Long-term variations in surface ozone at the Longfengshan Regional Atmosphere Background Station in Northeast China and related influencing factors.

Surface ozone (O) is a crucial air pollutant that affects air quality, human health, agricultural production, and climate change. Studies on long-term O variations and their influencing factors are essential for understanding O pollution and its impact. Here, we conducted an analysis of long-term variations in O during 2006-2022 at the Longfengshan Regional Atmosphere Background Station (LFS; 44.44°N, 127.36°E, 330.5 m a.s.l.) situated on the northeastern edge of the Northeast China Plains. The maximum daily 8-h average (MDA8) O fluctuated substantially, with the annual MDA8 decreasing significantly during 2006-2015 (-0.62 ppb yr, p < 0.05), jumping during 2015-2016 and increasing clearly during 2020-2022. Step multiple linear regression models for MDA8 were obtained using meteorological variables, to decompose anthropogenic and meteorological contributions to O variations. Anthropogenic activities acted as the primary drivers of the long-term trends of MDA8 O, contributing 73% of annual MDA8 O variability, whereas meteorology played less important roles (27%). Elevated O at LFS were primarily associated with airflows originating from the North China Plain, Northeast China Plain, and coastal areas of North China, primarily occurring during the warm months (May-October). Based on satellite products of NO and HCHO columns, the O photochemical regimes over LFS revealed NO-limited throughout the period. NO increased first, reaching peak in 2011, followed by substantial decrease; while HCHO exhibited significant increase, contributing to decreasing trend in MDA8 O during 2006-2015. The plateauing NO and decreasing HCHO may contribute to the increase in MDA8 O in 2016. Subsequently, both NO and HCHO exhibited notable fluctuations, leading to significant changes in O. The study results fill the gap in the understanding of long-term O trends in high-latitude areas in the Northeast China Plain and offer valuable insights for assessing the impact of O on crop yields, forest productivity, and climate change.