Characteristics of surface O₃ over Qinghai Lake area in Northeast Tibetan Plateau, China

Surface O₃ was monitored continuously during Aug. 12, 2010 to Jul. 21, 2011 at a high elevation site (3200 m above sea level) in Qinghai Lake area (36°58′37″N, 99°53′56″E) in Northeast Tibetan Plateau, China. Daily average O₃ ranged from 21.8 ppbv to 65.3 ppbv with an annual average of 41.0 ppbv. Seasonal average of O₃ followed a decreasing order of summer > autumn > spring > winter. Diurnal variations of O₃ showed low concentrations during daytime and high concentrations during late night and early morning. An intensive campaign was also conducted during Aug. 13–31, 2010 to investigate correlations between meteorological or chemical conditions and O₃. It was found that O₃ was poorly correlated with solar radiation due to the insufficient NO_x in the ambient air, thus limiting O₃ formation under strong solar radiation. In contrast, high O₃ levels always coincided with strong winds, suggesting that stratospheric O₃ and long range transport might be the main sources of O₃ in this rural area. Back-trajectory analysis supported this hypothesis and further indicated the transport of air masses from northwest, northeast and southeast directions. - Highlights: • Surface O₃ was measured in Qinghai Lake area in Northeast Tibetan Plateau, China. • The O₃ chemical formation was under a strong NOx-limited in Qinghai Lake areas. • Stratospheric O₃ and transport might be the main sources of O₃ in this area