Tropospheric ozone and NOx: A review of worldwide variation and meteorological influences

Tropospheric ozone ( O 3 ) has increased globally since the end of 20th century. Its formation undergoes complicated photochemical reactions and processes in the lower boundary layer. As a result, changes in O 3 levels are not about one specific factor but a combined process of other effects such as anthropogenic emissions, topographic characteristics, and meteorological influences. Consequently, published studies often show conflicting findings on O 3 levels. NO x is one of the significant O 3 precursors generated during anthropogenic combustion processes. Therefore, despite efforts in emission controls, reducing NO x will not guarantee a downward ozone trend. Furthermore, specific weather phenomena (e.g., anticyclones and sea-land breezes) can enhance specific meteorological parameters that govern the transport and diffusion of O 3 and precursors. The review summarizes current knowledge of O 3 levels and NO x emissions in recent years. It helps to understand how meteorological parameters and specific regional features influence ozone and its precursors, which is beneficial for efficient surface ozone evaluation and control. • Developed countries emit more NO x per capita than developing countries. • O 3 reduction was counteracted by meteorological tendencies and pollution transporting. • Interaction of meteorological factors may cause bias on ozone mitigation policy analysis. • Climate change exerted indirect long-term effects on tropospheric ozone.