The Study of Synoptic Patterns of Air Pollution in Mashhad Metropolis

1- Introduction From the time human settlements has been formed as concentrated and fixed communities, air pollution on human life has become perceptible. Air pollution is one of the most important environmental crisis of Iran metropolises which has made life in these cities costly and even dangerous during recent four decades. An increase in urbanization and high consumption of fossil fuels on the one hand, and use changes and industrial development on the other hand, have led to an increase of the concentration of pollutants in the air of cities. Understanding Climate and Pollution is a prerequisite for any sustainable urban planning. Increased air pollution causes changes and disruption in the climatic patterns of the planet and the environment. 2- Theoretical framework The Association of Engineers of air pollution and its control have provided the following definition for air pollution: air pollution means the existence of one or more contaminants such as dust, fumes, gas, mist, smoke or vapor in the air backsets, features and time of remains which is dangerous for human, plant or animal life i.e. the unbearable ease of use of life and property. In general, any change in the physical and chemical components of air is called air pollution.3- Methodology In this study daily data of air pollution in Mashhad (Vahdat station) for a 4 year period (2007-2010), which was provided by the Environmental Protection Agency of Khorasan Razavi province is used. Standard contaminent threshold were determined using Air Quality Index (AQI). Afterwards, the days that were polluted by two pollutants of carbon monoxide (CO) and aerosols (PM10) were determined. According to the first data processing and high frequency of days with CO and PM10 pollutants in the cold half of the year; the analyses were limited to fall and winter. The data includes 29 polluted days in autumn and 23 polluted days in winter for carbon monoxide during a period of four years. The data for polluted days by aerosols includes 74 polluted days in autumn and 63 polluted days in winter. To identify the atmospheric patterns of the days with air pollution in the cold half of the year, 500 hPa height and surface pressure data were collected from Environmental Prediction National Center and Atmospheric Research National Center website. Then, to identify atmospheric patterns, principle component analysis method and clustering statistics method were employed. First, data was prepared in the S mode of principal component analysis, the array in which the nodes were the columns and rows represented observations (days). In this method, points of high correlation and spatial homogenous limits were determined using a linear relationship for the nodes during the study procedure. In the next phase, primary factors were determined considering the correlations in the data for each array. In this array, the value for each node in the new factors is specified and if they change to a map, they show the spatial centers of pressures in the study scope. Then the value for each of those days in the new factors which are known as factor scores (pc score)was determined by the principal component analysis method. This array also shows temporal-series of factors, which represent the relation of each day with the new factor. During this phase, those factors whose eigenvalues were higher than 1 and justified more than 4 percent of diffraction in data were selected. These factors were used to determine the pressure patterns. The ultimate result of principal component analysis method was the factor scores which are the primary data input for clustering method. Clustering method with Ward array was used for the classification of pressure patterns, and polluted days for two pollutants of carbon monoxide (CO) and aerosols (PM10) were determined for autumn and winter. Ultimately, in order to identify pressure patterns, compound maps of days for each group were prepared. These maps, which are prepared for the ground level and 500 hPa level, indicate that synoptic patterns are the resonators of the discussed pollutants in autumn and winter in Mashhad. 4- Discussion Atmospheric pollution synoptic results in autumn and winter for both carbon monoxide (CO) and aerosols (PM10) pollutants in Mashhad indicate that the high level atmospheric patterns and earth surface play significant roles in air pollution in Mashhad. As a result, autumn and winter patterns for main atmospheric pollutants of carbon monoxide, trough of westerly winds of North and East of Caspian Sea in high atmospheric levels, East of Aral Lake Siberian high pressure and immigrant anticyclones from Eastern Europe and North West of Iran on high pressure patterns of earth surface, are the main synoptic factors. With the arrival of cold waves, these patterns which are linked together lead to a decrease in temperature, a decrease of the atmospheric mixed layer (atmospheric boundary layer), and an increase and high concentration of carbon monoxide over the earth's surface. Consequently, much of the flows from the North, North East and North West in these two seasons have air pollution concentration for the city. In addition, central Mediterranean trough, low pressures of Turkmenistan and Kazakhstan, the cut-off in Caspian Sea and the entry of dust from the deserts of Touran plateau, including Qara Qum, Serakhs and central deserts of Iran, bring contaminants of aerosols for Autumn and Winter in Mashhad. Furthermore, in some patterns, Mediterranean cyclones become weak and carry aerosols approaching Mashhad. Furthermore, the other synoptic studies in Iran indicate that the Siberian high-pressure and input air masses from north are associated with severe reduction in temperature in the cold half of the year, which in most high levels are observed as major centers in East of Lake Aral and the North of Caspian Sea. 5- Conclusion and Suggestions Atmospheric pollution synoptic results in autumn and winter for both carbon monoxide (CO) and aerosols (PM10) pollutants in Mashhad indicate As a result, autumn and winter patterns for main atmospheric pollutants of carbon monoxide, trough of westerly winds of North and East of Caspian Sea in high atmospheric levels, East of Aral Lake Siberian high pressure and immigrant anticyclones from Eastern Europe and North West of Iran on high pressure patterns of earth surface, are the main synoptic factors. Furthermore, in some patterns, Mediterranean cyclones become weak and carry aerosols approaching Mashhad. It is recommended that the relevant agencies gather accurate statistics which are essential for a healthy society. Polluted days can be identified and appropriate measures be conducted based on these statistics and the study of synoptic maps