Determining the Sources and Transport of Brown Carbon Using Radionuclide
Tracers and Modeling
Abstract
The isotope tracer technique plays a key role in identifying the sources
and atmospheric processes affecting pollution. The sources of brown
carbon (BrC) at Guangzhou during 2017-2018 was characterized by positive
matrix factorization with carbon isotope constraints and multiple linear
regression analysis. The primary emission factors of fossil fuel
combustion (FF) and biomass burning (BB) accounted for 34% and 27% of
dissolved BrC absorption at λ = 365 nm, respectively. The total mean
light absorption contributed by secondary sources was 39%. The
absorption of FF-origin BrC was relatively stable and dominant in the
summer monsoon period, whereas the absorption of BrC from BB and
secondary nitrate formation increased and contributed larger fractions
during the winter monsoon period. Transported BrC was estimated using an
index of 7 Be/(7 Be+n 210 Pb). Higher values were generally accompanied
by lower BrC absorption, whereas lower values were associated with
higher BrC absorption, indicating that BrC absorption of aerosols
transported from the upper-atmosphere is lower than that of aerosols
transported near the surface. Based on the positive correlations between
210 Pb and BrC absorption and non-fossil dissolved organic carbon in the
winter monsoon period, we estimated that the contribution of invasive
BrC (include ground and upper-atmosphere level) to total absorption
during the period of elevated BrC was approximately 50%, which was
likely related to BB organic aerosols and secondary nitrate formation
processes. This study supports radionuclides as a novel method for
characterizing the sources and transport of BrC that can be applied in
future atmospheric research.