Articles | Volume 18, issue 9
Research article
09 May 2018
Research article |  | 09 May 2018

Photochemical aging of aerosol particles in different air masses arriving at Baengnyeong Island, Korea

Eunha Kang, Meehye Lee, William H. Brune, Taehyoung Lee, Taehyun Park, Joonyoung Ahn, and Xiaona Shang

Abstract. Atmospheric aerosol particles are a serious health risk, especially in regions like East Asia. We investigated the photochemical aging of ambient aerosols using a potential aerosol mass (PAM) reactor at Baengnyeong Island in the Yellow Sea during 4–12 August 2011. The size distributions and chemical compositions of aerosol particles were measured alternately every 6 min from the ambient air or through the highly oxidizing environment of a potential aerosol mass (PAM) reactor. Particle size and chemical composition were measured by using the combination of a scanning mobility particle sizer (SMPS) and a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Inside the PAM reactor, O3 and OH levels were equivalent to 4.6 days of integrated OH exposure at typical atmospheric conditions. Two types of air masses were distinguished on the basis of the chemical composition and the degree of aging: air transported from China, which was more aged with a higher sulfate concentration and O  :  C ratio, and the air transported across the Korean Peninsula, which was less aged with more organics than sulfate and a lower O  :  C ratio. For both episodes, the particulate sulfate mass concentration increased in the 200–400 nm size range when sampled through the PAM reactor. A decrease in organics was responsible for the loss of mass concentration in 100–200 nm particles when sampled through the PAM reactor for the organics-dominated episode. This loss was especially evident for the mz 43 component, which represents less oxidized organics. The mz 44 component, which represents further oxidized organics, increased with a shift toward larger sizes for both episodes. It is not possible to quantify the maximum possible organic mass concentration for either episode because only one OH exposure of 4.6 days was used, but it is clear that SO2 was a primary precursor of secondary aerosol in northeast Asia, especially during long-range transport from China. In addition, inorganic nitrate evaporated in the PAM reactor as sulfate was added to the particles. These results suggest that the chemical composition of aerosols and their degree of photochemical aging, particularly for organics, are also crucial in determining aerosol mass concentrations.

Short summary
A potential aerosol mass (PAM) reactor expedites slow atmospheric oxidation reactions and enables the observation of chemical aging processes and the determination of the aerosol-forming power of an air mass. A PAM reactor was deployed at Baengnyeong Island in the Yellow Sea. Experimental results confirm the key role of SO2 in generating secondary aerosols in northeast Asia, and the contribution of organics to secondary aerosols is more variable during transport in the atmosphere.
Final-revised paper