This study reports molecular-level
characterization of brown carbon
(BrC) attributed to water-soluble organic carbon in six snowpack samples
collected from northern Xinjiang, China. The molecular composition
and light-absorbing properties of BrC chromophores were unraveled
by application of high-performance liquid chromatography (HPLC) coupled
to a photodiode array (PDA) detector and high-resolution mass spectrometry.
The chromophores were classified into five major types, that is, (1) phenolic/lignin-derived
compounds, (2) flavonoids, (3) nitroaromatics, (4) oxygenated aromatics, and (5) other chromophores. Identified chromophores account for ∼23–64% of the
total light absorption measured by the PDA detector in the wavelength
range of 300–370 nm. In the representative samples from urban
and remote areas, oxygenated aromatics and nitroaromatics dominate the absorption in the wavelengths
below and above 320 nm, respectively. The highly polluted urban sample
shows the most complex HPLC-PDA chromatogram, and more other chromophores
contribute to the bulk absorption. Phenolic/lignin-derived
compounds are the most light-absorbing species in the soil-influenced
sample. Chromophores in two remote samples exhibit ultraviolet–visible
features distinct from other samples, which are attributed to flavonoids. Identification of individual chromophores and
quantitative analysis of their optical properties are helpful for
elucidating the roles of BrC in snow radiative balance and photochemistry.
Light-absorbing particles (LAPs) deposited on snow can decrease snow albedo and affect climate through snow-albedo radiative forcing. In this study, we use MODIS observations combined with a snow-albedo model (SNICAR -Snow, Ice, and Aerosol Radiative) and a radiative transfer model (SBDART -Santa Barbara DISORT Atmospheric Radiative Transfer) to retrieve the instantaneous spectrally integrated radiative forcing at the surface by LAPs in snow (RF LAPs MODIS ) under clear-sky conditions at the time of MODIS Aqua overpass across northeastern China (NEC) in January-February from 2003 to 2017. RF LAPs MODIS presents distinct spatial variability, with the minimum (22.3 W m −2 ) in western NEC and the maximum (64.6 W m −2 ) near industrial areas in central NEC. The regional mean RF LAPs MODIS is ∼ 45.1 ± 6.8 W m −2 in NEC. The positive (negative) uncertainties of retrieved RF LAPs MODIS due to atmospheric correction range from 14 % to 57 % (−14 % to −47 %), and the uncertainty value basically decreases with the increased RF LAPs MODIS . We attribute the variations of radiative forcing based on remote sensing and find that the spatial variance of RF LAPs MODIS in NEC is 74.6 % due to LAPs and 21.2 % and 4.2 % due to snow grain size and solar zenith angle. Furthermore, based on multiple linear regression, the BC dry and wet deposition and snowfall could explain 84 % of the spatial variance of LAP contents, which confirms the reasonability of the spatial patterns of retrieved RF LAPs MODIS in NEC. We validate RF LAPs MODIS using in situ radiative forcing estimates. We find that the biases in RF LAPs MODIS are negatively correlated with LAP concentrations and range from ∼ 5 % to ∼ 350 % in NEC.
Coal and coal gangue spontaneous combustion (CGSC) occurs globally, causing significant environmental pollution. However, its emissions are poorly quantified and are overlooked in global or regional air pollutant emission inventories in previous studies, resulting in the underestimation of its impacts on climate, environment, and public health. This study quantified the emissions of various air pollutants originating from CGSC in Wuhai, a city in China, investigated emission characteristics, and estimated the contribution of CGSC emissions to fine particulate matter (PM 2.5 ) air pollution and related health impacts on a regional scale. The results revealed that the CGSC-related PM 2.5 emissions were approximately 4643 t a −1 (95% confidence interval (95% CI): 721; 10447), accounting for 26.3% of the total PM 2.5 emissions. Alkanes, alkenes, and aromatics accounted for 69.4, 17.9, and 2.9%, respectively, of the total emissions of volatile organic compounds (VOCs). Due to CGSC emissions, the ambient PM 2.5 concentration in Wuhai increased by 5.7 μg m −3 on average, while the nitrate concentration decreased. The number of premature deaths caused by exposure to ambient PM 2.5 associated with CGSC reached 381 (95% CI: 290; 452) in Wuhai and surrounding cities in 2017. Urgent control strategies and engineering techniques are needed to mitigate CGSC to protect public health.
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