Assessment of carbonaceous aerosols at Mukteshwar: A high-altitude (~2200 m amsl) background site in the foothills of the Central Himalayas

Rahul Sheoran; U C Dumka; A P Hyvärinen; V P Sharma; Rakesh K Tiwari; H Lihavainen; A Virkkula; Rakesh K Hooda

doi:10.1016/j.scitotenv.2022.161334

Assessment of carbonaceous aerosols at Mukteshwar: A high-altitude (~2200 m amsl) background site in the foothills of the Central Himalayas

Sci Total Environ. 2023 Mar 25:866:161334. doi: 10.1016/j.scitotenv.2022.161334. Epub 2022 Dec 31.

Authors

Rahul Sheoran¹, U C Dumka², A P Hyvärinen³, V P Sharma⁴, Rakesh K Tiwari⁵, H Lihavainen⁶, A Virkkula³, Rakesh K Hooda⁷

Affiliations

¹ Aryabhatta Research Institute of Observational Sciences, Nainital 263001, India; Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273009, India. Electronic address: rahul.sheoran@aries.res.in.
² Aryabhatta Research Institute of Observational Sciences, Nainital 263001, India. Electronic address: dumka@aries.res.in.
³ Finnish Meteorological Institute, Erik Palménin Aukio 1, FI-00560 Helsinki, Finland.
⁴ The Energy and Resources Institute, New Delhi, India.
⁵ Department of Physics, D.D.U. Gorakhpur University, Gorakhpur 273009, India.
⁶ Finnish Meteorological Institute, Erik Palménin Aukio 1, FI-00560 Helsinki, Finland; Svalbard Integrated Arctic Earth Observing System, 156, 9171 Longyearbyen, Norway.
⁷ Finnish Meteorological Institute, Erik Palménin Aukio 1, FI-00560 Helsinki, Finland. Electronic address: Rakesh.Hooda@fmi.fi.

PMID: 36596417
DOI: 10.1016/j.scitotenv.2022.161334

Abstract

The present study examined the equivalent black carbon (eBC) mass concentrations measured over 10.5 years (September 2005-March 2016) using a 7-wavelength Aethalometer (AE-31) at Mukteshwar, a high-altitude and regional background site in the foothills of Indian central Himalayas. The total spectral absorption coefficient (b_abs) was divided into three categories: black carbon (BC) and brown carbon (BrC); fossil fuels (FF) and wood/biomass burning (WB/BB); and primary and secondary sources. At the wavelength of 370 nm, a significant BrC contribution (25 %) to the total b_abs is identified, characterized by a pronounced seasonal variation with winter (December-January-February) maxima (31 %) and post-monsoon (October and November) minima (20 %); whereas, at 660 nm, the contribution of BrC is dramatically less (9 %). Climatologically, the estimated BC_FF at 880 nm ranges from 0.25 ± 0.19 μg m^-3 in July to 1.17 ± 0.80 μg m^-3 in May with the annual average of 0.67 ± 0.63 μg m^-3, accounting for 79 % of the BC mass. The maximum BC_FF/BC fraction reaches its peak value during the monsoon (July and August, 85 %), indicating the dominance of local traffic emissions due to tourism activities. Further, the highest BC_WB concentration observed during pre-monsoon (March-May) suggests the influence of local forest fires along with long-range transported aerosols from the low-altitude plains. The increased contribution of BrC (26 % at 370 nm) and WB absorption (61 % at 370 nm) to the total absorption at the shorter wavelengths suggests that wood burning is one of the major sources of BrC emissions. Secondary BrC absorption accounts for 24 % [91 %] of the total absorption [BrC absorption] at 370 nm, implying the dominance of secondary sources in BrC formation. A trend analysis for the measured BC concentration shows a statistically significant increasing trend with a slope of 0.02 μgm^-3/year with a total increase of about 22 % over the study period. A back trajectory-based receptor model, potential source contribution function (PSCF), was used to identify the potential regional source region of BC. The main source regions of BC are the northwest states of India in the IGP region and the northeast Pakistan region.

Keywords: Biomass burning; Black carbon; Brown carbon; Central Himalayas; Fossil fuel; High-altitude; Long-term; Secondary absorption; Trend analysis.