Aerosol optical properties at urban and coastal sites in Shandong Province, Northern China

In-situ observations of aerosol optical properties were conducted in Jinan, an urban site, from December 2013 to May 2014 and on Tuoji Island, a coastal site, from December 2014 to January 2015; both locations are located in Shandong Province, Northern China. Aerosol optical properties, such as the scattering coefficient (σsp), absorption coefficient (σap) and single-scattering albedo (ω), were obtained using nephelometer and aethalometer. The mean values (± standard deviation) for σsp at 550 nm and σap at 532 nm, were 204 ± 188 Mm− 1 and 43 ± 33 Mm− 1, respectively, in Jinan and 210 ± 246 Mm− 1 and 8 ± 6 Mm− 1 on Tuoji Island, respectively. The average ω at 532 nm was 0.80 ± 0.09 in Jinan and 0.93 ± 0.04 on Tuoji Island. Pronounced diurnal cycles were observed at both locations for σsp, σap and ω, but the diurnal cycles at the two locations exhibited distinct properties for some of the aerosol optical parameters. The values of σsp and σap peaked between 0800 and 1100 local time (LT) due to traffic emissions and low wind speeds at both locations. And a unimodal ω diurnal cycle, which peaked between 1000 and 1400 LT, was observed in the spring in Jinan. This spring diurnal pattern was mainly related to secondary aerosol formation and aging processes. The high σsp and σap values in Jinan winter were accompanied by calm winds (< 2 m/s) from 0° to 90°, while the high σsp and σap values on Tuoji Island were observed during the period of stronger wind speeds (> 2 m/s) from 180° to 270°. This indicates that local emissions were a key source of strongly absorbing and scattering aerosols in Jinan during heating period, whereas, high σsp and σap values on Tuoji Island were mainly influenced by middle- and long-distance transport from Shandong Province and the Jing-Jin-Ji region. Additionally, middle- and long-distance regional transport from direction at 180° to 270° occasionally enhanced the σsp and σap values in the spring at Jinan after heating period. The σsp values in Jinan and Tuoji Island both exhibited relatively profound correlation with the accumulation-mode particle number concentrations.