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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/acp-2017-863
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
04 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).
Aerosol Optical Properties at SORPES in Nanjing, East China
Yicheng Shen1, Aki Virkkula1,2,3,4, Aijun Ding1,2, Jiaping Wang1, Xuguang Chi1,2, Wei Nie1,2, Ximeng Qi1,2, Xin Huang1,2, Qiang Liu1, Longfei Zheng1,2, Zheng Xu1,2, Tuukka Petäjä4, Pasi P. Aalto4, Congbin Fu1,2, and Markku Kulmala4 1Joint International Research Laboratory of Atmospheric and Earth System Sciences, and School of Atmospheric Sciences, Nanjing University, 210023, China
2Collaborative Innovation Center of Climate Change, Jiangsu Province, China
3Finnish Meteorological Institute, 00560, Helsinki, Finland
4Department of Physics, University of Helsinki, 00014, Helsinki, Finland
Abstract. Aerosol optical properties (AOPs) and supporting parameters – particle number size distributions, mass concentrations and trace gases (NOx and NOy) – were measured at SORPES, a regional background station in Nanjing, China from June 2013 to May 2015. The aerosol was highly scattering: the average scattering coefficient was σsp = 410 ± 320 Mm−1, the absorption coefficient σap = 26 ± 19 Mm−1 and the single-scattering albedo SSA = 0.93 ± 0.03 for the green light. The SSA in Nanjing appears to be slightly higher than published values from several other sites in China and elsewhere. The average Ångström exponent of absorption (AAE) for the wavelength range 370–950 nm was 1.04 and the AAE range 0.7–1.4. These AAE values can be explained with different amounts of non-absorbing coating on pure BC cores and different core sizes so the data does not suggest any significant contribution to absorption by brown carbon. The AOPs had typical seasonal cycles with high σsp and σap in winter and lower in summer: the averages were σsp = 545 ± 425 Mm−1 and σap = 36 ± 24 Mm−1 in winter and σsp = 364 ± 294 Mm−1 and σap = 20 ± 13 Mm−1 in summer. The intensive AOPs had no clear seasonal cycles, the variations of them were rather related to the evolution of pollution episodes. The diurnal cycles of the intensive AOPs were clear and in in agreement with the cycle of the particle number size distribution. The diurnal cycle of SSA was similar to that of the air photochemical age, suggesting that the darkest aerosol originated from fresh traffic emissions. A Lagrangian retroplume analysis showed that the sources of high σsp and σap are mainly in eastern China. Synoptic weather dominated the cycle of AOPs in a temporal scale of 2–7 days. During pollution episodes, modeled PBLH decreased, whereas PM2.5 concentrations, σsp and σap typically increased gradually and remained high during several days but decreased faster, sometimes by even more than an order of magnitude within some hours. During the growth phase of the pollution episodes the intensive AOPs evolved clearly. The mass scattering efficiency MSE of of PM2.5 grew during the extended pollution episodes from ~4 m2 g−1 to ~6 m2 g−1 and the mass fraction of BCe decreased from ~10 % to ~2 % during the growth phase of the episodes. Particle growth resulted in b decreasing from more than 0.16 to less than 0.10, SSA growing from less than 0.9 to more than 0.95 and radiative forcing efficiency RFE growing from less than −26 W m−2 τ−1 to more than −24 W m−2 τ−1. In other words, the darker aerosol – the aerosol that had a higher BC mass fraction – had a more negative radiative forcing efficiency, i.e., they have the property of cooling the atmosphere more efficiently per unit optical depth than the aerosol with the higher SSA and a lower BC mass fraction. This counterintuitive result is due to the size of the particles: the upscatter fraction of small particles is higher than that of the big ones which more than compensates the darkness of them. The RFE probability distribution at SORPES was clearly more narrow than at a clean background site which is in agreement with a published RFE climatology.

Citation: Shen, Y., Virkkula, A., Ding, A., Wang, J., Chi, X., Nie, W., Qi, X., Huang, X., Liu, Q., Zheng, L., Xu, Z., Petäjä, T., Aalto, P. P., Fu, C., and Kulmala, M.: Aerosol Optical Properties at SORPES in Nanjing, East China, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2017-863, in review, 2017.
Yicheng Shen et al.
Yicheng Shen et al.
Yicheng Shen et al.

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Short summary
Aerosol optical properties (AOPs) were measured at SORPES, a regional background station in Nanjing, China from June 2013 to May 2015. The aerosol was highly scattering. The single-scattering albedo in Nanjing appears to be slightly higher than at several other sites. The data do not suggest any significant contribution to absorption by brown carbon. The sources of high values are mainly in eastern China. During pollution episodes, pollutant concentrations increased gradually but decreased fast.
Aerosol optical properties (AOPs) were measured at SORPES, a regional background station in...
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