RESEARCH ARTICLE Levels and sources of organic compounds in fine ambient aerosols over National Capital Region of India Shivani 1 & Ranu Gadi 1 & Sudhir Kumar Sharma 2 & Tuhin Kumar Mandal 2 & Ravi Kumar 3 & Sharma Mona 4 & Sachin Kumar 3 & Sanchit Kumar 4 Received: 31 May 2018 /Accepted: 22 August 2018 # Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract The study presents the spatial and temporal variation of fine ambient aerosols (PM 2.5 ) over National Capital Region (NCR), India, during January to June 2016. The investigation includes three sampling sites, one in Delhi and two in the adjoining states of Delhi (Uttar Pradesh and Haryana), across NCR, India. The average PM 2.5 concentration was highest for Delhi (128.5 ± 51.5 μgm -3 ) and lowest for Mahendragarh, Haryana (74.5 ± 28.7 μgm -3 ), during the study period. Seasonal variation was similar for all the sites with highest concentration during winter and lowest in summer. PM 2.5 samples were analysed for organic compounds using gas chromatograph (GC). The concentration of three organic compound classes, n-alkanes (C11–C35), polycyclic aromatic hydrocarbons (PAHs), and phthalates, present in PM 2.5 samples has been reported. Diagnostic ratios for n-alkanes demonstrated that biogenic emissions were dominant over Mahendragarh while major contributions were observed from petrogenic emissions over Delhi and Modinagar, Uttar Pradesh. Molecular diagnostic ratios were calculated to distinguish between different sources of PAHs, which revealed that the fossil fuel combustion (diesel and gasoline emissions), traffic emissions, and biomass burning are the major source contributors. Health risk associated with human exposure of phthalates and PAHs was also assessed as daily intake (DI, ng kg -1 day -1 ) and lung cancer risk, respectively. Backward trajectory analysis explained the local, regional, and long- range transport routes of PM 2.5 for all sites. Principal component analysis (PCA) results summarized that the vehicular emissions, biomass burning, and plastic burning were the major sources of the PAHs and phthalates over the sampling sites. Keywords n-Alkanes . PAHs . Phthalates . Daily intake . Lung cancer risk . Trajectories Introduction Deterioration of air quality is a consequence of rapid urbaniza- tion and industrialization worldwide, especially in developing countries. As a result, in recent years, air quality has become societal and scientific issue of concern all over the world. In India, atmospheric aerosol load in the last decade (2000–2010) has increased rapidly (Dey and Di Girolamo 2011). Fine parti- cles (PM 2.5 ) present in ambient air have more detrimental health effects than coarse particles (PM 10 ) because of their small size which aids them to reach and settle in the lungs. Exposure to PM 2.5 over long period has a potential to pose premature death as a major health risk (Brauer et al. 2012; Pope et al. 2002). Health risks associated with exposure to PM 2.5 have resulted in loss in life expectancy of 6.3 ± 2.2 years for Delhi region (Ghude et al. 2016). Water-soluble ionic species, mineral dust, and carbona- ceous aerosols are the constituents of atmospheric aerosols. Carbonaceous aerosols include high organic carbon (OC) fraction ranging from polar to non-polar organic compounds and low elemental carbon (EC). In India, major and variable fraction of PM 10 (≈ 8%) and PM 2.5 (≈ 12%) mass is composed of the organic carbon (Satsangi et al. 2012; Ram and Sarin 2010). Atmospheric organic aerosols are of potential Responsible editor: Constantini Samara * Ranu Gadi ranugadi@igdtuw.ac.in 1 Indira Gandhi Delhi Technical University for Women, New Delhi 110006, India 2 National Physical Laboratory, Council of Scientific and Industrial Research (CSIR), New Delhi 110012, India 3 Multanimal Modi College, Modinagar, Uttar Pradesh 201204, India 4 Central University of Haryana, Mahendragarh, Haryana 123031, India Environmental Science and Pollution Research https://doi.org/10.1007/s11356-018-3044-5