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Characterization of Natural and Affected Environments
Water-soluble Brown Carbon in Atmospheric Aerosols from Godavari (Nepal), A Regional Representative of South Asia Guangming Wu, Kirpa Ram, Pingqing Fu, Wan Wang, Yanlin Zhang, Xiaoyan Liu, Elizabeth A Stone, Bidya Banmali Pradhan, Pradeep Man Dangol, Arnico Panday, Xin Wan, Zhi-peng Bai, Shichang Kang, Qianggong ZHANG, and Zhiyuan Cong Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b00596 • Publication Date (Web): 08 Mar 2019 Downloaded from http://pubs.acs.org on March 9, 2019
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Environmental Science & Technology
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Water-soluble Brown Carbon in Atmospheric Aerosols from
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Godavari (Nepal), A Regional Representative of South Asia
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Guangming Wu1,10, Kirpa Ram1,2, Pingqing Fu3, Wan Wang4, Yanlin Zhang5, Xiaoyan
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Liu5, Elizabeth A. Stone6, Bidya Banmali Pradhan7, Pradeep Man Dangol7, Arnico K.
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Panday7, Xin Wan1,10, Zhipeng Bai4, Shichang Kang8,9, Qianggong Zhang1,9, Zhiyuan
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Cong1,9*
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1. Key Laboratory of Tibetan Environment Changes and Land Surface Processes,
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Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101,
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China
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2. Institute of Environment and Sustainable Development, Banaras Hindu University,
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Varanasi 221005, India
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3. Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China
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4. State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese
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Research Academy of Environmental Sciences, Beijing 100012, China
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5. Yale-NUIST Center on Atmospheric Environment, Nanjing University of
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Information Science and Technology, Nanjing 210044, China
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6. Department of Chemistry, University of Iowa, Iowa City, IA 52246, USA
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7. International Centre for Integrated Mountain Development, Khumaltar, Lalitpur
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009771, Nepal
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8. State Key Laboratory of Cryospheric Sciences, Northwest Institute of Eco-
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Environment and Resources, Chinese Academy of Sciences, Lanzhou 730000, China
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9. Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of
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Sciences, Beijing 100101, China
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10. University of Chinese Academy of Sciences, Beijing 100049, China
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ABSTRACT
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Brown carbon (BrC) has recently emerged as an important light-absorbing aerosol.
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This study provides inter-annual and seasonal variations in light absorption properties,
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chemical composition and sources of water-soluble BrC (WS-BrC) based on PM10
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samples collected in Godavari, Nepal, from April 2012 to May 2014. The mass
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absorption efficiency of WS-BrC at 365 nm (MAE365) shows a clear seasonal variability
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with the highest MAE365 of 1.05 ± 0.21 m2 g-1 in pre-monsoon season and the lowest in
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monsoon (0.59 ± 0.16 m2 g-1). The higher MAE365 values in non-monsoon seasons are
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associated with fresh biomass burning emissions. This is further substantiated by a
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strong correlation (r=0.79, P
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Na+ > NO3- > Ca2+ > NH4+ > K+ > Cl- > Mg2+ (Table 1). SO42- is the dominant anion
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Environmental Science & Technology
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with annual concentration of 1.91 ± 1.33 μg m-3 followed by NO3-. SO42- and NO3- show
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relatively higher concentrations during pre-monsoon and winter season, with values
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almost a factor of 2 higher than that in the monsoon season. In addition, SO42- exhibits
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a strong correlation with NO3- (r=0.86, P340 nm)56, 57 compared to C3 and naphthalene.
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Therefore, we conclude, based on above facts, that C3 at Godavari is more likely related
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with fossil fuel combustion.
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From the seasonal patterns of ratios of fluorescence intensity between the three
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identified atmospheric chromophores, the ratio of chromophore C1 to C2 is relatively
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stable throughout the sampling period (Figure S4), which suggest that they might share
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same sources and/or have consistent relative emission factors. In contrast, the ratios of
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C3 to C1 and C2 are relatively higher during monsoon season compared to that in non-
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monsoon. This is reasonable because biomass burning activities (represented by C1 and
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C2)47 mainly take place during non-monsoon seasons and to a lesser extent in monsoon
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season. However, vehicle emissions are relatively constant through the year, which
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make them an important source of organic aerosols during monsoon season.58 Thus,
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atmospheric WS-BrC at Godavari are complex organic mixtures consisted by HULIS
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and PRLIS.
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Origins of BrC EC is mainly derived from incomplete combustion of biomass and fossil fuels.14,
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emissions.34 In this study, OC and EC are significantly correlated during the entire
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sampling period (r>=0.86, Figure 4a), highlighting the contribution of primary
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emissions to OC and EC. The Abs365 is usually taken as proxy of BrC in extraction.42,
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43, 59
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Figure 4b) indicates that combustion emissions are important sources of BrC both in
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non-monsoon and monsoon seasons.
The refractory nature of EC makes it an important and specific tracer for combustion
Therefore, a good linear correlation between Abs365 and EC (r=0.69, P
