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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.)

Secondary particulate matter exerts adverse effects on air quality and human health. The production or reaction rate of secondary aerosols in polluted environments remains uncertain and is complicated by diverse emissions and meteorological conditions. By concurrently measuring the mass spectra of compounds in both particulate (using an aerosol mass spectrometer) and gas phases (using proton‐transfer‐reaction mass spectrometry) in suburban Beijing, we linked the secondary organic aerosol (OA) and volatile organic compounds (VOCs) to photochemical age (tage) and obtained their reaction or production rates. Factorization analysis of the mass spectra of OA and the 108 VOC species resolved three oxygenated OAs (OOA) and three secondary VOC factors at different oxidation levels. Primary organic aerosols and VOCs from traffic sources were determined to be important sources for secondary aerosol formation. At high pollution levels under the conditions of weaker solar radiation and higher relative humidity, moderately oxygenated OA (O/C = 0.61) and secondary inorganics were coproduced in combination with rapid consumption of all VOCs. At lower pollution levels, the intense solar radiation caused substantial and rapid production of OOA (O/C = 0.81) and intermediate VOCs (both in a high oxidation state) at a rate of 15.0% h−1 and 14.0% h−1, respectively. These results highlight the feedback effects between radiation and moisture in terms of altering the formation mechanism of secondary aerosols. In particular, highly oxygenated secondary airborne products under strong radiation should be considered in regard to their environmental impact. Plain Language Summary: In this study, the compositions of submicron aerosols and volatile organic compounds (VOCs) in suburban Beijing were concurrently characterized for their detailed mass spectra, and based on these spectra, the primary and secondary sources were apportioned to investigate their evolution and conversion. Our results demonstrate the contrasting phenomena of chemical evolution under the influence of solar radiation and moisture. Photo‐oxidation was observed to rapidly produce organic aerosol (OA) and secondary VOCs in a considerably high oxidation state, while higher relative humidity induced overall moderately oxygenated OA and secondary inorganic aerosols but resulted in more rapid consumption of all VOCs. Key Points: Mass spectra of organic compounds in both aerosols and gases were concurrently characterized in suburban BeijingThe production and consumption rates of organic aerosols (OAs) and gases were obtained under high radiation or moist conditionsHighly oxidized OAs and intermediate volatile gases are rapidly produced through photo oxidation under strong solar radiation [ABSTRACT FROM AUTHOR]

Water-soluble organic aerosols (OA) are an important component of air particles and one of the key drivers that impact both climate and human health. Understanding the processes involving water-soluble OA depends on how well the chemical composition of this aerosol component is decoded. Yet, obtaining detailed information faces several challenges, including water-soluble OA collection, extraction, and chemical complexity. This review highlights the multidimensional non-targeted analytical strategies that have been developed and employed for providing new insights into the structural and molecular features of water-soluble organic components present in air particles. First, the most prominent high-resolution mass spectrometric methods for near real-time measurements of water-soluble OA and their limitations are discussed. Afterward, a special emphasis is given to the degree of compositional information provided by offline multidimensional analytical techniques, namely excitation–emission (EEM) fluorescence spectroscopy, high-resolution mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy and their hyphenation with chromatographic systems. The major challenges ahead on the application of these multidimensional analytical strategies for OA research are also addressed so that they can be used advantageously in future studies. [ABSTRACT FROM AUTHOR]

Two approaches were applied for characterization of organic compounds in the atmospheric aerosols. These were chemical and statistical grouping analysis. We applied chemical group analysis as a new approach using the GC×GC data. Based on the principle of GC×GC, analytes in two dimensional data were divided into 6 chemical group depending on their volatility and polarity. Using this classification standards, all analytes were classified as one of 6 chemical groups, HP-VOC, LP-VOC, HP-SVOC, LP-SVOC, HPNVOC and LP-NVOC. The relationship between the sum of the peak areas of each chemical group with other variables such as the concentrations of OC, EC, OCPOC, OC/EC and OCSOC were studied. However, no apparent relationship was observed. The principle component analysis (PCA) was carried out to find out the relationship among the analytes based on their sources. The OVOCs were dominant compounds in 3 out of 4 factors in summer. In winter, factor 1 was related to secondary organic aerosol and factor 3 was related to primary emission sources. The proposed approach looks promising in characterization of chemical groups but have limitations at current stage which are discussed. [ABSTRACT FROM AUTHOR]

The characteristics of non-refractory submicron aerosols (NR-PM 1), focusing on organic aerosols, are examined over a tropical coastal location, Thumba, in southern peninsular India. The measurements were carried out using an aerosol chemical speciation monitor during 2017–2021. The results indicated organic aerosols as the major component (67–85%) in the NR-PM 1 mass loading during all seasons. Positive matrix factorization (PMF) analysis on the OA mass spectra yielded two factors resolving Hydrocarbon-like organic aerosols (HOA) and Oxygenated organic aerosols (OOA), with the major contribution to OA coming from OOA (mass fraction >50%) during all the seasons. Examination of the diurnal variations revealed the daytime enhancement in OOA and sulfate mass fractions, indicating photochemical production overwhelming the dilution at the surface due to local atmospheric boundary layer expansion. The OOA mass concentration showed a good correlation (R > 0.5) with odd oxygen (O 3 +NO 2) and with an increase in oxygen-to-carbon ratio (ΔO:C = 0.11 to 0.35 with Δodd oxygen = 60 μg m−3 for different seasons) (i.e., increased oxidation degree of OA) signifying the dominance of photochemistry and subsequent enhanced atmospheric oxidative capacity in OOA formation. Interestingly, the aerosol liquid water content (ALWC) doubled during the nighttime (>40 μg m−3) compared to the daytime (<20 μg m−3) in different seasons, indicating the combined impact of varying submicron aerosol composition and ambient relative humidity. Since highly humid (relative humidity >85%) conditions prevail over this tropical coastal station, especially during the nighttime, the role of aqueous-phase formation of OA is also examined. It was found that less oxidized/less-hygroscopic OA were prevalent during the nighttime, resulting in lower aqueous-phase OA processing. During all the seasons, the hygroscopicity of organics (к organics) reached as high as > 0.22 and was mainly driven by photochemical processing rather than aqueous-phase chemistry. These results highlight the importance of the OA formation pathways in affecting their hygroscopic properties over the tropical atmosphere. • Organics are the dominant NR-PM 1 species in all seasons. • Oxygenated species dominated (>50%) the overall OA. • Photochemical reactions dominated OOA production. • The hygroscopicity of organics is mainly driven by photochemical processing. [ABSTRACT FROM AUTHOR]

Organic aerosols (OA) are universally regarded as an important component of the atmosphere that have far-ranging impacts on climate forcing and human health. Many of these impacts are related to OA molecular characteristics. Despite the acknowledged importance, current uncertainties related to the source apportionment of molecular properties and environmental impacts make it difficult to confidently predict the net impacts of OA. Here we evaluate the specific molecular compounds as well as bulk structural properties of total suspended particulates in ambient OA collected from key emission sources (marine, biomass burning, and urban) using ultrahigh resolution mass spectrometry (UHR-MS) and proton nuclear magnetic resonance spectroscopy (¹H NMR). UHR-MS and ¹H NMR show that OA within each source is structurally diverse, and the molecular characteristics are described in detail. Principal component analysis (PCA) revealed that (1) aromatic nitrogen species are distinguishing components for these biomass burning aerosols; (2) these urban aerosols are distinguished by having formulas with high O/C ratios and lesser aromatic and condensed aromatic formulas; and (3) these marine aerosols are distinguished by lipid-like compounds of likely marine biological origin. This study provides a unique qualitative approach for enhancing the chemical characterization of OA necessary for molecular source apportionment. [ABSTRACT FROM AUTHOR]

Abstract: 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 &y& Elsevier]

Abstract: Organic aerosol chemical markers from normalized concentrations of independent measurements of mass fragments (using Aerosol Mass Spectrometry, AMS) are compared to bond-based functional groups (from Fourier Transform Infrared spectroscopy, FTIR) during eight field projects in the western hemisphere. Several field projects show weak correlations between alcohol group fractions and m/z 60 fractions, consistent with the organic hydroxyl groups and the fragmentation of saccharides, but the weakness of the correlations indicate chemical differences among the relationships for ambient aerosols in different regions. Carboxylic acid group fractions and m/z 44 fractions are correlated weakly for three projects, with correlations expected for aerosols dominated by di-acid compounds since their fragmentation is typically dominated by m/z 44. Despite differences for three projects with ratios of m/z 44 to m/z 57 fragments less than 10, five projects showed a linear trend between the project-average m/z 44 to m/z 57 ratio and the ratio of acid and alkane functional groups. While this correlation explains only a fraction of the fragment and bond variability measured, the consistency of this relationship at multiple sites indicates a general agreement with the interpretation of the relative amount of m/z 44 as a carboxylic acid group marker and m/z 57 as an alkane group marker. [Copyright &y& Elsevier]

A previously constructed semi-rotating cryogenic modulator was modified for comprehensive two-dimensional gas chromatography (GC×GC). The retention time repeatability was improved by replacing the modulator control program unit with a new system. Peak widths obtained with the modified modulator were comparable with those obtained with the previous modulator and other modulator types. The modulator was easy to construct and it can be installed in any commercial GC system. The constructed GC×GC–FID system and data obtained by gas chromatography–mass spectrometry (GC–MS) were used for identification of unknowns in forest aerosol samples. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The photooxidation of α-humulene in the presence of NOx, natural sunlight, and rural background air was investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). Identification and quantification of gas and particulate reaction products were reported over the course of the reaction. The daytime photooxidation was carried out in a large outdoor smog chamber (190 m3). A wide range of ring retaining and ring opening products in the gas and particle phase are reported. On average, measured gas and particle phase products accounted for ∼ 44% of the reacted α-humulene carbon. Measurements show that a number of reaction products with low vapor pressures (e.g. 3-seco-α-humulone aldehyde, 7-seco-α-humulone aldehyde, α-humulal aldehyde, α-humulene 3-oxide or α-humulene 7-oxide, α-humulaic/alic acid isomers, and 3-seco-α-14-hydroxyhumulone aldehyde) were found in the early stage of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation. [ABSTRACT FROM AUTHOR]

Gas and particulate reaction products from the ozonolysis of β -caryophyllene (I) in the presence of atmospheric air were investigated using a combination of gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study secondary organic aerosol formation. The nighttime oxidation was carried out in a large outdoor smog chamber (190 m3). A wide range of ring retaining and ring opening products in the gas and particle phase are reported over the course of the reaction. On average, measured gas and particle phase products accounted for ∼64% of the reacted β -caryophyllene (I) carbon. Measurements show that a number of reaction products with low vapor pressure (e.g., β-caryophyllone aldehyde (IV), β-norcaryophyllone aldehyde (V), β-caryophyllonic acid (VIII), β-14-hydroxycaryophyllonic acid (XIV)) were found in the sample taken during the first 20 min of the reaction and may play an important role in the early formation of secondary organic aerosol. A detailed mechanism is proposed to account for most products observed in this investigation. [ABSTRACT FROM AUTHOR]

The gas and particle phase products from the reaction of β-pinene with the atmospheric oxidants O3 and OH radicals in the presence of NOx were investigated using both gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC) for identification and quantification of reaction products. The nighttime oxidation of β-pinene in the presence of O3/air and the daytime oxidation of β-pinene in the presence of NOx/air and natural sunlight were carried out in the University of North Carolina large outdoor smog chamber (190 m3) located in Chatham County, North Carolina. A Scanning Mobility Particle Sizer system (3936, TSI) and a Condensation Particle Counter (3025A, TSI) were used to study the secondary organic aerosol (SOA) formation, and a filter pack/denuder sampling system was used for simultaneously collecting gas and particle phase products for analysis. A gas chromatograph coupled to a mass spectrometer (GC-EIMS or GC-CIMS) was used for the identification and quantification of gas and aerosol products. A HPLC method was used for the measurement of small carbonyl compounds (aldehydes and ketones) as their 2,4-dinitrophenylhydrazones (DNPH) derivatives. Mass balances for gaseous and aerosol reaction products were reported over the course of the reaction. More than sixteen products were identified and/or quantified in this study. On average, measured gas and particle phase products accounted for ∼57 to ∼71% of the reacted β-pinene carbon. Measurements showed that a number of reaction products were found in both O3 and NOx systems (pinic acid, pinalic-3-acid, 4-hydroxypinalic-3-acid, 4-oxonopinone, 1-hydroxynopinone, 3-hydroxynopinone, and nopinone). Pinic acid, pinalic-3-acid, and 4-hydroxypinalic-3-acid were observed in the early stage in the aerosol phase and may play an important role in the early formation of secondary aerosols. Detailed reaction schemes are presented to account for most of the observed reaction products. [ABSTRACT FROM AUTHOR]

A modified atmospheric pressure chemical ionization ion source is applied for direct analysis of volatile or low volatile organic compounds in air. The method is based on the direct introduction of the analytes in the gas phase and/or particle phase into the ion source of a commercial ion-trap mass spectrometer. Two methods are employed for the production of primary ions at atmospheric pressure, photoionization and corona discharge. It is shown that in the presence of a dopant, photoionization can be a highly efficient ionization method also for real-time analysis with detection limits for selected analytes in the lower ppt-range. Using corona discharge for the production of primary ions, which is instrumentally easier since no additional chemicals have to be added to the sample flow, we demonstrate the analytical potential of on-line atmospheric pressure chemical ionization mass spectrometry for reaction monitoring experiments. To do so, an atmospherically relevant gas phase reaction is carried out in a 500 l reaction chamber and gaseous and particulate compounds are monitored in the positive and negative ion mode of the mass spectrometer. [Copyright &y& Elsevier]

Particulate n-alkanes are major constituents of organic aerosols (OA). Being primary in origin, chemically stable and thus long-lived, n-alkanes retains source signatures and along with diagnostic parameters have extensively been used to identify source(s) of OA. Systematic, yearlong study was carried out in the Dhauladhar region of North-Western Himalaya (NWH) to investigate dynamics in the composition and concentration of aerosol-associated n-alkanes. PM10 samples were collected for 24 h, once every week, at an urban mid-altitude location (Dharamshala) and a rural low-altitude site (Pohara). Particulate bound n-alkanes were identified and quantified using thermal desorption gas chromatography mass spectrometry (TD-GCMS). Annual mean concentrations of total n-alkanes (TNA) were 211 ± 99 ng m−3 and 223 ± 83 ng m−3, while mass fractions of TNA in PM10 were 4410 ± 1759 ppm and 3622 ± 1243 ppm at Dharamshala and Pohara, respectively. At both sites, a slight dominance of odd carbon-numbered n-alkanes was noticed. The TNA concentration and associated diagnostic parameters indicated unique source profiles at rural and urban locations. Significant seasonal variations were attributed to the contrasting land-use settings and meteorological variations. Influence of petrogenic contributions at urban location and predominance of biogenic contributions at rural location were observed in spring and autumn seasons. Preliminary insights on sources of organic aerosols are presented here. The diagnostic parameters allowed apportionment of biogenic and petrogenic sources. Biogenic emissions from agricultural practices viz. harvesting and threshing were predominant in the rural settings, while tourism-led anthropogenic contributions significantly add to petrogenic contributions in urban environment of the NWH region. [ABSTRACT FROM AUTHOR]