Distributions of SO2 and NO2 in the lower atmosphere of an industrial area in Bhutan.

Two important air pollutants, sulfur dioxide (SO2) and nitrogen dioxide (NO2), were sampled and monitored in the spring season in the biggest industrial area of Bhutan. Field measurements of SO2 and NO2 were performed using standard colorimetric methods, and air samples were collected using an active sampling technique. Sampling sites were selected to cover all the potential catchment areas like settlements, staff quarters, shops and schools. The main objective of this sampling work was to see the distribution of these two pollutants from the source of emission (small scale industries) and to obtain and establish a baseline data. The active sampler was first tested and validated in a laboratory using liquid and gas standards of SO2 and NO2. Good linearity from 0.050 to 1.0 µg mL-1 for SO2 and from 0.010 to 1.0 µg mL-1 for NO2 were obtained (R2 > 0.99) with limits of detection of 30 and 50 ng mL-1 for SO2 and NO2, respectively. Daylong sampling was done at selected sites with a range of distances away from the sources of emission. The ambient concentration of SO2 and NO2 were in the range of 0.45-4.46 and 0.56-5.68 µg m-3, respectively.