Modeling the influence of chain length on secondary organic aerosol (SOA) formation via multiphase reactions of alkanes

• Published in: Atmospheric chemistry and physics Vol. 23; no. 2; pp. 1661 - 1675
• Main Authors: Madhu, Azad, Jang, Myoseon, Deacon, David
• Format: Journal Article
• Language: English
• Published: Katlenburg-Lindau Copernicus GmbH 27-01-2023; Copernicus Publications
• Subjects: Aerosols; Air pollution; Aliphatic hydrocarbons; Alkanes; Autoxidation; Carbon; Carbon 13; Carbon isotopes; Chains; Chambers; Coefficients; Diesel; Diesel fuels; Hydrocarbons; Hydrophobicity; Mass; Modelling; Multiphase; Nitrogen compounds; Oligomerization; Oxidation; Oxides; Partitioning; Peroxy radicals; Photochemical smog; Photochemicals; Photochemistry; Photooxidation; Saturated hydrocarbons; Secondary aerosols; Simulation; Smog; Smog chambers; Urban areas; Vapor phases; Volatility; United States > US
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-23-1661-2023

Secondary organic aerosol (SOA) from diesel fuel is known to be
significantly sourced from the atmospheric oxidation of aliphatic
hydrocarbons. In this study, the formation of linear alkane SOA was
predicted using the Unified Partitioning Aerosol Phase Reaction (UNIPAR)
model that simulated multiphase reactions of hydrocarbons. In the model, the
formation of oxygenated products from the photooxidation of linear alkanes
was simulated using a nearly explicit gas kinetic mechanism. Autoxidation
paths integrated with alkyl peroxy radicals were added to the Master
Chemical Mechanism v3.3.1 to improve the prediction of low-volatility
products in the gas phase and SOA mass. The resulting gas products were then
lumped into volatility- and reactivity-based groups that are linked to mass-based
stoichiometric coefficients. The SOA mass in the UNIPAR model is produced
via three major pathways: partitioning of gaseous oxidized products onto
both the organic and wet inorganic phases, oligomerization in the organic phase,
and reactions in the wet inorganic phase (acid-catalyzed oligomerization and
organosulfate formation). The model performance was demonstrated for SOA
data that were produced through the photooxidation of a homologous series of
linear alkanes ranging from C9–C15 under varying environments (NOx
levels and inorganic seed conditions) in a large outdoor photochemical smog
chamber. The product distributions of linear alkanes were mathematically
predicted as a function of carbon number using an incremental volatility
coefficient (IVC) to cover a wide range of alkane lengths. The prediction of
alkane SOA using the incremental volatility-based product distributions,
which were obtained with C9–C12 alkanes, was evaluated for C13
and C15 chamber data and further extrapolated to predict the SOA from longer-chain alkanes (≥ C15) that can be found in diesel. The model simulation
of linear alkanes in diesel fuel suggests that SOA mass is mainly produced
by alkanes C15 and higher. Alkane SOA is insignificantly impacted by the
reactions of organic species in the wet inorganic phase due to the
hydrophobicity of products but significantly influenced by gas–particle
partitioning.