Feng Qiao, Liu Haijiao, Dai Wenting, Cao Yue, Shen Minxia, Liu Yali, Qi Weining, Chen Yukun, Guo Xiao, Zhang Yifan, Li Lu, Zhou Bianhong, Li Jianjun
State Key Laboratory of Loess and Quaternary Geology, Key Lab of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; College of Geography and Environment, Baoji University of Arts and Sciences, Shaanxi Key Laboratory of Disaster Monitoring and Mechanism Simulation, Baoji 721013, China.
Xi'an Institute for Innovative Earth Environment Research, Xi'an 710061, China.
Sci Total Environ. 2023 Dec 20;905:166985. doi: 10.1016/j.scitotenv.2023.166985. Epub 2023 Sep 11.
Aerosol pH is not only a diagnostic indicator of secondary aerosol formation, but also a key factor in the specific chemical reaction routes that produce sulfate and nitrate. To understand the characteristics of aerosol acidity in the Mt. Hua, the chemical fractions of water-soluble inorganic ions in the atmospheric PM and size-resolved particle at the top and foot of Mt. Hua in summer 2020 were studied. The results showed the mass concentrations of PM and water-soluble ions at the foot were 2.0-2.6 times higher than those at the top. The secondary inorganic ions, i.e., SO, NO, and NH (SNA) were 56 %-61 % higher by day than by night. SO was mainly distributed in the fine particles (D < 2.1 μm). NO showed a unimodal size distribution (peaking at 0.7-1.1 μm) at the foot and a bimodal (0.7-1.1 μm and 4.7-5.8 μm) size distribution at the top. At the top site, the distribution of NO in coarse particles (> 2.1 μm) was mainly attributed to the gaseous HNO volatilized from fine particles reacting with cations in coarse particles to form non-volatile salts (such as Ca(NO)). The pH values of PM were 2.7 ± 1.3 and 3.3 ± 0.42 at the top and foot, respectively. NH/NH(g) plays a decisive role in stabilizing aerosol acidity. In addition, the increase of the liquid water content (LWC) at the foot facilitates the gas-particle conversion of NH, while the H concentration was diluted, resulting in a decrease in acidity at the foot. NH/NH had good linear correlations with SO, NO, and LWC during the daytime at both sites, indicating that SO, NO, and LWC together affect the gas-particle distribution of ammonia by day: however, the effect of LWC at night was not evident.
