Mete Tayanç

URBANIZATION EFFECTS ON REGIONAL CLIMATE CHANGE IN THE CASE OF FOUR LARGE CITIES OF TURKEY

The growing interest in urbanization problems is stimulating detailed studies of their effects on local climate change in the developed world. The absence of such studies in developing countries is restricting many decisions to be made and applied by policymakers. In one developing country, Turkey, results of the study of four urban stations and their neighboring rural sites for the 1951-1990 time period reveal that there is a shift towards the warmer side in the frequency distributions of daily minimum and 21.00 hr temperature difference series. This shift is an indication of urban heat island. The maximum urban heat island intensity trend that is obtained from the temperature differences database agrees well with Okes (1973) formula for European cities. Seasonal analysis of individual 21.00 hr temperature series suggests that the regional warming is strongest in spring and weakest in autumn and winter. Urban warming is detected to be more or less equally distributed over the year wi th a slight increase in the autumn months. The Mann-Kendall trend test is applied to the temperature difference series, and the urban heat island effect is found to be significant in all urban sites. On the other hand, almost no significant urban effect on precipitation can be detected.

An assessment of spatial and temporal variation of sulfur dioxide levels over Istanbul, Turkey.

Sulfur dioxide concentration levels are investigated in Istanbul to assess air pollution during the heating seasons in which the concentration of air pollutants reach high levels due to the consumption of low-quality fossil fuels. Results reveal that in the 1985-91 period there is an increasing trend in the concentrations of air pollutants. One reason for this increase is found to be the switching to use of low-quality fossil fuels instead of cleaner ones; the consumption ratio of coal/fuel-oil increased drastically in the 1980s from the ratio of 0.62 during 1980 to 3.09 by 1990. Linear regression analysis also indicated the similar variability of sulfur dioxide and particulate matter curves with a correlation coefficient R2=0.87. An optimum interpolation technique, kriging, is used to obtain the spatial distribution of sulfur dioxide over the area. Results indicated that the maximum concentration regions over the European side, exceeding 300 microg/m(3) monthly averages, are found to be the Fatih-Gaziosmanpaşa-Bayrampaşa, Beyoğlu-Sişli, and Eminönü areas. On the Asian side, the Göztepe-Kadiköy area received a major threat from sulfur dioxide pollution. Results also indicated that there was a considerable decrease in air pollution levels over Istanbul in the 1995-96 season compared with the previous two seasons. This can be explained by (1) the increase in ventilation, (2) switching to natural gas as a home and business heating fuel, and (3) treatment of coal before its entrance to the city. The variability in weather conditions is explained by the adoption of a ventilation index, which is the product of wind speed and inversion height.

Effects of urbanization on climate of İstanbul and Ankara

The purpose of this work is to study regional climate change and investigate the effects of urbanization on climates of two largest cities in Turkey: Istanbul and Ankara. Air temperature (mean, maximum and minimum) data of Istanbul and Ankara are analyzed to study regional climate change and to understand the possible effects of urbanization on the climate of these regions owing to industrialization and large flux of migration from rural parts of the country. For the trend analysis, linear regression and the sequential version of the Mann-Kendall test is used. A significant upward trend is found in the urban temperatures of southern Istanbul, which is the most highly populated and industrialized part of the city compared to its rural parts. Northern stations do not show any warming trend; instead, they have a cooling trend. Urbanization and industrialization in the southern part of Istanbul has a negative effect on regional cooling. In spite of Ankaras urban geometry and air pollution problem, the urban station in Ankara does not show any warming trend. A significant urban heat island intensity (urban-rural) is not observed in Ankara.

Cyclone track variability over Turkey in association with regional climate

In this study a set of cyclone frequency statistics is developed and the prevailing tracks of cyclones are derived for a region of the world that has not been previously investigated in detail. Analysis reveals that Turkey experiences the effects of five dominant cyclone trajectories. Investigation of the seasonal variability of the cyclone frequencies shows that the highest number of cyclones occurs during winter. The variability of the subtropical jetstream latitude is analysed by multi-variable regression involving cyclone numbers, the numbers of occurrences of the Mediterranean Persistence High Pressure (MPHP), which is an extension of the Azore High Pressure and their periods. This analysis revealed that the most important factor among the three factors chosen is the number of observed blocking cases over Turkey. Although the northern parts of Turkey are accepted as having a transitional type climate between the Mediterranean and temperate regions, our results showed that they are more influenced by cyclones of Mediterranean origin. Copyright

Composition of wet deposition in Kaynarca, Turkey.

In this work, composition of wet deposition in Kaynarca, Turkey is studied by collecting precipitation samples during more than a 2-year period. August 1993-November 1995. Concentrations of the main cations Na+, Mg2+, Ca2+, K+, NH4+ and the main anions Cl-, NO3- and SO4(2-) together with pH were studied. The average pH value at Kaynarca was near neutral, 5.59. Results indicated that SO4(2-) concentration in precipitation was very high, as was Ca2+, neutralizing the acidity. Acidic wet deposition samples were generally obtained in winter. Enrichment factors for sea and soil indicate the strong effects of sea and soil, specifically limestone on the composition of precipitation. Non-sea salt fractions of SO4(2-) were found to range from 0.955 to 0.980, showing the effect of non-sea sources, especially emissions from fossil-fuel combustion, on the pH of samples. Trajectory analysis showed that cyclones originating from northwestern, central and eastern parts of Europe have generally high sulfate and nitrate concentrations and low pH.

Annual and seasonal air temperature trend patterns of climate change and urbanization effects in relation to air pollutants in Turkey

With a view to estimating climate change and its urban-induced bias in selected Turkish cities, we have used data from the period 1951 to 1990 recorded by 54 climate stations, four of which are corrected for their inhomogeneities. Two sets are produced; S1, including the large urban stations, and S2, consisting of rural, small urban and medium urban stations. Nonnalized Kendall trend test coefficients with a spatial prediction scheme, kriging, are used to construct spatial patterns of both sets together and separately. Results reveal a statistically significant cooling in mean temperatures mostly in northem regions and warming in minimum temperatures specific to large urban areas. Seasonal analysis shows that most of this cooling has been occurring in the summer and urban warming in the spring. The causes of cooling is investigated in relation to some air pollutants, SO 2 and particulate matter (PM). Linear regressions perfomred on the time series resulted in a significant urban bias of 0.24°C per 40 years on mean temperatures and 0.56°C/40 years on minimum temperatures. In association with the above results, a decrease in the temperature range of 0.48°C over the period owing to urban bias was found. A 0.24°C urban bias magnitude of mean temperature trends is much greater than the results found on other three regions of the Earth [Jones et al., 1990]. An overall average cooling in mean temperatures, -0.07°C per decade, detected here is the same as Nasrallah and Ballings [1993] average result for the two grid points located over Turkey.

Chemical analyses of the major ions in the precipitation of Istanbul, Turkey

Abstract The issue of acid deposition and associated environmental problems has received spescial attention during recent decades and has been the subject of extensive research in North America and Western Europe. However, similar studies in developing countries are very limited due to technological and financial restrictions. In this study, chemical composition of the precipitation in · Istanbul was investigated. Precipitation samples were obtained from three urban areas Bahcelievler, Florya, and Goztepe for the period of January to October 1996. In the initial phase of the study (January to April 1996), samples were analyzed for hydrogen, sulfate and nitrate ions, and in the final phase (May to October 1996) calcium, bicarbonate and ammonium ions were included in the measurement program. The effect of the urban heating demand on the chemical composition of the precipitation was observed clearly. During the heating season (December to March period), sulfate and nitrate concentrations in the precipitation were very high; sulfate fluctuating between 0 and 150 mg/litre and nitrate between 0 and 70 mg/litre. On the other hand, they dropped to very low levels during the April to October period when the urban heating demand decreases or ceases. High pH values associated with high sulfate and high nitrate concentrations reveal that the acidity of the precipitation is neutralized. Correlations between calcium and sulfate, and ammonium and sulfate imply that CaSO 4 and (NH 4 ) 2 SO 4 aerosols may merge with the precipitation, and neutralize the acidity.

Analyses of wet and bulk deposition in four different regions of Istanbul, Turkey

This study presents the chemical composition of wet deposition that was collected at four different regions of Istanbul, Topkapi, Bagcilar, Maltepe and Goztepe, during the period January 2001–May 2001. Bulk deposition was collected together with the wet deposition at only one station, Goztepe, during the period of January 2001–December 2001. Fifty four wet deposition samples and 21 bulk samples were collected during the study period. The mean value of pH of wet deposition samples for all regions was found to be 5.26. Results indicate that Ca2+ concentration in precipitation was high, as was SO42−, neutralizing the acidity. The mean value of the non-sea-salt fraction in the wet deposition for Ca2+ and SO42− were 98%, 91% indicating that Ca2+ and SO42− were mainly coming from sources other than sea. Difference between bulk and wet deposition of Ca2+ and SO42− was found to be highest. Those differences between bulk and wet samples with respect to the overall concentration (wet+bulk) were lower than 30% for ammonium and nitrate, while the differences of SO42−, Ca2+, Mg2+, Cl−, Na+ vary between 62% and 36%. Higher enrichment factors were found for most ions and higher correlation coefficients were obtained among most of the ions in dry and bulk deposition, in comparison with wet deposition.

The impact of anthropogenic and biogenic emissions on surface ozone concentrations in Istanbul.

Surface ozone concentrations at Istanbul during a summer episode in June 2008 were simulated using a high resolution and urban scale modeling system coupling MM5 and CMAQ models with a recently developed anthropogenic emission inventory for the region. Two sets of base runs were performed in order to investigate for the first time the impact of biogenic emissions on ozone concentrations in the Greater Istanbul Area (GIA). The first simulation was performed using only the anthropogenic emissions whereas the second simulation was performed using both anthropogenic and biogenic emissions. Biogenic NMVOC emissions were comparable with anthropogenic NMVOC emissions in terms of magnitude. The inclusion of biogenic emissions significantly improved the performance of the model, particularly in reproducing the low night time values as well as the temporal variation of ozone concentrations. Terpene emissions contributed significantly to the destruction of the ozone during nighttime. Biogenic NMVOCs emissions enhanced ozone concentrations in the downwind regions of GIA up to 25ppb. The VOC/NO(x) ratio almost doubled due to the addition of biogenic NMVOCs. Anthropogenic NO(x) and NMVOCs were perturbed by ±30% in another set of simulations to quantify the sensitivity of ozone concentrations to the precursor emissions in the region. The sensitivity runs, as along with the model-calculated ozone-to-reactive nitrogen ratios, pointed NO(x)-sensitive chemistry, particularly in the downwind areas. On the other hand, urban parts of the city responded more to changes in NO(x) due to very high anthropogenic emissions.

Analysis of surface ozone and nitrogen oxides at urban, semi-rural and rural sites in Istanbul, Turkey

Ozone (O(3)) mixing ratios were measured at three different sites (urban/traffic, semi-rural and rural/island) in Istanbul from September 2007 to December 2009 in order to determine the diurnal, monthly and seasonal variations of O(3) and nitrogen oxides (NO(x)) and to study the local and regional impacts. This is the first study that evaluates the O(3) levels in semi-rural and rural sites in Istanbul in addition to the urban sites. The diurnal O(3) variations are generally characterized by afternoon maxima (64 ppb at the urban, 80 ppb at the semi-rural and 100 ppb at the rural site) and the nighttime minimum being more pronounced at the polluted urban site. The monthly mean O(3) mixing ratios start to increase in March, reaching their maximum values in August for the urban (~25 ppb) and semi-rural sites (30 ppb). However, at the rural site, the monthly mean O(3) levels reach their maximum value in June (35 ppb). The O(3) mixing ratios for weekends were higher than those on weekdays at each site by up to 28%, possibly due to changes in VOC sensitivity and reduction in NO(x) levels. In order to better understand and characterize the relationship between air masses and O(3) levels, cluster analysis was applied to the back-trajectories calculated by the HYSPLIT model for the semi-rural site. The analyses clearly showed that major transport is characterized by northern and western clusters, particularly from the Eastern Europe and the Mediterranean region, as well as recirculation over Istanbul due to high pressure systems leading to accumulated levels of O(3). The results clearly suggest that extended measurement networks from urban to rural sites should be considered for a more comprehensive evaluation of O(3) levels.