Vol.:(0123456789) 1 3 Aerosol Science and Engineering https://doi.org/10.1007/s41810-020-00053-7 ORIGINAL PAPER Seasonal Variation of OC, EC, and WSOC of PM 10 and Their CWT Analysis Over the Eastern Himalaya Akansha Rai 1,2  · Sauryadeep Mukherjee 3  · Abhijit Chatterjee 3  · Nikki Choudhary 1  · Garima Kotnala 1,2  · T. K. Mandal 1,2  · S. K. Sharma 1,2 Received: 2 December 2019 / Revised: 1 January 2020 / Accepted: 22 January 2020 © Institute of Earth Environment, Chinese Academy Sciences 2020 Abstract In the present study, seasonal transport trends and potential source regions of carbonaceous species [organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), secondary organic carbon (SOC) and total carbonaceous aerosols (TCAs)] of PM 10 was evaluated over Darjeeling, an eastern Himalayas of India during August 2018–June 2019. Backward trajectories, cluster analysis, and concentration-weighted trajectory (CWT) analysis were performed to evaluate the seasonal transport pathway of carbonaceous aerosols over the region. The annual average concentration of PM 10 was recorded to be 55 ± 18 μg m −3 , which is close to National Ambient Air Quality Standard (NAAQS; 60 μg m −3 for annual PM 10 ) of India. The concentration of PM 10 showed maxima in pre-monsoon season (63 ± 21 μg m −3 ) followed by post- monsoon (56 ± 16 μg m −3 ), monsoon (51 ± 13 μg m −3 ) and winter seasons (49 ± 17 μg m −3 ). The study revealed that the WSOC comprises about 72% of OC concentration with maxima in post-monsoon (81% of OC) followed by winter (74% of OC), pre-monsoon (67% of OC) and monsoon seasons (66% of OC). The concentration of SOC were estimated as 1.4 ± 0.9, 1.7 ± 1.0, 2.4 ± 0.9 and 1.9 ± 0.9 µg m −3 during pre-monsoon, monsoon, post-monsoon and winter, respectively (which are accounted for 27%, 49%, 41% and 35% to the OC mass concentration, respectively). The results indicated that biomass burning could be one of the major sources of carbonaceous aerosols in Darjeeling. Five days backward trajectory analysis (including cluster and CWT analysis) revealed that the air-mass fow of pollutants towards the sampling site of Darjeeling majorly coming from continental sites (Nepal and Indo-Gangetic plain (IGP) region of India) and the Bay of Bengal (BOB). Keywords PM 10  · OC · EC · Carbonaceous aerosols · WSOC · Trajectory analysis · CWT 1 Introduction South Asia has witnessed a rapid increase in population and industrialization over the past few decades, resulting in the increased anthropogenic activity of fossil fuel emissions, biomass burning, land-use changes. Consequently, it con- tributes to the 2–6 fold rise in atmospheric carbonaceous aerosols (Ram et al. 2012; Mahapatra et al. 2018). The main concern in the current scenario has been focused on carbo- naceous aerosols through systematic studies of their abun- dance, sources, and spatial variations, which signifcantly contribute to the particulate matter (PM) in the tropospheric atmosphere (Dinoi et al. 2017; Dumka et al. 2019). Mean- while, due to its direct infuence on air quality and visibility, it has received considerable support from the research com- munity. It also has an indirect efect on biodiversity, crop production, human health, and the Earth’s energy balance of radiation, which infuences the global climate (Ghosh et al. 2014; Wu et al. 2019; Bikkina and Sarin 2019). Many inves- tigations showed that such suspended particles of airborne carbon cause asthma, various respiratory diseases, lung can- cer, premature death, cardiovascular disease, and congenital disabilities (Pant et al. 2019). Electronic supplementary material The online version of this article (https://doi.org/10.1007/s41810-020-00053-7) contains supplementary material, which is available to authorized users. * S. K. Sharma sudhircsir@gmail.com; sudhir.npl@nic.in 1 Environmental Sciences and Biomedical Metrology Division, CSIR-National Physical Laboratory, Dr. K S Krishnan Road, New Delhi 110 012, India 2 Academy of Scientifc and Innovative Research (AcSIR), Ghaziabad 201 002, India 3 Centre for Astroparticle Physics and Space Sciences, Bose Institute, Darjeeling 734 102, India