D. K. Papanastasiou

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.

Preliminary findings on seasonal heat stress of sheep.

This paper studies the heat stress conditions imposed onto sheep housed in a naturally ventilated sheep barn during the four seasons of a year. The barn is located near the east coast of central Greece. Heat stress is assessed by means of the hourly temperature-humidity index (THI). The analysis shows that animals were exposed to heat stress in 11%, 80% and 17% of spring, summer and autumn hours, respectively, whereas no heat stress was identified during winter. As expected, animals are more prone to severe heat stress during summer, as the daily maximum hourly values of THI remained higher than the extreme severe heat stress threshold (i.e. THI = 25.6) in 90% of the summer days. Additionally, THI remained higher than 25.6 during the vast majority of the summer daytime hours. Measures have to be taken so as to improve the indoor climate conditions and to alleviate animal’s heat stress.