title: Limitation of the Use of the Absorption Angstrom Exponent for Source Apportionment of Equivalent Black Carbon: a Case Study from the North West Indo-Gangetic Plain.
abstract: Angstrom exponent measurements of equivalent black carbon (BCeq) have recently been introduced as a novel tool to apportion the contribution of biomass burning sources to the BCeq mass. The BCeq is the mass of ideal BC with defined optical properties that, upon deposition on the aethalometer filter tape, would cause equal optical attenuation of light to the actual PM2.5 aerosol deposited. The BCeq mass hence is identical to the mass of the total light-absorbing carbon deposited on the filter tape. Here, we use simultaneously collected data from a seven-wavelength aethalometer and a high-sensitivity proton-transfer reaction mass spectrometer installed at a suburban site in Mohali (Punjab), India, to identify a number of biomass combustion plumes. The identified types of biomass combustion include paddy- and wheat-residue burning, leaf litter, and garbage burning. Traffic plumes were selected for comparison. We find that the combustion efficiency, rather than the fuel used, determines αabs, and consequently, the αabs can be ∼1 for flaming biomass combustion and >1 for older vehicles that operate with poorly optimized engines. Thus, the absorption angstrom exponent is not representative of the fuel used and, therefore, cannot be used as a generic tracer to constrain source contributions.
authors.affiliation: Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali , Sector 81, S.A.S Nagar, Punjab 140306, India.
authors.forename: Saryu
authors.initials: S
authors.lastname: Garg
authors.affiliation: Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali , Sector 81, S.A.S Nagar, Punjab 140306, India.
authors.forename: Boggarapu Praphulla
authors.initials: BP
authors.lastname: Chandra
authors.affiliation: Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali , Sector 81, S.A.S Nagar, Punjab 140306, India.
authors.forename: Vinayak
authors.initials: V
authors.lastname: Sinha
authors.affiliation: LSCE, Laboratoire des Sciences du Climat et de l'Environnement, CNRS-CEA-UVSQ , Orme des Merisiers, F91191 Gif-sur-Yvette, France.
authors.forename: Roland
authors.initials: R
authors.lastname: Sarda-Esteve
authors.affiliation: LSCE, Laboratoire des Sciences du Climat et de l'Environnement, CNRS-CEA-UVSQ , Orme des Merisiers, F91191 Gif-sur-Yvette, France.
authors.forename: Valerie
authors.initials: V
authors.lastname: Gros
authors.affiliation: Department of Earth and Environmental Sciences, Indian Institute of Science Education and Research Mohali , Sector 81, S.A.S Nagar, Punjab 140306, India.
authors.forename: Baerbel
authors.initials: B
authors.lastname: Sinha
mesh_terms: D000336:Aerosols / Q000032:analysis; D018533:Biomass; D002244:Carbon; D005390:Fires; D007194:India; D008027:Light; D053260:Soot / Q000032:analysis*; D001335:Vehicle Emissions / Q000032:analysis
chemical_list: D000336:Aerosols; D053260:Soot; D001335:Vehicle Emissions; D002244:Carbon