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. An improved two-sphere integration (TSI) technique has beendeveloped to quantify black carbon (BC) concentrations in the atmosphere andseasonal snow. The major advantage of this system is that it combines twodistinct integrated spheres to reduce the scattering effect due tolight-absorbing particles and thus provides accurate determinations oftotal light absorption from BC collected on Nuclepore filters. The TSItechnique can be calibrated using a series of 15 filter samples of standardfullerene soot. This technique quantifies the mass of BC by separating thespectrally resolved total light absorption into BC and non-BC fractions. Toassess the accuracy of the improved system, an empirical procedure formeasuring BC concentrations with a two-step thermal–optical method is alsoapplied. Laboratory results indicate that the BC concentrations determined usingthe TSI technique and theoretical calculations are well correlated(R2=0.99), whereas the thermal–optical method underestimates BCconcentrations by 35 %–45 % compared to that measured by the TSI technique.Assessments of the two methods for atmospheric and snow samples revealedexcellent agreement, with least-squares regression lines with slopes of 1.72(r2=0.67) and 0.84 (r2=0.93), respectively. However, theTSI technique is more accurate in quantifications of BC concentrations inboth the atmosphere and seasonal snow, with an overall lower uncertainty.Using the improved TSI technique, we find that light absorption at awavelength of 550 nm due to BC plays a dominant role relative to non-BClight absorption in both the atmosphere (62.76 %–91.84 % of totallight absorption) and seasonal snow (43.11 %–88.56 %) over northernChina.

Development of an improved two-sphere integration technique for quantifying black carbon concentrations in the atmosphere and seasonal snow