Inter-comparison of thermal and optical methods for determination of atmospheric black carbon and attenuation coefficient from an urban location in northern India

Abstract

The simultaneous measurements of black carbon (BC, based on Aethalometer) and elemental carbon (EC, using thermo-optical EC-OC analyzer) in airborne particles collected from an urban location (Kanpur) in northern India are reported here. The strategy for site-selection is most relevant in order to assess the relative dominance of emissions from coal-fired industries, fossil-fuel combustion and biomass burning on the seasonal variability of EC (BC) concentrations. An inter-comparison of the analytical data (n = 32) suggests that BC mass concentration is ~20% higher than that of EC. However, attenuation coefficient (b_ATN) measured by the two analytical instruments shows good agreement (slope = 0.97, n = 27), establishing the validity of b_ATN derived from thermo-optical EC-OC analyzer. Furthermore, slope (20.7 m² g^-1) of a linear-fit to the data (n = 48, R² = 0.86) for surface EC concentration (EC_s ≤ 8 µg C cm^-2) and optical-attenuation (ATN ≤ 180) measured at 678 nm on thermo-optical analyzer provides an independent and novel way of determining the "site-specific" attenuation cross-section (σ_ATN).