بررسي تغييرات فصلي و روزانه آلاينده هاي هوا و ارتباط آن با پارامترهاي هواشناسي

Seasonal and daily variation of air pollutants and their relation to meteorological parameters

In this paper, seasonal and diurnal variation of pollutants and the relation between meteorological parameters and the amount of pollutant concentrations is investigated. The data used were obtained from the Air Quality Department of the Municipality and from the synoptic station of the Institute of Geophysics. In this survey, the data used are from 2004 to 2007. The result of survey for seasonal variation of pollutants showed that for CO, NO, and PM-IO, two maxima exist one of which occurs in summer and the other in winter, the maximum of SO, is in winter and the maximum of OJ occurs in spring. The existence of maximum in winter may be from increasing consumption of fuels in thermal sources, besides meteorological conditions like increased air pressure, stability and temperature inversion. Maximum in summer may be from various factors like surface temperature inversion and decreased precipitation. In October, often because of the reopening of schools and universities, and the consequent increased traffic, a temporary rise in the quantity of pollutants. The increased ozone production of photochemical reactions in spring and summer can be one of the effective factors for the existence of an ozone maximum in these seasons. Increased dry air in summer can help to raise PM-I 0 concentration in this season. The comparison of diurnal pattern of various pollutants in spring shows that all pollutants other than OJ have two maxima, one of which occurs in the early morning and the other late at night. But the pattern of OJ is different from other pollutants and its maximum occurs generally in the afternoon. Transport vehicles cause an increase in pollutants in early morning and at night. So, temperature inversion is effective in these maxima. Winter and summer CO diurnal pattern also shows morning and night maxima. Photochemical reactions of ozone production, are effective in its maximum. In general, the height of mixing layer is decreased at nights and air pollutants are trapped under this layer, so that the concentration of pollutants is increased at nights. Also the katabatic wind has a tremendous effect on the increase of pollutants. For the first six month period (from January till June) of 2007, the highest averages of concentrations of CO, NO" PM-1O and 0) pollutants, occurred at temperatures of more than 30°C but for SO, the highest concentration was at less than 10°C. In this period, for 0) , NO, and PM-I 0 pollutants the highest concentration is at relative humidity less than 40% and for SO, and CO from 41% to 60%. MultivariabIe regression statistical analysis between the concentration of ozone and NO, pollutants with meteorological parameters like temperature and relative humidity for the first six months of 2007 showed that both parameters had effects on pollutant concentrations but temperature was more effective on ozone and relative humidity was more important for NO, concentration. In other words, although between 0) and NO, pollutants and the temperature parameter, there is a positive correlation, between these pollutants and relative humidity there exists a negative relation. The inversion of surface temperature (22 m height) in the early morning hours is one of the effective parameters in daily pollutant concentration and its effect is more important in summer months. The investigation the effect of holidays on pollutant concentration, shows that in the stations like the Grand Bazaar Station where traffic is decreased on weekends and holidays in relation to other days, a decrease in CO pollutant is observed. In this case, the average decrease in CO pollutant is nearly 19 percent.