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.
Modification in light absorption cross section of laboratory-generated black carbon-brown carbon particles upon surface reaction and hydration
