Abstract
This work presents the outcome of a research conducted during pilgrimage period of 1402 H (1982 AD) where 2 million persons gathered in Muna valley of the 4 km super(2) area. Photochemical oxidants had been found to exceed the limit which can be taken as evidence of photochemical smog formation in the valley under appropriate weather condition that exist. High concentrations of carbon monoxide were detected in the atmosphere of the valley. For example, more than 50 ppm, average over 1 hr, was recorded during morning peak time of pilgrims movement form Arafat to the valley due to high traffic density and the noctural stable condition. Moreover, the CO air quality standard of 9 ppm, average over 8 hrs. was exceeded as an average over 24 hrs. during pilgrims full occupancy of the valley. Control measures should be undertaken to avoid future air pollution episode. Conclusions and recommendations are included.