Spatial and temporal variations of SPM, RPM, SO2 and NOx concentrations in an opencast coal mining area

Abstract

A study for assessment and management of air quality was carried out in the Ib Valley area of the Ib Valley coalfield in Orissa state, India. The 24 h average concentrations of suspended particulate matter (SPM), respirable particulate matter (RPM), sulfur dioxide (SO₂) and oxides of nitrogen (NO_x) were determined at regular intervals throughout one year at twelve monitoring stations in residential areas and six monitoring stations in mining/industrial areas. The 24 h average SPM and RPM concentrations were 124.6–390.3 µg m⁻³ and 25.9–119.9 µg m⁻³ in residential areas, and were 146.3–845.2 µg m⁻³ and 45.5–290.5 µg m⁻³ in industrial areas. During the study period, 24 h and annual average SPM and RPM concentrations exceeded the respective standards set in the Indian national ambient air quality standard (NAAQS) protocol as well as USEPA, EU, WHO and World Bank standards at most of the residential and industrial areas. However, concentrations of SO₂ (annual average: 24.6–36.1 µg m⁻³ and 24 h average: 17.0–46.3 µg m⁻³) and NO_x (annual average: 23.6–40.9 µg m⁻³ and 24 h average: 18.3–53.6 µg m⁻³) were well within the prescribed limit of the NAAQS and international standards in both residential and industrial areas. The temporal variations of SPM and RPM fitted polynomial trends well and on average in the mining area 31.91% of the SPM was RPM. The linear regression correlation coefficients between SPM and RPM and between NO_x and SO₂ were 0.94 (±0.04) and 0.66 (±0.10), respectively. The optimum interpolation technique, kriging, determined that maximal concentrations of SPM and RPM occurred within the mining site. Highest concentrations of particulate matter were observed during the winter season followed by summer, autumn and rainy seasons. An action plan is formulated for effective control of air pollution at source, and mitigative measures should include implementation of green belts around the sensitive areas where the concentration of air pollutants exceeds the standard limit.