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

Tropospheric ozone (O3) 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 O3 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 O3 levels. NOx is one of the significant O3 precursors generated during anthropogenic combustion processes. Therefore, despite efforts in emission controls, reducing NOx 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 O3 and precursors. The review summarizes current knowledge of O3 levels and NOx 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.