Spatial and seasonal variation and source apportionment of volatile organic compounds (VOCs) in a heavily industrialized region

Abstract

Source apportionment is generally applied to a time series of pollutant concentrations measured at a single site. However, in a complex airshed having multiple pollutant sources, it may be helpful to collect samples from several sites to ensure that some of them have low contributions from specific sources. Ambient air samples (n = 160) were collected by passive sampling during four seasons in 2009 and 2010 at forty different sites in Aliaga, Turkey to determine the spatial, seasonal variations and possible sources of volatile organic compounds (VOCs). Fifty-eight VOCs (Σ58VOC) were detected. Σ58VOC concentrations ranged between 0.1 and 1770 μg m−3 (avg ± SD, 67 ± 193 μg m−3). Aliphatic hydrocarbons were generally predominant with a high percentage of contribution (31%–88%) at all sites. Aromatic VOCs were the second highest group (8–50%), followed by halogenated VOCs (1–24%) and oxygenated VOCs (0.04–5.9%). Highly variable spatial distribution of ambient VOC concentrations suggested that the major sources in this region were industrial plants. Generally, VOC concentrations were higher in summer than in winter probably due to increased volatilization from their sources at higher ambient temperatures. However, high atmospheric VOC concentrations were also observed in winter and fall near the petroleum refinery and petrochemical complex, probably due to the calm conditions and high atmospheric stability that is commonly encountered during the winter months in the area, restricting the dilution of pollutants. The newest version of EPA PMF (V5.0) (Positive Matrix Factorization) having the capability of handling multiple site data was used for source apportionment. Refinery and petroleum products, petrochemical industry, solvent use and industrial processes, and vehicle exhaust were the identified VOC sources in the study area, contributing 56%, 22%, 12%, and 10%, respectively to the Σ58VOC concentrations. Carcinogenic risks due to lifetime exposure to seven VOCs were also estimated. Estimated risks were the highest for 1,2-dichloroethane, followed by benzene, chloroform, and carbon tetrachloride. Carcinogenic risks for trichloroethene, 1,1,2-trichloroethane, and bromoform were lower than the general acceptable risk level of 1.0 × 10−6. However, risks for 1,2-dichloroethane, benzene, chloroform, and carbon tetrachloride were substantially higher than the acceptable level. It was concluded that carcinogenic risks may reach considerably high levels for a significant portion of the population living in the study area.