Sulphur dioxide is a toxic pollutant in the atmosphere emitted from natural sources and human activities. Normally, SO₂ has a life-time of about 2 days in the atmosphere and is not transported to long distances from its source region. However, under favourable circumstances such as low humidity or high wind speed, it can travel intercontinental distances from the point of emission. In this article, we have analysed the surface mixing-ratio of SO₂ measured over the time period from January 2010 to April 2012 at a rural region in south India. It is found that SO₂ mixing-ratio is very low over this region with an annual mean value in the range of 0.21–0.24 ppbv. OMI satellite estimates an annual mean value of 0.5 Dobson Units (DU) over the same location and period. However, during January to May relatively higher concentrations of SO₂ are observed, mainly coming from power plants located in southern and eastern India as indicated by higher SO₂/NO₂ ratios of greater than 0.5. In one instance, on June 20th, 2011, it is found that the OMI SO₂ value was a factor of 13 higher than 2011 annual mean at Gadanki. Using the FLEXible PARTicle dispersion model (FLEXPART) and satellite data, it is found that the observed higher SO₂ value on 20th June was due to intercontinental transport of SO₂ from Nabro volcanic eruption. Using the FLEXPART model with ECLIPSE-v5 emission inventory, the observed seasonal variation of SO₂ could be well reproduced; however, the mixing ratios are found to be overestimated. CAMS (Copernicus Atmosphere Monitoring Service) SO₂ reanalysis values available through its implementation in the ECMWF Integrated Forecasting System are a factor of 7.8 higher than observations, possibly due to incorrect vertical profile used in the model.

二氧化硫是大气中自然来源和人类活动所排放的有毒污染物。通常，SO ₂在大气中的寿命约为2天，并且不会从其来源区域转移到很远的距离。但是，在低湿度或高风速等有利条件下，它可以从发射点传播到洲际距离。在本文中，我们分析了从2010年1月至2012年4月在印度南部农村地区测得的SO ₂的表面混合比。发现SO ₂该区域的混合比率非常低，年平均值在0.21-0.24 ppbv的范围内。OMI卫星在相同位置和相同时期估计的年均值为0.5 Dobson Units（DU）。然而，在一月至五月期间，观察到相对较高的SO ₂浓度，主要来自印度南部和东部的发电厂，这表明较高的SO ₂ / NO ₂比值大于0.5。在2011年6月20日的一个实例中，发现OMI SO ₂值比Gadanki的2011年平均水平高13倍。使用FLEXible Particle弥散模型（FLEXPART）和卫星数据，发现观察到的较高的SO ₂6月20日的价值是由于纳布罗火山喷发引起的SO _2的洲际运输。使用带有ECLIPSE-v5排放清单的FLEXPART模型，可以很好地再现观察到的SO _2的季节变化；然而，发现混合比被高估了。通过在ECMWF综合预报系统中实施CAMS（哥白尼大气监测服务）SO ₂再分析值，比观测值高7.8倍，这可能是由于模型中使用的垂直剖面不正确所致。