SO 2 Oxidation Efficiency Patterns during an Episode of Plume Transport over Northeast India: Implications to an OH Minimum

摘要: Systematic monitoring of the fluctuations in atmospheric SO2 oxidation efficiency—measured as a molar ratio SO42- to total SOx (SOx=SO2+SO42-), referred S-ratio—have been performed during major long range plume transport northeast India (Shillong: 25.67°N, 91.91°E, 1064 m ASL) March 2009. Anomalously low S-ratios (median, 0.03) were observed episode—associated with cyclonic circulation—and and exhibited unusual features ‘relative phase’ their peaks. During initial days, when levels dictated by influx, variabilities anti-phase—for differing mobility/loss mechanisms. When governed boundary layer diurnality latter anti-phase is explained ‘depleted OH level’—major portion being consumed period elevated other pollutants. Simulations global 3D chemical model, GEOS-Chem (v8-03-01), also indicated ‘suppressed conditions’—with characteristic poor phase agreements. The modelled decreased steadily from normalized SO2—referred OHspecific—was consistently S-ratio period’. Further, geographical distribution showed pronounced minimum over region surrounding (20°N, 95°E) spanning parts adjacent regions southeast it—prevalent throughout year, though magnitude area influence have seasonality it—with significant implications for reducing oxidizing power regional atmosphere. A second set measurements January 2010—when prominent transports absent—exhibited no anomalies, well within acceptable limits 0.32). This work highlights model skill simulating/detecting ‘transient fluctuations’ efficiency, down scale.