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Carboxylic acids in PM₂.₅ over Pinus morrisonicola forest and related photoreaction mechanisms identified via Raman spectroscopy

Kuo, Su-Ching, Tsai, Ying I., Tsai, Cheng-Hsien, Hsieh, Li-Ying
Atmospheric environment 2011 v.45 no.37 pp. 6741-6750
Pinus parviflora, Raman spectroscopy, aerosols, atmospheric chemistry, carbon dioxide, emissions, forests, formic acid, maleic acid, molecular weight, oxalic acid, tartaric acid, Taiwan
The PM₂.₅ aerosol from within an area of Pinus morrisonicola Hayata in Taiwan was collected and analyzed for its low molecular weight carboxylic acid (LMWCAs) content. Oxalic acid was the major LMWCA in the aerosol, followed by acetic, tartaric and maleic acids. This differs significantly from the LMWCA composition of PM₂.₅ aerosol reported for a southern Taiwan suburban region (oxalic > succinic > malonic) [Atmospheric Environment 42, 6836–6850 (2008)]. P. morrisonicola Hayata emits oxalic, malic and formic acids and yet there was an abundance of maleic and tartaric acids in the PM₂.₅ forest aerosol, indicating that tartaric acid is derived from the transformation of other P. morrisonicola Hayata emissions. Raman spectroscopy was applied and 28 species of LMWCAs and inorganic species were identified. The photochemical mechanisms of maleic and tartaric acids were studied and it was found that the abundant tartaric acid in forest aerosol is most probably the photochemical product from reactions of maleic acid. Furthermore, tartaric acid is photochemically transformed into formic acid and ultimately into CO₂.