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.
