| SOA was the main component of atmospheric particles and it contributed about 20～80% of organic aerosols in fine particles globally. Recently, research related to SOA formations indicated that the contribution from aqueous-phase reactions was increasing and even reached the comparable level to gas-phase reactions.In this research, we simulated the aqueous-phase SOA formation in the dark condition with glycolaldehyde severed as the precursor. The reactions of glycolaldehyde in sulfate ammonium/glycine/methylamine solutions were monitoring by UV-vis absorption at 200-800 run in real time. The results showed that there appeared out two main absorption band with similar absorption shape of the three different salt solutions, peaking at 209-230 nm and 280-310 nm. At 216 nm, the absorption bands were built at the first time of reaction and were attributed to the hydration reaction of glycolaldehyde. These were base-catalyzed first order reaction with the reaction rates of methylamine> glycine> ammonium sulfate. At 300 nm, the absorption bands were slowly built at a relative long reaction time and it was the catalytic reaction of glycolaldehyde by amine/ammonium salt solutions. These were acid-catalyzed first order reaction with reaction rates of glycine> methylamine>ammonium sulfate. In these reactions, reation rates were accelerated with higher concentration of amine/ammonium salt solutions and the productions were Schiff imines, which had the characteristics absorption of BrC.To further study aqueous-phase formation of SOA, we carried out the field observations experiments in urban of Jinan in winter and measured the concentrations of PM2.5, water-soluble ions, organic/element carbons, WSOC and the UV-Vis absorption spectrums of water-soluble species. The results showed that the average concentration of PM2.5 was 150.38 μg/m3 and the main species were SO42-, NH4+, NO3-, Cl-, OC constituting 9.77%,6.15%,2.49%,4.99%,15.11% of PM2.5, respectively. The OC to EC ratios was 6.85, and SOC accounted for 30.10% of TC, proving the existence of secondary pollutions in carbon aerosols during the period of observation, but primary emissions were still the main sources. In the observation, the average concentration of WSOC was 10.89 μg/m3, occupying 49.26 ± 6.62% of OC Good correlation (R2=0.94,0.75) was found between WSOC and SOC, SO42-, indicating the secondary nature of WSOC formed in the aqueous-phase in winter of Jinan. Here, we adopted WSOC to represent aqueous-phase SOA concentrations. The aqueous-phase SOA levels was mainly affected by meteorological conditions, like higher RH, temperature and lower wind speed, which was beneficial for SOA formation. In the combination of lower temperature and higher RH, which benefit the shift to the particle phase in the gas-particle partition of SOA, with lower boundary layer at night, the SOA levels are comparable to those in the daytime. The relative stable meteorological conditions in haze days were also favorable for aqueous-phase SOA levels to increase. The UV-Vis absorption spectrums of water-soluble species showed that the peak at 200-210 nm, which was similar to the absorption of BrC in the atmosphere. The acidity analysis of the solution indicated that weakly acidic conditions were advantageous to aqueous-phase SOA formation, which was in conformity with the results from the laboratory simulation reaction. |
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