Abstract
Abstract. An improved two-sphere integration (TSI) technique has been developed to quantify black carbon (BC) concentrations in the atmosphere and seasonal snow. The major advantage of this system is that it combines two distinct integrated spheres to reduce the scattering effect due to light-absorbing particles and thus provides accurate determinations of total light absorption from BC collected on Nuclepore filters. The TSI technique can be calibrated using a series of 15 filter samples of standard fullerene soot. This technique quantifies the mass of BC by separating the spectrally resolved total light absorption into BC and non-BC fractions. To assess the accuracy of the improved system, an empirical procedure for measuring BC concentrations with a two-step thermal–optical method is also applied. Laboratory results indicate that the BC concentrations determined using the TSI technique and theoretical calculations are well correlated (R2=0.99), whereas the thermal–optical method underestimates BC concentrations by 35 %–45 % compared to that measured by the TSI technique. Assessments of the two methods for atmospheric and snow samples revealed excellent agreement, with least-squares regression lines with slopes of 1.72 (r2=0.67) and 0.84 (r2=0.93), respectively. However, the TSI technique is more accurate in quantifications of BC concentrations in both the atmosphere and seasonal snow, with an overall lower uncertainty. Using the improved TSI technique, we find that light absorption at a wavelength of 550 nm due to BC plays a dominant role relative to non-BC light absorption in both the atmosphere (62.76 %–91.84 % of total light absorption) and seasonal snow (43.11 %–88.56 %) over northern China.
Highlights
Black carbon (BC) has long been recognized as the major light-absorbing particle (LAP) in both natural and anthropogenic emissions (Slater et al, 2002; Koch et al, 2009; Zhang et al, 2009; Pan et al, 2010; McMeeking et al, 2011; Pavese et al, 2012; Bond et al, 2013; IPCC, 2013)
To further assess the accuracy of the two-sphere integration (TSI) system, we use standard fullerene soot and quantify BC concentrations using theoretical calculations for comparison with BC values measured by a laboratory-based TSI spectrophotometer
We developed an improved two-sphere integration (TSI) spectrophotometer to quantify BC concentrations in snow and atmospheric samples over northern China
Summary
Black carbon (BC) has long been recognized as the major light-absorbing particle (LAP) in both natural and anthropogenic emissions (Slater et al, 2002; Koch et al, 2009; Zhang et al, 2009; Pan et al, 2010; McMeeking et al, 2011; Pavese et al, 2012; Bond et al, 2013; IPCC, 2013). Several field campaigns have collected atmospheric, snow, and ice core samples to measure BC and EC concentrations globally (Wolff and Cachier, 1998; von Schneidemesser et al, 2009; Doherty et al, 2010, 2014; Ming et al, 2010; Huang et al, 2011; Xu et al, 2012; Cong et al, 2015), biases remain in determinations of BC concentrations, as is evident from a comparison among the results obtained with the SP2, ISSW, and thermal–optical methods (Schwarz et al, 2012; Lim et al, 2014).
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