Variability in ozone and its precursors over the Bay of Bengal during post monsoon: Transport and emission effects

Abstract

Simultaneous measurements of O₃, CO, NOx, CH₄, and light nonmethane hydrocarbons were made over the Bay of Bengal (BoB) during 28 October to 17 November 2010 to study the role of chemistry and dynamics. The measurements revealed large variability in O₃ (11 to 60 ppbv) and CO (45 to 260 ppbv). Estimated south to north latitudinal gradients in O₃ (3.95 ppbv/°) and CO (16.56 ppbv/°) were significantly higher than those observed during earlier campaigns. Hybrid Single-Particle Lagrangian Integrated Trajectory simulated back air trajectories were used to classify these measurements into pollution plumes from nearby sources (India-Bangladesh region and Southeast Asia), influenced by long-range transport and pristine marine air from the Indian Ocean. Interspecies correlations were used to identify emission signatures in these air masses, e.g., chemical proxies suggested influence of biofuel/biomass burning in NE-BoB and E-BoB air masses. Principle component analysis indicated contributions of ship emissions to NOx levels over the BoB. Influences of fire from the Myanmar and Thailand regions are shown to be the potential contributor to enhanced CO levels (>250 ppbv) over the BoB during 14–15 November. Diurnal variations in surface O₃ revealed effects of advection, entrainment, and photochemistry. A chemical box model simulated the photochemical buildup in O₃ in polluted air masses and daytime destruction in pristine oceanic air masses.