Isothermal evaporation of α-pinene secondary organic aerosol particles formed under low NO_x and high NO_x conditions

Abstract

Abstract. Many recent secondary organic aerosol (SOA) studies mainly focus on biogenic SOA particles formed under low NOx conditions and thus are applicable to pristine environments with minor anthropogenic influence. Although interactions between biogenic volatile organic compounds and NOx are important in, for instance, suburban areas, there is still a lack of knowledge about the volatility and processes controlling the evaporation of biogenic SOA particles formed in the presence of high concentrations of NOx. Here we provide detailed insights into the isothermal evaporation of α-pinene SOA particles that were formed under low NOx and high NOx conditions to investigate the evaporation process and the evolution of particle composition during the evaporation in more detail. We coupled Filter Inlet for Gases and AEROsols-Chemical Ionization Mass Spectrometer (FIGAERO-CIMS) measurements of the molecular composition and volatility of the particle phase with isothermal evaporation experiments conducted under a range of relative humidity (RH) conditions from low RH (<7 % RH) to high RH (80 % RH). Very similar changes were observed in particle volatility at any set RH during isothermal evaporation for the α-pinene SOA particles formed under low NOx and high NOx conditions. However, there were distinct differences in the initial composition of the two SOA types, possibly due to the influence of NOx on the RO2 chemistry during SOA formation. Such compositional differences consequently impacted the primary type of aqueous-phase processes in each type of SOA particle in the presence of particulate water.

Prolonged Dark Chemical Processes in Secondary Organic Aerosols on Filters and in Aqueous Solution

“…These observations suggest that on filters oligomers are formed through particle-phase reactions even under conditions where no photochemistry occurs and in the absence of oxidants, continuously changing the composition of SOA particles and leading to a decrease in monomer concentrations. These reactions observed on filters during storage at room temperature are similar to particle composition changes seen for aging of SOA in other studies, where oligomer formation in the particle phase has been reported for time scales of minutes to hours. − An additional effect that could explain the temporal changes seen on filters for monomers could be the depletion of higher-volatility species through evaporative losses. − While this will certainly have an effect in the reduction of monomers over time, it would likely mainly explain part of the signal decrease we observe for monomers during the first day (as continuous evaporation over weeks is unlikely), and it would not explain the continuous concentration increase of dimers on filters due to their high molecular weight and thus low volatility. Hence, we assume that it is a combination of several effects taking place during the storage of filters.…”

Can we achieve atmospheric chemical environments in the laboratory? An integrated model-measurement approach to chamber SOA studies

“…Oxidation flow reactors (OFRs), which can be considered as a limiting case for small chambers, have become increasingly popular for studying SOA formation over longer aging timescales. Though OFRs can access the full range of β (64,65), most OFR experiments have accessed τbi for RO2 that are shorter than those in the atmosphere (66,67). Further details about the chemical environments achieved in these previous approaches are included in Section S1.…”

Saturation vapor pressure characterization of selected low-volatility organic compounds using a residence time chamber

“…Prior to the size selection, either a silica gel diffusion dryer or a large dilution flow of dry purified air was used to remove the used solvent (i.e., water or acetonitrile). Isothermal evaporation of the particles was measured in a setup similar to that used to study volatilities of biogenic SOA particles in previous studies (Yli-Juuti et al, 2017;Buchholz et al, 2019;Li et al, 2021;Li et al, 2023). The schematic diagram of the measurement setup is…”