Temporal variability of MODIS aerosol optical depth and chemical characterization of airborne particulates in Varanasi, India

• Published in: Environmental science and pollution research international Vol. 22; no. 2; pp. 1329 - 1343
• Main Authors: Murari, Vishnu, Kumar, Manish, Barman, S. C, Banerjee, T
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.01.2015; Springer Berlin Heidelberg; Springer Nature B.V
• Subjects: Aerosols; Aerosols - chemistry; Air Pollutants - chemistry; Air pollution; Airborne particulates; Ammonium; Aquatic Pollution; Atmosphere; Atmospheric Protection/Air Quality Control/Air Pollution; Cadmium; Cardiovascular diseases; Chromium; cobalt; Copper; Dominant species; Dust; Earth and Environmental Science; Earth crust; Ecotoxicology; Environment; Environmental Chemistry; Environmental Health; Environmental Monitoring; Fossil fuels; Health hazards; Heterogeneity; India; iron; lead; magnesium; manganese; Metals; Metals - chemistry; moderate resolution imaging spectroradiometer; monitoring; nickel; nitrates; Optical analysis; Outdoor air quality; Particle Size; Particulate matter; Particulate Matter - chemistry; particulates; Research Article; Respiratory diseases; respiratory tract diseases; risk; seasonal variation; Seasonal variations; Seasons; sodium; soil; Solvent extraction; solvents; Spectrophotometry; summer; Temporal variations; toxicity; Trace metals; Waste Water Technology; Water Management; Water Pollution Control; zinc; India; India, Uttar Pradesh, Varanasi; Particulate; Organics; Water-soluble ions; Metal; Aerosol optical depth; Varanasi
• ISSN: 0944-1344; 1614-7499
• DOI: 10.1007/s11356-014-3418-2

Temporal variation of airborne particulate mass concentration was measured in terms of toxic organics, metals and water-soluble ionic components to identify compositional variation of particulates in Varanasi. Information-related fine particulate mass loading and its compositional variation in middle Indo-Gangetic plain were unique and pioneering as no such scientific literature was available. One-year ground monitoring data was further compared to Moderate Resolution Imaging Spectroradiometer (MODIS) Level 3 retrieved aerosol optical depth (AOD) to identify trends in seasonal variation. Observed AOD exhibits spatiotemporal heterogeneity during the entire monitoring period reflecting monsoonal low and summer and winter high. Ground-level particulate mass loading was measured, and annual mean concentration of PM₂.₅(100.0 ± 29.6 μg/m³) and PM₁₀(176.1 ± 85.0 μg/m³) was found to exceed the annual permissible limit (PM₁₀: 80 %; PM₂.₅: 84 %) and pose a risk of developing cardiovascular and respiratory diseases. Average PM₂.₅/PM₁₀ratio of 0.59 ± 0.18 also indicates contribution of finer particulates to major variability of PM₁₀. Particulate sample was further processed for trace metals, viz. Ca, Fe, Zn, Cu, Pb, Co, Mn, Ni, Cr, Na, K and Cd. Metals originated mostly from soil/earth crust, road dust and re-suspended dust, viz. Ca, Fe, Na and Mg were found to constitute major fractions of particulates (PM₂.₅: 4.6 %; PM₁₀: 9.7 %). Water-soluble ionic constituents accounted for approximately 27 % (PM₁₀: 26.9 %; PM₂.₅: 27.5 %) of the particulate mass loading, while sulphate (8.0–9.5 %) was found as most dominant species followed by ammonium (6.0–8.2 %) and nitrate (5.5–7.0 %). The concentration of toxic organics representing both aliphatic and aromatic organics was determined by organic solvent extraction process. Annual mean toxic organic concentration was found to be 27.5 ± 12.3 μg/m³(n = 104) which constitutes significant proportion of (PM₂.₅, 17–19 %; PM₁₀, 11–20 %) particulate mass loading with certain exceptions up to 50 %. Conclusively, compositional variation of both PM₂.₅and PM₁₀was compared to understand association of specific sources with different fractions of particulates.