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

Abstract

Measurements of surface ozone (O3), 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 O3 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 O3 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 O3 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 O3 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 O3 values observed in 2011 may cause observable damage to the vegetation, adding stress to an ecosystem ready under the threat of desertification.