Organic aerosol in the summertime southeastern United States: components and their link to volatility distribution, oxidation state and hygroscopicity

The volatility distribution of the organic aerosol (OA) and its sources during the Southern Oxidant and Aerosol Study (SOAS; Centreville, Alabama) was constrained using measurements from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a thermodenuder (TD). Positive matrix factorization (PMF) analysis was applied on both the ambient and thermodenuded high-resolution mass spectra, leading to four factors: more oxidized oxygenated OA (MO-OOA), less oxidized oxygenated OA (LO-OOA), an isoprene epoxydiol (IEPOX)-related factor (isoprene-OA) and biomass burning OA (BBOA). BBOA had the highest mass fraction remaining (MFR) at 100 °C, followed by the isoprene-OA, and the LO-OOA. Surprisingly the MO-OOA evaporated the most in the TD. The estimated effective vaporization enthalpies assuming an evaporation coefficient equal to unity were 58 ± 13 kJ mol^(−1) for the LO-OOA, 89 ± 10 kJ mol^(−1) for the MO-OOA, 55 ± 11 kJ mol^(−1) for the BBOA, and 63 ± 15 kJ mol^(−1) for the isoprene-OA. The estimated volatility distribution of all factors covered a wide range including both semi-volatile and low-volatility components. BBOA had the lowest average volatility of all factors, even though it had the lowest O  :  C ratio among all factors. LO-OOA was the more volatile factor and its high MFR was due to its low enthalpy of vaporization according to the model. The isoprene-OA factor had intermediate volatility, quite higher than suggested by a few other studies. The analysis suggests that deducing the volatility of a factor only from its MFR could lead to erroneous conclusions. The oxygen content of the factors can be combined with their estimated volatility and hygroscopicity to provide a better view of their physical properties

Organic aerosol in the summertime southeastern United States: components and their link to volatility distribution, oxidation state and hygroscopicity

The volatility distribution of the organic aerosol (OA) and its sources during the Southern Oxidant and Aerosol Study (SOAS; Centreville, Alabama) was constrained using measurements from an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a thermodenuder (TD). Positive matrix factorization (PMF) analysis was applied on both the ambient and thermodenuded high-resolution mass spectra, leading to four factors: more oxidized oxygenated OA (MO-OOA), less oxidized oxygenated OA (LO-OOA), an isoprene epoxydiol (IEPOX)-related factor (isoprene-OA) and biomass burning OA (BBOA). BBOA had the highest mass fraction remaining (MFR) at 100 °C, followed by the isoprene-OA, and the LO-OOA. Surprisingly the MO-OOA evaporated the most in the TD. The estimated effective vaporization enthalpies assuming an evaporation coefficient equal to unity were 58 ± 13 kJ mol^(−1) for the LO-OOA, 89 ± 10 kJ mol^(−1) for the MO-OOA, 55 ± 11 kJ mol^(−1) for the BBOA, and 63 ± 15 kJ mol^(−1) for the isoprene-OA. The estimated volatility distribution of all factors covered a wide range including both semi-volatile and low-volatility components. BBOA had the lowest average volatility of all factors, even though it had the lowest O  :  C ratio among all factors. LO-OOA was the more volatile factor and its high MFR was due to its low enthalpy of vaporization according to the model. The isoprene-OA factor had intermediate volatility, quite higher than suggested by a few other studies. The analysis suggests that deducing the volatility of a factor only from its MFR could lead to erroneous conclusions. The oxygen content of the factors can be combined with their estimated volatility and hygroscopicity to provide a better view of their physical properties

Χρήση της φασματομετρίας μάζας αεροζόλ για τη μέτρηση των φυσικών και χημικών ιδιοτήτων των ατμοσφαιρικών νανοσωματιδίων

The overall objective of this dissertation is to improve our understanding of the organic and inorganic atmospheric particles combining laboratory and field studies and state-of-the-art instrumentation. The recent development of on-line aerosol mass spectrometry and other continuous techniques allows for the first time detailed high time resolution investigations of atmospheric particulate matter and its chemical and physical properties (e.g. volatility, density etc). Organic aerosol (OA) consists of compounds with a wide range of volatilities and its ambient concentration is sensitive to this volatility distribution. Recent field studies have shown that the typical mass spectrum of ambient oxygenated organic aerosol (OOA) as measured by the Aerodyne Aerosol Mass Spectrometer (AMS) is quite different from the secondary organic aerosol (SOA) mass spectra reported in smog chamber experiments. Part of this discrepancy is due to the dependence of SOA composition on the organic aerosol concentration. High precursor concentrations lead to higher concentrations of the more volatile species in the produced SOA while at lower concentrations the less volatile compounds dominate the SOA composition. α-pinene, β-pinene, d-limonene and β-caryophyllene ozonolysis experiments were performed at moderate concentration levels. Using a thermodenuder the more volatile SOA species were removed achieving even lower SOA concentration. The less volatile fraction was then chemically characterized by an AMS. The signal fraction of m/z 44, and thus the concentration of CO2+, is significantly higher for the less volatile SOA. High NOx conditions result in less oxidized SOA than low NOx conditions, while increasing relative humidity levels results in more oxidized products for limonene but has little effect on α-and β-pinene SOA. Combing a smog chamber with a thermodenuder model employing the volatility basis-set framework the AMS SOA mass spectrum for each experiment and for each precursor is deconvoluted into low, medium and high volatility component mass spectra. The spectrum of the surrogate component with the lower volatility is quite similar to that of ambient OOA. The density of organic aerosol is another poorly-characterized property and there is still no general method for its estimation in aerosol systems with size-dependent composition where the organic-inorganic fraction changes fast. An algorithm for the calculation of organic aerosol density in mixed organic-inorganic particles combining measurements by the AMS and the Scanning Mobility Particle Sizer (SMPS) was developed. The approach is applicable to particles with size-dependent composition. The estimated density of secondary organic aerosol (SOA) formed by α-pinene, β-pinene and d-limonene ozonolysis was in the range of 1.4-1.65 g cm-3. However, in two cases the SOA had much lower density (0.9-1.0 g cm-3) indicating that there may be changes in particle morphology depending on the conditions of SOA formation. The high estimated density for these systems suggests that SOA particles may be solid or waxy. Based on our results, SOA yields in smog chamber experiments may be a lot higher (up to 50%) than the currently assumed values. Most of the literature results have been calculated by measuring the SOA number distribution with an SMPS and then multiplying the volume concentration with a density equal to 1 or 1.2 g cm-3. This method is also applicable to the primary organics and to ambient particles assuming that these particles are close to spherical and can also provide the collection efficiency (CE) of the AMS. For example this approach was used for field data during the Finokalia Aerosol Measurement Experiments (FAMEs). Real-time measurements of non-refractory submicron aerosols (NR-PM1) were conducted during the FAME-08 (early summer 2008) and FAME-09 (winter 2009) field studies. Both campaigns were part of the intensive EUCAARI Pan-European campaigns. The Finokalia site, located at a remote coastal place on Crete (Greece), is isolated and away from anthropogenic sources of pollution and this allows the study of aged organic aerosol coming from different directions. In order to measure the size-resolved chemical composition of the NR-PM1 particles an AMS was used. During FAME-08 ammonium sulfate and ammonium bisulfate were the largest components of the NR-PM1, followed by organics and water. There was practically zero nitrate. The organic aerosol was mainly regional, since the total organic aerosol mass changed little with source region. During FAME-09 organics, ammonium sulfate and ammonium bisulfate had almost equal fractions with the organics, but the nitrate was very low. The aerosol concentrations were almost a factor of 3 lower in FAME-09 than in FAME0-08 but more variable. A thermodenuder coupled with the Q-AMS and an SMPS were operated as well. We used the algorithm that combines AMS and SMPS measurements to estimate the AMS CE and organic particle density both for ambient and thermodenuder samples. Using these values the concentrations measured by the AMS for the ambient particles were in a good agreement with the other independent concentration measurements (filters, steam sampler). The Finokalia Station is ideal for studying organic aerosol of different photochemical age. The site is isolated, away from human activities and the wind may come from various directions: Europe, Balkans, Africa and sea. Further, the oxidation levels can vary, being stronger in the summer and weaker during winter. This allows the investigation of particles originating from the same sources but transferred under different metrological and photochemical conditions. The AMS-SMPS thermodenuder system was employed as well, for organic aerosol volatility measurements. For the volatility corrections we used the organic density and the CE of the AMS both of ambient and thermodenuded aerosol as calculated by the algorithm that combines AMS and SMPS data. The organic aerosol sampled during FAME-08 is quite uniform and highly oxidized more than one order of magnitude less volatile than laboratory-generated α-pinene SOA. The final goal of this research is to expand methods for measurement of the semi-volatile inorganic species of atmospheric aerosol and the gases that are in equilibrium with them. Modifying the steam jet aerosol collector (SJAC) technique both particulate phase (e.g. sulfate, nitrate, chloride, ammonium) and gas phase (e.g. ammonia, nitric acid, nitrous acid) can be measured. For this approach a denuded (from the gas species) and an undenuded line are used. From their difference the gas phase contribution can be estimated. Evaluating this system in an agricultural environment the concentrations of NH3, HONO, and HCl were measured. The HNO3 concentration was close to the detection limit (0.5 ppb) of our system

Ambient Aerosol Measurements in Different Environments

International audienceParticulate matter (PM) in the atmosphere has diverse natural and anthropogenic sources, and is a complex, heterogeneous mixture [...

Formation of secondary organic aerosol during the dark ozonolysis of α-humulene

<p>Sesquiterpenes (C15H24) are a class of biogenic volatile organic compounds that are significant secondary organic aerosol (SOA) precursors due to their high reactivity with oxidants and their high SOA yields. Previous studies have focused almost exclusively on β-caryophyllene, and there is relatively little known about the other sesquiterpenes. In this study, we focus on another major sesquiterpene, α-humulene, which has three endo-cyclic double bonds. A series of experiments quantified the SOA production during the ozonolysis of α-humulene in the Carnegie Mellon atmospheric simulation chamber. The experiments resulted in high SOA yields ranging from 30 to 70% for SOA concentration in the range 10 to 100 μg m-3. Most of the SOA had effective volatility equal or less than 1 μg m-3 at 298 K and the average SOA effective vaporization enthalpy was 115 ± 23 kJ mol-1. The SOA aerosol mass spectrometer (AMS) spectrum was slowly evolving during experiments, which suggested modest differences, from the AMS point of view, between the SOA compounds produced initially and the SOA compounds produced towards the end of the experiment. The α-humulene SOA mass spectrum resembled that of βcaryophyllene SOA but it was less similar to α-pinene SOA.</p><p>Sippial, D., Uruci, P., Kostenidou, E., and Pandis, S. N.: Formation of secondary organic aerosol during the darkozonolysis of α-humulene, Env. Sci. Atmos., 3, 1025–1033, https://doi.org/10.1039/d2ea00181k, 2023.</p&gt

The Interplay between Air Quality and Energy Efficiency in Museums, a Review

Energy efficiency in museums and buildings that house works of art or cultural heritage appears to be a difficult achievement if indoor air quality has to be kept at appropriate levels for artefacts’ long-term sustainability. There is a gap in our scientific literature on the relationship between indoor air quality and energy efficiency, meaning that there are no numerical data that examine both of them simultaneously, although this is a theme that is broadly discussed by museum managers, curators, and scientists. It is certain that the two parameters, indoor air quality (IAQ) and energy efficiency (EEF) are conflicting and difficult to reconcile. Furthermore, IAQ is not only the determination of temperature, relative humidity, and CO2, as is usually presented. Using green or renewable energy does not make a building “energy efficient”. Hence, in the manuscript we review the literature on IAQ of museums and exhibition buildings, in conjunction with the consideration of their EEF. Hopefully, reviewing the literature for this problem may lead to carefully designed monitoring experiments. The selection, application, and testing of appropriate technological measures can lead to a new balance between the two conflicting parameters. Not only must solutions be found, but these solutions are necessary in the mitigation battle against climate change

Secondary organic aerosol formed by Euro 5 gasoline vehicle emissions: chemical composition and gas-to-particle phase partitioning

International audienceIn this study we investigated the photo-oxidation of Euro 5 gasoline vehicle emissions during cold urban, hot urban and motorway Artemis cycles. The experiments were conducted in an environmental chamber with average OH concentrations ranging between 6.6 × 105–2.3 × 106 molec. cm−3, relative humidity (RH) between 40 %–55 % and temperatures between 22–26 °C. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) and the CHemical Analysis of aeRosol ON-line (CHARON) inlet coupled with a PTR-ToF-MS were used for the gas- and particle-phase measurements respectively. This is the first time that the CHARON inlet has been used for the identification of the secondary organic aerosol (SOA) produced from vehicle emissions. The secondary organic gas-phase products ranged between C1 and C9 with one to four atoms of oxygen and were mainly composed of small oxygenated C1–C3 species. The SOA formed contained compounds from C1 to C14, having one to six atoms of oxygen, and the products' distribution was centered at C5. Organonitrites and organonitrates contributed 6 %–7 % of the SOA concentration. Relatively high concentrations of ammonium nitrate (35–160 µg m−3) were formed. The nitrate fraction related to organic nitrate compounds was 0.12–0.20, while ammonium linked to organic ammonium compounds was estimated only during one experiment, reaching a fraction of 0.19. The SOA produced exhibited log C∗ values between 2 and 5. Comparing our results to theoretical estimations for saturation concentrations, we observed differences of 1–3 orders of magnitude, indicating that additional parameters such as RH, particulate water content, aerosol hygroscopicity, and possible reactions in the particulate phase may affect the gas-to-particle partitioning

Secondary organic aerosol formed by EURO 5 gasoline vehicle emissions: chemical composition and gas-to-particle phase partitioning

In this study we investigated the photo-oxidation of EURO 5 gasoline vehicle emissions during cold urban, hot urban and motorway Artemis cycles. The experiments were conducted in an environmental chamber with average OH concentrations ranging between 6.6x105–2.3x106 molecules cm-3, relative humidity (RH) 40–55 % and temperatures between 22–26 °C. A proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) and the chemical analysis of aerosol on-line (CHARON) inlet coupled with a PTR-ToF-MS were used for the gas and particle phase measurements respectively. This is the first time that CHARON inlet was used for the identification of the secondary organic aerosol (SOA) produced from vehicle emissions. The secondary organic gas phase products ranged between C1 and C9 with 1 to 4 atoms of oxygen and were mainly composed of small oxygenated C1–C3 species. The formed SOA contained compounds from C1 to C14, having 1 to 6 atoms of oxygen and the products’ distribution was centered at C5. Organonitrites and organonitrates contributed 6–7 % of the SOA concentration. Relatively high concentrations of ammonium nitrate (35–160 µg m-3) were formed. The nitrate fraction related to organic nitrate compounds was 0.12–0.20, while ammonium linked to organic ammonium compounds was estimated only during one experiment reaching a fraction of 0.19. The produced SOA exhibited logC* values between 2 and 5. Comparing our results to the theoretical estimations, we observed differences of 1–3 orders of magnitude indicating that additional parameters such as RH, particulate water content, aerosol hygroscopicity, and possible reactions in the particulate phase may affect the gas-to-particle partitioning

Properties and Atmospheric Oxidation of Norpinic Acid Aerosol

Norpinic acid is a major semi-volatile oxidation product of α-pinene and β-pinene, two of the most important biogenic atmospheric volatile organic compounds. In this study we characterized the physicochemical properties of norpinic acid aerosol using a variety of techniques, and we investigated its reaction with OH radicals. The Aerosol Mass Spectrometer (AMS) spectrum of norpinic acid was characterized by a pronounced peak at m/z 82 (C5H6O+), which can be used as its chemical signature. The measured density of norpinic acid particles was 1.3 g cm−3. Its saturation concentration at 298 K was estimated to be equal to 8.9 μg m−3 using thermodenuder measurements and 12.8 μg m−3 using isothermal dilution. Its vaporization enthalpy was equal to 71 kJ mol−1. After reaction with OH radicals for an equivalent atmospheric period of 0.6–5 days under UV radiation and low RH, there were no noticeable changes in the AMS spectrum of the particles, while the wall-loss corrected mass concentration slightly decreased. This suggests that the atmospheric aging products of norpinic acid particles are quite similar to the parent molecule when measured by the AMS, and the aging reactions lead to a small change in particle mass concentration