Impacts of aerosol chemical compositions on optical properties in urban Beijing, China--颗粒学报PARTICUOLOGY

Tian, P., Wang, G., Zhang, R., Wu, Y., & Yan, P. (2015). Impacts of aerosol chemical compositions on optical properties in urban Beijing, China. Particuology, 18, 155–164. https://doi.org/10.1016/j.partic.2014.03.014

Impacts of aerosol chemical compositions on optical properties in urban Beijing, China

Ping Tian ^a, Guangfu Wang ^a *, Renjian Zhang ^{b c}, Yunfei Wu ^c, Peng Yan ^d

a Key Laboratory of Beam Technology and Materials Modification of the Ministry of Education, College of Nuclear Science and Technology, Beijing Normal University, Beijing 100875, China
b Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, Nanjing University of Information Science & Technology, Nanjing 210044, China
c Key Laboratory of Regional Climate-Environment for East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China
d Centre for Atmosphere Watch and Services, Meteorological Observation Center of China Meteorological Administration, Beijing 100081, China

10.1016/j.partic.2014.03.014

Volume 18, February 2015, Pages 155-164

Received 21 November 2013, Revised 3 March 2014, Accepted 21 March 2014, Available online 4 July 2014.

E-mail: guangfu_w@bnu.edu.cn

Highlights

• The mean concentration of PM_2.5 in Beijing in summer 2012 was 103.2 μg/m³, PM_2.5/PM₁₀was 61.5%.

• SO₄^2-, NO₃^- and NH₄⁺ were the main ions in PM_2.5 and PM₁₀, the average NO₃^-/SO₄^2- was 0.8.

• The mean values of σsc and σab were 312.9 and 28.7 Mm⁻¹, respectively. The mean SSA was 0.85.

• The IMPROVE reconstructed σ_sc agreed well with the measured σ_sc.

• Ammonium sulfate was the largest contributor to dry σ_sc, followed by OM and ammonium nitrate.

Abstract

The optical properties of aerosols and their chemical composition, including water-soluble ions, organic carbon (OC), and elemental carbon (EC) in PM_2.5 and PM₁₀, were measured from 26 May to 30 June of 2012 at an urban site in Beijing. The daily average concentrations of PM_2.5 and PM₁₀ were 103.2 and 159.6 μg/m³, respectively. On average, the OC and EC contributed 20.1% and 4.3%, respectively, to PM_2.5 and 16.3% and 3.9%, respectively, to PM₁₀. Secondary ions (SO₄^2-, NO₃^- and NH₄⁺) dominated the water-soluble ions and accounted for 57.9% and 62.6% of PM_2.5 and PM₁₀, respectively. The wind dependence of PM_2.5, OC, SO₄^2-, and NO₃^- implied that the pollution sources mainly came from south and southeast of Beijing during the summer. The monthly mean values of the scattering coefficient (σ_sc) and absorption coefficient (σ_ab) at 525 nm were 312.9 and 28.7 Mm⁻¹, respectively, and the mean single-scattering albedo (ω) was 0.85. The wind dependence of σ_sc revealed that this value was mainly influenced by regional transport during the summer, and the relationship between σ_ab and wind indicated that a high σab resulted from the joint effects of local emissions and regional transport. The reconstructed σ_sc that was derived from the revised IMPROVE equation agreed well with the observations. The contribution of different chemical species to σ_sc was investigated under different pollution levels, and it was found that secondary inorganic aerosols accounted for a large part of σ_sc during pollution episodes (35.7%), while organic matter was the main contributor to σ_sc under clean conditions (33.6%).

Graphical abstract

Keywords

Urban aerosol; PM_2.5; Optical property; Chemical composition

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