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.
During the summer of 2012 a coordinated field campaign was conducted in multiple locations in Greece in order to characterize the ambient particulate matter (PM) levels, its chemical composition and ...the contribution of the regional and local sources. PM1, PM2.5 and PM10 samples were collected simultaneously at seven different sites in Greece: an urban and a suburban station in Patras, a suburban station in Thessaloniki, a suburban and an urban background station in Athens, a rural background station at the Navarino Environmental Observatory (NEO) in southwestern Peloponnese and a remote background site at Finokalia in the northeastern part of Crete. The sites were selected to facilitate the estimation of the contribution of the local emission sources and long range transport.
Sulfate and organics were the major PM1 components in all sites suggesting that high sulfate levels still remain in parts of Europe. The photochemistry of the Eastern Mediterranean can convert rapidly the emitted sulphur dioxide to sulfate. Our analysis indicated significant sulfate production over the area, with high sulfate levels, especially in the remote site of Finokalia, associated with air masses that had passed over Turkey. There was high regional secondary organic aerosol production dominating organic aerosol levels even in a major city like Athens. High organic aerosol levels were associated with air masses that had crossed the Balkans with a significant biogenic component. The average PM2.5 concentration ranged from 13 to 18 μg m−3 in the different sites. There were unexpected significant gradients in the concentrations of secondary aerosol components in length scales of a few hundred kilometers. The low concentrations of measured PM2.5 nitrate are mostly organic nitrates and supermicrometer nitrate associated with sea-salt and dust. Dust was a significant PM10 constituent in all areas and was quite variable in space showing the importance of the local sources.
•High sulfate levels still remain in parts of Europe.•High regional secondary organic aerosol production during summer.•Significant spatial gradients in secondary organic aerosol levels.•Most of the fine PM nitrates are organonitrates.
In the context of the international experimental campaign Hygroscopic Aerosols to Cloud Droplets (HygrA-CD, 15 May to 22 June 2014), dry aerosol size distributions were measured at Demokritos station ...(DEM) using a Scanning Mobility Particle Sizer (SMPS) in the size range from 10 to 550nm (electrical mobility diameter), and an Optical Particle Counter (OPC model Grimm 107 operating at the laser wavelength of 660nm) to acquire the particle size distribution in the size range of 250nm to 2.5 μm optical diameter. This work describes a method that was developed to align size distributions in the overlapping range of the SMPS and the OPC, thus allowing us to retrieve the real part of the aerosol equivalent refractive index (ERI). The objective is to show that size distribution data acquired at in situ measurement stations can provide an insight to the physical and chemical properties of aerosol particles, leading to better understanding of aerosol impact on human health and earth radiative balance. The resulting ERI could be used in radiative transfer models to assess aerosol forcing direct effect, as well as an index of aerosol chemical composition. To validate the method, a series of calibration experiments were performed using compounds with known refractive index (RI). This led to a corrected version of the ERI values, (ERICOR). The ERICOR values were subsequently compared to model estimates of RI values, based on measured PM2.5 chemical composition, and to aerosol RI retrieved values by inverted lidar measurements on selected days.
We present comprehensive results on continuous atmospheric cluster and particle measurements in the size range ~1-42 nm within the European Integrated project on Aerosol Cloud Climate and Air Quality ...interactions (EUCAARI) project. We focused on characterizing the spatial and temporal variation of new particle formation events and relevant particle formation parameters across Europe. Different types of air ion and cluster mobility spectrometers were deployed at 12 field sites across Europe from March 2008 to May 2009. The measurements were conducted in a wide variety of environments, including coastal and continental locations as well as sites at different altitudes (both in the boundary layer and the free troposphere). New particle formation events were detected at all of the 12 field sites during the year-long measurement period. From the data, nucleation and growth rates of newly formed particles were determined for each environment. In a case of parallel ion and neutral cluster measurements, we could also estimate the relative contribution of ion-induced and neutral nucleation to the total particle formation. The formation rates of charged particles at 2 nm accounted for 1-30% of the corresponding total particle formation rates. As a significant new result, we found out that the total particle formation rate varied much more between the different sites than the formation rate of charged particles. This work presents, so far, the most comprehensive effort to experimentally characterize nucleation and growth of atmospheric molecular clusters and nanoparticles at ground-based observation sites on a continental scale.
Cloud condensation nuclei counter (CCNC) measurements performed at 14 locations around the world within the European Integrated project on Aerosol Cloud Climate and Air Quality interactions (EUCAARI) ...framework have been analysed and discussed with respect to the cloud condensation nuclei (CCN) activation and hygroscopic properties of the atmospheric aerosol. The annual mean ratio of activated cloud condensation nuclei (NCCN) to the total number concentration of particles (NCN), known as the activated fraction A, shows a similar functional dependence on supersaturation S at many locations – exceptions to this being certain marine locations, a free troposphere site and background sites in south-west Germany and northern Finland. The use of total number concentration of particles above 50 and 100 nm diameter when calculating the activated fractions (A50 and A100, respectively) renders a much more stable dependence of A on S; A50 and A100 also reveal the effect of the size distribution on CCN activation. With respect to chemical composition, it was found that the hygroscopicity of aerosol particles as a function of size differs among locations. The hygroscopicity parameter κ decreased with an increasing size at a continental site in south-west Germany and fluctuated without any particular size dependence across the observed size range in the remote tropical North Atlantic and rural central Hungary. At all other locations κ increased with size. In fact, in Hyytiälä, Vavihill, Jungfraujoch and Pallas the difference in hygroscopicity between Aitken and accumulation mode aerosol was statistically significant at the 5 % significance level. In a boreal environment the assumption of a size-independent κ can lead to a potentially substantial overestimation of NCCN at S levels above 0.6 %. The same is true for other locations where κ was found to increase with size. While detailed information about aerosol hygroscopicity can significantly improve the prediction of NCCN, total aerosol number concentration and aerosol size distribution remain more important parameters. The seasonal and diurnal patterns of CCN activation and hygroscopic properties vary among three long-term locations, highlighting the spatial and temporal variability of potential aerosol–cloud interactions in various environments.
Airborne particulate matter in the PM sub(2.5) and PM sub(1) size ranges has been sampled at three sites within the Mediterranean urban area of the Athens Basin, representing background, ...roadside-industrialized and coastal background locations. With the principal aim to identify the sources and discriminate the contribution of the regional input versus the local one, simultaneous chemical characterization with respect to carbonaceous and ionic species was also carried out on the collected samples. In general, the average recorded values were within the Mediterranean concentration range. The constant prevalence of the ionic mass (52%-79%) over one of the carbonaceous, being combined with the occurrence of its maximum rates at the coastal background environment (74%-79% and 73%-77% for PM sub(2.5) and PM sub(1), respectively) leads to the hypothesis that the fine PM pollution in the basin, especially for the remote locations, is evidently governed by the external intrusion. Even at the polluted atmosphere of the roadside-industrialized environment, the PM mass was regionally originated, with the corresponding input reaching up to 87% (northward flow). Applying factor analysis on the PM sub(2.5) database it came obvious that the sources which were responsible for the configured PM burden were not fully differentiated not only between the different types of environment but also between the exceedances and the clean air events. The contribution of the secondary, marine and combustion processes was constant at all the stations of the network, while a continuous input of crustal particles characterized both the roadside-industrialized and the coastal atmosphere. Finally, the episodic values show a general common signal of secondary mixed rho mu emissions, high influence of both regional and local pollution spikes, confirming the earlier findings for the significance of transportation.
The international experimental campaign Hygroscopic Aerosols to Cloud Droplets (HygrA-CD), organized in the Greater Athens Area (GAA), Greece from 15 May to 22 June 2014, aimed to study the ...physico-chemical properties of aerosols and their impact on the formation of clouds in the convective Planetary Boundary Layer (PBL). We found that under continental (W-NW-N) and Etesian (NE) synoptic wind flow and with a deep moist PBL (~2–2.5km height), mixed hygroscopic (anthropogenic, biomass burning and marine) particles arrive over the GAA, and contribute to the formation of convective non-precipitating PBL clouds (with droplets of ~16–20μm mean diameter) with vertical extent up to 500m. Under these conditions, high updraft velocities (1–2ms−1) and cloud condensation nuclei (CCN) concentrations (~2000cm−3 at 1% supersaturation), generated clouds with an estimated cloud droplet number of ~600cm−3. Under Saharan wind flow conditions (S-SW) a shallow PBL (<1–1.2km height) develops, leading to much higher CCN concentrations (~3500–5000cm−3 at 1% supersaturation) near the ground; updraft velocities, however, were significantly lower, with an estimated maximum cloud droplet number of ~200cm−3 and without observed significant PBL cloud formation. The largest contribution to cloud droplet number variance is attributed to the updraft velocity variability, followed by variances in aerosol number concentration.
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•First coordinated measurements over Athens to study the impact of aerosols on PBL cloud formation (HygrA-CD campaign).•Under continental and Etesians wind flow he PBL height was quite deep (~2–2.5km), while under Saharan wind flow conditions, the PBL height remained quite shallow (<1–1.2km).•The origin of the atmospheric air masses, the prevailing meteorological conditions and aerosol hygroscopicity play a major role on the cloud formation at the vicinity of the PBL.•Upward aerosol fluxes determine the number of the activated CCN at the cloud base.
Similarities and differences in the submicron atmospheric aerosol chemical composition are analyzed from a unique set of measurements performed at 21 sites across Europe for at least one year. These ...sites are located between 35 and 62°N and 10° W – 26°E, and represent various types of settings (remote, coastal, rural, industrial, urban). Measurements were all carried out on-line with a 30-min time resolution using mass spectroscopy based instruments known as Aerosol Chemical Speciation Monitors (ACSM) and Aerosol Mass Spectrometers (AMS) and following common measurement guidelines. Data regarding organics, sulfate, nitrate and ammonium concentrations, as well as the sum of them called non-refractory submicron aerosol mass concentration (NR-PM1) are discussed. NR-PM1 concentrations generally increase from remote to urban sites. They are mostly larger in the mid-latitude band than in southern and northern Europe. On average, organics account for the major part (36–64%) of NR-PM1 followed by sulfate (12–44%) and nitrate (6–35%). The annual mean chemical composition of NR-PM1 at rural (or regional background) sites and urban background sites are very similar. Considering rural and regional background sites only, nitrate contribution is higher and sulfate contribution is lower in mid-latitude Europe compared to northern and southern Europe. Large seasonal variations in concentrations (μg/m³) of one or more components of NR-PM1 can be observed at all sites, as well as in the chemical composition of NR-PM1 (%) at most sites. Significant diel cycles in the contribution to NR-PM1 of organics, sulfate, and nitrate can be observed at a majority of sites both in winter and summer. Early morning minima in organics in concomitance with maxima in nitrate are common features at regional and urban background sites. Daily variations are much smaller at a number of coastal and rural sites. Looking at NR-PM1 chemical composition as a function of NR-PM1 mass concentration reveals that although organics account for the major fraction of NR-PM1 at all concentration levels at most sites, nitrate contribution generally increases with NR-PM1 mass concentration and predominates when NR-PM1 mass concentrations exceed 40 μg/m³ at half of the sites.
•Long term on line submicron aerosol chemical speciation measurements performed at 21 European sites were analysed.•Seasonal and diel variations in the aerosol chemical composition can generally be observed.•Most submicron aerosol mass consists of organics.•Nitrate contribution increases with the aerosol mass concentration at most sites.
With the principal aim to assess the typical Mediterranean profile of the PM
and PM
pollution, three intensive monitoring campaigns took place simultaneously within different types of environment ...across an urban location of the basin. Focusing on the PM components with numerous anthropogenic sources and increased potential health risk, the samples were chemically analyzed for 20 p.m.-bound Polycyclic Aromatic Hydrocarbons (PAHs). Carbonaceous and ionic constituents were quantified as well. In order to uncover the spatiotemporal variation of the PM profile the key sources were identified, the seasonal effects and the role of the prevailing mesoscale atmospheric circulation were evaluated and most importantly the potential health risk was estimated. In general, the pollution status of the basin was the result of a complex interaction between the local and external input with Particulate Organic Matter (POM) and Secondary Inorganic Aerosols (SIA) being the main aerosols' components. PM
was a better indicator of the anthropogenic emissions while according to the results of factor analysis the co-existence of various combustion sources was determinant. Chemically, the maxima of the ΣPAHs, the differentiation of their structure in accordance with their molecular weight and the distribution of the individual compounds confirmed the significance of the emission sources. Similarly, the estimated carcinogenicity/mutagenicity was emission-dependent with the maximum contribution coming from BaP, IndP, BghiPer, BeP and BbF. Seasonally, the highest potential health risk of the PAHs' mixture was recorded during the cold season while meteorologically, it was mostly associated with the south flow.
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