Seasonal variations and chemical characterization of ambient PM 10 at residential and industrial sites of an urban region of Kolkata (Calcutta), India

Abstract

Monitoring of ambient PM 10 (particulate matter which passes through a size selective impactor inlet with a 50% efficiency cut-off at 10 μm aerodynamic diameter) has been done at residential (Kasba) and industrial (Cossipore) sites of an urban region of Kolkata during November 2003 to November 2004. The measurements have been performed once a week during the study period. PM 10 mass concentrations ranged from 68.2 to 280.6 μg/m 3 at a residential site and 62.4 to 401.2 μg/m 3 at an industrial site. Metal constituents of ambient PM 10 deposited on quartz microfibre filter papers were identified using Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). Chromium (Cr), zinc (Zn), lead (Pb), cadmium (Cd), nickel (Ni), manganese (Mn) and iron (Fe) are the seven toxic trace metals quantified from the measured PM 10 concentrations. Results identified zinc with maximum contribution of PM 10 among measured metals having concentrations of 0.49 μg/m 3 at the residential site, and 0.53 μg/m 3 at the industrial site. The PAH (polycyclic aromatic hydrocarbon) compounds namely, fluoranthene (Fl), pyrene (Py), benzo(a)anthracene (BaA), benzo(b)fluoranthene (BbF) and benzo(a)pyrene (BaP) have been analyzed using gas chromatography. The major PAH compound at the monitoring sites was BbF with 0.03 μg/m 3 at the residential site and 0.02 μg/m 3 at the industrial site. Total carbon (TC), inorganic carbon (IC) and organic carbon (OC) of PM 10 were analyzed using a carbon analyzer. Exposed quartz microfibre filter papers were also analyzed for water-soluble anions of fluoride (F −), chloride (Cl −), nitrate (NO 3 −), phosphate (PO 4 3−) and sulfate (SO 4 2−) using ion chromatography. Sulfate was found in maximum concentration among anionic species with a value of 1.2 μg/m 3 at the residential site, and 1.7 μg/m 3 at the industrial site. Meteorological parameters such as wind speed, wind direction, rainfall, temperature and relative humidity were collected simultaneously during the sampling period from the Indian Meteorological Department, Kolkata. A simultaneous meteorological study was performed to assess the influence of air masses by measured meteorological parameters. Winter concentrations of PM 10 and its chemical constituents were mainly higher than in other seasons, irrespective of the monitoring sites. It indicates a longer residence time of particulates in the atmosphere during winter due to low winds and low mixing height. Winter to monsoon ratio for PM 10 is 1.6 and 2.3 for residential and industrial sites, respectively. Summer to monsoon ratio of PM 10 observed in the study period was 1.3 for the residential site, and 1.4 for the industrial site. The higher particulate pollution in the industrial area may be attributed to resuspension of road dust, soil dust, automobile traffic and nearby industrial emissions. Spearman rank correlation coefficient analysis showed an inverse relationship between PM 10 and its chemical constituents with wind speed, temperature, rainfall and relative humidity.