Articles | Volume 17, issue 2
Atmos. Chem. Phys., 17, 1143–1160, 2017

Special issue: Regional transport and transformation of air pollution in...

Atmos. Chem. Phys., 17, 1143–1160, 2017

Research article 25 Jan 2017

Research article | 25 Jan 2017

The surface aerosol optical properties in the urban area of Nanjing, west Yangtze River Delta, China

Bingliang Zhuang1, Tijian Wang1, Jane Liu1,2, Shu Li1, Min Xie1, Yong Han1, Pulong Chen1, Qiduo Hu1, Xiu-qun Yang1, Congbin Fu1, and Jialei Zhu3 Bingliang Zhuang et al.
  • 1School of Atmospheric Sciences, CMA-NJU Joint Laboratory for Climate Prediction Studies, Jiangsu Collaborative Innovation Center for Climate Change, Nanjing University, Nanjing 210023, China
  • 2Department of Geography and Planning, University of Toronto, Toronto, M5S 3G3, Canada
  • 3Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, Michigan, USA

Abstract. Observational studies of aerosol optical properties are useful for reducing uncertainties in estimations of aerosol radiative forcing and forecasting visibility. In this study, the observed near-surface aerosol optical properties in urban Nanjing are analysed from March 2014 to February 2016. Results show that near-surface urban aerosols in Nanjing are mainly from local emissions and the surrounding regions. They have lower loadings but are more scattering than aerosols in most cities in China. The annual mean aerosol extinction coefficient (EC), single-scattering albedo (SSA) and asymmetry parameter (ASP) at 550 nm are 381.96 Mm−1, 0.9 and 0.57, respectively. The aerosol absorption coefficient (AAC) is about 1 order of magnitude smaller than its scattering coefficient (SC). However, the absorbing aerosol has a larger Ångström exponent (AAE) value, 1.58 at 470∕660 nm, about 0.2 larger than the scattering aerosols (SAE). All the aerosol optical properties follow a near-unimodal pattern, and their values are mostly concentrated around their averages, accounting for more than 60 % of the total samplings. Additionally, they have substantial seasonality and diurnal variations. High levels of SC and AAC all appear in winter due to higher aerosol and trace gas emissions. AAE (ASP) is the smallest (largest) in summer, possibly because of high relative humidity (RH) which also causes considerably larger SC and smaller SAE, although intensive gas-to-particle transformation could produce a large number of finer scattering aerosols in this season. Seasonality of EC is different from the columnar aerosol optical depth. Larger AACs appear during the rush hours of the day while SC and back-scattering coefficient (Bsp) only peak in the early morning. Aerosols are fresher in the daytime than at night-time, leading to their larger Ångström exponent and smaller ASP. Different temporal variations between AAC and SC cause the aerosols to be more absorbing (smaller SSA) in autumn, winter and around rush hours. ASP has a good quasi-log-normal growth trend with increasing SC when RH is below 60 %. The correlation between AAC and SC at the site is close but a little smaller than that in suburban Nanjing in spring. Atmospheric visibility decreases exponentially with increasing EC or SC, more sharply in spring and summer, and it could be further deteriorated with increasing SSA and ASP.

Short summary
The observed near-surface aerosol optical properties in urban Nanjing are analysed from March 2014 to February 2016. Substantial analysis in the key optical properties of the surface aerosol fill the gaps in the study on aerosols in Nanjing, even in the Yangtze River Delta (YRD). Relationships between the aerosol extinction coefficient (single scattering albedo) and atmospheric visibility are also carried out in different seasons to figure out the effect of aerosol on the visibility in Nanjing, YRD.
Final-revised paper