23 primary schools have been selected in Tiaret city, and the collection of PM2.5 was performed in the morning, afternoon and evening, in the presence and absence of the pupils. The results found have shown a gradient of concentrations of PM2.5 by site typology. Low and average concentrations are recorded in the areas close to forests: 23.32±2.77 µg/m3 and the high concentrations are observed in the sites exposed to road traffic: 33.57±3.27 µg/m3 in winter. However, concentrations recorded in the urban sites are lower in the summer (sites exposed to road traffic: 25.33±2.85 µg/m3, sites close to the forests 23.78± 1.92µg/m3). We also noticed that the dominance of PM2.5 has been observed in the vicinity of the major axes of movement. The dispersion of these particles is illustrated by a detailed maps. The maps present information obtained by hierarchical classification, they aim to answer a need for spatial knowledge of the problem of particulate pollution in urban areas in the city of Tiaret. The hierarchical classification allowed to distinguish three groups of schools: urban, urban highly subject to dense road traffic and schools close to green spaces and forests. The results obtained revealed a high contamination of the atmospheric environment of the city of Tiaret by PM2.5 aerosols, taking into account the results recorded in primary schools. Mass concentration of PM2.5 in the 1st period (autumn and winter) is higher than that of the 2nd period (spring and summer). Indeed, the highest concentrations are recorded in the presence of pupils in winter.
The data from several weather stations in Western Algeria show a semi-arid climate during last decades. The entire study region showed a great variability in the occurrences of the first and second rainy days in the year. This variability is associated with a positive trend, showing a continuous increasing aridity in the south Mediterranean and the late arrival of the rainy season is well marked. The rainy season in the north of Algeria, spreads from September to June. The origin of the rains differ according to the seasons. The rainfall from June to October is of localized stormy origin, whereas in winter, the rainfall comes from the classical atmospherically perturbations arriving from North or North West. This work objective was to give a definition of the rainy season onset and to show its inter - annual variability according to the Niño and Niña years. The El - Niño phenomenon by its positive and negative phases seems to affect the start of the rainy season. The variability of the rainfall onset indices is very significant. There is a relative stability of the rainy season length over the long term period. A significant delay in the precipitation onset was observed during certain years. A method to define rainy season onset based on daily rainfall data from a weather station in the Algerian highlands was proposed. This approach is based on a climatic point of view, using a frequency analysis of precipitation and dates of their first occurrence. It delays the first heavy rain day (20 mm) when La - Niña settles. If EL-Niño settles, the first heavy rain (20 mm) day will be earlier. These results will improve the probabilistic forecasts of the beginning of the rainy seasons, the cessation as well as the lengths. This work is a preliminary confirmation that the El-Niño phenomenon really affects the Mediterranean climate.
According to the data obtained in the autumn-winter period, the excess of PM2.5 in air during the schoolday after a short stay by pupils in the school yards was 1.5 –2 times. The PM2.5 concentration in the autumn - winter period was up to 1.5 times higher than that of the spring – summer time. High concentrations of dust particles are observed in areas close to heavy traffic in winter in the South-Eastern part of the city. Low concentrations were recorded in the autumn-winter time in areas adjacent to forests in the North –Western part of the city of Tiaret. However, the protective function of forest stands in the spring – summer period in the North-Western part of the city of Tiaret is less evident. The need for introduction of several nature protection measures in the city is obvious. Among them: fuel quality control and fines for the use of low-grade fuel, increasing the density of trees and shrubs in the city in the areas uncovered by vegetation.
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