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

ABSTRACT

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.

KEYWORDS:

• Active sampler
• baseline data
• Bhutan
• nitrogen dioxide
• sulfur dioxide

Acknowledgments

The authors thank Dr. Brian Hodgson for assistance with the English.

Funding

This project was supported by Prince of Songkla University, PhD Scholarship; Trace Analysis and Biosensor Research Center (TAB-RC); the Center of Excellence for Innovation in Chemistry (PERCH-CIC); Department of Chemistry, Faculty of Science and Graduate School, Prince of Songkla University, Hat Yai, Songkhla, Thailand.