Source characteristics of O3 and CO2 at Mt. Waliguan Observatory, Tibetan Plateau implied by using 7Be and 210Pb

Abstract

The weekly averages of near-surface 7Be, 210Pb, O3, and CO2 concentrations at the Global Atmospheric Watch Observatory, Mt. Waliguan (101.98°E, 36.287°N, 3810 m a.s.l.), from October 2002 to January 2004 are presented. With the establishment of the new datasets of DCCW (Differential Concentrations in Contiguous Weeks) of 7Be, 210Pb, and O3, CO2 (Δ7Be, Δ210Pb, ΔO3, ΔCO2, respectively, the impacts of upper-level downward transports and land-surface emissions on O3 and CO2 concentrations are implied by 7Be and 210Pb being as independent tracers. The relations among Δ7Be, Δ210Pb, and ΔO3, ΔCO2 are examined statistically and compared. The results indicate that with the DCCWs, the interferences with the tracing significance of 7Be and 210Pb from the seasonal wet scavenging of atmospheric aerosol are greatly reduced, and the weighting sources of O3 or CO2 variations are more pronounced. Basically, the variability of surface O3 is controlled predominately by air mass transported from the upper atmosphere levels while the emission from the Continent Boundary Layer (CBL) has an obvious input for CO2. The relation between Δ210Pb and ΔO3 reflects that influences of CBL emission are generally positive/negative for surface O3 budget in summer/winter, and the relation of Δ7Be and ΔCO2 also reveals that upper level downward transport has positive/negative inputs for CO2 in summer/winter. With the highly correlated relations between 7Be and O3, a quantitative estimation is made of the stratospheric contributions to the budget of surface O3 at WLG: the monthly averages of stratospheric O3 range from 6 × 10−9 to 8 × 10−9 (volume mixing ratio) in April and from June to August, and 2×10−9 to 4×10−9 in the remaining months. For the ultimate sources of the baseline concentration of surface O3, which consist of only stratospheric transport and tropospheric photochemistry production, the contribution from stratospheric transport is estimated to be about 20 × 10−9 from May to July, and (12−15)×10−9 in the remaining months, and the total relative contribution rate is about 35% to 40%.