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).
As a part of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) and
Cyprus Aerosols and Gas Precursors (ENVI-Med CyAr) programs, this study aims
primarily to provide an improved understanding ...of the sources and the fate of
volatile organic compounds (VOCs) in the eastern Mediterranean. More than 60
VOCs, including biogenic species (isoprene and eight monoterpenes) and
oxygenated VOCs, were measured during a 1-month intensive field campaign
performed in March 2015 at the Cyprus Atmospheric Observatory (CAO), a
regional background site in Cyprus. VOC measurements were conducted using
complementary online and offline techniques. Biogenic VOCs (BVOCs) were
principally imputed to local sources and characterized by compound-specific
daily cycles such as diurnal maximum for isoprene and nocturnal maximum for
α- and β-pinenes, in connection with the variability of emission
sources. The simultaneous study of pinene and isoprene temporal evolution and
meteorological parameters has shown that BVOC emissions were mainly
controlled by ambient temperature, precipitation and relative humidity. It
was found that isoprene daytime emissions at CAO depended on temperature and
solar radiation changes, whereas nocturnal BVOC concentrations (e.g., from
oak and pine forests) were more prone to the relative humidity and
temperature changes. Significant changes in monoterpene mixing ratios
occurred during and after rainfall. The second part of the study focused on
new particle formation (NPF) events at CAO. BVOCs are known to potentially
play a role in the growth as well as in the early stages of formation of new
atmospheric particles. Based on observations of the particle size
distribution performed with a differential mobility particle sizer (DMPS) and
the total number concentrations of particles larger than 1 nm diameter
measured by particle size magnifier (PSM), NPF events were found on 14 out of
20 days of the field campaign. For all possible proxy parameters
(meteorological parameters, calculated H2SO4 and measured gaseous
compounds) having a role in NPF, we present daily variations of different
classes during nucleation event and non-event days. NPF can occur at various
condensational sink (CS) values and both under polluted and clean atmospheric
conditions. High H2SO4 concentrations coupled with high BVOC
concentrations seemed to be one of the most favorable conditions to observe
NPF at CAO in March 2015. NPF event days were characterized by either
(1) a predominant anthropogenic influence (high concentrations of
anthropogenic source tracers observed), (2) a predominant biogenic influence
(high BVOC concentrations coupled with low anthropogenic tracer
concentrations), (3) a mixed influence (high BVOC concentrations coupled with
high anthropogenic tracer concentrations) and (4) a marine influence (both
low BVOC and anthropogenic tracer
concentrations). More pronounced NPF events were identified during mixed
anthropogenic–biogenic conditions compared to the pure anthropogenic or
biogenic ones, for the same levels of precursors. Analysis of a specific NPF
period of the mixed influence type highlighted that BVOC interactions with
anthropogenic compounds enhanced nucleation formation and growth of newly
formed particles. During this period, the nucleation-mode particles may be
formed by the combination of high H2SO4 and isoprene amounts, under
favorable meteorological conditions (high temperature and solar radiation and
low relative humidity) along with low CS. During the daytime, growth of the
newly formed particles, not only sulfate but also oxygen-like organic aerosol
(OOA) mass contributions, increased in the particle phase. High BVOC
concentrations were observed during the night following NPF events,
accompanied by an increase in CS and in semi-volatile OOA contributions,
suggesting further BVOC contribution to aerosol nighttime growth by
condensing onto pre-existing aerosols.
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.
In complex atmospheric emission environments such as urban agglomerates, multiple sources control the ambient chemical composition driving air quality and regional climate. In contrast to pristine ...sites, where reliance on single or a few chemical tracers is often adequate for resolving pollution plumes and source influences, the comprehensive chemical fingerprinting of sources using non-methane hydrocarbons (NMHCs) and the identification of suitable tracer molecules and emission ratios becomes necessary. Here, we characterise and present chemical fingerprints of some major urban and agricultural emission sources active in South Asia, such as paddy stubble burning, garbage burning, idling vehicular exhaust and evaporative fuel emissions. A total of 121 whole air samples were actively collected from the different emission sources in passivated air sampling steel canisters and then analysed for 49 NMHCs (22 alkanes, 16 aromatics, 10 alkenes and one alkyne) using thermal desorption gas chromatography flame ionisation detection. Several new insights were obtained. Propane was found to be present in paddy stubble fire emissions (8 %), and therefore, for an environment impacted by crop residue fires, the use of propane as a fugitive liquefied petroleum gas (LPG) emission tracer must be done with caution. Propene was found to be ∼ 1.6 times greater (by weight) than ethene in smouldering paddy fires. Compositional differences were observed between evaporative emissions of domestic LPG and commercial LPG, which are used in South Asia. While the domestic LPG vapours had more propane (40 ± 6 %) than n-butane (19 ± 2 %), the converse was true for commercial LPG vapours (7 ± 6 % and 37 ± 4 %, respectively). Isoprene was identified as a new tracer for distinguishing paddy stubble and garbage burning in the absence of isoprene emissions at night from biogenic sources. Analyses of source-specific inter-NMHC molar ratios revealed that toluene/benzene ratios can be used to distinguish among paddy stubble fire emissions in the flaming (0.38 ± 0.11) and smouldering stages (1.40 ± 0.10), garbage burning flaming (0.26 ± 0.07) and smouldering emissions (0.59 ± 0.16), and traffic emissions (3.54 ± 0.21), whereas i-pentane ∕ n-pentane can be used to distinguish biomass burning emissions (0.06–1.46) from the petrol-dominated traffic and fossil fuel emissions (2.83–4.13). i-butane ∕ n-butane ratios
were similar (0.20–0.30) for many sources and could be used as a tracer
for photochemical ageing. In agreement with previous studies, i-pentane,
propane and acetylene were identified as suitable chemical tracers for
petrol vehicular and evaporative emissions, LPG evaporative and vehicular
emissions and flaming-stage biomass fires, respectively. The secondary
pollutant formation potential and human health impact of the sources was
also assessed in terms of their hydroxyl radical (OH) reactivity (s−1), ozone formation potential (OFP; gO3/gNMHC) and fractional benzene, toluene, ethylbenzene and xylenes (BTEX) content. Petrol vehicular emissions, paddy stubble fires and garbage fires were found to have a higher pollution potential (at ≥95 % confidence interval) relative to the other sources studied in this work. Thus, many results of this study provide a new foundational framework for quantitative source apportionment studies in complex emission environments.
Environmental context. Oceans represent 70% of the blue planet, and surprisingly, ocean emission in term of volatile organic compounds is poorly understood. The potential climate impacts on a global ...scale of various trace organic gases have been established, and the terrestrial inputs are well studied, but little is known about which of these can be emitted from oceanic sources. In the present study, atmospheric samples were taken over the Southern Indian Ocean, while crossing some oceanic fronts and different phytoplankton species. Such a study should aid in understanding oceanic emission, especially from phytoplankton, and will help modellers to determine concentrations of organic traces in the remote marine troposphere. Abstract. Considering its size and potential importance, the ocean is poorly characterised in terms of volatile organic compounds (VOC) that play important roles in global atmospheric chemistry. In order to better understand their potential sources and sinks over the Southern Indian Austral Ocean, shipborne measurements of selected species were made during the MANCHOT campaign during December 2004, on board the research vessel Marion Dufresne. Along the transect La Réunion to Kerguelen Island, air measurements of selected VOC (including dimethylsulfide (DMS) isoprene, carbonyls and organohalogens), carbon monoxide and ozone were performed, crossing subtropical, temperate and sub-Antarctic waters as well as pronounced subtropical and sub-Antarctic oceanic fronts. The remote marine boundary layer was characterised at latitudes 45-50°S. Oceanic fronts were associated with enhanced chlorophyll and biological activity in the seawater and elevated DMS and organohalogens in the atmosphere. These were compared with a satellite-derived phytoplankton distribution (PHYSAT). Diurnal variation for isoprene, terpenes, acetone and acetaldehyde was observed, analogously to recent results observed in mesocosm experiments.
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.
Levels and sources of non-Methane Hydrocarbons (NMHCs) were investigated at the urban background Thissio station, close to the historical center of Athens (Greece) from March 2016 to February 2017 ...(12 months), by means of an automated GC-FID. Alkanes dominated over aromatics and alkenes, with hourly mean levels ranging from detection limit up to 60 μg m−3 for i-pentane and 90 μg m−3 for toluene. Higher levels were recorded in the cold period relative to the warmer one. In addition, NMHCs seasonal diurnal cycles were characterized by a bimodal pattern, following the trend of tracers of anthropogenic sources. The Positive Matrix Factorization (PMF) was used for the allocation of NMHC to their sources. Five factors were identified and quantified, with traffic-related sources being the main one contributing up to 60% to total NMHCs, while biomass burning contributes up to 19%. A supplementary PMF assimilation was applied on a seasonal basis further including α-pinene, C6-C16 alkanes and aromatics. This PMF resulted to a seven-factor solution that allowed the examination of two additional sources, in addition to five already identified, highlighting the main contribution of anthropogenic sources (70%) to α-pinene.
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•Sources and levels of C2–C12 NMHCs in Athens, Greece based on annual sampling•Significant impact of traffic-related sources contributing ~60% to the total NMHCs•Wood burning although a seasonal source of NMHCs contributes 19% on an annual basis•Identification of additional emission sources by including α-pinene and C6–C16 VOC•Wood burning, fuel evaporation and fugitive emissions affect α-pinene levels (~70%).
More than 7000 atmospheric measurements of over 60 C2 − C16 volatile organic compounds (VOCs) were conducted at a background site in Cyprus during a 1-month intensive field campaign held in ...March 2015. This exhaustive dataset consisted of primary anthropogenic and biogenic VOCs, including a wide range of source-specific tracers, and oxygenated VOCs (with various origins) that were measured online by flame ionization detection–gas chromatography and proton transfer mass spectrometry. Online submicron aerosol chemical composition was performed in parallel using an aerosol mass spectrometer. This study presents the high temporal variability in VOCs and their associated sources. A preliminary analysis of their time series was performed on the basis of independent tracers (NO, CO, black carbon), meteorological data and the clustering of air mass trajectories. Biogenic compounds were mainly attributed to a local origin and showed compound-specific diurnal cycles such as a daily maximum for isoprene and a nighttime maximum for monoterpenes. Anthropogenic VOCs as well as oxygenated VOCs displayed higher mixing ratios under the influence of continental air masses (i.e., western Asia), indicating that long-range transport significantly contributed to the VOC levels in the area. Source apportionment was then conducted on a database of 20 VOCs (or grouped VOCs) using a source receptor model. The positive matrix factorization and concentration field analyses were hence conducted to identify and characterize covariation factors of VOCs that were representative of primary emissions as well as chemical transformation processes. A six-factor PMF solution was selected, namely two primary biogenic factors (relative contribution of 43 % to the total mass of VOCs) for different types of emitting vegetation; three anthropogenic factors (short-lived combustion source, evaporative sources, industrial and evaporative sources; 21 % all together), identified as being either of local origin or from more distant emission zones (i.e., the south coast of Turkey); and a last factor (36 %) associated with regional background pollution (air masses transported both from the Western and Eastern Mediterranean regions). One of the two biogenic and the regional background factors were found to be the largest contributors to the VOC concentrations observed at our sampling site. Finally, a combined analysis of VOC PMF factors with source-apportioned organic aerosols (OAs) helped to better distinguish between anthropogenic and biogenic influences on the aerosol and gas phase compositions. The highest OA concentrations were observed when the site was influenced by air masses rich in semi-volatile OA (less oxidized aerosols) originating from the southwest of Asia, in contrast with OA factor contributions associated with the remaining source regions. A reinforcement of secondary OA formation also occurred due to the intense oxidation of biogenic precursors.
Non-methane hydrocarbons (NMHCs) play an important role in
atmospheric chemistry, contributing to ozone and secondary organic aerosol
formation. They can also serve as tracers for various emission ...sources such as
traffic, solvents, heating and vegetation. The current work presents, for the
first time to our knowledge, time-resolved data of NMHCs, from two to six
carbon atoms, for a period of 5 months (mid-October 2015 to
mid-February 2016) in the “greater Athens area” (GAA), Greece. The measured NMHC
levels are among the highest reported in the literature for the Mediterranean
area during winter months, and the majority of the compounds demonstrate a
remarkable day-to-day variability. Their levels increase by up to factor of
4 from autumn (October–November) to winter (December–February). Microscale
meteorological conditions, especially wind speed in combination with
the planetary boundary layer (PBL) height, seem to contribute significantly to the variability of NMHC
levels, with an increase of up to a factor of 10 under low wind speed (<3 m s−1) conditions; this reflects the impact of local sources rather than long-range
transport. All NMHCs demonstrated a pronounced bimodal, diurnal pattern with
a morning peak followed by a second peak before midnight. The amplitude of
both peaks gradually increased towards winter, in comparison to autumn, by
a factor of 3 to 6 and closely followed that of carbon monoxide (CO), which
indicates a contribution from sources other than traffic, e.g.,
domestic heating (fuel or wood burning). By comparing the NMHC diurnal
variability with that of black carbon (BC), its fractions associated with
wood burning (BCwb) and fossil fuel combustion
(BCff), and with source profiles we conclude that the morning peak is attributed to
traffic while the night peak is mainly attributed to heating. With respect to the night peak, the
selected tracers and source profiles clearly indicate a contribution from both
traffic and domestic heating (fossil fuel and wood burning). NMHCs slopes
versus BCwb are similar when compared with those versus BCff
(slight difference for ethylene), which indicates that NMHCs are most likely equally
produced by wood and oil fossil fuel burning.
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