Abstract
This paper presents a one-year record of in situ air-quality data from nine sites throughout Saudi Arabia. The data set is composed of hourly measurements of ozone (O
3
), nitrogen dioxide (NO
2
), and carbon monoxide (CO) at six of the largest cities in Saudi Arabia (Riyadh, Jeddah, Makkah, Yanbu, Dammam, Hafouf) and two remote locations in the mountainous southwestern region of Alsodah for the year 2007. The authors found that international O
3
and CO standards were routinely exceeded throughout the year at many sites, and that exceedances increased during Ramadan (Sep. 12 - Oct. 13), the Islamic month of fasting when much of normal daily activity is shifted to nighttime hours. In general NO
2
and CO levels were higher in Saudi cities compared to U.S. cities of comparable population, while O
3
levels were lower. There was a general trend for O
3
and NO
2
to be negatively correlated in Saudi cities in contrast to U.S. cities where the correlation is positive, suggesting that ozone chemistry in Saudi Arabia is limited by volatile organic compound emissions. This may be caused by low biogenic emissions from vegetation. Pollutant levels were lower at most Saudi sites during the four day Hajj period (Dec. 18-21) but higher in Makkah which receives millions of visitors during Hajj. The authors also found that ozone levels were elevated during the weekend (Thursday & Friday) relative to weekday levels despite lower NO
2
, a phenomenon known as the "weekend effect." As little air quality data is available from Saudi Arabia in the English-language literature, this data set fills a knowledge gap and improves understanding of air quality in an important but under-reported region of the world.
Implications: Air quality measurements at nine sites in Saudi Arabia provide a detailed look at spatial and temporal patterns of ozone (O
3
), nitrogen dioxide (NO
2
), and carbon monoxide (CO). NO
2
and CO levels increased in most cities during the fasting month of Ramadan, whereas O
3
levels decreased. This led to an increased frequency of CO exceedances based on international standards. NO
2
and CO also increased in Makkah during the Hajj pilgrimage. In general, NO
2
and O
3
levels were anticorrelated at most sites, suggesting that O
3
chemistry is limited by volatile organic compound emissions throughout much of Saudi Arabia.