate of k = 7.7 × 10 -4 s -1 . The rapid reaction makes this probe suitable for targeted ambient sampling of HONO. This was investigated through a proof-of-concept experiment with gaseous HONO produced by a custom high-purity calibration source delivering the sample to the BODIPY probe in an acidic aqueous solution in clean air and a real indoor air matrix. The probe showed quantitative uptake of HONO in both cases to form the same products observed from reaction with nitrite, with no indication of interferences from ambient NO or NO 2 . The chemical and physical characteristics of the probe therefore make it ideal for use in passive samplers for selective sampling of HONO from the atmosphere.

Increasing emissions from sources such as construction and burning of biomass from crop residues, roadside and municipal solid waste have led to a rapid increase in the atmospheric concentrations of fine particulate matter (≤2.5 μm; PM 2.5 ) over many Indian cities. Analyses of their chemical profiles are important for receptor models to accurately estimate the contributions from different sources. We have developed chemical source profiles for five important pollutant sources - construction (CON), paved road dust (PRD), roadside biomass burning (RBB), solid waste burning (SWB), and crop residue burning (CPB) - during three intensive campaigns (winter, summer and post-monsoon) in and around Delhi. We obtained chemical characterisations of source profiles incorporating carbonaceous material such as organic carbon (OC) and elemental carbon (EC), water-soluble ions (F - , Cl - , NO 2 - , NO 3 - , SO 4 2- , PO 4 3- , Na + and NH 4 + ), and elements (Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Br, Rb, Sr, Ba, and Pb). CON was dominated by the most abundant elements, K, Si, Fe, Al, and Ca. PRD was also dominated by crustal elements, accounting for 91% of the total analysed elements. RBB, SWB and CPB profiles were dominated by organic matter, which accounted for 94%, 86.2% and 86% of the total PM 2.5 , respectively. The database of PM emission profiles developed from the sources investigated can be used to assist source apportionment studies for accurate quantification of the causes of air pollution and hence assist governmental bodies in formulating relevant countermeasures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Daytime atmospheric oxidation chemistry is conventionally considered to be driven primarily by the OH radical, formed via photolytic sources. In this paper we examine how, during winter when photolytic processes are slow, chlorine chemistry can have a significant impact on oxidative processes in the urban boundary layer. Photolysis of nitryl chloride (ClNO 2 ) provides a significant source of chlorine atoms, which enhances the oxidation of volatile organic compounds (VOCs) and the production of atmospheric pollutants. We present a set of observations of ClNO 2 and HONO made at urban locations in central England in December 2014 and February 2016. While direct emissions and in-situ chemical formation of HONO continue throughout the day, ClNO 2 is only formed at night and is usually completely photolyzed by midday. Our data show that, during winter, ClNO 2 often persists through the daylight hours at mixing ratios above 10-20 ppt (on average). In addition, relatively high mixing ratios of daytime HONO (>65 ppt) provide a strong source of OH radicals throughout the day. The combined effects of ClNO 2 and HONO result in sustained sources of Cl and OH radicals from sunrise to sunset, which form additional ozone, PAN, oxygenated VOCs, and secondary organic aerosol. We show that radical sources such as ClNO 2 and HONO can lead to a surprisingly photoactive urban atmosphere during winter and should therefore be included in atmospheric chemical models., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Wintertime urban air pollution in many global megacities is characterised by episodic rapid increase in particulate matter concentrations associated with elevated relative humidity - so-called haze episodes, which have become characteristic of cities such as Beijing. Atmospheric chemistry within haze combines gas- and condensed-phase chemical processes, leading to the growth in secondary species such as sulphate aerosols. Here, we integrate observations of reactive gas phase species (HONO, OH, NO x ) and time-resolved aerosol composition, to explore observational constraints on the mechanisms responsible for sulphate growth during the onset of haze events. We show that HONO abundance is dominated by established fast gas-phase photochemistry, but the consideration of the additional formation potentially associated with condensed-phase oxidation of S species by aqueous NO 2 leading to NO 2 - production and hence HONO release, improves agreement between observed and calculated gas-phase HONO levels. This conclusion is highly dependent upon aerosol pH, ionic strength and particularly the parameterisation employed for S(iv) oxidation kinetics, for which an upper limit is derived.

Despite much work in recent years, vehicle emissions remain a significant contributor in many areas where air quality standards are under threat. Policy-makers are actively exploring options for next generation vehicle emission control and local fleet management policies, and new monitoring technologies to aid these activities. Therefore, we report here on findings from two separate but complementary blind evaluation studies of one new-to-market real-world monitoring option, HEAT LLC's Emission Detection And Reporting system or EDAR, an above-road open path instrument that uses Differential Absorption LIDAR to provide a highly sensitive and selective measure of passing vehicle emissions. The first study, by Colorado Department of Public Health and Environment and Eastern Research Group, was a simulated exhaust gas test exercise used to investigate the instrumental accuracy of the EDAR. Here, CO, NO, CH 4 and C 3 H 8 measurements were found to exhibit high linearity, low bias, and low drift over a wide range of concentrations and vehicle speeds. Instrument accuracy was high (R 2 0.996 for CO, 0.998 for NO; 0.983 for CH 4 ; and 0.976 for C 3 H 8 ) and detection limits were 50 to 100ppm for CO, 10 to 30ppm for NO, 15 to 35ppmC for CH 4 , and, depending on vehicle speed, 100 to 400ppmC 3 for C 3 H 8 . The second study, by the Universities of Birmingham and Leeds and King's College London, used the comparison of EDAR, on-board Portable Emissions Measurement System (PEMS) and car chaser (SNIFFER) system measurements collected under real-world conditions to investigate in situ EDAR performance. Given the analytical challenges associated with aligning these very different measurements, the observed agreements (e.g. EDAR versus PEMS R 2 0.92 for CO/CO 2 ; 0.97 for NO/CO 2 ; ca. 0.82 for NO 2 /CO 2 ; and, 0.94 for PM/CO 2 ) were all highly encouraging and indicate that EDAR also provides a representative measure of vehicle emissions under real-world conditions., (Copyright © 2017 Elsevier B.V. All rights reserved.)

London, like many major cities, has a noted air pollution problem, and a better understanding of the sources of airborne particles in the different size fractions will facilitate the implementation and effectiveness of control strategies to reduce air pollution. Thus, the trace elemental composition of the fine and coarse fraction were analysed at hourly time resolution at urban background (North Kensington, NK) and roadside (Marylebone Road, MR) sites within central London. Unlike previous work, the current study focuses on measurements during the summer providing a snapshot of contributing sources, utilising the high time resolution to improve source identification. Roadside enrichment was observed for a large number of elements associated with traffic emissions (Al, S, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Rb and Zr), while those elements that are typically from more regional sources (e.g. Na, Cl, S and K) were not found to have an appreciable increment. Positive Matrix Factorization (PMF) was applied for the source apportionment of the particle mass at both sites with similar sources being identified, including sea salt, airborne soil, traffic emissions, secondary inorganic aerosols and a Zn-Pb source. In the fine fraction, traffic emissions was the largest contributing source at MR (31.9%), whereas it was incorporated within an "urban background" source at NK, which had contributions from wood smoke, vehicle emissions and secondary particles. Regional sources were the major contributors to the coarse fraction at both sites. Secondary inorganic aerosols (which contained influences from shipping emissions and coal combustion) source factors accounted for around 33% of the PM 10 at NK and were found to have the highest contributions from regional sources, including from the European mainland. Exhaust and non-exhaust sources both contribute appreciably to PM 10 levels at the MR site, highlighting the continuing importance of vehicle-related air pollutants at roadside., (Copyright © 2016 The Authors. Published by Elsevier Ltd.. All rights reserved.)

A substantial body of recent literature has shown that boundary layer HONO levels are higher than can be explained by simple, established gas-phase chemistry, to an extent that implies that additional HONO sources represent a major, or the dominant, precursor to OH radicals in such environments. This conclusion may be reached by analysis of point observations of (for example) OH, NO and HONO, alongside photochemical parameters; however both NO and HONO have non-negligible atmospheric lifetimes, so these approaches may be problematic if substantial spatial heterogeneity exists. We report a new dataset of HONO, NOx and HOx observations recorded at an urban background location, which support the existence of additional HONO sources as determined elsewhere. We qualitatively evaluate the possible impacts of local heterogeneity using a series of idealised numerical model simulations, building upon the work of Lee et al. (J. Geophys. Res., 2013, DOI: 10.1002/2013JD020341). The simulations illustrate the time required for photostationary state approaches to yield accurate results following substantial perturbations in the HOx/NOx/NOy chemistry, and the scope for bias to an inferred HONO source from NOx and VOC emissions in either a positive or negative sense, depending upon the air mass age following emission. To assess the extent to which these impacts may be present in actual measurements, we present exploratory spatially resolved measurements of HONO and NOx abundance obtained using a mobile instrumented laboratory. Measurements of the spatial variability of HONO in urban, suburban and rural environments show pronounced changes in abundance are found in proximity to major roads within urban areas, indicating that photo-stationary steady state (PSS) analyses in such areas are likely to be problematic. The measurements also show areas of very homogeneous HONO and NOx abundance in rural, and some suburban, regions, where the PSS approach is likely to be valid. Implications for future exploration of HONO production mechanisms are discussed.

Open biomass burning from wildfires and the prescribed burning of forests and farmland is a frequent occurrence in South-East Queensland (SEQ), Australia. This work reports on data collected from 10 to 30 September 2011, which covers the days before (10-14 September), during (15-20 September) and after (21-30 September) a period of biomass burning in SEQ. The aim of this project was to comprehensively quantify the impact of the biomass burning on air quality in Brisbane, the capital city of Queensland. A multi-parameter field measurement campaign was conducted and ambient air quality data from 13 monitoring stations across SEQ were analysed. During the burning period, the average concentrations of all measured pollutants increased (from 20% to 430%) compared to the non-burning period (both before and after burning), except for total xylenes. The average concentration of O3, NO2, SO2, benzene, formaldehyde, PM10, PM2.5 and visibility-reducing particles reached their highest levels for the year, which were up to 10 times higher than annual average levels, while PM10, PM2.5 and SO2 concentrations exceeded the WHO 24-hour guidelines and O3 concentration exceeded the WHO maximum 8-hour average threshold during the burning period. Overall spatial variations showed that all measured pollutants, with the exception of O3, were closer to spatial homogeneity during the burning compared to the non-burning period. In addition to the above, elevated concentrations of three biomass burning organic tracers (levoglucosan, mannosan and galactosan), together with the amount of non-refractory organic particles (PM1) and the average value of f60 (attributed to levoglucosan), reinforce that elevated pollutant concentration levels were due to emissions from open biomass burning events, 70% of which were prescribed burning events. This study, which is the first and most comprehensive of its kind in Australia, provides quantitative evidence of the significant impact of open biomass burning events, especially prescribed burning, on urban air quality. The current results provide a solid platform for more detailed health and modelling investigations in the future., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Ambient ultrafine particle number concentrations (PNC) have inhomogeneous spatio-temporal distributions and depend on a number of different urban factors, including background conditions and distant sources. This paper quantitatively compares exposure to ambient ultrafine particles at urban schools in two cities in developed countries, with high insolation climatic conditions, namely Brisbane (Australia) and Barcelona (Spain). The analysis used comprehensive indoor and outdoor air quality measurements at 25 schools in Brisbane and 39 schools in Barcelona. PNC modes were analysed with respect to ambient temperature, land use and urban characteristics, combined with the measured elemental carbon concentrations, NOx (Brisbane) and NO2 (Barcelona). The trends and modes of the quantified weekday average daily cycles of ambient PNC exhibited significant differences between the two cities. PNC increases were observed during traffic rush hours in both cases. However, the mid-day peak was dominant in Brisbane schools and had the highest contribution to total PNC for both indoors and outdoors. In Barcelona, the contribution from traffic was highest for ambient PNC, while the mid-day peak had a slightly higher contribution for indoor concentrations. Analysis of the relationships between PNC and land use characteristics in Barcelona schools showed a moderate correlation with the percentage of road network area and an anti-correlation with the percentage of green area. No statistically significant correlations were found for Brisbane. Overall, despite many similarities between the two cities, school-based exposure patterns were different. The main source of ambient PNC at schools was shown to be traffic in Barcelona and mid-day new particle formation in Brisbane. The mid-day PNC peak in Brisbane could have been driven by the combined effect of background and meteorological conditions, as well as other local/distant sources. The results have implications for urban development, especially in terms of air quality mitigation and management at schools., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Children are particularly susceptible to air pollution and schools are examples of urban microenvironments that can account for a large portion of children's exposure to airborne particles. Thus this paper aimed to determine the sources of primary airborne particles that children are exposed to at school by analyzing selected organic molecular markers at 11 urban schools in Brisbane, Australia. Positive matrix factorization analysis identified four sources at the schools: vehicle emissions, biomass burning, meat cooking and plant wax emissions accounting for 45%, 29%, 16% and 7%, of the organic carbon respectively. Biomass burning peaked in winter due to prescribed burning of bushland around Brisbane. Overall, the results indicated that both local (traffic) and regional (biomass burning) sources of primary organic aerosols influence the levels of ambient particles that children are exposed at the schools. These results have implications for potential control strategies for mitigating exposure at schools., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

The charge and chemical composition of ambient particles in an urban environment were determined using a neutral particle and air ion spectrometer and an aerodyne compact time-of-flight aerosol mass spectrometer. Particle formation and growth events were observed on 20 of the 36 days of sampling, with eight of these events classified as strong. During these events, peaks in the concentration of intermediate and large ions were followed by peaks in the concentration of ammonium and sulfate, which were not observed in the organic fraction. Comparison of days with and without particle formation events revealed that ammonium and sulfate were the dominant species on particle formation days while high concentrations of biomass burning OA inhibited particle growth. Analyses of the degree of particle neutralization lead us to conclude that an excess of ammonium enabled particle formation and growth. In addition, the large ion concentration increased sharply during particle growth, suggesting that during nucleation the neutral gaseous species ammonia and sulfuric acid react to form ammonium and sulfate ions. Overall, we conclude that the mechanism of particle formation and growth involved ammonia and sulfuric acid, with limited input from organics.

An Aerodyne Aerosol Mass Spectrometer was deployed at five urban schools to examine spatial and temporal variability of organic aerosols (OA) and positive matrix factorization (PMF) used for the first time in the Southern Hemisphere to apportion the sources of the OA across an urban area. The sources identified included hydrocarbon-like OA (HOA), biomass burning OA (BBOA) and oxygenated OA (OOA). At all sites, the main source was OOA, which accounted for 62-73% of the total OA mass and was generally more oxidized compared to those reported in the Northern Hemisphere. This suggests that there are differences in aging processes or regional sources in the two hemispheres. Unlike HOA and BBOA, OOA demonstrated instructive temporal variations but not spatial variation across the urban area. Application of cluster analysis to the PMF-derived sources offered a simple and effective method for qualitative comparison of PMF sources that can be used in other studies., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Aerosol Mass Spectrometers (AMS) are powerful tools in the analysis of the chemical composition of airborne particles, particularly organic aerosols which are gaining increasing attention. However, the advantages of AMS in providing on-line data can be outweighed by the difficulties involved in its use in field measurements at multiple sites. In contrast to the on-line measurement by AMS, a method which involves sample collection on filters followed by subsequent analysis by AMS could significantly broaden the scope of AMS application. We report the application of such an approach to field studies at multiple sites. An AMS was deployed at 5 urban schools to determine the sources of the organic aerosols at the schools directly. PM1 aerosols were also collected on filters at these and 20 other urban schools. The filters were extracted with water and the extract run through a nebulizer to generate the aerosols, which were analyzed by an AMS. The mass spectra from the samples collected on filters at the 5 schools were found to have excellent correlations with those obtained directly by AMS, with r(2) ranging from 0.89 to 0.98. Filter recoveries varied between the schools from 40 to 115%, possibly indicating that this method provides qualitative rather than quantitative information. The stability of the organic aerosols on Teflon filters was demonstrated by analysing samples stored for up to two years. Application of the procedure to the remaining 20 schools showed that secondary organic aerosols were the main source of aerosols at the majority of the schools. Overall, this procedure provides accurate representation of the mass spectra of ambient organic aerosols and could facilitate rapid data acquisition at multiple sites where AMS could not be deployed for logistical reasons., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Long-term exposure to vehicle emissions has been associated with detrimental health effects. Children are amongst the most susceptible group and schools represent an environment where they can experience significant exposure to vehicle emissions. However, there are limited studies on children's exposure to vehicle emissions in schools. The aim of this study was to quantify the concentration of organic aerosol (OA) and in particular, vehicle emissions that children are exposed to during school hours. Therefore an Aerodyne compact time-of-flight aerosol mass spectrometer (TOF-AMS) was deployed at five urban schools in Brisbane, Australia. TOF-AMS enabled the chemical composition of the non-refractory (NR-PM1) to be analysed with a high temporal resolution to assess the concentration of vehicle emissions and other OA components during school hours. The organic fraction at each school comprised the majority of NR-PM1. Primary emissions were found to dominate the OA at only one school which had an O:C ratio of 0.17, due to fuel powered gardening equipment used near the TOF-AMS. A significant source of the OA at two of the schools was aged vehicle emissions from nearby highways. More oxidised OA was observed at the remaining two schools, which also recorded strong biomass burning influences. In general, the diurnal cycle of the total OA concentration varied between schools and was found to be at a minimum during school hours. The major organic component that school children were exposed to during school hours was secondary OA at all schools. Peak exposure of school children to vehicle emissions occurred during school drop-off and pick-up times. Unless a school is located near major roads, children are exposed predominately to regional secondary OA as opposed to local emissions during school hours in urban environments., (Copyright © 2013 Elsevier B.V. All rights reserved.)

It has not yet been established whether the spatial variation of particle number concentration (PNC) within a microscale environment can have an effect on exposure estimation results. In general, the degree of spatial variation within microscale environments remains unclear, since previous studies have only focused on spatial variation within macroscale environments. The aims of this study were to determine the spatial variation of PNC within microscale school environments, in order to assess the importance of the number of monitoring sites on exposure estimation. Furthermore, this paper aims to identify which parameters have the largest influence on spatial variation as well as the relationship between those parameters and spatial variation. Air quality measurements were conducted for two consecutive weeks at each of the 25 schools across Brisbane, Australia. PNC was measured at three sites within the grounds of each school, along with the measurement of meteorological and several other air quality parameters. Traffic density was recorded for the busiest road adjacent to the school. Spatial variation at each school was quantified using coefficient of variation (CV). The portion of CV associated with instrument uncertainty was found to be 0.3, and, therefore, CV was corrected so that only noninstrument uncertainty was analyzed in the data. The median corrected CV (CVc) ranged from 0 to 0.35 across the schools, with 12 schools found to exhibit spatial variation. The study determined the number of required monitoring sites at schools with spatial variability and tested the deviation in exposure estimation arising from using only a single site. Nine schools required two measurement sites and three schools required three sites. Overall, the deviation in exposure estimation from using only one monitoring site was as much as 1 order of magnitude. The study also tested the association of spatial variation with wind speed/direction and traffic density, using partial correlation coefficients to identify sources of variation and nonparametric function estimation to quantify the level of variability. Traffic density and road to school wind direction were found to have a positive effect on CVc and, therefore, also on spatial variation. Wind speed was found to have a decreasing effect on spatial variation when it exceeded a threshold of 1.5 (m/s), while it had no effect below this threshold. Traffic density had a positive effect on spatial variation and its effect increased until it reached a density of 70 vehicles per five minutes, at which point its effect plateaued and did not increase further as a result of increasing traffic density.