Investigation of hygroscopic growth effect on aerosol scattering coefficient at a rural site in the southern North China Plain

• Published in: The Science of the total environment Vol. 599-600; pp. 76 - 84
• Main Authors: Wu, Yunfei, Wang, Xiaojia, Yan, Peng, Zhang, Leiming, Tao, Jun, Liu, Xinyu, Tian, Ping, Han, Zhiwei, Zhang, Renjian
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2017
• Subjects: Aerosol scattering hygroscopicity; Chemical composition; Particle size distribution; Particle size distribution; Chemical composition; Aerosol scattering hygroscopicity
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2017.04.194

Aerosol optical properties and the effect of hygroscopic growth on the scattering coefficients at a rural site in the southern North China Plain were investigated based on a two-month observation conducted in the summer of 2014. The scattering coefficient of dry aerosols was high, with a mean (±standard deviation) of 338.8±209.9Mm−1 (520nm) during the observation period. A noticeable enhancement in aerosol scattering due to hygroscopic growth was observed, e.g., by a factor of 2.28±0.69 at RH of 80% (referred to as f(RH=80%)) and 3.39±1.14 at RH of 85% (f(RH=85%)). The high content of water-soluble secondary inorganic aerosols (SIAs), accounting for 53.1% of fine particulate matter (i.e., PM2.5) on average, was mainly responsible for the high hygroscopicity. f(RH=80%) increased with increasing SIA mass fraction in PM2.5. This was especially the case when SIAs were mainly in finer particulate matter, i.e., PM1. A number of considerably low f(RH=80%) values was observed due to relatively low mass fraction of SIAs in PM1 despite high fraction in PM2.5. Particle size distributions, especially those of SIAs, also played a remarkable role in the hygroscopicity of ambient aerosols. No significant difference in hygroscopicity was found between different pollution episodes due to the dominance of SIAs in all the cases. Slightly higher hygroscopic growth factors were observed during the clean episode, which were attributed to the smaller particle sizes. [Display omitted] •Noticeable high hygroscopicity was observed with a mean enhancement factor of 2.28 at RH of 80%.•High fraction of secondary inorganic aerosols in PM2.5 caused high hygroscopicity.•Secondary inorganic aerosols in smaller particles have stronger impact on aerosol hygroscopicity.