the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Characterization of Brown Carbon absorption in different European environments through source contribution analysis
Abstract. Brown carbon (BrC) is a fraction of Organic Aerosols (OA) that absorbs radiation in the ultraviolet and short visible wavelengths. Its contribution to radiative forcing is uncertain due to limited knowledge of its imaginary refractive index (k ). This study investigates the variability of k for OA from wildfires, residential, shipping, and traffic emission sources over Europe. The MONARCH atmospheric chemistry model simulated OA concentrations and source contributions, feeding an offline optical tool to constrain k values at 370 nm. The model was evaluated against OA mass concentrations from Aerosol Chemical Speciation Monitors (ACSM) and filter sample measurements, and aerosol light absorption measurements at 370 nm derived from AethalometerTM from 12 sites across Europe. Results show that MONARCH captures the OA temporal variability across environments (regional, suburban and urban background). Residential emissions are a major OA source in colder months, while secondary organic aerosols (SOA) dominate in warmer periods. Traffic is a minor primary OA contributor. Biomass and coal combustion significantly influence OA absorption, with shipping emissions also notable near harbors. Optimizing k values at 370 nm revealed significant variability in OA light absorption, influenced by emission sources and environmental conditions. Derived k values for biomass burning (0.03 to 0.13), residential (0.008 to 0.13), shipping (0.005 to 0.08), and traffic (0.005 to 0.07) sources improved model representation of OA absorption compared to a constant k. Introducing such emission source-specific constraints is an innovative approach to enhance OA absorption in atmospheric models.
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Status: open (until 06 Sep 2024)
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CC1: 'Comment on egusphere-2024-2086', Ye Kuang, 27 Jul 2024
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Some latest advancements in derivations of brown carbon absorptions from multiwavelength aerosol absorption measurements that account for the spectral dependence[Li et al., 2019; Luo et al., 2022; Wang et al., 2018] of AAE_BC should be included and discussed. In addition, the first percentile of AAE_BC might suffer from systematic bias from covariance of BrC influences and variations embedded in AAE_BC. The used method is based on the assumption that when influence of BrC is negligible, the AAE_BC is smallest. However, AAE_BC itself varies a lot, the smallest AAE_BC likely does not correspond to situations when influence of BrC is negligible, the representativeness of the first percentile is questionable. Indeed, 0.928 to 1.088 looks reasonable, however, the so-called better consideration is not better than using 1.
Li, Z., et al. (2019), Light absorption properties and potential sources of particulate brown carbon in the Pearl River Delta region of China, Atmos. Chem. Phys., 19(18), 11669-11685.
Luo, B., et al. (2022), Parameterizations of size distribution and refractive index of biomass burning organic aerosol with black carbon content, Atmos. Chem. Phys., 22(18), 12401-12415.
Wang, J., et al. (2018), Light absorption of brown carbon in eastern China based on 3-year multi-wavelength aerosol optical property observations and an improved absorption Ångström exponent segregation method, Atmos. Chem. Phys., 18(12), 9061-9074.
Citation: https://doi.org/10.5194/egusphere-2024-2086-CC1
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