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© Author(s) 2020. This work is distributed under
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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Sep 2020

21 Sep 2020

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This preprint is currently under review for the journal ACP.

Measurement report: PM2.5-bound nitrated aromatic compounds in Xi'an, Northwest China: Seasonal variations and contributions to optical properties of brown carbon

Wei Yuan1,6, Ru-Jin Huang1,2, Lu Yang1, Ting Wang1,6, Jing Duan1,6, Jie Guo1, Haiyan Ni1,7, Yang Chen3, Qi Chen4, Yongjie Li5, Ulrike Dusek7, Colin O'Dowd8, and Thorsten Hoffmann9 Wei Yuan et al.
  • 1State Key Laboratory of Loess and Quaternary Geology, Center for Excellence in Quaternary Science and Global Change, Key Laboratory of Aerosol Chemistry & Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China
  • 2Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China
  • 3Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China
  • 4State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
  • 5Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau SAR 999078, China
  • 6University of Chinese Academy of Sciences, Beijing 100049, China
  • 7Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), University of Groningen, 9747 AG, The Netherlands
  • 8School of Physics and Centre for Climate and Air Pollution Studies, Ryan Institute, National University of Ireland Galway, University Road, Galway H91CF50, Ireland
  • 9Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz, 23 Duesbergweg 10–14, 55128 Mainz, Germany

Abstract. Nitrated aromatic compounds (NACs) are a group of key chromophores for brown carbon aerosol (light absorbing organic carbon, i.e., BrC), which affects radiative forcing. The chemical composition and sources of NACs and their contributions to BrC absorption, however, are still not well understood. In this study, PM2.5-bound NACs in Xi'an, Northwest China, were investigated for 112 daily PM2.5 filter samples from 2015 to 2016. Both the total concentrations and contributions from individual species of NACs show distinct seasonal variations. The seasonally averaged concentrations of NACs are 2.1 (spring), 1.1 (summer), 12.9 (fall), and 56.3 ng m−3 (winter). Thereinto, 4-nitrophenol is the major NAC component in spring (58 %). The concentrations of 5-nitrosalicylic acid and 4-nitrophenol dominate in summer (70 %), and the concentrations of 4-nitrocatechol and 4-nitrophenol dominate in fall (58 %) and winter (55 %). The NAC species show different seasonal patterns in concentrations, indicating differences in emissions and formation pathways. Source apportionment results using positive matrix factorization (PMF) further show large seasonal differences in the sources of NACs. Specifically, in summer, NACs were highly influenced by secondary formation and vehicle emissions (~ 80 %), while in winter, biomass burning and coal combustion contributed the most (~ 75 %). Furthermore, the light absorption contributions of NACs to BrC are wavelength dependent and vary greatly by seasons, with maximum contributions at ~ 330 nm in winter and fall and ~ 320 nm in summer and spring. The differences in the contribution to light absorption are associated with the higher mass fractions of 4-nitrocatechol (λmax = 345 nm) and 4-nitrophenol (λmax = 310 nm) in fall and winter, 4-nitrophenol in spring, and 5-nitrosalicylic acid (λmax = 315 nm) and 4-nitrophenol in summer. The mean contributions of NACs to BrC light absorption at the wavelength of 365 nm in different seasons are 0.14 % (spring), 0.09 % (summer), 0.36 % (fall) and 0.91 % (winter), which are about 6–9 times higher than their mass fractional contributions of carbon in total organic carbon. Our results indicate that the composition and sources of NACs have profound impacts on the BrC light absorption.

Wei Yuan et al.

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Short summary
We characterized the seasonal variations of nitrated aromatic compounds (NACs) in composition, sources, and their light absorption contribution to brown carbon aerosol in Xi'an, northwest China. Our results show that secondary formation and vehicular emission were dominant sources in summer (~ 80 %), while biomass burning and coal combustion were major sources in winter (~ 75 %). Our results indicate that the composition and sources of NACs have profound impact on the light absorption of BrC.
We characterized the seasonal variations of nitrated aromatic compounds (NACs) in composition,...