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Measurements of surface ozone (O), nitrogen oxides (NO = NO + NO), 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 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 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 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 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 values observed in 2011 may cause observable damage to the vegetation, adding stress to an ecosystem ready under the threat of desertification. [ABSTRACT FROM AUTHOR]

The concentrations, size distributions, and mixing states of refractory black carbon (rBC) aerosols were measured with a ground-based Single Particle Soot Photometer (SP2), and aerosol absorption was measured with an Aethalometer at Qinghai Lake (QHL), a rural area in the Northeastern Tibetan Plateau of China in October 2011. The area was not pristine, with an average rBC mass concentration of 0.36 μg STP-m(-3) during the two-week campaign period. The rBC concentration peaked at night and reached the minimal in the afternoon. This diurnal cycle of concentration is negatively correlated with the mixed layer depth and ventilation. When air masses from the west of QHL were sampled in late afternoon to early evening, the average rBC concentration of 0.21 μg STP-m(-3) was observed, representing the rBC level in a larger Tibetan Plateau region because of the highest mixed layer depth. A lognormal primary mode with mass median diameter (MMD) of ~175 nm, and a small secondary lognormal mode with MMD of 470-500 nm of rBC were observed. Relative reduction in the secondary mode during a snow event supports recent work that suggested size dependent removal of rBC by precipitation. About 50% of the observed rBC cores were identified as thickly coated by non-BC material. A comparison of the Aethalometer and SP2 measurements suggests that non-BC species significantly affect the Aethalometer measurements in this region. A scaling factor for the Aethalometer data at a wavelength of 880 nm is therefore calculated based on the measurements, which may be used to correct other Aethalometer datasets collected in this region for a more accurate estimate of the rBC loading. The results present here significantly improve our understanding of the characteristics of rBC aerosol in the less studied Tibetan Plateau region and further highlight the size dependent removal of BC via precipitation., (Copyright © 2014 Elsevier B.V. All rights reserved.)