Trends of Ambient Concentrations of Gaseous Air Pollutants in Almadinah Al Menawwarah, Central Area, Saudi Arabia

Nitrogen monoxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NOx), sulfur dioxide (SO2), ozone (O3), carbon monoxide (CO), methane (CH4) and non-methane hydrocarbons (NMHCs) were measured in Almadinah Al Menawwarah, Saudi Arabia. From Ramadan to Hajj season (October, 2005 January, 2006) daily average concentrations of NO, NO2, NOx, SO2, O3, CO, CH4 and NMHCs, were 0.055, 0.040, 0.095, 0.011, 0.009, 2.82, 3.83 and 1.12 ppm, respectively. The SO2/NOx and SO2/NO2 concentration ratios were 0.12 and 0.28, respectively, suggesting that the mobile emissions are the predominant sources within the study area. The diurnal variations of NO, NO2, NOx, SO2, CO, NMHCs concentrations were similar and showed two daily peaks, in the morning and late evening. These peaks concentrations are linked to traffic density, boundary layer mixing processes and chemical processes in the atmosphere. The diurnal cycles of O3 concentrations revealed a uni-modal peak in the mid-day time. The highest concentrations of the measured pollutants were found in Ramadan and Hajj seasons, due to increasing human activities. Significant positive correlation coefficients (p<0.05) were found between NO, NO2, NOx, NMHCs and CO, and also between SO2 and NO, NO2, NOx, NMHCs and CH4. Significant negative correlation coefficients were found between O3 concentrations and NO2. These results indicate that an increase in O3 level is associated with a drop in the concentration of NO2, CO and NMHCs.