The SDU-C Atmospheric Simulation Chamber for Multiphase Chemistry─An Initial Study on Methylglyoxal SOA

Atmospheric simulation chambers are controlled experimental platforms used for studying atmospheric processes under near-realistic conditions. Here, a new facility specifically designed for research on tropospheric multiphase chemistry is presented. After introducing the facility and its characteristics, the effects of initial methylglyoxal (MGLY) concentration, seed acidity, and relative humidity (RH) on secondary organic aerosol (SOA) formation from MGLY photooxidation in a coupled gas–particle system are examined. The Shandong University atmospheric simulation chamber (SDU-C), located on Qingdao Campus, China, is a fully computer-controlled, collapsible 18 m³ cylindrical chamber made of a 0.7 mm thick Teflon film, with a diameter of 3 m and a height of 2.4 m. Characterization experiments determined the SDU-C light intensity and wall-loss rates of NO₂, NO, O₃, and seed particles. The NO₂ photolysis frequency, J(NO₂), was (4.5 ± 0.02) ×10^–4·s^–1, while the wall-loss rates for NO, NO₂, O₃, and seed particles were (1.6 ± 0.1) ×10^–6·s^–1, (6.6 ± 1.4) ×10^–6·s^–1, (4.2 ± 0.7) ×10^–6·s^–1, and (4.4 ± 0.4) ×10^–5·s^–1, respectively. As its first application, a series of MGLY photooxidation experiments were conducted with gas-phase oxidation initiated by OH radicals. Results showed that the initial MGLY uptake and photooxidation-driven SOA formation increased with higher initial MGLY concentration [MGLY]₀, seed acidity, and RH. At 11% RH with neutral seeds, particle mass increased from 0.4 to 26.9 and 31.4 μg·m^–3 as the initial MGLY concentration increased from 72 to 144 and 216 ppb, respectively. After ultraviolet A (UVA) irradiation, SOA mass reached 43.2 μg·m^–3 for super acidic seeds at 50% RH and 216 ppb MGLY. Most particle-phase MGLY exists as oligomers (>95%), with higher [MGLY]₀ and RH, while strong acidity raises monomer levels. Overall, the characterization findings and first application indicate that SDU-C offers a reliable experimental platform for exploring atmospheric multiphase chemistry, gas–particle partitioning, and SOA formation under controlled conditions.