Fluorescence characteristics, absorption properties, and radiative effects of water-soluble organic carbon in seasonal snow across northeastern China

Abstract

Abstract. Water-soluble organic carbon (WSOC) in the cryosphere can significantly influence the global carbon cycle and radiation budget. However, WSOC in the snowpack has received little scientific attention to date. This study reports the fluorescence characteristics, absorption properties, and radiative effects of WSOC based on 34 snow samples collected from sites in northeastern China. A significant degree of regional WSOC variability is found, with concentrations ranging from 0.5±0.2 to 5.7±3.7 µg g−1 (average concentration: 3.6±3.2 µg g−1). The three principal fluorescent components of WSOC are identified as (1) the high-oxygenated humic-like substances (HULIS-1) of terrestrial origin, (2) the low-oxygenated humic-like substances (HULIS-2) of mixed origin, and (3) the protein-like substances (PRLIS) derived from autochthonous microbial activity. In southeastern Inner Mongolia (SEIM), a region dominated by desert and exposed soils, the WSOC exhibits the highest humification index (HIX) but the lowest fluorescence (FI) and biological (BIX) indices; the fluorescence signal is mainly attributed to HULIS-1 and thus implicates soil as the primary source. By contrast, the HIX (FI and BIX) value is the lowest (highest), and the percentage of PRLIS is the highest in the remote area of northeastern Inner Mongolia (NEIM), suggesting a primarily biological source. For south and north of northeastern China (SNC and NNC), both of which are characterized by intensive agriculture and industrial activity, the fluorescence signal is dominated by HULIS-2, and the HIX, FI, and BIX values are all moderate, indicating the mixed origins for WSOC (anthropogenic activity, microbial activity, and soil). We also observe that, throughout northeastern China, the light absorption of WSOC is dominated by HULIS-1, followed by HULIS-2 and PRLIS. The contribution of WSOC to albedo reduction (average concentration: 3.6 µg g−1) in the ultraviolet–visible (UV–Vis) band is approximately half that of black carbon (BC average concentration: 0.6 µg g−1). Radiative forcing is 3.8 (0.8) W m−2 in old (fresh) snow, equating to 19 % (17 %) of the radiative forcing of BC. These results indicate that WSOC has a profound impact on snow albedo and the solar radiation balance.

Long‐Emission‐Wavelength Humic‐Like Component (L‐HULIS) as a Secondary Source Tracer of Brown Carbon in the Atmosphere

“…Niu et al. (2022) reported that a PARAFAC component in snow samples, similar to our L‐HULIS, substantially contributes to the light absorption of WSOC at UV wavelengths.…”

“…Therefore, it is reasonable to speculate that this portion of secondary BrC, as identified by L-HULIS, may potentially represent these strong BrC chromophores. Niu et al (2022) reported that a PARAFAC component in snow samples, similar to our L-HULIS, substantially contributes to the light absorption of WSOC at UV wavelengths.…”

“…Therefore, the PARAFAC components could be considered as a subgroup of BrC chromophores. In a previous study, the contributions of PARAFAC components to the light absorption of WSOC were investigated (Niu et al., 2022). Based on this, source attribution of BrC could be achieved by determining the possible source of these PARAFAC components.…”

Divergent features of the upper-tropospheric carbonaceous aerosol layer: effects of atmospheric dynamics and pollution emissions in Asia, South America, and Africa

“…Radiative effect induced by CAs is approximately twice that of massequivalent sulfate aerosol (Liu et al 2022). Further, the interactions between CAs and radiation can effectively disturb atmospheric stratification and circulation by heating atmosphere (Ding et al 2016), and accelerate glacier and snow melting due to darkening effect (Pu et al 2021, Niu et al 2022. In ATAL, atmospheric warming induced by CAs causes increased precipitation over Asia through strengthening the monsoon Hadley circulation (Fadnavis et al 2017).…”

Exhaust emissions of gaseous and particle size-segregated water-soluble organic compounds from diesel-biodiesel blends

“…WSOC can reach approximately 27–83% of the organic carbon mass of aerosols (Yu et al 2004 and references therein) and is primarily emitted from combustion of biomass and fossil fuels, or secondarily formed from oxidation of VOCs, aromatic compounds, and high molecular weight hydrocarbons with anthropogenic or biogenic origin (Du et al, 2014 ; Park et al, 2015 ). WSOC affect the formation and physical properties of clouds, Earth’s radiative balance, and atmospheric chemistry with implications for regional and global climate change (Duarte et al, 2015 , 2019 ; Niu et al 2022 ; Tang et al, 2020 ). Moreover, due to their toxicity, particle-bound WSOC has been associated with human cardio-respiratory diseases (Cheung et al 2009 ; Ramgolam et al 2009 ).…”