Weakened Gas-to-Particle Partitioning of Oxygenated Organic Molecules in Liquified Aerosol Particles

Abstract

Aqueous-phase chemistry plays an important role in secondary organic aerosol (SOA) formation. However, the mechanism of the interaction between aerosol physics and chemistry is still poorly understood. Here continuous measurements of the gas- and particle-phase composition of organics were conducted using an iodine-adduct time-of-flight chemical ionization mass spectrometer coupled with a filter inlet for gases and aerosols in Beijing to understand the physicochemical processes related to SOA formation. Our results showed that SOA contributed 65.9% to the OA mass and 17.1% to the nonrefractory PM2.5 during the whole campaign. These values are lower than those reported in previous studies. Aqueous-phase oligomerization from methylglyoxal (C3H4O2) to oligomers (C4–7H6–10O5) is a probable path of SOA formation. However, direct gas-to-particle partitioning of some C x H y O z with a particle-gas partition coefficient of ≳1.0 × 10–5 is weakened when the aerosol water content (AWC) exceeds 15 μg m–3, corresponding to a relative glass transition temperature below 0.85 compared with the AWC of <15 μg m–3. A phase transition from solid/semisolid to liquid, increasing the diffusivity of organics in particles, should explain the observed inhibition of gas-to-particle partitioning and, subsequently, the low OA mass fraction at high relative humidity in pollution events. This study provides new insights into the SOA formation mechanism.

Particle Phase State and Aerosol Liquid Water Greatly Impact Secondary Aerosol Formation: Insights into Phase Transition and Role in Haze Events

“…However, we observed that secondary transformation of SIA and SOA was significantly enhanced after phase transition with higher ALW mass during the observation. Our findings indicate that the secondary aerosol formation could be impeded on non-liquid particles due to limited mass transfer between gas and particle phase for relevant reaction components (Ravishankara, 1997;Shiraiwa et al, 2011;Abbatt et al, 2012;Ma et al, 2022), whereas it is facilitated in liquid particles. It is therefore recommended that non-liquid to liquid phase transition may be considered to be the kick-off for the positive feedback loops between ALW and secondary aerosol formation during haze events.…”

Reactive Chlorine Species Advancing the Atmospheric Oxidation Capacities of Inland Urban Environments

“…Continuous field observations from October 1, 2021, to September 31, 2022, were conducted at the Aerosols and Haze Laboratory (AHL) at Beijing University of Chemical Technology (AHL/BUCT, 39.94°N, 116.30°E, Figure S1). Detailed descriptions of this site have been provided elsewhere. , An I-LToF-CIMS was used to measure the Cl 2 and ClNO 2 levels. The Cl 2 measurements were calibrated with permeation tubes (KIN-TEC Corp.) exhibiting permeation rates of 250 ng min –1 .…”

“…Detailed descriptions of this site have been provided elsewhere. 33,34 An I-LToF-CIMS was used to measure the Cl 2 and ClNO 2 levels. The Cl 2 measurements were calibrated with permeation tubes (KIN-TEC Corp.) exhibiting permeation rates of 250 ng min −1 .…”

Observations and Modeling of Gaseous Nitrated Phenols in Urban Beijing: Insights From Seasonal Comparison and Budget Analysis

“…The field measurements were performed at the west campus of Beijing University of Chemical Technology (BUCT, longitude 116.31°E and latitude 39.95°N). Detailed site descriptions have been recorded in previous studies (Liu et al., 2020; Ma et al., 2022; Yan et al., 2022). Briefly, BUCT is located in the western part of the Beijing metropolitan area (Figure S1 in Supporting Information ).…”