Total hydroxyl radical (OH) reactivity, the total loss frequency of the hydroxyl radical in ambient air, provides the total loading of OH reactants in air. We measured the total OH reactivity for the ...first time during summertime at a coastal receptor site located in the western Mediterranean Basin. Measurements were performed at a temporary field site located in the northern cape of Corsica (France), during summer 2013 for the project CARBOSOR (CARBOn within continental pollution plumes: SOurces and Reactivity)–ChArMEx (Chemistry and Aerosols Mediterranean Experiment). Here, we compare the measured total OH reactivity with the OH reactivity calculated from the measured reactive gases. The difference between these two parameters is termed missing OH reactivity, i.e., the fraction of OH reactivity not explained by the measured compounds. The total OH reactivity at the site varied between the instrumental LoD (limit of detection = 3 s−1) to a maximum of 17 ± 6 s−1 (35 % uncertainty) and was 5 ± 4 s−1 (1σ SD – standard deviation) on average. It varied with air temperature exhibiting a diurnal profile comparable to the reactivity calculated from the concentration of the biogenic volatile organic compounds measured at the site. For part of the campaign, 56 % of OH reactivity was unexplained by the measured OH reactants (missing reactivity). We suggest that oxidation products of biogenic gas precursors were among the contributors to missing OH reactivity.
Near real‐time measurements of carbonaceous aerosols were performed in fine aerosols for a 10‐day period during winter at a suburban site of Paris (France). These measurements were performed using an ...OCEC Sunset Field instrument for elemental carbon (EC) and organic carbon (OC); a Particle‐Into‐Liquid‐Sampler coupled with a Total Organic Carbon (PILS‐TOC) instrument for water‐soluble OC (WSOC); and a 7‐λ aethalometer for absorption. A successful comparison was performed with filter sampling performed in parallel for EC, OC, and WSOC, providing further confidence on the results obtained by the online analyzers. A modified version of the aethalometer model was used to derive hourly concentrations of 3 organic aerosol (OA) sources: fossil fuel, wood burning, and secondary. This source apportionment was validated for primary OA (fossil fuel, wood burning) using time‐resolved measurements of specific tracers (including levoglucosan, water‐soluble potassium and methanol for wood burning) and showed that secondary organic aerosols (SOA) were the most abundant OA species during our study. Water‐soluble properties of these different OA sources were investigated from the reconstruction of experimentally determined water‐soluble/insoluble OC. About 23% of WSOC was found to be of a secondary (photochemical) origin. A large fraction of SOA was assigned as water‐insoluble and could originate from semi‐volatile primary OA from wood burning and/or anthropogenic emissions. These results have been obtained at a typical suburban site in France and may be then representative of a larger European area. They bring new light on the commonly accepted idea that SOA is mainly water‐soluble.
Key Points
Real‐time measurements of organic aerosols
Source apportionment of primary and secondary organic aerosols
Water soluble/insoluble secondary organic aerosols
Rationale
Secondary organic aerosols (SOAs) represent a significant portion of total atmospheric aerosols. They are generated by the oxidation of volatile organic compounds (VOCs), and particularly ...biogenic VOCs (BVOCs). The analysis of such samples is usually performed by targeted methods that often require time‐consuming preparation steps that can induce loss of compounds and/or sample contaminations.
Methods
Recently, untargeted methods using high‐resolution mass spectrometry (HRMS) have been successfully employed for a broad characterization of chemicals in SOAs. Herein we propose a new application of the direct analysis in real time (DART) ionization method combined with HRMS to quickly detect several hundred chemicals in SOAs collected on a quartz filter without sample preparation or separation techniques.
Results
The reproducibility of measurements was good, with several hundred elemental compositions common to three different replicates. The relative standard deviations of the intensities of the chemical families ranged from 6% to 35%, with sufficient sensitivity to allow the unambiguous detection of 4 ng/mm2 of pinic acid. The presence of oligomers and specific tracers was highlighted by MSn (n ≤ 4) experiments, an achievement that is difficult to attain with other ultrahigh‐resolution mass spectrometers. Contributions of this untargeted DART‐HRMS method were illustrated by the analysis of fresh and aged SOAs from different gaseous precursors such as limonene, a β‐pinene/limonene mixture or scots pines emissions.
Conclusions
The results show that it is possible to use DART‐HRMS for the identification of tracers of specific aging reactions, or for the identification of aerosols from specific biogenic precursors.
Dimethyl sulfide (DMS) plays an important role in the atmosphere by influencing the formation of aerosols and cloud condensation nuclei. In
contrast, the role of methanethiol (MeSH) for the budget ...and flux of reduced sulfur remains poorly understood. In the present study, we
quantified DMS and MeSH together with the trace gases carbon monoxide (CO), isoprene, acetone, acetaldehyde and acetonitrile in
North Atlantic and Arctic Ocean surface waters, covering a transect from 57.2 to 80.9∘ N in high spatial resolution in May–June
2015. Whereas isoprene, acetone, acetaldehyde and acetonitrile concentrations decreased northwards, CO, DMS and MeSH retained
substantial concentrations at high latitudes, indicating specific sources in polar waters. DMS was the only compound with a higher average concentration in
polar (31.2 ± 9.3 nM) than in Atlantic waters (13.5 ± 2 nM), presumably due to DMS originating from sea ice. At
eight sea-ice stations north of 80∘ N, in the diatom-dominated marginal ice zone, DMS and chlorophyll a markedly correlated
(R2 = 0.93) between 0–50 m depth. In contrast to previous studies, MeSH and DMS did not co-vary, indicating decoupled
processes of production and conversion. The contribution of MeSH to the sulfur budget (represented by DMS + MeSH) was on
average 20 % (and up to 50 %) higher than previously observed in the Atlantic and Pacific oceans, suggesting MeSH as an important
source of sulfur possibly emitted to the atmosphere. The potential importance of MeSH was underlined by several correlations with bacterial
taxa, including typical phytoplankton associates from the Rhodobacteraceae and Flavobacteriaceae families. Furthermore, the
correlation of isoprene and chlorophyll a with Alcanivorax indicated a specific relationship with isoprene-producing
phytoplankton. Overall, the demonstrated latitudinal and vertical patterns contribute to understanding how concentrations of central marine trace
gases are linked with chemical and biological dynamics across oceanic waters.
This research builds upon a previous study that explored the potential of the modified WIBS-4+ to selectively differentiate and detect different bioaerosol classes. The current work evaluates the ...influence of meteorological and air quality parameters on bioaerosol concentrations, specifically pollen and fungal spore dynamics.
Temperature was found to be the most influential parameter in terms of pollen production and release, showing a strong positive correlation. Wind data analysis provided insights into the potential geographic origins of pollen and fungal spore concentrations. Fungal spores were primarily shown to originate from a westerly direction, corresponding to agricultural land use, whereas pollen largely originated from a North-easterly direction, corresponding to several forests.
The influence of air quality was also analysed to understand its potential impact on the WIBS fluorescent parameters investigated. Most parameters had a negative association with fungal spore concentrations, whereas several anthropogenic influences showed notable positive correlations with daily pollen concentrations. This is attributed to similar driving forces (meteorological parameters) and geographical origins. In addition, the WIBS showed a significant correlation with anthropogenic pollutants originating from combustion sources, suggesting the potential for such modified spectroscopic instruments to be utilized as air quality monitors.
By combining all meteorological and pollution data along with WIBS-4+ channel data, a set of Multiple Linear Regression (MLR) analyses were completed. Successful results with R2 values ranging from 0.6 to 0.8 were recorded. The inclusion of meteorological parameters was dependent on the spore or pollen type being examined.
Display omitted
•The WIBS-4+ study unveils the origins and environmental correlations of pollen and fungal spores in Île-de-France.•Findings include positive correlation of some pollens with temperature and an inverse relationship with relative humidity.•Challenges were encountered with the WIBS-4+ in capturing large fluorescent particles at high windspeeds.•We traced the origins of spores from the west, while pollen came from the north-east.•An interesting discovery was the lack of correlation between fungal spores and all measured pollutants.
In Central Europe the most common allergies are provoked by grass or birch pollen allergens. We determined the intra-daily behavior of airborne pollen grains of grasses (Poaceae) and birch (Betula ...ssp.) in Central Europe, based on data obtained from a network of automatic pollen monitors over Europe (www.pollenscience.eu). Our aim was to determine the time of day when the lowest concentrations occur, to provide allergic individuals the optimal time to ventilate their homes. The study was carried out in three Central European capitals, Berlin (Germany), Paris-Saclay (France), and Luxembourg (Luxembourg), as well as in eight stations in Germany (Altötting, Feucht, Garmisch-Partenkirchen, Hof, Marktheidenfeld, Mindelheim, Munich and Viechtach). The diurnal rhythm of these eleven locations was analyzed for either the complete, first week, peak week, peak day and last week of the pollen season. The data studied were reported as pollen/m3 measured in 3 h periods. Stations were classified as city, semi-populated or countryside areas using land-use and population density criteria.
Grass pollen has a more pronounced diurnal rhythm than birch pollen concentrations. A significant difference was observed when comparing day (6–21 h) versus night (21–6 h) for all stations. No difference was detected between city and countryside for both pollen types, although for Poaceae a longer period of maximum concentrations was observed in big cities and higher day/night-time differences were registered in the countryside (6.4) than in cities (3.0). The highest pollen concentrations were observed between 9 and 18 h for grass, but the rhythm was less pronounced for birch pollen. For allergic individuals who want to bring in fresh air in their homes, we recommend opening windows after 21 h, but even better early in the morning between 6 and 9 h before pollinations (re)starts.
Display omitted
•Grass pollen has a pronounced diurnal rhythm, birch pollen has not.•No differences in diurnal rhythm between city and countryside•Between 9 and 18 h are the highest pollen concentration for Poaceae and Betula.•Bring in fresh air into homes is best early in the morning, between 6 and 9 h a.m.
In September 2017, we conducted a
proton-transfer-reaction mass-spectrometry (PTR-MS) intercomparison campaign at the CESAR observatory, a rural site in the central Netherlands near the village of ...Cabauw. Nine research groups
deployed a total of 11 instruments covering a wide range of instrument
types and performance. We applied a new calibration method based on fast
injection of a gas standard through a sample loop. This approach allows
calibrations on timescales of seconds, and within a few minutes an automated
sequence can be run allowing one to retrieve diagnostic parameters that indicate
the performance status. We developed a method to retrieve the mass-dependent transmission from the fast calibrations, which is an essential
characteristic of PTR-MS instruments, limiting the potential to calculate
concentrations based on counting statistics and simple reaction kinetics in
the reactor/drift tube. Our measurements show that PTR-MS instruments follow
the simple reaction kinetics if operated in the standard range for pressures
and temperature of the reaction chamber (i.e. 1–4 mbar, 30–120∘,
respectively), as well as a reduced field strength E∕N in the range of 100–160 Td. If
artefacts can be ruled out, it becomes possible to quantify the signals of
uncalibrated organics with accuracies better than ±30 %. The
simple reaction kinetics approach produces less accurate results at E∕N levels
below 100 Td, because significant fractions of primary ions form water
hydronium clusters. Deprotonation through reactive collisions of protonated
organics with water molecules needs to be considered when the collision
energy is a substantial fraction of the exoergicity of the proton transfer
reaction and/or if protonated organics undergo many collisions with water
molecules.
Initiated in 1997, the year‐round study of formic and acetic acids was maintained until 2011 at the coastal Antarctic site of Dumont d'Urville. The records show that formic and acetic acids are ...rather abundant in summer with typical mixing ratios of 200 pptv and 700 pptv, respectively. With the aim to constrain their budget, investigations of their potential marine precursors like short‐chain alkenes and acetaldehyde were initiated in 2011. Acetic acid levels in December 2010 were four times higher than those observed over summers back to 1997. These unusually high levels were accompanied by unusually high levels of ammonia, and by an enrichment of oxalate in aerosols. These observations suggest that the guano decomposition in the large penguin colonies present at the site was particularly strong under weather conditions encountered in spring 2010 (important snow storms followed by sunny days with mild temperatures). Although being dependent on environmental conditions, this process greatly impacts the local atmospheric budget of acetic acid, acetaldehyde, and acetone during the entire summer season. Present at levels as high as 500 pptv, acetaldehyde may represent the major precursor of acetic acid, alkene‐ozone reactions remaining insignificant sources. Far less influenced by penguin emissions, the budget of formic acid remains not fully understood even if alkene‐ozone reactions contribute significantly.
Key Points
Ornithogenic soil emission emits NH3 as well as CH3COOH and other OVOCs
Within the framework of air quality studies at the megacity scale, highly time-resolved volatile organic compound (C2–C8) measurements were performed in downtown Paris (urban background sites) from ...January to November 2010. This unique dataset included non-methane hydrocarbons (NMHCs) and aromatic/oxygenated species (OVOCs) measured by a GC-FID (gas chromatograph with a flame ionization detector) and a PTR-MS (proton transfer reaction – mass spectrometer), respectively. This study presents the seasonal variability of atmospheric VOCs being monitored in the French megacity and their various associated emission sources. Clear seasonal and diurnal patterns differed from one VOC to another as the result of their different origins and the influence of environmental parameters (solar radiation, temperature). Source apportionment (SA) was comprehensively conducted using a multivariate mathematical receptor modeling. The United States Environmental Protection Agency's positive matrix factorization tool (US EPA, PMF) was used to apportion and quantify ambient VOC concentrations into six different sources. The modeled source profiles were identified from near-field observations (measurements from three distinct emission sources: inside a highway tunnel, at a fireplace and from a domestic gas flue, hence with a specific focus on road traffic, wood-burning activities and natural gas emissions) and hydrocarbon profiles reported in the literature. The reconstructed VOC sources were cross validated using independent tracers such as inorganic gases (NO, NO2, CO), black carbon (BC) and meteorological data (temperature). The largest contributors to the predicted VOC concentrations were traffic-related activities (including motor vehicle exhaust, 15 % of the total mass on the annual average, and evaporative sources, 10 %), with the remaining emissions from natural gas and background (23 %), solvent use (20 %), wood-burning (18 %) and a biogenic source (15 %). An important finding of this work is the significant contribution from wood-burning, especially in winter, where it could represent up to ∼ 50 % of the total mass of VOCs. Biogenic emissions also surprisingly contributed up to ∼ 30 % in summer (due to the dominating weight of OVOCs in this source). Finally, the mixed natural gas and background source exhibited a high contribution in spring (35 %, when continental air influences were observed) and in autumn (23 %, for home heating consumption).
PDF
