D. Melas

Temperature, comfort and pollution levels during heat waves and the role of sea breeze

During the summer of 2007 several Greek regions suffered periods of extreme heat, with midday temperatures of over 40°C on several consecutive days. High temperatures were also recorded on the east coast of central Greece, where a complex sea breeze circulation system frequently develops. The more intense events occurred at the end of June and July. The highest temperatures were observed on 26 June and 25 July, while the sea breeze developed only on 25 July. Meteorological data collected at two sites—a coastal urban location and an inland suburban site that is not reached by the sea breeze flow—as well as pollution data collected at the urban site, were analysed in order to investigate the relationship between sea breeze development and the prevailing environmental conditions during these two heat wave events. The analysis revealed that sea breeze development affects temperature and pollution levels at the shoreline significantly, causing a decrease of ~4°C from the maximum temperature value and an increase of ~30% in peak PM10 levels. Additionally, several stress indices were calculated in order to assess heat comfort conditions at the two sites. It was found that nocturnal comfort levels are determined mainly by the urban heat island effect, the intensity of which reaches up to 8°C, while the applied indices do not demonstrate any significant daytime thermal stress relief due to sea breeze development.

Statistical characteristics of ozone and PM10 levels in a medium-sized Mediterranean city

A statistical analysis of ozone and PM10 concentration levels in the area of Volos, a medium-sized Greek coastal city, was carried out for the period 2001-2003. The data analysis revealed that the Daily Maximum Hourly (DMH) value of ozone concentration reaches a maximum of 160 µg/m³ during summer; it is observed during afternoon hours and is associated usually with winds from southern directions. This is attributed to the impact of the sea breeze on pollution levels. Concerning PM10 concentration, it was found that its DMH values are quite high and that its Daily Average (DA) value exceeds the limit value of 50 µg/m³ for approximately 38% of the days. The daily cycle shows two maxima (morning-evening) and in these cases the wind is typically from north-northwest directions. The weekly and seasonal variance of DA values of PM10 concentration is not very significant.

Is the ozone climate penalty robust in Europe

Ozone air pollution is identified as one of the main threats bearing upon human health and ecosystems, with 25 000 deaths in 2005 attributed to surface ozone in Europe (IIASA 2013 TSAP Report #10). In addition, there is a concern that climate change could negate ozone pollution mitigation strategies, making them insufficient over the long run and jeopardising chances to meet the long term objective set by the European Union Directive of 2008 (Directive 2008/50/EC of the European Parliament and of the Council of 21 May 2008) (60 ppbv, daily maximum). This effect has been termed the ozone climate penalty. One way of assessing this climate penalty is by driving chemistry-transport models with future climate projections while holding the ozone precursor emissions constant (although the climate penalty may also be influenced by changes in emission of precursors). Here we present an analysis of the robustness of the climate penalty in Europe across time periods and scenarios by analysing the databases underlying 11 articles published on the topic since 2007, i.e. a total of 25 model projections. This substantial body of literature has never been explored to assess the uncertainty and robustness of the climate ozone penalty because of the use of different scenarios, time periods and ozone metrics. Despite the variability of model design and setup in this database of 25 model projection, the present meta-analysis demonstrates the significance and robustness of the impact of climate change on European surface ozone with a latitudinal gradient from a penalty bearing upon large parts of continental Europe and a benefit over the North Atlantic region of the domain. Future climate scenarios present a penalty for summertime (JJA) surface ozone by the end of the century (2071–2100) of at most 5 ppbv. Over European land surfaces, the 95% confidence interval of JJA ozone change is [0.44; 0.64] and [0.99; 1.50] ppbv for the 2041–2070 and 2071–2100 time windows, respectively.

Air Quality During Heat Waves

Meteorological and air pollution data observed during the last decade in Athens, Thessaloniki and Volos were analyzed to assess the air quality during heat waves. The identification of a heat wave day was based on two temperature criteria applied to the data recorded at the cities centre: the daily maximum and the daily average temperature value are at least 37°C and 31°C, respectively. Heat wave days were identified every year in Athens but only in 2007 in Thessaloniki and Volos. Air quality was aggravated during heat wave days, a fact that was verified by the means of the common air quality index. PM10 concentration levels increased 30% in the centre of Athens and more than 100% in Thessaloniki and Volos, while O3 concentration levels increased 29% in Thessaloniki’s suburb. The increase of pollution levels triggered exceedances of the air quality standards. Temperature and pollution levels during the heat waves occurred in 2007 were separately examined.

Evaluation of WRF Parameterization Schemes During Heat-Wave Events Over the Greater Area of South–East Mediterranean

Heat-waves are strongly connected with environmental, health and socioeconomic impacts. The frequency of occurrence and the intensity of those events tend to increase across the Mediterranean due to climate change. Numerical weather prediction models are considered to be an important tool for predicting heat-wave events. Additionally, they are suitable for studying human biometeorology. The aim of this paper is to evaluate the performance of the Weather Research and Forecasting (WRF) model under different physical options during heat-wave events taking place in the greater area of South–East Mediterranean, considering also the impacts on human thermal comfort. For this, 15 heat-wave events (52 total heat-wave days) were identified in a 10-year period (2004–2013). Seven (7) alternative model configurations were tested on a 6 km horizontal resolution domain and the results for air temperature, wind speed and vapor pressure were compared against ground-based observations. The micro-scale RayMan model was also employed, in order to evaluate predictions of the Universal Thermal Climate Index (UTCI). Results show that under certain physics options WRF is capable of reproducing successfully the key characteristics of the examined heat-wave episodes.

Study of the Impact of an Intense Biomass Burning Event on the Air Quality in the Eastern Mediterranean

Aim of this work is to study the impact of the intense forest fires that tookplace in Greece at the end of summer 2007 on the air quality in the Eastern Mediterranean. For this reason the meteorological model MM5 and the photochemical model CAMx are applied over the study area with 10 km spatial resolution. CAMx model is implemented for two emission scenarios; with and without biomass burning emissions. High spatial resolution wildfire emission data are used that are based on the Global Fire Emissions Database (GFED3). The CAMx chemical boundary conditions are taken from the TM4 global model. The nonradiative impact on the composition of the atmosphere and on environmental indices (e.g. Aggregate Risk Index) is quantified in regional scale. The impact of the atmospheric processes on the air pollution levels due to the biomass burning event is also studied giving more emphasis on the boundary layer. The intense biomass burning event in the Eastern Mediterranean at the end of August 2007 results in an enhancement of the CO, NOx and PM2.5 concentrations over almost all the study area, which can range from several times to two order of magnitude over the fire hot spots. The increases in O3 levels are less pronounced and are found mainly downwind the burnt areas. On the 25th August 2007, when fire counts in the study area are maximum, in the daytime boundary layer, the inclusion of biomass burning emissions results in a change of the chemical regime from O3 destruction to O3 production.

Evaluation of WRF-ARW Model in Reproducing a Heavy Rainfall Event Over Chalkidiki, Greece: The Effect of Land-Surface Features on Rainfall

A record breaking 24 h accumulated rainfall event was observed in Chalkidiki Peninsula, Greece on the 8th of October 2006. Intense precipitation was associated with strong low level convergence imposed by a low pressure system developed over the Aegean Sea and topographical lifting in the area of interest. Severe flooding and damage was reported especially in the east coast of Chalkidiki. The ability of WRF model to simulate this extreme precipitation episode using three different operational microphysical schemes was tested by comparing the high resolution results with available raingauge data. The verification results indicate that WRF configuration using ETA Ferrier microphysics provides better statistical scores for heavy hourly precipitation rates while it was able to reproduce the spatial rainfall distribution of this event. PLIN scheme captures the measured 24 h accumulations especially where maximum precipitation is observed. Sensitivity experiments suggest that highly localized heavy rainfall was the result of an interaction between synoptic conditions and the topographical features, with large scale forcing imposing a low-level convergent flow field that produced heavy rain and topography enhancing highly localized precipitation maxima.

An Overview of Forest Fires and Meteorology in Turkey and Greece

The relation between fires and meteorological parameters, such as wind, temperature and humidity, are investigated in Greece and western and south western parts of Turkey. The study comprises a five - year period between 1993 and 1998 for Greece and 1999 and 2004 for Turkey. The selected areas examined in this study are Achaia (NW Peloponnese) and Crete (Heraklion area) in Greece; and Antalya, Izmir, Canakkale, Denizli, Isparta and Balikesir in Turkey. The results show that the highest number of fires was experienced in the year 2000. Similarly, the highest amount of forested area was also burned in the year 2000. Mugla experienced the highest number of fires, 1389 fires, during the study period. On the other hand, the highest amount of burned - area is observed in Balikesir, as 6946 ha. The annual analysis showed that the highest number of fires was observed in Mugla in year 2000 (330 fires) and a second highest in Antalya in year 200 (263 fires). Meteorological conditions during these five - year period are also analyzed in order to find any relationship between forest fires and meteorological parameters in the study region. Maximum monthly temperatures that were observed in year 2000 as well as the minimum humidity values confirms that high temperatures and low humidity increases the ignition potential and thus initiating forest fires.

Impact of Tropospheric Ozone on Summer Climate in China

The spatial distribution, radiative forcing, and climatic effects of tropospheric ozone in China during summer were investigated by using the regional climate model RegCM4. The results revealed that the tropospheric ozone column concentration was high in East China, Central China, North China, and the Sichuan basin during summer. The increase in tropospheric ozone levels since the industrialization era produced clear-sky shortwave and clear-sky longwave radiative forcing of 0.18 and 0.71 W m–2, respectively, which increased the average surface air temperature by 0.06 K and the average precipitation by 0.22 mm day–1 over eastern China during summer. In addition, tropospheric ozone increased the land–sea thermal contrast, leading to an enhancement of East Asian summer monsoon circulation over southern China and a weakening over northern China. The notable increase in surface air temperature in northwestern China, East China, and North China could be attributed to the absorption of longwave radiation by ozone, negative cloud amount anomaly, and corresponding positive shortwave radiation anomaly. There was a substantial increase in precipitation in the middle and lower reaches of the Yangtze River. It was related to the enhanced upward motion and the increased water vapor brought by strengthened southerly winds in the lower troposphere.

Evaluation of Ozone Levels from MACC Global and Regional Modelling Systems Over Eastern Mediterranean—The Influence of Etesian Winds

This work focuses on the evaluation of the simulated ozone levels from the global MACC (Monitoring Atmospheric Composition and Climate) reanalysis and an ensemble of MACC regional air quality models with ozone measurements from three baseline stations in Central and Eastern Mediterranean Sea, located in Malta, Greece (island of Crete) and Cyprus. Τhis region and especially the Aegean Sea are under the influence of the Etesian winds that start blowing in late spring and stop in early autumn. The evaluation is performed by calculating statistical metrics for a period of two years (2011–2012) for both models separately for the selected Etesian days and the non-selected days. Moreover, in order to examine whether the stratosphere-troposphere ozone transport contributes to ozone concentrations, four different pressure levels (1013, 850, 700 and 500 hPa) from the global model are also assessed. The analysis reveals that both global reanalysis and the ensemble of regional models underestimate the near surface ozone levels. In general, the underestimation is lower at Malta and Cyprus stations during non-selected days. The ensemble of the regional models presents a better performance compared to the global reanalysis approach.