56 research outputs found
Size-resolved CCN distributions and activation kinetics of aged continental and marine aerosol
We present size-segregated measurements of cloud condensation nucleus (CCN) activity of aged aerosol sampled at Finokalia, Crete, during the Finokalia Aerosol Measurement Experiment of summer 2007 (FAME07). From analysis of the data, hygroscopicity and activation kinetics distributions are derived. The CCN are found to be highly hygroscopic, (expressed by a size- and time- averaged hygroscopicity parameter κ ∼ 0.22), with the majority of particles activating at ~0.5â0.6 % supersaturation. Air masses originating from Central-Eastern Europe tend to be associated with higher CCN concentrations and slightly lower hygroscopicity (κ ∼ 0.18) than for other airmass types. The particles were always well mixed, as reflected by the high activation ratios and narrow hygroscopicity distribution widths. Smaller particles (~40 nm) were found to be more hygroscopic (~0.1Îș units higher) than the larger ones (~100 nm). The particles with diameters less than 80 nm exhibited a diurnal hygroscopicity cycle (with Îș peaking at ~14 h local time), consistent with photochemical aging and volatilization of less hygroscopic material from the aerosol. Use of bulk chemical composition and the aerosol number distribution results in excellent CCN closure when applying Köhler theory in its simplest form. Using asymptotic and threshold droplet growth analysis, the "aged" organics present in the aerosol were found not to suppress or delay the water uptake kinetics of particles in this environment
Size-segregated mass distributions of aerosols over Eastern Mediterranean: seasonal variability and comparison with AERONET columnar size-distributions
International audienceThis work provides long-term (2004?2006) size segregated measurements of aerosol mass at a remote coastal station in the southern Europe, with the use of size-selective samplings (SDI impactor). Seven distinct modes were identified in the range 0?10 ”m and the dominant were the "Accumulation 1" (0.25?0.55 ”m) and the "Coarse 2" (3?7 ”m) modes. The seasonal characteristics of each mode were thoroughly studied and different sources for submicron and supermicron particles were identified, the first being related to local/regional and transported pollution with maximum in summer and the latter to dust from deserted areas in Northern Africa maximizing in spring. On average, PM2.5 and PM1 accounted for 60% and 40% of PM10 mass, respectively.The representativity of the ground-based measurements for the total column was also investigated by comparing the measured aerosol mass distributions with the AERONET volume size distribution data. Similar seasonal patterns were revealed and AERONET was found adequate for the estimation of background levels of both fine and coarse particles near surface, with certain limitations in the case of pollution or dust abrupt episodes due to its low temporal coverage
Particle size distributions in the Eastern Mediterranean troposphere
Atmospheric particle size distributions were measured on Crete island, Greece in the Eastern Mediterranean during an intensive field campaign between 28 August and 20 October, 2005. Our instrumentation combined a differential mobility particle sizer (DMPS) and an aerodynamic particle sizer (APS) and measured number size distributions in the size range 0.018 ÎŒmâ10 ÎŒm. Four time periods with distinct aerosol characteristics were discriminated, two corresponding to marine and polluted air masses, respectively. In marine air, the sub-ÎŒm size distributions showed two particle modes centered at 67 nm and 195 nm having total number concentrations between 900 and 2000 cmâ3. In polluted air masses, the size distributions were mainly unimodal with a mode typically centered at 140 nm, with number concentrations varying between 1800 and 2900 cmâ3. Super-ÎŒm particles showed number concentrations in the range from 0.01 to 2.5 cmâ3 without any clear relation to air mass origin. A small number of short-lived particle nucleation events were recorded, where the calculated particle formation rates ranged between 1.1â1.7 cmâ3 sâ1. However, no particle nucleation and growth events comparable to those typical for the continental boundary layer were observed. Particles concentrations (Diameter <50 nm) were low compared to continental boundary layer conditions with an average concentration of 300 cmâ3. The production of sulfuric acid and its subsequently condensation on preexisting particles was examined with the use of a simplistic box model. These calculations suggested that the day-time evolution of the Aitken particle population was governed mainly by coagulation and that particle formation was absent during most days
Hygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: Implications for regional direct radiative forcing under clean and polluted conditions
This work examines the effect of direct radiative forcing of aerosols in the eastern Mediterranean troposphere as a function of air mass composition, particle size distribution and hygroscopicity, and relative humidity (RH). During intensive field measurements on the island of Crete, Greece, the hygroscopic properties of atmospheric particles were determined using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Hygroscopicity Differential Mobility Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former studies, the H-TDMA identified three hygroscopic sub-fractions of particles in the sub-ÎŒm range: a more hygroscopic group, a less hygroscopic group and a nearly hydrophobic particle group. The average hygroscopic particle growth factors at 90 % RH were a significant function of particle mobility diameter (Dp): 1.42 (± 0.05) at 30 nm compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified up to three hygroscopic sub-fractions at mobility diameters of 1.0 and 1.2 ÎŒm. The data recorded between 12 August and 20 October 2005 were classified into four distinct synoptic-scale air mass types distinguishing between different regions of origin (western Mediterranean vs. the Aegean Sea) as well as the degree of continental pollution (marine vs. continentally influenced). The hygroscopic properties of particles with diameter Dpâ„150 nm showed the most pronounced dependency on air mass origin, with growth factors in marine air masses exceeding those in continentally influenced air masses. Particle size distributions and hygroscopic growth factors were used to calculate aerosol light scattering coefficients at ambient RH using a Mie model. A main result was the pronounced enhancement of particle scattering over the eastern Mediterranean due to hygroscopic growth, both in the marine and continentally influenced air masses. When RH reached its summer daytime values around 70â80 %, up to 50â70 % of the calculated visibility reduction was due to the hygroscopic growth of the particles by water compared to the effect of the dry particles alone. The estimated aerosol direct radiative forcings for both, marine and continentally influenced air masses were negative indicating a net cooling of the atmosphere due to the aerosol. The radiative forcing ÎFr was nevertheless governed by the total aerosol concentration most of the time: ÎFr was typically more negative for continentally influenced aerosols (ca. â4 W mâ2) compared to rather clean marine aerosols (ca. â1.5 W mâ2). When RH occasionally reached 90 % in marine air masses, ÎFr even reached values down to â7 W mâ2. Our results emphasize, on the basis of explicit particle hygroscopicity measurements, the relevance of ambient RH for the radiative forcing of regional atmospheres
Evidence of gravity waves into the atmosphere during the March 2006 total solar eclipse
This study aims at providing experimental evidence, to support the hypothesis according to which the movement of the moon's shadow sweeping the ozone layer at supersonic speed, during a solar eclipse, creates gravity waves in the atmosphere. An experiment was conducted to study eclipse induced thermal fluctuations in the ozone layer (via measurements of total ozone column, ozone photolysis rates and UV irradiance), the ionosphere (Ionosonde Total Electron Content &ndash; ITEC, peak electron density height &ndash; hmF2), and the troposphere (temperature, relative humidity), before, during and after the total solar eclipse of 29 March 2006. We found the existence of eclipse induced dominant oscillations in the parameters related to the ozone layer and the ionosphere, with periods ranging between 30&ndash;40 min. Cross-spectrum analyses resulted to statistically significant square coherences between the observed oscillations, strengthening thermal stratospheric ozone forcing as the main mechanism for GWs. Additional support for a source below the ionosphere was provided by the amplitude of the oscillations in the ionospheric electron density, which increased upwards from 160 to 220 km height. Even though similar oscillations were shown in surface temperature and relative humidity data, no clear evidence for tropospheric influence could be derived from this study, due to the modest amplitude of these waves and the manifold rationale inside the boundary layer
Hygroscopic properties of atmospheric aerosol particles over the Eastern Mediterranean: implications for regional direct radiative forcing under clean and polluted conditions
This work examines the effect of direct radiative forcing of aerosols in the eastern Mediterranean troposphere as a function of air mass composition, particle size distribution and hygroscopicity, and relative humidity (RH). During intensive field measurements on the island of Crete, Greece, the hygroscopic properties of atmospheric particles were determined using a Hygroscopicity Tandem Differential Mobility Analyzer (H-TDMA) and a Hygroscopicity Differential Mobility Analyzer-Aerodynamic Particle Sizer (H-DMA-APS). Similar to former studies, the H-TDMA identified three hygroscopic sub-fractions of particles in the sub-ÎŒm range: a more hygroscopic group, a less hygroscopic group and a nearly hydrophobic particle group. The average hygroscopic particle growth factors at 90 % RH were a significant function of particle mobility diameter (<i>D</i><sub><i>p</i></sub>): 1.42 (± 0.05) at 30 nm compared to 1.63 (± 0.07) at 250 nm. The H-DMA-APS identified up to three hygroscopic sub-fractions at mobility diameters of 1.0 and 1.2 ÎŒm. The data recorded between 12 August and 20 October 2005 were classified into four distinct synoptic-scale air mass types distinguishing between different regions of origin (western Mediterranean vs. the Aegean Sea) as well as the degree of continental pollution (marine vs. continentally influenced). The hygroscopic properties of particles with diameter <i>D</i><sub><i>p</i></sub>&ge;150 nm showed the most pronounced dependency on air mass origin, with growth factors in marine air masses exceeding those in continentally influenced air masses. Particle size distributions and hygroscopic growth factors were used to calculate aerosol light scattering coefficients at ambient RH using a Mie model. A main result was the pronounced enhancement of particle scattering over the eastern Mediterranean due to hygroscopic growth, both in the marine and continentally influenced air masses. When RH reached its summer daytime values around 70â80 %, up to 50â70 % of the calculated visibility reduction was due to the hygroscopic growth of the particles by water compared to the effect of the dry particles alone. The estimated aerosol direct radiative forcings for both, marine and continentally influenced air masses were negative indicating a net cooling of the atmosphere due to the aerosol. The radiative forcing &Delta;<i>F</i><sub>r</sub> was nevertheless governed by the total aerosol concentration most of the time: &Delta;<i>F</i><sub>r</sub> was typically more negative for continentally influenced aerosols (ca. â4 W m<sup>â2</sup>) compared to rather clean marine aerosols (ca. â1.5 W m<sup>â2</sup>). When RH occasionally reached 90 % in marine air masses, &Delta;<i>F</i><sub>r</sub> even reached values down to â7 W m<sup>â2</sup>. Our results emphasize, on the basis of explicit particle hygroscopicity measurements, the relevance of ambient RH for the radiative forcing of regional atmospheres
Formation and growth of atmospheric nanoparticles in the eastern Mediterranean: results from long-term measurements and process simulations
Atmospheric new particle formation (NPF) is a common phenomenon all over
the world. In this study we present the longest time series of NPF records in
the eastern Mediterranean region by analyzing 10 years of aerosol number size
distribution data obtained with a mobility particle sizer. The measurements
were performed at the Finokalia environmental research station on Crete,
Greece, during the period June 2008âJune 2018. We found that NPF took place
on 27 % of the available days, undefined days were 23 % and non-event
days 50 %. NPF is more frequent in April and May probably due to the
terrestrial biogenic activity and is less frequent in August. Throughout the
period under study, nucleation was observed also during the night. Nucleation
mode particles had the highest concentration in winter and early spring,
mainly because of the minimum sinks, and their average contribution to the
total particle number concentration was 8 %. Nucleation mode particle
concentrations were low outside periods of active NPF and growth, so there
are hardly any other local sources of sub-25 nm particles. Additional
atmospheric ion size distribution data simultaneously collected for more than
2 years were also analyzed. Classification of NPF events based on ion
spectrometer measurements differed from the corresponding classification
based on a mobility spectrometer, possibly indicating a different
representation of local and regional NPF events between these two measurement
data sets. We used the MALTE-Box model
for simulating a case study of NPF in the eastern Mediterranean region.
Monoterpenes contributing to NPF can explain a large fraction of the observed
NPF events according to our model simulations. However the adjusted
parameterization resulting from our sensitivity tests was significantly
different from the initial one that had been determined for the boreal
environment.</p
Atmospheric new particle formation as a source of CCN in the eastern Mediterranean marine boundary layer
While cloud condensation nuclei (CCN) production associated with atmospheric new particle formation (NPF) is thought to be frequent throughout the continental boundary layers, few studies on this phenomenon in marine air exist. Here, based on simultaneous measurement of particle number size distributions, CCN properties and aerosol chemical composition, we present the first direct evidence on CCN production resulting from NPF in the eastern Mediterranean atmosphere. We show that condensation of both gaseous sulfuric acid and organic compounds from multiple sources leads to the rapid growth of nucleated particles to CCN sizes in this environment during the summertime. Sub-100 nm particles were found to be substantially less hygroscopic than larger particles during the period with active NPF and growth (the value of kappa was lower by 0.2-0.4 for 60 nm particles compared with 120 nm particles), probably due to enrichment of organic material in the sub-100 nm size range. The aerosol hygroscopicity tended to be at minimum just before the noon and at maximum in the afternoon, which was very likely due to the higher sulfate-to-organic ratios and higher degree of oxidation of the organic material during the afternoon. Simultaneous with the formation of new particles during daytime, particles formed during the previous day or even earlier were growing into the size range relevant to cloud droplet activation, and the particles formed in the atmosphere were possibly mixed with long-range-transported particles.Peer reviewe
GARRLiC and LIRIC: strengths and limitations for the characterization of dust and marine particles along with their mixtures
The Generalized Aerosol Retrieval from Radiometer and Lidar Combined data algorithm (GARRLiC) and the LIdar-Radiometer Inversion Code (LIRIC) provide the opportunity to study the aerosol vertical distribution by combining ground-based lidar and sun-photometric measurements. Here, we utilize the capabilities of both algorithms for the characterization of Saharan dust and marine particles, along with their mixtures, in the south-eastern Mediterranean during the CHARacterization of Aerosol mixtures of Dust and Marine origin Experiment (CHARADMExp). Three case studies are presented, focusing on dust-dominated, marine-dominated and dustâmarine mixing conditions. GARRLiC and LIRIC achieve a satisfactory characterization for the dust-dominated case in terms of particle microphysical properties and concentration profiles. The marine-dominated and the mixture cases are more challenging for both algorithms, although GARRLiC manages to provide more detailed microphysical retrievals compared to AERONET, while LIRIC effectively discriminates dust and marine particles in its concentration profile retrievals. The results are also compared with modelled dust and marine concentration profiles and surface in situ measurements.The research leading to these results has
received funding from the European Unionâs Horizon 2020 Research and Innovation Programme ACTRIS-2 (grant agreement
no. 654109). The work has been developed under the auspices of the ESA-ESTEC project âCharacterization of Aerosol mixtures of Dust And Marine originâ contract no. IPL-PSO/FF/lf/14.489. The work was also supported by the European Research Council under the European Communityâs Horizon 2020 research and innovation framework programme/ERC grant agreement 725698 (D-TECT). The publication was supported by the European Unionâs Horizon 2020 Research and Innovation programme under grant agreement no. 602014, project ECARS (East European Centre for Atmospheric Remote Sensing). The authors acknowledge support through the Stavros Niarchos Foundation. BSC-DREAM8b
simulations were performed on the Mare Nostrum supercomputer hosted by the Barcelona Supercomputing Center-Centro Nacional de SupercomputaciĂłn (BSC).Peer ReviewedPostprint (published version
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