The effects of Southeast Asia fire activities on tropospheric ozone, trace gases and aerosols at a remote site over the Tibetan Plateau of Southwest China

Tropospheric ozone (O₃), carbon monoxide (CO), total reactive nitrogen (NO_y) and aerosols (PM_2.5 and PM₁₀) were measured on the southeastern Tibetan Plateau at Tengchong (25.01◦N, 98.3◦E, 1960 m a.s.l.) in Southwest China, where observational data is scarce, during a field campaign of the TAPTO-China (Transport of Air Pollutants and Tropospheric O₃ over China) in the spring of 2004. Fire maps derived from satellite data and backward air trajectories were used to trace the source regions and transport pathways of pollution. Ozone, CO, NO_y, PM₁₀ and PM_2.5 had average concentrations of 26 ± 8 ppb, 179 ± 91 ppb, 2.7 ± 1.2 ppb and 34 ± 23 and 28 ± 19 μg/m³, respectively. The measured O₃ level is low when compared with those reported for similar longitudinal sites in Southeast (SE) Asia and northeastern Tibetan Plateau in Northwest China suggesting that there exist complex O₃ variations in the Tibetan Plateau and its neighbouring SE Asian region. High levels of pollution with hourly averages of O₃, CO, NO_y, PM₁₀ and PM_2.5 concentrations up to 59, 678 and 7.7 ppb and 158 and 137 μg/m^-3, respectively, were observed. The increase of pollutants in the lower troposphere was caused by regional built-up and transport of pollution from active fire regions of the SE Asia subcontinent and from northern South Asia. Our results showed that pollution transport from SE Asia and South Asia had relatively stronger impacts than that from Central and South China on the abundance of O₃, trace gases and aerosols in the background atmosphere of the Tibetan Plateau of Southwest China.