ENVIRONMENTAL-STUDIES OF SO2, SPM AND NOX OVER AGRA, WITH VARIOUS METHODS OF TREATING CALMS

A comparative study between predicted and observed concentrations of m ajor pollutants SO2, suspended particulate matter (SPM) and NOx in Agr a, India has been undertaken using two Gaussian plume models. A Gaussi an plume model (IITLT) and climatological dispersion model (CDM) have been used to estimate long-term concentrations of non-reactive polluta nts due to emissions from area and point sources. The IITLT model is d esigned to treat the calm wind conditions (u < 2 m s-1). The computati ons show that about 10% of the total concentration of each type of pol lutant at each station is due to calm winds alone. Therefore, consider ation of calm winds is quite important. A comparative study of various methods of treating calm winds in IITLT model has been made. It is no ted that in CDM model the central wind speed of the lowest wind speed class was arbitrarily taken as 1.5 m s-1. This means that light winds or calm winds reported in the first wind speed class (0-1.54 m s-1) ar e assigned this value. IITLT model has different dispersion parameters for moderate winds and calm winds, whereas CDM uses the same dispersi on parameters for both the winds. The monthly wind frequency tables an d monthly mean concentrations of SO2, SPM and NOx for the period Novem ber 1975-March 1977 (Mathura Refinery Report, 1978) have been computed . The results obtained from the two models are found to be in good agr eement with the observed values. A statistical error analysis of the o bserved and the predicted concentrations show a satisfactory performan ce of both models with RMSE of 1.38 for the IITLT model and 1.62 for t he CDM. The value of index of agreement for IITLT model is 0.6 whereas for CDM it is 0.54.