Observations of high level of ozone at Qinghai Lake basin in the northeastern Qinghai-Tibetan Plateau, western China

Measurements of surface ozone (O-3), nitrogen oxides (NOx = NO + NO2), carbon monoxide (CO), and dew point were made at Qinghai Lake (QHL), China, a basin in the remote Tibetan Plateau area, in October 2010 and October 2011. The O-3 mixing ratio was found to be high with average of 41 +/- 9 ppb in October 2010 and 57 +/- 10 ppb in October 2011. The observed diurnal pattern of O-3 mixing ratio was characterized by a minimum between 07:00 and 10:00 local standard time (LST) increasing 20 ppb to a broad peak occurring between 13:00 and 18:00 LST. This diurnal pattern differs substantially from that observed at WMO's GAW Baseline Observatory located above the basin on Mount Waliguan, 130 km southeast of QHL. The elevated O-3 mixing ratios observed in the afternoon are attributed to in situ photochemical production in the air trapped in the QHL basin by surrounding mountains. The low O-3 mixing ratios observed in the morning are most likely due to surface removal in a shallow nocturnal boundary layer. The data indicate substantial impacts of pollution on air quality even in this remote area. The high O-3 values observed in 2011 may cause observable damage to the vegetation, adding stress to an ecosystem ready under the threat of desertification.