Archontoula Chaloulakou

Comparative Assessment of Neural Networks and Regression Models for Forecasting Summertime Ozone in Athens.

A comparison study has been performed with neural networks (NNs) and multiple linear regression models to forecast the next days maximum hourly ozone concentration in the Athens basin at four representative monitoring stations that show very different behavior. All models use 11 predictors (eight meteorological and three persistence variables) and are developed and validated between April and October from 1992 to 1999. Performance results based on a wide set of forecast quality measures indicate that the NNs provide better estimates of ozone concentrations at the monitoring sites, whilst the more often used linear models are less efficient at accurately forecasting high ozone concentrations. The violation of the European information threshold of 180 microg/m(3) is successfully predicted by the NN in 72% of the cases on average. Results at all stations are consistent with similar ozone forecast studies using NNs in other European cities.

Neural Network and Multiple Regression Models for PM10 Prediction in Athens: A Comparative Assessment

Abstract Particulate atmospheric pollution in urban areas is considered to have significant impact on human health. Therefore, the ability to make accurate predictions of particulate ambient concentrations is important to improve public awareness and air quality management. This study examines the possibility of using neural network methods as tools for daily average particulate matter with aerodynamic diameter <10 µm (PM10) concentration forecasting, providing an alternative to statistical models widely used up to this day. Based on a data inventory, in a fixed central site in Athens, Greece, ranging over a two-year period, and using mainly meteorological variables as inputs, neural network models and multiple linear regression models were developed and evaluated. Comparison statistics used indicate that the neural network approach has an edge over regression models, expressed both in terms of prediction error (root mean square error values lower by 8.2–9.4%) and of episodic prediction ability (false alarm rate values lower by 7–13%). The results demonstrate that artificial neural networks (ANNs), if properly trained and formed, can provide adequate solutions to particulate pollution prognostic demands.

Mass and chemical composition of size-segregated aerosols (PM 1 , PM 2.5 , PM 10 ) over Athens, Greece: local versus regional sources

To identify the relative contribution of local versus regional sources of particulate matter (PM) in the Greater Athens Area (GAA), simultaneous 24-h mass and chemical composition measurements of size segregated particulate matter (PM1, PM2.5 and PM10) were carried out from September 2005 to August 2006 at three locations: one urban (Goudi, Central Athens, “GOU”), one suburban (Lykovrissi, Athens, “LYK”) in the GAA and one at a regional background site (Finokalia, Crete, “FKL”). The two stations in the GAA exceeded the EU-legislated PM10 limit values, both in terms of annual average (59.0 and 53.6 μg m−3 for Lykovrissi and Goudi, respectively) and of 24-h value. High levels of PM2.5 and PM1 were also found at both locations (23.5 and 18.6 for Lykovrissi, while 29.4 and 20.2 μg m−3 for Goudi, respectively). Significant correlations were observed between the same PM fractions at both GAA sites indicating important spatial homogeneity within GAA. During the warm season (April to September), the PM 1 ratio between GAA and FKL ranged from 1.1 to 1.3. On the other hand this ratio was significantly higher (1.6–1.7) during the cold season (October to March) highlighting the role of long-range transport and local sources during the warm and cold seasons respectively. Regarding the coarse fraction no seasonal trend was observed for both GAA sites with their ratio (GAA site/FKL) being higher than 2 indicating significant contribution from local sources such as soil and/or road dust. Chemical speciation data showed that on a yearly basis, ionic and crustal mass represent up to 67–70 % of the gravimetrically determined mass for PM 10 samples in the GAA Correspondence to: N. Mihalopoulos (mihalo@chemistry.uoc.gr) and 67 % for PM1 samples in LYK. The unidentified mass might be attributed to organic matter (OM) and elemental carbon (EC), in agreement with the results reported by earlier studies in central Athens. At all sites, similar seasonal patterns were observed for nss-SO 2− 4 , a secondary compound, indicating significant contribution from regional sources in agreement with PM1 observations. The contribution of local sources at both GAA sites was also estimated by considering mass and chemical composition measurements at Finokalia as representative of the regional background. Particulate Organic Matter (POM) and EC, seemed to be the main contributor of the local PM mass within the GAA (up to 62 % in PM1). Dust from local sources contributed also significantly to the local PM 10 mass (up to 33 %).

Spatial and Temporal Variation of PM10 Mass Concentrations within the Greater Area of Athens, Greece

This study presents the results of a yearlong PM10 measurement campaign, conducted at four sampling sites, within the Greater Athens Area, between June 2001 and May 2002. Daily average PM10 concentrations were determined using reference samplers installed in two urban locations (Maroussi and Aristotelous), a mixed urban–industrial location (Elefsina) and a background location (Thrakomacedones). The 24-h and annual PM10 average concentrations were calculated and compared to the corresponding air quality standards, promulgated by the European Union, revealing severe exceedances of the limit values. The mean concentrations for the sampling periods were 73.8, 83.2, 32.9 and 54.9 μg/m3 for Maroussi (MAR), Aristotelous (ARI), Thrakomacedones (THR) and Elefsina (ELE), respectively. The spatial variation of PM10, was investigated resulting at a coefficient of variation of 0.36 within the study area and correlation coefficients ranging from 0.57 to 0.84. In addition, strong associations between PM10 and other primary gaseous pollutants were found. Regression analysis of PM10 against NOx (used as an indicator for road traffic emissions) revealed significant vehicular contributions to the measured PM10 concentrations. Higher PM10 levels were recorded during prevailing winds of the S–SW sectors, while lower levels were observed during strong northerly flows. The overall results allowed a first assessment of the severity of PM10 air pollution in the Athens basin, and of the potential sources responsible for it. The control of traffic-related particle emissions appears to be a principal objective, for the confrontation of the PM10 pollution problem affecting the area.

Exposure to carbon monoxide in the Athens urban area during commuting

An extensive survey has been designed to provide detailed information on carbon monoxide (CO) concentration in the main transport modes and along heavy traffic routes in the Athens urban area. Specifically the study identifies the main factors affecting CO exposure during commuting. Several portable, electrochemical CO monitors (Solomats MPM4100), were used to record the in-vehicle CO concentrations every 15 s. Measurements were performed during rush hour periods. Field monitoring was conducted in summer 1998 and winter 1998-1999. Exposure estimates were compared to WHO guidelines. The findings showed that the mean CO level over trips of 30 min was 21.4 ppm for private car against 10.4, 9.6, 4 and 11.5 ppm for bus, trolley, electric train and pedestrians, respectively. Transport mode, route, monitoring period and season had a significant influence on the measured CO concentrations. The study points out the importance of microenvironmental monitoring, instead of using fixed-site data in assessing commuters CO exposure.

Indoor and outdoor carbon monoxide concentration relationships at different microenvironments in the Athens area.

Simultaneous measurements of indoor and outdoor carbon monoxide (CO) concentrations conducted at two different microenvironments in Athens, Greece, using a non-dispersive infrared analyzer, are described in this paper. The two selected microenvironments, an office and a public school, were located in the vicinity of two streets with heavy traffic, near the center of Athens. A statistical correlation analysis of indoor concentration levels with outdoor concentrations monitored at the school and at the office, as well as with meteorological parameters and outdoor concentrations monitored at a fixed monitoring site, was conducted. Hourly indoor concentrations at the office and at the school showed a significant positive correlation with outdoor concentrations measured at both measurement locations (with correlation coefficient values R=0.74 and R=0.83 respectively) and at the fixed site (with R=0.70 and R=0.67 respectively). The correlation between indoor and outdoor concentrations was even better when hourly concentrations averaged over a 4 h period were considered (correlation coefficient values between indoor and outdoor concentrations measured at the office and at the school were R=0.85 and R=0.92 respectively and the correlation coefficient value between indoor and outdoor fixed site concentrations was R=0.75 for both sites). Mean hourly outdoor concentrations at the fixed monitoring site explained approximately 56% (R=0.75) of the variation of outdoor concentrations at the office and approximately 68 % (R=0.83) of the variation of outdoor concentrations at the school. The mean daily indoor to outdoor (I/O) ratio ranged between 0.74 and 1.00 at the office and between 0.53 and 0.89 at the school.

Determinants of personal exposure to ozone in school children. Results from a panel study in Greece

Background: In the wider framework of the RESPOZE (ReSPiratory effects of OZone Exposure in Greek children) panel study, we investigated possible determinants of O3 exposure of school children, measured with personal passive samplers, in Athens and Thessaloniki, Greece. Methods: Personal exposure to O3 was measured for five weeks spread along the academic year 2013‐14, in 186 school children in Athens and Thessaloniki, Greece. At the same time, at‐school outdoor measurements were performed and ambient levels of 8‐h daily maximum O3 from fixed sites were collected. We also collected information on lifestyle and housing characteristics through an extended general questionnaire (GQ) and each participant completed daily time activity diaries (TADs) during the study period. Results: Mean outdoor concentrations were higher during the warmer months, in the suburbs of the cities and in Athens. Personal exposure concentrations were significantly lower compared to outdoor. Daily levels of at‐school outdoor and ambient levels of O3 from fixed sites were significant determinants of personal exposure to O3. For a 10 &mgr;g/m3 increase in at‐school outdoor O3 concentrations and PM10 measurements a 20.9% (95% CI: 13%, 28%) increase in personal exposure to O3 was found. For a half an hour more spent in transportation an average increase of 7% (95% CI: 0.3%, 14.6%) in personal exposure to O3 was observed. Among other possible determinants, time spent in transportation (TAD variable) and duration of open windows were the ones associated with personal O3 exposure levels. Conclusions: Our results support the use of outdoor and ambient measurements from fixed sites in epidemiological studies as a proxy of personal exposure to O3, but this has to be calibrated taking into account personal measurements and time‐activity patterns. HighlightsPossible determinants of personal ozone exposure of school children were investigated.Methods rely on personal passive samplers and simultaneously at‐school measurements.Epidemiological studies may use ambient measurements as a proxy for personal exposure.

Ultrafine particles dispersion modeling in a street canyon: Development and evaluation of a composite lattice Boltzmann model

Recently, a branch of particulate matter research concerns on ultrafine particles found in the urban environment, which originate, to a significant extent, from traffic sources. In urban street canyons, dispersion of ultrafine particles affects pedestrians short term exposure and residents long term exposure as well. The aim of the present work is the development and the evaluation of a composite lattice Boltzmann model to study the dispersion of ultrafine particles, in urban street canyon microenvironment. The proposed model has the potential to penetrate into the physics of this complex system. In order to evaluate the model performance against suitable experimental data, ultrafine particles levels have been monitored on an hourly basis for a period of 35 days, in a street canyon, in Athens area. The results of the comparative analysis are quite satisfactory. Furthermore, our modeled results are in a good agreement with the results of other computational and experimental studies. This work is a first attempt to study the dispersion of an air pollutant by application of the lattice Boltzmann method.

Ozone exposure assessment for children in Greece - Results from the RESPOZE study

Ozone exposure of 179 children in Athens and Thessaloniki, Greece was assessed during 2013-2014, by repeated weekly personal measurements, using passive samplers. O3 was also monitored at school locations of participants to characterize community-level ambient exposure. Average personal concentrations in the two cities (5.0 and 2.8ppb in Athens and Thessaloniki, respectively) were considerably lower than ambient concentrations (with mean personal/ambient ratios of 0.13-0.15). The temporal variation of personal concentrations followed the -typical for low-latitude areas- pattern of cold-warm seasons. However, differences were detected between temporal distributions of personal and ambient concentrations, since personal exposures were affected by additional factors which present seasonal variability, such as outdoor activity and house ventilation. Significant spatial contrasts were observed between urban and suburban areas, for personal concentrations in Athens, with higher exposure for children residing in the N-NE part of the area. In Thessaloniki, spatial variations in personal concentrations were less pronounced, echoing the spatial pattern of ambient concentrations, a result of complex local meteorology and the smaller geographical expansion of the study area. Ambient concentration was identified as the most important factor influencing personal exposures (correlation coefficients between 0.36 and 0.67). Associations appeared to be stronger with ambient concentrations measured at school locations of children, than to those reported by the nearest site of the air quality monitoring network, indicating the importance of community-representative outdoor monitoring for characterization of personal-ambient relationships. Time spent outdoors by children was limited (>90% of the time they remained indoors), but -due to the lack of indoor sources- it was found to exert significant influence on personal concentrations, affecting inter-subject and spatiotemporal variability. Additional parameters that were identified as relevant for the determination of personal concentrations were indoor ventilation conditions (specifically indoor times with windows open) and the use of wood-burning in open fireplaces for heating as an ozone sink.

Streamlining environmental monitoring networks: application to nitrogen dioxide in north Italy

This article presents a methodology for streamlining a monitoring network. The approach shows that risk maps, which provide decision-makers with the probabilities of a pollutant to be above a regulatory threshold, can also be used to identify monitoring stations that are providing redundant information. The method is applied to an air quality network of 102 stations monitoring nitrogen dioxide (NO2) concentrations in north Italy. The limitations of the network have first been identified in order to specify the annual concentration levels for which reliable risk maps can be designed. This has been achieved by a fractal analysis of the spatial correlation for several NO2 concentration levels. Two predefined annual thresholds at 40 and 50 µg/m3 were used as reference to investigate the possible redundancy of the information provided by the existing network. It was shown that the number of stations could be reduced by almost 20% without losing any information with respect to describing the annual pollution levels.