Diurnal and Seasonal Variations of Surface Ozone and Its Precursors in the Atmosphere of Yanbu, Saudi Arabia

Surface ozone (O3) and its precursor’s gases (nitrogen monoxide (NO), nitrogen dioxide (NO2), nitrogen oxides (NOx), carbon monoxide (CO), methane (CH4) and non-methane hydrocarbons (NMHCs), and sulfur dioxide (SO2) were measured in Yanbu, Saudi Arabia from January 2004-December 2004. The annual average concentrations of O3, NO, NO2, NOx, SO2, CO, CH4, TNMHCs and THC were 22.51 ppb, 15.58 ppb, 17.25 ppb, 23.84 ppb, 6.66 ppb, 165.13 ppb, 3.44 ppm, 0.56 ppm and 3.88 ppm, respectively. The SO2/NOx and SO2/NO2 concentration ratios during the period of study indicate that the mobile emissions are the predominant sources in yanbu. The diurnal cycles of O3 concentrations revealed highest levels in the daytime and lowest levels in night time. The diurnal variations of NO, NO2, NOx, SO2, CO, NMHCs concentrations were similar and showed peaks concentrations linked to traffic density, boundary layer mixing processes and chemical processes in the atmosphere. The mean concentrations of O3 in different seasons follow the order of summer > spring > autumn > winter. In contrary to O3, NO has higher concentrations in autumn and winter than those in summer and spring seasons. The highest concentrations of NO2, NOx, SO2, CO, and TNMHCs were found in autumn and spring, whereas the lowest concentrations were found in summer and winter. THC and CH4 have no significant change over winter, autumn and summer seasons, while their concentrations decrease sharply in spring. Although the studied area does not suffer from NO2, O3, SO2 and CO pollution and no health risk, comprehensive and long-term air quality management programmes are needed in order to keep air quality in a good condition.