ORIGINAL ARTICLE Characteristics and Variability of Carbonaceous Aerosols over a Semi Urban Location in Garhwal Himalayas K. Sandeep 1,2 & R. S. Negi 3 & A. S. Panicker 1,2 & Alok Sagar Gautam 3 & D. S. Bhist 1 & G. Beig 1 & B. S. Murthy 1 & R. Latha 1 & Santosh Singh 3 & S. Das 4 Received: 13 February 2019 /Revised: 24 October 2019 /Accepted: 1 November 2019 # Korean Meteorological Society and Springer Nature B.V. 2019 Abstract Extraction of organic carbon (OC) and elemental carbon (EC) were carried out over Srinagar, India, an ecologically sensitive semi-urban site in Garhwal Himalays. The PM 2.5 sampling was carried out during January to December, 2017 over the site. The OC and EC were extracted from PM 2.5 samples using a thermo optical OC/EC analyzer. Highest OC and EC concncentrations were found during postmonsoon (17.67 ± 1.1 μg/m 3 OC and 6.34 ± 0.75 EC) and Winter (17.31 ± 3.045 μg/m 3 OC and 6.32 ± 0.585 μg/m 3 EC) seasons are attributed to boundary layer dynamics and anthropogenic activities. The lower concentration of OC/ EC was observed during monsoon season (11.64 ± 1.75 μgm -3 OC and 3.46 ± 0.19μgm -3 EC) owing to wet scavenging of aerosols and minimum count of forest fire/biomass buring incidences. Both pre-monsoon and post-monsoon season concentra- tions are also influenced by biomass burning in the IGP (Indo-Gangetic Plain) region and forest fires in the adjecent areas. The OC/EC ratio sounds that vehicular exhaust and biomass burning are the major source of OC/EC over the site. Generation of secondary organic carbon (SOC) at the region causes variability in OC/EC ratio in different seasons. It is found that 24–32% of PM2.5 is contributed by carbonaceous aerosols (OC and EC) over Srinagar. The pivotal role of meteorology in modulating OC/ EC concentrations has been illustared in detail. Keywords Himalayan valley . Elemental carbon . Organic carbon . Seasonal variation . Biomass burning . Influence on meteorology 1 Introduction Carbonaceous aerosols are potential climate forcing agents and majorly exist in size range below 2.5 μm. Subset of these par- ticles mainly include carbonaceous species like organic carbon (OC) and elemental carbon (EC). The chemical and optical properties of BC and EC are almost same and constitute the most solar absorptive particulates among the fine mode partic- ulate matter (Chung and Seinfeld 2002; Watson et al. 2005). Carbonaceous aerosols account for almost 40% of total PM 2.5 mass in urban areas (Seinfeld and Pandis 1998). Incomplete combustion of fossil fuels and biomass burning produce EC in the atmosphere. However, oxidation of volatile organic com- pound (VOC) generate secondary organic carbon in the atmo- sphere in addition to primarily emitted organic carbon (Turpin and Huntzicker 1995). Intense combustion processes release EC in to the atmosphere. Temperature and oxygen availability are the major factors determining the amount of EC formed during a combustion process. Low temperature and less avail- ability of oxygen produces more EC and vice versa in a closed chamber combustion process (Panicker et al. 2018). Fresh EC aerosols are more or less hydrophobic in nature and barely probable to act as CCN in usual atmospheric conditions due to non-significant hygroscopic growth and cloud condensation nuclei (CCN) activity (Tritscher et al. 2011). The ageing Responsible Editor: Yunsoo Choi. * K. Sandeep sandeepkapsara@gmail.com * R. S. Negi rsnegi64@rediffmail.com * Alok Sagar Gautam phyalok@mail.com 1 Indian Institute of Tropical Meteorology, Pune 411008, India 2 Savitribhai Phule Pune University, Pune, India 3 H.N.B. Garhwal University, Srinagar, Uttarakhand, India 4 International Centre for Theoretical Physics, Trieste, Italy Asia-Pacific Journal of Atmospheric Sciences https://doi.org/10.1007/s13143-019-00158-1 Online ISSN 1976-7951 Print ISSN 1976-7633 Korean Meteorological Society