Elucidating the Factors Governing the Interannual Variability of Ozone Concentrations During Fall 2015-2019 in Sanya, China

While ozone pollution has been a major air pollution concern in metropolitans in China, the characteristics and governing factors of ozone concentrations in Sanya remains unclear. In this study, we first analyze the interannual variability of ozone based on observational data in Sanya, and identify it is in general characterized by a peak ozone season in fall and minimal ozone season in summer. Meanwhile, the substantial ozone enhancement in 2019 compared to the previous three to four years over Sanya clearly stands out. To elucidate the possible governing factors, we design a few numerical experiments based on regional air quality model, and find that the modulation of meteorology is key to steering the interannual variability of ozone in fall in Sanya. The spatial evolution further indicates that the transport from upwind regions like Pearl River Delta region is crucial in stimulating the ozone accumulation in Sanya. In addition, ship emissions play important roles in further enhancing their ozone concentration, ranging from 7% -10% during 2015-2019. The findings in this study imply that whereas an overall low ozone concentration in Sanya, ozone exceedance may still occur in particular under unfavorable meteorological conditions together with the concomitant transport from other regions facing ozone pollution. It stresses the importance of regional emission control, including anthropogenic emissions and ship emissions, on improving air quality in Sanya