Seasonal Variation and Sources of NOx of Beibu Gulf

The concentration of NO(x) of Beibu Gulf was analyzed on four voyages in four seasons respectively between 2006 and 2007. We also studied its distribution characters as well as sources in different seasons. The results showed that the concentration of NO(x) of Beibu Gulf was ranging from under detection limit to 0.77 mg/m(3). The annual average concentration is 0.017 mg/m(3), which was lower than other reported gulfs of China. The general trend was inshore > offshore. The higher areas were Qiongzhou Bay estuary and coastal of western Hainan Island. Besides, it was relatively higher in the southern Hainan Island. It was lower in coastal of Guangxi Province and the middle of the gulf. The seasonal variation of NO(x) of Beibu Gulf combined this order: winter > autumn > spring > summer. The concentration of winter and autumn was much higher than the other two seasons. Based on these above results, it was inferred that NO(x) of Beibu Gulf was mainly controlled by continental air which was transported to ocean by wind. The next important source was emission from ships while natural emission was minor.