Atmospheric SO2 oxidation efficiency over a semi-arid region: Seasonal patterns from observations and GEOS-Chem model

摘要: The oxidation efficiency of atmospheric SO2, measured as a molar ratio SO42− to total SOx (SOx = SO2 + SO42−), referred S-ratio, have been studied from high altitude site (Gurushikhar, Mt. Abu: 24.6° N, 72.7° E, 1680 m ASL) in semi-arid region western India. A global 3-dimensional Chemical Transport Model (CTM), GEOS-Chem (v8-03-01), is employed interpret the observed patterns. S-ratios derived time series SO2 and measurements exhibited pronounced seasonality, with relatively low ratios Feb–Mar 2010, Nov–Dec 2009 intermediate values Sep–Oct 2009. lower for Feb ‘10 Mar (median 0.10 0.08 respectively) attributed planetary boundary layer (PBL) heights – reduce loss atmosphere via dry deposition well OH radical levels ‘aged air mass influx’ during these months. On other hand, PBL significant long range transport contributions are projected be possible causes higher Nov ‘09 Dec 0.30 0.28 respectively). seasonal patterns predicted by CTM 4° × 5° grid cell containing sampling showed highest Jul–Aug, lowest Apr. model has further study various parameters such PBL, OH, RH, dust load, pattern deposition. Sensitivity simulations enhancing load peak May (∼4.7% (median)). Similarly, ‘dry deposition’ seen boost August (∼66.3% Also, assess ‘altitudinal dependence S-ratios’ revealed behaviour.