Indoor sources have been identified as a major contributor to the increase of particle concentration in indoor environments. The work presented here is a study of the characteristics of particulate ...matter number size distribution and mass concentration under controlled indoor activities in a laboratory room. The objective is to characterize particulate matter concentrations indoors resulted under the influence of specific sources. Measurements were performed in an empty laboratory (period September–October 2006) using a GRIMM SMPS+C system (particle size range between 11.1 and 1083.3 nm), a DustTrak Aerosol Monitor (TSI) and a P-Trak Ultrafine Particle Counter (TSI). The studied indoor activities included candle burning, hot plate heating, water boiling, onion frying, vacuuming, hair drying, hair spraying, smoking and burning of incense stick. The
AMANpsd computer algorithm was used to evaluate the modal structure of measured particle number size distribution data. Furthermore, the change of the particle number size distribution shape under the influence of different emission sources was studied versus time. Finally the particle emission rates were computed. High particle number concentrations were observed during smoking, onion frying, candle burning and incense stick burning. The highest particle mass concentrations were measured during smoking and hair spraying. The shift of the particle size distribution to larger diameters suggests the presence of strong coagulation effect during candle burning, incense stick burning, smoking and onion frying. The size distribution was mainly bimodal during onion frying and candle burning, whereas the size distribution remained unimodal during incense stick burning and smoking experiments.
Particle number concentration was measured between June 2009 and June 2010 at Akrotiri research station in a rural/suburban region of western Crete (Greece). Overall, the available data covered 157 ...days during the aforementioned period of measurements. The objectives were to study the number size distribution characteristics of ambient aerosols and furthermore to identify new particle formation events and to evaluate particle formation rates and growth rates of the newborn particles. Aerosol particles with mobility diameters between 10 and 1100 nm were measured using a Scanning Mobility Particle Sizer (SMPS) system. Measurements were performed at ambient relative humidities. The median total particle number concentration was 525 #/cm3 whereas the number concentration ranged between 130 #/cm3 and 9597 #/cm3. The average percentage of particles with diameters between 10 nm and 100 nm (N10–100) to total particles was 53% during summer and spring, but reached 80% during winter. Maximum average contribution of nano-particles (10 nm < Dp < 50 nm) to total particles was recorded also in winter and was attributed partly to the effect of local heating. Furthermore, back trajectories (HYSPLIT model) showed that different air mass origins are linked to different levels of particle number concentrations, with higher values associated with air masses passing from polluted areas before reaching the Akrotiri station. Modal analysis of the measured size distribution data revealed a strong nucleation mode during winter (15–25 nm), which can be correlated with emissions from local sources (domestic heating). The nucleation mode was observed also during the spring campaigns and was partly linked to new particle formation events. On the contrary, an accumulation mode (80–120 nm) prevailed in the measurements during summer campaigns, when the station area was influenced by polluted air masses arriving mainly from Eastern Europe. In total, 13 new particle formation events were recorded during the 157 days of measurements. Nucleation events were associated with low values of N100 particle number concentration and reduced coagulation sinks. Mean growth and formation rates were calculated and showed values equal to 6 nm hr−1 and 13 cm−3 s−1, respectively.
•Particle number concentration was measured at Akrotiri research station (Greece).•The data were analysed according to the origin of the air masses reaching the site.•The characteristics of size distributions were analysed.•New particle formation events were investigated.
Ozone measurements have been performed in the period 2003–2009 at Akrotiri (suburban) and Finokalia (coastal) monitoring stations on the island of Crete, Greece. The main objectives were to ...investigate the concentration levels of ozone in the region of Crete, its spatial and temporal variability, the effect of air mass origin and local sources on ozone levels, and the frequency of exceedances of the EU limits for ozone concentrations in the area. The observed mean values for Akrotiri and Finokalia stations were 44.5 ± 8.5 and 49.1 ± 10.6 ppb
v
, respectively. Ozone concentrations were higher during the 8-month period between March and October (52.3 ± 6.8 and 53.0 ± 7.4 ppb
v
for Akrotiri and Finokalia station, respectively) whereas, in the period November–February, the concentrations were lower (37.7 ± 4.7 and 39.1 ± 6.9 ppb
v
, respectively). The above values indicate that there is not a west-east gradient of ozone concentration in the studied area. At both stations, AOT40 limit values were higher than the limit set by the European Union (Directive 2008/50/EC). Exceedances of the EU target value were encountered during 88 and 67 % of the time in Akrotiri and Finokalia stations, respectively. Differences on the diurnal patterns and daily ozone maxima between the two stations were attributed to the different characteristics of the two stations and to the effect of local pollution sources to Akrotiri station. The average value of the amplitude of the daily cycle (calculated as the difference between maximum and minimum values) in the case of Akrotiri was 8.3 ppb
v
, and it was about two times the corresponding value in Finokalia (4.7 ppb
v
), which is an indication of the effect of the anthropogenic emission produced in the city of Chania to the Aktotiri station environment. At Finokalia, the maximum values were observed 2–4 h later than those at Akrotiri. During springtime, the difference in the maximum values appearance was close to 4 h, with the maximum at Akrotiri at 16:00 (LT) and at Finokalia at about 20:00 (LT). This time difference supports the transfer of gaseous precursors and already formed ozone molecules toward Finokalia.
Background
Particulate matter, microorganisms in air and environmental conditions present a potential risk to museum collections. There are also limited studies of simultaneous measurements of ...airborne particles and microorganisms inside museums and the effects of seasonal variations. Therefore, extensive indoor/outdoor measurements of particulate matter mass/number concentrations and viable, cultivable microbial load were performed in two museums and a library in Greece for a period of 2 years at selected time intervals. The culture heritage collections are located at coastal (Historical Museum of Crete in Heraklion), urban (Criminology Museum of the University of Athens) and mountainous (
Neophytos Doukas
Library in Zagori) environments and their collections consist mainly of organic materials. Measurements of inhalable particulate mass (PM
10
, PM
2.5
, PM
1
) and viable, cultivable airborne microorganism concentrations (heterotrophic bacteria, cellulose metabolizing bacteria, acid producing bacteria and mesophilic fungi) in air were performed.
Results and conclusions
The indoor PM
10
and microbial concentrations were higher than the outdoor levels showing the influence of the indoor sources, such as the presence of people and indoor activities, as well as, anthropogenic outdoor sources, and natural emissions. Elevated PM
1
particle number concentrations were also encountered in the Historical Museum of Crete in Heraklion and the Criminology Museum of the University of Athens due to the high anthropogenic emissions of the urban areas. The lowest concentrations of viable, cultivable airborne microorganisms were measured in the Historical Museum of Crete at the coastal site, which encounters also well controlled microclimatic conditions. In comparison to the other two naturally ventilated sites, the highest concentrations of viable, cultivable airborne fungi were measured in the
Neophytos Doukas
Library at the mountainous site, whereas the highest concentrations of viable, cultivable airborne heterotrophic bacteria were measured in the Criminology Museum of the University of Athens at an urban site, where mummified tissues and dry specimens are exhibited. The closed showcases of the two museums and the library could only protect the exhibits from viable, cultivable airborne fungi, but not from specific categories of bacteria. Acid producing bacteria in the Historical Museum of Crete, cellulose metabolizing bacteria in the
Neophytos Doukas
Library, and opportunistic pathogenic heterotrophic bacteria in the Criminology Museum of the University of Athens showed to be enriched inside the closed showcases.
Graphical abstract:
Average indoor/outdoor and showcase/outdoor ratios of the viable, cultivable airborne microbes in the two museums and the library. Photos of showcases in the Historical Museum of Crete (
left
) and
Neophytos Doukas
Library in Zagori (
right
)
Large amounts of solid waste are disposed in landfills and the potential of particulate matter (PM) emissions into the atmosphere is significant. Particulate matter emissions in landfills are the ...result of resuspension from the disposed waste and other activities such as mechanical recycling and composting, waste unloading and sorting, the process of coating residues and waste transport by trucks. Measurements of ambient levels of inhalable particulate matter (PM
10) were performed in a landfill site located at Chania (Crete, Greece). Elevated PM
10 concentrations were measured in the landfill site during several landfill operations. It was observed that the meteorological conditions (mainly wind velocity and temperature) influence considerably the PM
10 concentrations. Comparison between the PM
10 concentrations at the landfill and at a PM
10 background site indicates the influence of the landfill activities on local concentrations at the landfill. No correlation was observed between the measurements at the landfill and the background sites. Finally, specific preventing measures are proposed to control the PM concentrations in landfills.
Particulate matter (PM
10, PM
2.5) measurements were performed during the period 2003–2009 at the Akrotiri monitoring station (suburban/rural) on the island of Crete, Greece. Concurrent measurements ...of PM
10 size distribution/chemical composition were also performed at selected time intervals to determine the PM sources in the region and the factors controlling their levels. Using a beta radiation attenuation monitor, the mean PM
10 concentration during the measuring period (15.04.2003–31.12.2009) was equal to 36.1
±
9.5
μg/m
3, whereas the PM
2.5 concentration was equal to 23.6
±
5.8
μg/m
3. Back trajectories showed that the dominant air mass origin was from North and Northwest Europe but the intrusion of southern air masses lead to elevated PM concentrations due to Saharan dust events. The 24-h EU limit value of 50
μg/m
3 (PM
10) was exceeded approximately 13.5% during the measured period. Furthermore, the PM
10 mass size distribution of metals, ions and organic carbon/elemental carbon (OC/EC) was characterized using a 9-stage Andersen non-viable impactor and a gravimetric sequential PM
10 sampler during two selected periods. The mean PM
10 concentration during the first sampling period was equal to 28.3
±
12.4
μg/m
3 (10.08.2007–28.08.2007), whereas during the second sampling period (09.07.2008–19.07.2008) was 41.6
±
14.0
μg/m
3. The measurements showed a bimodal size distribution for the aerosol mass concentration. PM
2.1 accounted for 41.0% and 37.2% for PM
10 during the two periods respectively. Over the measurement campaigns ions dominated the PM
10 mass (50–80%) with the organic mass and metals comprising the major part of the rest. The OC concentration was equal to 2.3
±
1.2
μg/m
3, whereas the EC concentration was equal to 0.8
±
0.2
μg/m
3. Finally, black carbon concentrations were measured in August 2007 with an aethalometer. The mean daily value of black carbon was 0.69
±
0.22
μg/m
3. The measurements showed that the PM values measured at the station correspond to a background/rural station in the region and are in agreement with other measurements in the Eastern Mediterranean region.
► We examine aerosol levels and variability in conjunction with their sources and their chemical signatures. ► Size distribution aerosol data chemically resolved are examined showing a bimodal size distribution. ► Ions dominate the PM
10 mass with Organic mass and metals comprising the major part of the rest. ► The 24-h EU limit value of 50
μg/m
3 (PM
10) was exceeded approximately 13.5% during the measured period. ► It is the first study in this area where OC and EC were determined in the whole range of the aerosol size distribution.
Particulate matter measurements (PM₁₀, PM₂.₅) using a beta radiation attenuation monitor were performed at the Akrotiri research station (May 2003-March 2006) on the island of Crete (Greece). The ...mean PM₁₀ concentration during the measuring period (05/02/03-03/09/04) was equal to 35.0 ± 17.7 μg/m³ whereas the mean PM₂.₅ concentration (03/10/04-04/02/06) was equal to 25.4 ± 16.5 μg/m³. The aerosol concentration at the Akrotiri station shows a large variability during the year. Mean concentrations of particulate matter undergo a seasonal change characterised by higher concentrations during summer PM₁₀, 38.7 ± 10.8 μg/m³ (2003); PM₂.₅, 27.9 ± 8.7 μg/m³ (2004) and 27.8 ± 9.7 μg/m³ (2005) and lower concentrations during winter PM₁₀, 28.7 ± 22.5 μg/m³ (2003/2004); PM₂.₅, 21.0 ± 13.0 μg/m³ (2004/2005) and 21.4 ± 21.9 μg/m³ (2005/2006). Comparative measurements of the PM₁₀ concentration between the beta radiation attenuation monitor, a standardized low volume gravimetric reference sampler and a low volume sequential particulate sampler showed that PM₁₀ concentrations measured by the beta radiation attenuation monitor were higher than values given by the gravimetric samplers (mean ratio 1.17 ± 0.11 and 1.21 ± 0.08, respectively). Statistical and back trajectory analysis showed that elevated PM concentrations (PM₁₀, 93.8 ± 49.1 μg/m³; PM₂.₅: 102.9 ± 59.9 μg/m³) are associated to desert dust events. In addition regional transport contributes significantly to the aerosol concentration levels whereas low aerosol concentrations were observed during storm episodes.
Moving Object Databases (MOD), although ubiquitous, still call for methods that will be able to understand, search, analyze, and browse their spatiotemporal content. In this paper, we propose a ...method for trajectory segmentation and sampling based on the representativeness of the (sub)trajectories in the MOD. In order to find the most representative subtrajectories, the following methodology is proposed. First, a novel global voting algorithm is performed, based on local density and trajectory similarity information. This method is applied for each segment of the trajectory, forming a local trajectory descriptor that represents line segment representativeness. The sequence of this descriptor over a trajectory gives the voting signal of the trajectory, where high values correspond to the most representative parts. Then, a novel segmentation algorithm is applied on this signal that automatically estimates the number of partitions and the partition borders, identifying homogenous partitions concerning their representativeness. Finally, a sampling method over the resulting segments yields the most representative subtrajectories in the MOD. Our experimental results in synthetic and real MOD verify the effectiveness of the proposed scheme, also in comparison with other sampling techniques.
PM
10
concentration and its elemental content were measured inside a university classroom where painting and sketching activities took place. The primary goal was to investigate the impact of these ...activities to (1) indoor PM
10
concentrations, (2) identify PM
10
levels in the presence/absence of the activities and (3) investigate the corresponding impact on its elemental content. As such, indoor online measurements and 24-h gravimetric measurements took place at short-term fixed periods. Outdoor PM
10
concentrations were also available. It was found that PM
10
levels were substantially increased during the occupied hours with average PM
10
during activity ranged between 19 and 171 μg/m
3
, whereas during background periods it ranged between 12 and 66 μg/m
3
. Moreover, indoor concentrations during the activity were usually higher compared to outdoor levels, but the opposite behavior was found for background periods. Regarding the elemental content, positive correlations of heavy metals (Cu, Zn, Pb, Ba) found predominantly in the coarser fraction were associated with the use of painting powders. On the other hand, metals like Cr, Mn, Fe and Ni were primarily associated with anthropogenic sources, while the crustal origin of Ti, Mg and Al dominated indoors for particles > 1 μm. Other correlations between elements in the submicron fraction suggested origin from soil and anthropogenic sources as well as aged painting-originated particles. In summary, the present study demonstrated the significant impact of painting/sketching activities to indoor PM
10
levels. Direct emissions from the use of powders as well as resuspension activities of the occupants were identified as the major indoor sources that provoked elevated concentrations.
In this paper, we propose a novel scheme for efficient content-based medical image retrieval, formalized according to the PAtterns for Next generation DAtabase systems (PANDA) framework for pattern ...representation and management. The proposed scheme involves block-based low-level feature extraction from images followed by the clustering of the feature space to form higher-level, semantically meaningful patterns. The clustering of the feature space is realized by an expectation-maximization algorithm that uses an iterative approach to automatically determine the number of clusters. Then, the 2-component property of PANDA is exploited: the similarity between two clusters is estimated as a function of the similarity of both their structures and the measure components. Experiments were performed on a large set of reference radiographic images, using different kinds of features to encode the low-level image content. Through this experimentation, it is shown that the proposed scheme can be efficiently and effectively applied for medical image retrieval from large databases, providing unsupervised semantic interpretation of the results, which can be further extended by knowledge representation methodologies.
PDF
