Chemical Characterization and Source Apportionment of Air Borne Particulate Matter in Western Region of India

Abstract

Today’s world lost its quality of environment in search of better quality of living. The air we breathe, water we drink and the soil we live are deteriorating due to development without consideration of sustainability. Worldwide, air pollution is one of the biggest problems we are facing due to industrialization, population explosion, deforestation etc. The pollutants released into the air are particulate matter (PM), gaseous pollutants, ionic compound, metallic compound etc. The sources and impact of these pollutants are different. Therefore, air pollution of an area is depending upon its location, industrialization, population, atmospheric condition etc. The present study focused on the properties and sources of air pollutants along with the transport model of the aerosol and gaseous air pollutants characteristics of Rajkot city. Rajkot is the fourth largest city of Gujarat and is located in the center of the Saurashtra region of Gujarat. This city is one of the fastest growing cities globally and was recognized as 22nd economically growing city at global level. Rajkot has an estimated 8,000 industrial units, of which more than 400 are foundry units, and is well known throughout the world for its casting and forging industries. Being an industrial city, air pollution might harm the region and impact the peoples living around. Wind rose diagram resulted that the direction of wind is maximum in northwest direction and highest speed observed during summer and monsoon season. Two sampling sites were selected based on the wind rose diagram are Vimal Nagar (S2) and Marwadi University (S1). Total 72 samples of PM10, PM2.5, SO2 and NO2 were collected during one year span of time (December 2017 – November 2018). The range of temperature was found to be 10.5°C – 43.8°C, daily rainfall is found 0 – 376mm, and wind direction was found to be 0 – 9.38m/sec during the study period. PM2.5 concentration was found in the range of 15.34 – 65.70 µg/m3 with an average value of 40.17µg/m3 at S1 and 16.14 – 68.95 µg/m3 with an average value of 37.50µg/m3 at S2. PM10 concentration was found in the range of 40.71 – 111.40 µg/m3 with an average value of 80.08µg/m3 at S1 and 50.73 – 109.42µg/m3 with an average value of 68.95µg/m3 at S2. SO2 concentration was found in the range of 8.68 – 20.30 µg/m3 with an average value of 14.13µg/m3 at S1 and 8.39 – 18.50µg/m3 with an average value of 13.62µg/m3 at S2. NO2 concentration was observed in the range of 9.13 – 18.95 µg/m3 with an average value of 13.29µg/m3 at S1 and 6.39 – 18.43µg/m3 with an average value of 12.71µg/m3 at S2. Concentration of both PM2.5 and PM10 was higher during winter season and lower during monsoon season. The air quality index (AQI) was found satisfactory for Particulate matter and good for gaseous pollutant. Seasonal and yearly AQI calculation had shown PM2.5 as responsible pollutant. Z score calculation had shown that both rural and urban area can be categorized as PM2.5/SO2/NO2 and PM2.5 /PM10 pollution zone. Ratio of SO2 and NO2 showed equal contribution of vehicular and industrial emission in lowering the air quality. The filter paper used for PM2.5 sampling was further used for the analysis of water soluble ionic and metallic compounds. The average annual concentration of cationic compound was found to be 2.002, 1.274, 0.675, 0.668 and 0.168μg/m3 for NH4+, Ca2+, K+, Na+, and Mg2+, respectively. The annual average concentration was 0.033, 2.002, 1.274, 0.675, 0.668 and 0.168μg/m3 for F−, Cl−, SO42−, NO2−, NO3− and PO₄³⁻ respectively. The ion concentration was found higher during summer season and lower during monsoon and post-monsoon season. The concentration of the metals was analyzed to be Fe (0.5638μg/m3), Zn (0.1170μg/m3), Al (0.6467μg/m3), Pb (0.4319μg/m3), Na (9.0475μg/m3), Cr (0.1171μg/m3), Mg (1.507μg/m3), Cu (0.0697μg/m3), Mn (0.0652μg/m3), and As (0.0597μg/m3). The metal concentration was found higher during post-monsoon season and lowest during summer season. The source analysis of the pollutants was analyzed using the positive matrix factorizations (PMF) model. 20 species of ion and metal pollutants and 72 samples were applied to the matrix for finding out the sources of six factors are Sea Salt, Industrial Emission, Mineral Dust, Secondary Aerosol, Vehicular Emission, and Biomass Burning. The Q values of this study will be 1440 (72×20). Analysis showed that 95% of Q values were near about to 1440. Results demonstrates that the major contributors of Factor 1 (Sea salt) were Na+, Cl-, Mg2+ and K+ whereas the major contributors for Factor 2 (Industrial emissions) were Fe, Zn, Al, Pb, Cu, Cr, Mg, Mn and As. Ionic compound area the major contributors of other factors such as Mineral Dust, Secondary Aerosol, Vehicular Emission, and Biomass Burning. The long-range transport model of Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT4) Model was used for analysis of forward and back trajectories of pollutant. Forward trajectory analysis show that the air pollution of Rajkot city has potential to diffuse to other states including Maharashtra and Madhya Pradesh, India. The back trajectory analysis showed that Arabic countries can also contribute to the air pollution of Rajkot city providing evidence for global contribution in local air quality at Rajkot city. This analysis can be further extended to the health impacts of these pollutants at various sources.