Influence of Ammonium Sulfate Seed Particle on Optics and Compositions of Toluene Derived Organic Aerosol in Photochemistry

• Main Authors: Tingting Lu, Mingqiang Huang, Weixiong Zhao, Changjin Hu, Xuejun Gu, Weijun Zhang
• Format: Article
• Language: English
• Published: MDPI AG 2020-09-01
• Series: Atmosphere
• Subjects: secondary organic aerosol; complex refractive index; single-scattering albedo; brown carbon; imidazoles
• Online Access: https://www.mdpi.com/2073-4433/11/9/961

Aromatic secondary organic aerosol (SOA) particles are known to contribute to radiative forcing and light absorption of atmosphere. However, the complex refractive index (CRI), single-scattering albedo (SSA) and other optical parameters of aromatic SOA are not well understood. SOA generated from photooxidation of toluene with a variety concentration of ammonium sulfate ((NH₄)₂SO₄) seed particles in a smog chamber were investigated in the current study. The real part CRI of toluene SOA without seeds derived and based on aerosol albedometer measurements is 1.486 ± 0.002 at λ = 470 nm, showing a good agreement with available experimental data, and its SSA was measured to be 0.92 ± 0.02 at λ = 470 nm, indicating that the SOA particles without seeds have strong scattering ability. The SSA of SOA formed in the presence of 300 μg/m³ (NH₄)₂SO₄ seed was 0.81 ± 0.02 at λ = 470 nm, less than the SSA of SOA without seed. SSA of SOA decreased, while the imaginary part of CRI (k) of SOA increased with increasing concentration of (NH₄)₂SO₄ seed, demonstrating that the adsorption capacity of SOA formed in the presence of (NH₄)₂SO₄ seed is enhanced. Different from the carboxyl compounds measured in the SOA without seed, imidazoles with strong chromophores of C=N that are responsible for the light absorption were detected as the principal constituents of SOA formed in the presence of (NH₄)₂SO₄ seed. These would provide valuable information for discussing the optics and components of aromatic SOA in the urban atmosphere containing a high concentration of (NH₄)₂SO₄ fine particles.