Primary pollutants and potential photochemical smog formation in Makkah, Saudi Arabia

This study was conducted in Mina Valley and the central district of the holy city, Makkah, during the pilgrimage (Hajj) season of 1424 Hijri (2004). During this season, more than 2.5 million people gathered in Makkah to perform the Hajj rituals. Two mobile air pollution laboratories were used to monitor NO, NO2, NOx, non-methane hydrocarbons and ozone (O3) in the atmosphere in Mina and Makkah. Instruments were calibrated periodically against standard gases. The present investigation showed clearly an ideal diurnal cycle of local ozone formation. Although the intensity of the incoming UV radiation was the lowest compared with other months of the year, recorded ozone levels approached the maximum allowable levels of 150 ug/m3 in Mina, and exceeded 160 ug/m3 in Makkah during the pilgrimage period. The problem was intensified by the high record levels NOx, sometimes reaching more than 800 ug/m3, 1h average, coupled with 1h average concentration of about 3 ppm non-methane hydrocarbons. Furthermore, the average maximum hourly ozone concentrations increased gradually from less than 60 ug/m3 during February to reach more than 200 ug/m3 (as an indication of smog formation) during some days of May. This coincides with the increase in the intensity of the incoming UV radiation reaching its maximum level in May. Consequently, it can be concluded that Makkah may face severe air pollution episodes when the pilgrimage season shifts to the summer months in the next few years. This may pose acute health problems for the elderly people and those with respiratory health problems. Good air quality and transportation management as well as the use of alternative clean fuel are highly recommended. (author)