Issue 5 [December]

The urban planning, the buildings and covering materials of all surfaces, the distance between adjacent constructions, the height and the orientation of the buildings are some of the factors which affect the sustainable conditions in the city.

This paper presents a project that aims at investigating the influence of urban developments in microclimatic conditions. The purpose of the research is to investigate how the characteristics of built environment contribute the microclimatic conditions. The investigation was carried out in the urban center of Thessaloniki, Greece The urban geometry, the position and the height of the building inside the urban canyon, the orientation are factors that influence the surface temperature and microclimatic conditions (air temperature, wind speed, wind direction).  The results of the investigation could contribute at the urban planning and the sustainable development of the contemporary cities.

This paper deals with the impacts of the current economic crisis on the temporal variation of urban traffic (during 2008-11) and consequently, the impacts on the urban air pollutant levels using as case study the city of Thessaloniki, Greece.

The important temporal variations of the main economic indicators like the annual decreasing trend of the gross domestic product (GDP), the continuous decrease of wages and the labor cost index, the annual increase of unemployment and hence, the decreasing trend of consumption and domestic demand during the current recession period in Greece affect the vehicle traffic.

A considerable decreasing trend of vehicle traffic volume has been observed in all examined intersections of Thessaloniki urban area. The highest temporal decrease of traffic volume is occurred in the morning hours.

The traffic volume decrease determines decisively the concentrations of urban air pollutants and especially, the concentrations of NO₂ (nitrogen dioxide), which has mainly traffic emissions origin and the concentrations of PM10 (suspended particulate matter with aerodynamic diameter less than 10 μm), which has mainly diesel cars emissions origin.

The correlation between traffic and air pollution decreasing trend shows that the air pollutant concentrations decrease is more significant in relation to the traffic decrease due to the fact that, even a small traffic decrease leads to a significant amelioration of the traffic conditions, which lead to significant lower car emissions and therefore, to significant lower pollutant concentrations in the air of the urban area.

The economic crisis did not lead to an increase of the public transport use. It seems that, the traffic decrease of the passenger cars and taxis is due to the trips decrease because of unemployment, the trips decrease connected to lost work positions and the elastic importance trips decrease (shopping, entertainment, etc) during 2008-11.

Simultaneous PM₁₀ and PM_2.5 sampling was conducted for a six months period, at two sites of different characteristics. The first site was located in an urban background location in the North-Eastern part of GAA, affected by primary emission sources and particle transport from other parts of the GAA basin. The second site was located in central Athens, at a busy roadway, affected by heavy traffic-related and commercial activities. Additionally, continuous field measurements of PM fractions were also performed using direct-reading monitor in parallel with gravimetric samplers. The mean PM₁₀ and PM_2.5 concentrations for the sampling period were 26.2 and 13.7μg m^-3 and 40.1 and 22.8 μg m^-3 for ZOG and ARI, respectively. The PM_2.5/PM₁₀ ratio found 0.52 and 0.57 for ZOG and ARI, respectively. The coefficient of variation calculated equal to 0.40 for both fractions. Additionally, the weekday/weekend discernment of the particulate concentration levels for each site display different characteristics of the emission sources and composition, while the diurnal distribution of particulate levels demonstrated the dependence of the PM levels on anthropogenic activities and habits.

Both the local meteorological conditions and the air mass history indicating long-range atmospheric transport of particles are significant parameters that influence the levels of PM.