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Ozone is a pollutant of major concern because of its well recognized effects upon human health and crop yields. This study analyses in depth a new dataset for ozone from Jeddah, a coastal city in Saudi Arabia within the Middle Eastern region, for which very few ozone data are currently available, collected between March 2012 and February 2013. The measurements presented include NO, NO2 and ozone as well as relevant meteorological variables. The data show a marked seasonal variation in ozone with highest concentrations in the summer months and lowest average concentrations in the winter. Concentrations also show a substantial difference between weekdays and weekends, with higher NO and NO2 on weekdays, but lower concentrations of ozone. Plots of total oxidant versus NOx concentration indicate background concentrations of ozone (at zero NOx) ranging from 38.2 ppb in January to 59 ppb in May consistent with the northern hemisphere spring maximum in ozone concentrations. The slope of total oxidant/NOx varies from 0.13 in March to 0.68 in August. The two summer months of July and August are anomalous with slopes of around double that of other months, suggesting a higher efficiency of ozone production at lower primary pollutant concentrations arising from much reduced daytime traffic. A substantial weekend/weekday difference in ozone which is higher at weekends appears to be attributable to lower daytime traffic activity and hence reduced emissions of NOx to a “NOx-saturated” atmosphere.

Past measurements of volatile organic compound (VOC) concentrations from Middle Eastern countries are very few, and this study assesses the concentrations and processes affecting benzene, toluene, ethylbenzene and xylenes (BTEX) in the atmosphere of an urban background area of Jeddah, a coastal city in Saudi Arabia, and their potential for ozone formation. The measurements were carried out for a year (from December 2011 to November 2012) and include hourly BTEX and meteorological parameters. The annual average concentrations of BTEX species were 0.41 ppb for benzene, 1.40 ppb for toluene, 0.49 ppb for ethylbenzene, 1.56 ppb for m,p-xylene and 0.94 ppb for o-xylene. The annual mean benzene level (0.41 ppb, ∼1.31 μg m−3) did not exceed the annual threshold level (5 μg m−3) set by the European Union but still represents a small risk to human health. BTEX showed a seasonal variation, with higher concentrations during the spring and lower concentrations during the autumn. The diurnal variation of BTEX concentrations followed a commonly observed pattern, with two peaks associated with high traffic volumes. m,p-Xylene was the largest contributor to ozone formation potential followed by o-xylene, toluene and benzene. The significantly positive correlation between BTEX compounds as well as the ratio of toluene/benzene (average = 4.03) suggested that vehicle emissions were the major source of BTEX during the whole investigated period. m,p-Xylene-to-ethylbenzene ratios showed an annual mean of 3.18 with little variability during the different seasons indicating that the photochemical age in the study area is relatively young due to the continual fresh emissions experienced in Jeddah city.

Ground level ozone (O3) plays an important role in controlling the oxidation budget in the boundary layer and thus affects the environment and causes severe health disorders. Ozone gas, being one of the well-known greenhouse gases, although present in small quantities, contributes to global warming. In this study, we present a predictive model for the steady-state ozone concentrations during daytime (13:00&ndash, 17:00) and nighttime (01:00&ndash, 05:00) at an urban coastal site. The model is based on a modified approach of the null cycle of O3 and NOx and was evaluated against a one-year data-base of O3 and nitrogen oxides (NO and NO2) measured at an urban coastal site in Jeddah, on the west coast of Saudi Arabia. The model for daytime concentrations was found to be linearly dependent on the concentration ratio of NO2 to NO whereas that for the nighttime period was suggested to be inversely proportional to NO2 concentrations. Knowing that reactions involved in tropospheric O3 formation are very complex, this proposed model provides reasonable predictions for the daytime and nighttime concentrations. Since the current description of the model is solely based on the null cycle of O3 and NOx, other precursors could be considered in future development of this model. This study will serve as basis for future studies that might introduce informing strategies to control ground level O3 concentrations, as well as its precursors&rsquo, emissions.

Atmospheric aerosols have significant effects on human health and the climate. A large fraction of these aerosols originates from secondary new particle formation (NPF), where atmospheric vapors form small particles that subsequently grow into larger sizes. In this study, we characterize NPF events observed at a rural background site of Hada Al Sham (21.802∘ N, 39.729∘ E), located in western Saudi Arabia, during the years 2013–2015. Our analysis shows that NPF events occur very frequently at the site, as 73 % of all the 454 classified days were NPF days. The high NPF frequency is likely explained by the typically prevailing conditions of clear skies and high solar radiation, in combination with sufficient amounts of precursor vapors for particle formation and growth. Several factors suggest that in Hada Al Sham these precursor vapors are related to the transport of anthropogenic emissions from the coastal urban and industrial areas. The median particle formation and growth rates for the NPF days were 8.7 cm−3 s−1 (J7 nm) and 7.4 nm h−1 (GR7−12 nm), respectively, both showing highest values during late summer. Interestingly, the formation and growth rates increase as a function of the condensation sink, likely reflecting the common anthropogenic sources of NPF precursor vapors and primary particles affecting the condensation sink. A total of 76 % of the NPF days showed an unusual progression, where the observed diameter of the newly formed particle mode started to decrease after the growth phase. In comparison to most long-term measurements, the NPF events in Hada Al Sham are exceptionally frequent and strong both in terms of formation and growth rates. In addition, the frequency of the decreasing mode diameter events is higher than anywhere else in the world.