Browsing by Author "Yanlin Zhang"

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Aromatic acids as biomass-burning tracers in atmospheric aerosols and ice cores: A review
(Elsevier Ltd, 2019) Xin Wan; Kimitaka Kawamura; Kirpa Ram; Shichang Kang; Mark Loewen; Shaopeng Gao; Guangming Wu; Pingqing Fu; Yanlin Zhang; Hemraj Bhattarai; Zhiyuan Cong
Biomass burning (BB) is one of the largest sources of carbonaceous aerosols with adverse impacts on air quality, visibility, health and climate. BB emits a few specific aromatic acids (p-hydroxybenzoic, vanillic, syringic and dehydroabietic acids) which have been widely used as key indicators for source identification of BB-derived carbonaceous aerosols in various environmental matrices. In addition, measurement of p-hydroxybenzoic and vanillic acids in snow and ice cores have revealed the historical records of the fire emissions. Despite their uniqueness and importance as tracers, our current understanding of analytical methods, concentrations, diagnostic ratios and degradation processes are rather limited and scattered in literature. In this review paper, firstly we have summarized the most established methods and protocols for the measurement of these aromatic acids in aerosols and ice cores. Secondly, we have highlighted the geographical variability in the abundances of these acids, their diagnostic ratios and degradation processes in the environments. The review of the existing data indicates that the concentrations of aromatic acids in aerosols vary greatly with locations worldwide, typically more abundant in urban atmosphere where biomass fuels are commonly used for residential heating and/or cooking purposes. In contrast, their concentrations are lowest in the polar regions which are avoid of localized emissions and largely influenced by long-range transport. The diagnostic ratios among aromatic acids can be used as good indicators for the relative amounts and types of biomass (e.g. hardwood, softwood and herbaceous plants) as well as photochemical oxidation processes. Although studies suggest that the degradation processes of the aromatic acids may be controlled by light, pH and hygroscopicity, a more careful investigation, including closed chamber studies, is highly appreciated. © 2019 Elsevier Ltd; Current research trends on aromatic acids as biomass burning tracers were comprehensively reviewed. © 2019 Elsevier Ltd
Investigation of the Uncertainties of Simulated Optical Properties of Brown Carbon at Two Asian Sites Using a Modified Bulk Aerosol Optical Scheme of the Community Atmospheric Model Version 5.3
(John Wiley and Sons Inc, 2021) Lulu Xu; Yiran Peng; Kirpa Ram; Yanlin Zhang; Mengying Bao; Jing Wei
Recent studies have suggested that brown carbon (BrC), an absorbing component in organic aerosol, has strong absorption in the near-ultraviolet wavelengths, and contributes to regional and global radiative forcing (RF). However, the inclusion of BrC in global climate models leads to significant uncertainties in estimated RF, mainly attributed to uncertain BrC properties and relevant BrC parameters assigned in the model. In this study, we modified the bulk aerosol optical scheme (BAOS) in Community Atmospheric Model version 5.3 by including BrC absorption and evaluated the performance of the modified BAOS by comparing the simulated aerosol absorption with 2-year surface observational data in two Asian cities, Kanpur, India and Nanjing, China. The mean relative errors in the simulated total aerosol absorption (Babs) and absorption Angstrom exponent in modified BAOS are around 35% in Kanpur and even below 20% in Nanjing. Our results show that the inclusion of BrC remedies the underestimated total aerosol absorption by 20% and 14% on average at Kanpur and Nanjing, respectively, exhibiting a better agreement with ground-based observations of aerosol absorption at both sites. We also conducted a series of sensitivity experiments to quantify the uncertainties caused by varying parameters related to BrC. The model simulations suggest that the imaginary refractive index of BrC is the most significant factor contributing to the uncertainties in aerosol optical properties calculated in BAOS at the Kanpur site. While in the Nanjing site, both particle size distribution and mixing state have dominant impacts on the calculated aerosol optical properties. © 2021. American Geophysical Union. All Rights Reserved.
Water-Soluble Brown Carbon in Atmospheric Aerosols from Godavari (Nepal), a Regional Representative of South Asia
(American Chemical Society, 2019) Guangming Wu; Kirpa Ram; Pingqing Fu; Wan Wang; Yanlin Zhang; Xiaoyan Liu; Elizabeth A. Stone; Bidya Banmali Pradhan; Pradeep Man Dangol; Arnico K. Panday; Xin Wan; Zhipeng Bai; Shichang Kang; Qianggong Zhang; Zhiyuan Cong
Brown carbon (BrC) has recently emerged as an important light-absorbing aerosol. This study provides interannual and seasonal variations in light absorption properties, chemical composition, and sources of water-soluble BrC (WS-BrC) based on PM10 samples collected in Godavari, Nepal, from April 2012 to May 2014. The mass absorption efficiency of WS-BrC at 365 nm (MAE365) shows a clear seasonal variability, with the highest MAE365 of 1.05 ± 0.21 m2 g-1 in premonsoon season and the lowest in monsoon season (0.59 ± 0.16 m2 g-1). The higher MAE365 values in nonmonsoon seasons are associated with fresh biomass burning emissions. This is further substantiated by a strong correlation (r = 0.79, P < 0.01) between Abs365 (light absorption coefficient at 365 nm) and levoglucosan. We found, using fluorescence techniques, that humic-like and protein-like substances are the main chromophores in WS-BrC and responsible for 80.2 ± 4.1% and 19.8 ± 4.1% of the total fluorescence intensity, respectively. BrC contributes to 8.78 ± 3.74% of total light absorption over the 300-700 nm wavelength range. Considering the dominant contribution of biomass burning to BrC over Godavari, this study suggests that reduction in biomass burning emission may be a practical method for climate change mitigation in South Asia. Copyright © 2019 American Chemical Society.