تحليل اقليمي تغييرات ماهانه و فصلي ازون سطحي ايستگاه سنجش آلودگي زمينه جوّ فيروزكوه

Climatic Analysis of Monthly and Seasonal Variations in Surface Ozone at Background Air Pollution Monitoring Station in Firouzkooh

در اين تحقيق با استفاده از داده هاي ازونسطحي و فراسنج هاي هواشناسي اخذ شده از بانك اطلاعات سازمان هواشناسي كشور در طي دوره آماري 2003-1999، به بررسي نوسان روزانه و ماهانه ازون سطحي و همچنين تحليل رابطه بين فراسنج هاي هواشناسي با ازون سطحي؛ در ايستگاه سنجش آلودگي زمينه جوّ فيروزكوه پرداخته شده است. بررسي ميانگين ماهانه ازون سطحي نشان مي دهد كه ميانگين ماهانه ازون سطحي از ماه ژانويه شروع به افزايش نموده و در ماه جون به بيشينه خود مي‌رسدو در نيمه دوم سال؛ روند كاهشي تا دسامبر ادامه دارد. بررسي رابطه بين فراسنج هاي هواشناسي با ازون سطحي در مقياس ماهانه، بيانگر رابطه مثبت فراسنج هاي: تندي باد،دما، فشار سطح ايستگاه(QFE)  و به ويژه ساعت آفتابي و رابطه منفي فراسنج هاي: بارش، ابرناكي، فشار تبديل شده به سطح دريا(QFF) و به ويژه رطوبت نسبي، با ازون سطحي است. بررسي تأثير پديده هاي هواشناسي بر ازون سطحي بيانگر آن است كه پديده هاي: كدري آاسمان، گرد و خاك كاملاً گسترده، در افزايش ازون سطحي و پديده هاي دمه، مه و مه يخي و انواع بارش ها به ويژه برف با توجه به شرايط ايستگاه، در كاهش آن نقش به سزايي دارند. نتايج به دست آمده نشان مي دهد كه دوره خشك سال(منطبق بر دوره گرم سال) با افزايش ازون سطحي (به جز ماه جولاي) و دوره مرطوب (منطبق بر دوره سرد سال)، با كاهش ازون سطحي(به جز ماه مارس) همراه است كه نشان مي‌دهد تغييرات ازون سطحي در طي دوره‌هاي گرم و خشك و سرد و مرطوب سال معني دار مي باشد. دليل كاهش نسبي ازون سطحي در ماه جولاي؛ ناشي از افزايش بارش، ابرناكي و افزايش رطوبت نسبي در اين ماه نسبت به ساير ماه هاي دوره خشك سال مي‌باشد و عامل اصلي افزايش ازون سطحي درماه مارس علي رغم افزايش بارش به عنوان عامل كاهنده ازون سطحي، ناشي از افزايش ازون جو بالا و انتقال آن از پوشن سپهر به وردسپهر در فصل بهار مي تواند باشد.

Introduction Ozone is one of the atmospheric constituents which is very important in warming and pollution of the atmosphere. Its concentrations (above 120 ppb) in the upper atmosphere increase the earth’s temperature and in the lower atmosphere pollute the air and causes damages for human and plant life. It causes some problems such as respiratory diseases in humans. It is more dangerous in urban environments where the presence of moisture and other pollutants increases its polluting function. That is why studying its concentration and variation in the lower atmosphere is very important. In Iran there is only one surface ozone measuring station which is in Firouzkooh and is a Background Air Pollution Monitoring Station. The station was established in 1993 at the 2986m above sea level. Due to its higher elevation, the measurements reflect general or background of ozone concentration in the country.  In this paper we have investigated at first variations of the surface ozone concentration and then studied relations between ozone concentrations and important Meteorological Parameters such as temperature and wind. For the purposes the daily values of Ozone were obtained from the station for the period of 19992003 the maximum period of data availability. Weather elements such as temperature, precipitation, wind speed, sunshine duration, sea level and surface pressure, relative humidity, and cloudiness of the station were also extracted for the same period.   Results and discussion Mean concentration of surface ozone was 54.1 ppb for the period. 20 ppb was the lowest value measured during the study period in November and the highest value was 125 ppb in May. More than 70 percent of ozone concentrations were observed between 46 and 65 ppb. Survey of the monthly mean of the surface ozone shows that it increases from January and reaches its maximum in June, while in the second half of the year it has a decreasing trend until December. The monthly mean ranged from 50ppb in winter months to 60 ppb in summer months, Moreover based on the analysis made on the monthly and seasonal data, variations of the maximum is more than that of the minimum and so the seasonal variations were much less than the monthly values, which shows that it is strongly affected by the sunshine hours and the temperature. Consideration of surface ozone concentrations and the weather elements showed different positive and negative relations. Sea level pressure (QFF), relative humidity, cloudiness, and precipitation showed negative correlations while wind, temperature, sunshine duration, surface pressure (QFE), and visibility showed positive correlation with ozone concentrations. The Correlations of Ozone concentration with surface pressure, wind velocity, precipitation, and visibility was very low. Sunshine duration and sea level pressure had the highest control on the variations of ozone concentrations. Some weather phenomena such as thunderstorms had remarkable increasing effect on the ozone concentration while fog and haze decreased it effectively. Study results of the monthly and seasonal averages show that except for July, the surface ozone is increasing in the dry periods of the year (which is reconciled on the hot period of the year), and with the exception of March, it decreases in the wet period (the cold period of the year). These exceptions can be interpreted due to higher values of cloudiness, precipitation and relative humidity in July, and higher values of ozone in the upper levels and its transformation from the stratosphere to the troposphere in March. In general, concentrations of surface ozone were higher in warm months and lower in cold period of the year. Warm and sunny days increased the concentration while the cloudy and rainy days showed lower concentrations. Winds blowing from dry and warm regions from the south and southwest increased the concentration and winds from the cold humid northern regions lowered the concentration.