Characteristics of tropospheric ozone variability over an urban site in Southeast Asia: A study based on MOZAIC and MOZART vertical profiles

The Measurement of Ozone and Water Vapor by Airbus In-Service Aircraft (MOZAIC) profiles of O-3 and CO were analyzed to study their variation in the troposphere over Bangkok. Mixing ratios of O-3 and CO were enhanced in planetary boundary layer (PBL) being highest in winter followed by summer and wet seasons. The daytime profiles of O-3 show higher values compared to nighttime observations in PBL region, but little differences were observed in the free troposphere. The decreasing mixing ratios of O-3 in the lower and upper troposphere were associated with shallow and deep convections, respectively. Back trajectory and fire count data indicate that the seasonal variations in trace gases were caused mainly by the regional shift in long-range transport and biomass-burning patterns. In wet season, flow of oceanic air and negligible presence of local biomass burning resulted in lowest O-3 and CO, while their high levels in dry season were due to extensive biomass burning and transport of continental air masses. The Model for Ozone and Related Chemical Tracers (MOZART) underestimated both O-3 and CO in the PBL region but overestimated these in the free troposphere. Simulations of O-3 and CO also show the daytime/nighttime differences but do not capture several key features observed in the vertical distributions. The observed and simulated values of O-3 and CO during September-November 2006 were significantly higher than the same period of 2005. The year-to-year differences were mainly due to El Nino-led extensive fires in Indonesia during 2006 but normal condition during 2005.