Abstract
The mechanism of aqueous-phase OH-oxidation of pinic acid was investigated for the first time, and norpinic acid and 3-methyl-1,2,3-butanetricarboxylic acid were identified as major products. The mechanism is pH-dependent, with enhanced yields under basic conditions.
Highlights
Water-soluble organic acids (OAs) can undergo photochemistry in atmospheric aqueous phases
This indicates that the difference in pinic acid (PA)'s rst and second dissociation constants is small, and the equivalence point observed is from the merged neutralization of both acidic protons.[36]
The pKa(eff) is useful to estimate the fraction of neutral PA and pinate anion (PAn) in a solution
Summary
Water-soluble organic acids (OAs) can undergo photochemistry in atmospheric aqueous phases (cloud, fog droplets, and aerosol liquid water). The chemistry occurring in cloudwater, referred to as cloudwater processing, results in the decay of OAs, and further formation of secondary organic aerosols (SOA).[1,2,3] The gas-phase oxidation of biogenic volatile organic compounds (BVOC) are known sources of OAs and other multifunctional compounds found in cloud and fog waters.[4,5,6,7] One of the largest BVOCs emitted annually is a-pinene; numerous studies focused on its gas-phase kinetics and mechanisms leading to SOA formation.[4,5,8,9,10] It has been recognized that the aqueousphase processing of semi-volatile oxidation products of apinene can contribute to SOA formation,[1,6,11,12] but these processes are characterized poorly and limited to a few model compounds, such as cis-pinonic acid (CPA) and limononic acid.[13,14,15] Among the multifunctional a-pinene products, CPA and pinic acid (PA) are rst-generation OAs.[5,16,17] CPA is the most targeted among the OAs mainly due to its commercial availability, while PA is rarely the target of systematic studies, since it is not readily available, and needs to be synthesized
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