The characteristics of inorganic gases and volatile organic compounds at a remote site in the Tibetan Plateau

In order to study the characteristics of pollutants in the remote background site of Tibetan Plateau, volatile organic compounds (VOCs), NO, NO2, SO2, CO, O-3 and meteorological parameters (temperature, relative humidity, rainfall, horizontal wind speed and direction) were measured in the autumn of 2013 at Menyuan station (37.59 degrees N, 101.29 degrees E, 3250 ma.s.l.), which is a newly established background site located in the Tibetan Plateau. The significantly lower average concentrations of NO, NO2, SO2 and CO were observed, indicating the distinct background characteristics at Menyuan. The O-3 diurnal variation pattern and correlation analyses revealed the influence of in situ photochemical reactions and vertical mixing during the daytime and the long-range and vertically downslope transport from the upper troposphere or lower stratosphere during the nighttime. A total of 30 VOCs samples were collected and 66 VOCs species were analyzed. The oxygenated VOCs (OVOCs) were the most abundant components and high levels of acetone, acetaldehyde, nonanal, hexachloro-1,3-butadiene, 1,2-dichloroethane and CCl4 were observed. The L-OH and OFP analysis confirmed that OVOCs and aromatics were the most active substances, and the VOCs had relatively stable chemical compositions and low photochemical potential. The long-range transport air masses from the southeast of Menyuan station passed by some polluted areas, such as Xining, and could result in the elevated NOx, CO and SO2 concentrations at Menyuan. Therefore, this work enriches the understanding of O-3 cycles and transport influence in the Tibetan Plateau.