Distributions and sources of gaseous and particulate low molecular weight monocarboxylic acids in a deciduous broadleaf forest from northern Japan

Abstract. To better understand the distributions of low molecular weight (LMW) monocarboxylic acids (monoacids) and their sources in the forest, we conducted simultaneous collection of gaseous and particulate samples at a deciduous broadleaf forest site in northern Japan. LMW normal (C1–C10), branched chain (iC4–iC6), hydroxyl (lactic and glycolic) and aromatic (benzoic) monoacids were detected in the gas and particle phases. The dominant LMW monoacids in gas phase were formic (mean: 953 ng m−3) and acetic (528 ng m−3) acids. In particle phase, we found that isopentanoic (159 ng m−3) and acetic (104 ng m−3) acids are dominant species together with lactic acid. Concentrations of LMW monoacids did not correlate with SO42− that was used as an anthropogenic tracer, indicating that LMW monoacids are derived from the local sources within the forest ecosystem. Concentrations of C1–C6 monoacids in gas phase showed positive correlations (r2 = 0.21–0.91) with isobutyric acid (iC4), which is produced by soil microorganisms. These monoacids are closely linked to the microbial process in soils. Isopentanoic acid in particle phase showed a positive correlation with lactic acid (r2 = 0.98), which is produced by soil microbes. The observed high abundances of isopentanoic acid are involved with soil microbial activity. We found that acetic acid in particle phase positively correlated with nonanoic acid (C9) (r2 = 0.63), suggesting that formation of acetic and nonanoic acids are associated with the oxidation of unsaturated fatty acids. We found that forest floor with soil microbes contributes to the emissions of gaseous and particulate LMW monoacids. Our results suggest that forest ecosystem is an important source of organic gases and aerosols in the atmosphere.

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Distributions and sources of low-molecular-weight monocarboxylic acids in gas and particles from a deciduous broadleaf forest in northern Japan

Atmospheric Chemistry and Physics ◽

10.5194/acp-19-2421-2019 ◽

2019 ◽

Vol 19 (4) ◽

pp. 2421-2432 ◽

Cited By ~ 4

Author(s):

Tomoki Mochizuki ◽

Kimitaka Kawamura ◽

Yuzo Miyazaki ◽

Bhagawati Kunwar ◽

Suresh Kumar Reddy Boreddy

Keyword(s):

Molecular Weight ◽

Gas Phase ◽

Nonanoic Acid ◽

Low Molecular Weight ◽

Forest Site ◽

Particle Phase ◽

Broadleaf Forest ◽

Monocarboxylic Acids ◽

Deciduous Broadleaf Forest ◽

Northern Japan

Abstract. To better understand the distributions and sources of low-molecular-weight (LMW) monocarboxylic acids (monoacids) in the forest atmosphere, we conducted simultaneous collection of gaseous and particulate samples at a deciduous broadleaf forest site in northern Japan. LMW normal (C1–C10), branched (iC4–iC6), hydroxyl (glycolic and lactic) and aromatic (benzoic) monoacids were detected in the gas and particle phases. The dominant LMW monoacids in gas phase were formic (mean: 953 ng m−3) and acetic (528 ng m−3) acids followed by propionic (37 ng m−3) or isopentanoic (42 ng m−3) acid. In the particle phase, isopentanoic (159 ng m−3) was dominant, followed by acetic (104 ng m−3) and formic (71 ng m−3) or lactic (65 ng m−3) acids. Concentrations of LMW monoacids did not show correlations with anthropogenic tracers such as nss-SO42- and NO3-, indicating that anthropogenic contribution is not important. Concentrations of C1–C6 monoacids in the gas phase showed positive correlations (r2=0.21–0.91) with isobutyric acid (iC4), which may be produced by microbial activity in soil. The forest soil may be a source of gaseous C1–C6 monoacids in the forest atmosphere. Acetic acid in the particle phase positively correlated with nonanoic acid (C9) (r2=0.63), suggesting that formation of acetic and nonanoic acids is associated with the oxidation of biogenic unsaturated fatty acids in the aerosol phase, in addition to photochemical oxidation of biogenic volatile organic compounds. The particle-phase fractions (Fp) of formic and acetic acids showed negative correlation with ambient temperature (C1: r2=0.49, C2: r2=0.60) but showed positive correlation with relative humidity (C1: r2=0.30, C2: r2=0.55) in daytime, suggesting that these meteorological parameters are important for the gas and particle portioning of monoacids in the forest atmosphere.

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Development of an online-coupled MARGA upgrade for the two-hourly quantification of low-molecular weight organic acids in the gas and particle-phase

10.5194/amt-2018-299 ◽

2018 ◽

Author(s):

Bastian Stieger ◽

Gerald Spindler ◽

Dominik van Pinxteren ◽

Achim Grüner ◽

Markus Wallasch ◽

...

Keyword(s):

Molecular Weight ◽

Organic Acids ◽

Organic Acid ◽

Gas Phase ◽

Solid Phase ◽

Ambient Air ◽

Low Molecular Weight ◽

Gradient System ◽

Particle Phase ◽

Separation Columns

Abstract. A method is presented to quantify the low-molecular weight organic acids formic, acetic, propionic, butyric, pyruvic, glycolic, oxalic, malonic, succinic, malic, glutaric, and methanesulfonic acid in the atmospheric gas and particle phase in a two-hourly time resolution, based on a combination of the Monitor for AeRosols and Gases in ambient Air (MARGA) and an additional ion chromatography (IC) instrument. A proper separation of the organic target acids was initially tackled by a laboratory IC optimization study, testing different separation columns, eluent compositions and eluent flow rates both for isocratic and for gradient elution. Satisfactory resolution of all compounds was achieved using a gradient system with two coupled anion exchange separation columns. Online pre-concentration with an enrichment factor of approximately 400 was achieved by solid phase extraction consisting of a methacrylate polymer based sorbent with quaternary ammonium groups. The limits of detection of the method range between 7.1 ng m−3 for methanesulfonate and 150.3 ng m−3 for pyruvate. Precisions are below 1.0 %, except for glycolate (2.9 %) and succinate (1.0 %). Comparisons of inorganic anions measured at the TROPOS research site in Melpitz, Germany, by the original MARGA and the additional organic acid IC systems are in agreement with each other (R2 = 0.95 − 0.99). Organic acid concentrations from May 2017 as an example period are presented. Monocarboxylic acids were dominant in the gas phase with mean concentrations of 553 ng m−3 for acetic acid, followed by formic (286 ng m−3), pyruvic acid (182 ng m−3), propionic (179 ng m−3), butyric (98 ng m−3) and glycolic (71 ng m−3). Particulate glycolate, oxalate and methanesulfonate were quantified with mean concentrations of 63 ng m−3, 74 ng m−3 and 35 ng m−3, respectively. Elevated concentrations in the late afternoon of gas phase formic acid and particulate oxalate indicate a photochemical formation.

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