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 NOx 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.