Observational studies of aerosol optical properties are useful forreducing uncertainties in estimations of aerosol radiative forcing andforecasting visibility. In this study, the observed near-surface aerosoloptical 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, 0.9 and 0.57,respectively. The aerosol absorption coefficient (AAC) is about 1 order ofmagnitude smaller than its scattering coefficient (SC). However, theabsorbing aerosol has a larger Ångström exponent (AAE) value, 1.58 at470∕660 nm, about 0.2 larger than the scattering aerosols (SAE). All theaerosol optical properties follow a near-unimodal pattern, and their valuesare mostly concentrated around their averages, accounting for more than60 % of the total samplings. Additionally, they have substantialseasonality and diurnal variations. High levels of SC and AAC all appear inwinter due to higher aerosol and trace gas emissions. AAE (ASP) is thesmallest (largest) in summer, possibly because of high relative humidity (RH)which also causes considerably larger SC and smaller SAE, although intensivegas-to-particle transformation could produce a large number of finerscattering aerosols in this season. Seasonality of EC is different from thecolumnar aerosol optical depth. Larger AACs appear during the rush hours of theday while SC and back-scattering coefficient (Bsp) only peak in the earlymorning. Aerosols are fresher in the daytime than at night-time, leading to their larger Ångström exponent and smaller ASP. Different temporalvariations between AAC and SC cause the aerosols to be more absorbing (smallerSSA) in autumn, winter and around rush hours. ASP has a good quasi-log-normalgrowth trend with increasing SC when RH is below 60 %. The correlationbetween AAC and SC at the site is close but a little smaller than that insuburban Nanjing in spring. Atmospheric visibility decreases exponentiallywith increasing EC or SC, more sharply in spring and summer, and it could befurther deteriorated with increasing SSA and ASP.
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