Diurnal variation of surface ozone in mountainous areas: Case study of Mt. Huang, East China.

Abstract To explore the variations in atmospheric environment over mountainous areas, measurements were made from an intensive field observation at the summit of Mt. Huang (30.13°N, 118.15°E, 1841 m above sea level), a rural site located in East China, from June to August 2011. The measurements revealed a diurnal change of surface O 3 with low concentrations during the daytime and high concentrations during the nighttime. The causes of diurnal O 3 variations over the mountain peak in East China were investigated by using a fairly comprehensive WRF-Chem and HYSPLIT4 modeling approach with observational analysis. By varying model inputs and comparing the results to a baseline modeling and actual air quality observations, it is found that nearby ozone urban/anthropogenic emission sources were contributing to a nighttime increase in mountaintop ozone levels due to a regional transport lag and residual layer effects. Positive correlation of measured O 3 and CO concentrations suggested that O 3 was associated with anthropogenic emissions. Sensitivity modeling experiments indicated that local anthropogenic emissions had little impact on the diurnal pattern of O 3 . The diurnal pattern of O 3 was mainly influenced by regional O 3 transport from the surrounding urban areas located 100–150 km away from the summit, with a lag time of 10 h for transport.