Total Dicarboxylic Acids Research Articles

Investigation of dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and volatile organic compounds at the Yellow River Delta, northern China during summer: Contributions of anthropogenic hydrocarbons to secondary organic aerosols

Total suspended particulate (TSP) and air samples were collected at Yellow River Delta (YelRD) in summer 2016 to analyze the concentrations of diacids and related secondary organic aerosols (SOA) and volatile organic compounds (VOCs). 37 organic components (dicarboxylic acids, oxocarboxylic acids, α-dicarbonyls, and fatty acids) and 40 VOCs were analyzed. Most of the dicarboxylic acids showed a similar diurnal variation characteristic with a slightly higher concentration during the daytime than nighttime. Oxalic acid (C2) was the species with the highest contribution to the total dicarboxylic acids, followed by succinic acid (C4), phthalic acid (Ph), and malonic acid (C3). The concentration of total VOCs in YelRD was lower than that in some urban areas in China, alkanes were the dominant component. The oxidation of anthropogenic aromatics to dicarboxylic acids and related SOA is also likely in YelRD. Source apportionment by positive matrix factorization (PMF) revealed that biogenic emissions, diesel exhaust, and oil volatilization, vehicular emissions, coal combustion, and secondary oxidation were the most important sources of organic species and VOCs in YelRD. This study provides potential insights into the characteristics of dicarboxylic acids and related SOA formed from VOCs oxidation in YelRD.

Insight into Source and Evolution of Oxalic Acid: Characterization of Particulate Organic Diacids in a Mega-City, Shanghai from 2008 to 2020

Organic acids are important aerosol compositions with significant implications on particle formation, growth, acidity, phase state, and environmental impacts. Oxalic acid was found to be the most abundant particulate organic diacid in Shanghai during the study period, accounting for ~58% of the total dicarboxylic acids (C2–C10). Biomass burning (BB) explained a small but non-negligible fraction (less than 10%) of oxalate. Significant correlations between oxalate and sulfate indicated a potentially synergistic formation mechanism of oxalate and sulfate. In addition, meteorological factors such as ambient temperature and relative humidity were found to influence the formation of oxalate. Higher oxalate relative to inorganic particulate content was found in summer. Potential source contribution function analysis suggested that most of the oxalate observed in Shanghai was produced locally. The formation of oxalate was largely impacted by atmospheric oxidation capacity as indicated by its significant correlations with both secondary organic carbon (SOC) and sulfur oxidation ratio (SOR). The evolution of oxalate, oxalate/sulfate, oxalate/organic carbon were consistent with the emission trend of volatile organic carbons (VOCs) in recent years, indicating that oxalate may be derived from secondary oxidation of VOCs, which is further confirmed by a positive relationship between Ox and oxalate/VOCs over the study period. With a detailed characterization of oxalate in Shanghai, our study highlights the importance of regulating primary emissions, such as VOCs, as well as mitigation of atmospheric oxidation capacity in controlling air pollution in a coastal megacity.

Molecular characterization and spatial distribution of dicarboxylic acids and related compounds in fresh snow in China

Low molecular weight organic compounds are ubiquitous in the atmosphere. However, knowledge on their concentrations and molecular distribution in fresh snow remains limited. Here, twelve fresh snow samples collected at eight sites in China were investigated for dicarboxylic acids and related compounds (DCRCs) including oxocarboxylic acids and α-dicarbonyls. Dissolved organic carbon (DOC) concentrations in the snow samples ranged from 0.99 to 14.6 mg C L−1. Concentrations of total dicarboxylic acids were from 225 to 1970 μg L−1 (av. 650 μg L−1), while oxoacids (28.3–173, av. 68.1 μg L−1) and dicarbonyls (12.6–69.2, av. 31.3 μg L−1) were less abundant, accounting for 4.6–8.5% (6.2%), 0.45–1.4% (0.73%), and 0.12–0.88% (0.46%) of DOC, respectively. Molecular patterns of dicarboxylic acids are characterized by a predominance of oxalic acid (C2) (95.0–1030, av. 310 μg L−1), followed by phthalic (Ph) (9.69–244, av. 69.9 μg L−1) or succinic (C4) (23.8–163, av. 63.7 μg L−1) acid. Higher concentrations of Ph in snow from Beijing and Tianjin than other urban and rural regions suggest significant emissions from vehicular exhausts and other fossil fuel combustion sources in megacities. C2 constituted 40–54% of total diacids, corresponding to 1.5–2.6% of snow DOC. The total measured DCRCs represent 5.5–10% of snow DOC, which suggests that there are large amounts of unknown organics requiring further investigations. The spatial distributions of diacids exhibited higher loadings in megacities than rural and island sites. Molecular distributions of diacids indicated that the photochemical modification was restrained under the weak solar radiation during the snow events, while anthropogenic primary sources had a more significant influence in megacities than rural areas and islands.

Dicarboxylic acid emissions from a GDI engine equipped with a catalytic gasoline particulate filter

Dicarboxylic acids play an important role in atmospheric chemistry, yet their emissions from primary sources, such as internal combustion engines, has not been extensively studied. In this work, KOH impregnated quartz filters were loaded with exhaust gases from a gasoline direct injection (GDI) engine equipped with a catalytic gasoline particulate filter (GPF). All filters were analyzed for carboxylic and dicarboxylic acids using a derivatized gas chromatography-mass spectroscopy method. Exhaust gas was sampled from pre-GPF and post-GPF locations to determine the performance of the GPF regarding acid conversion. Lean and stoichiometric engine modes were considered with non-oxygenated gasoline and 10% splash blended ethanol in gasoline (E10) to examine the impact of stoichiometry and fuel type. Acid emissions represented as much as 0.51% of total unburned hydrocarbon emissions for total monocarboxylic acids and as much as 0.40% for total dicarboxylic acids. Individual acid concentrations were as high as 38 mg/kg-fuel for monocarboxylic acids and as high as 29 mg/kg-fuel for dicarboxylic acids. Overall, the study found that fuel oxygenates had mixed impact on the acid emissions. Engine-out monocarboxylic acids were reduced when using the E10 fuel by approximately 30–45% for the stoichiometric condition and increased marginally for the lean condition. Dicarboxylic acid emissions were generally insensitive to ethanol content. However, the engine condition significantly affected the acid emissions. Lean operation produced a factor of two to an order of magnitude higher emissions rates of both monocarboxylic and dicarboxylic acids than the stoichiometric condition. The catalytic GPF eliminated between 80 and 92% of the acids emitted from the engine, allowing some acids to be emitted into the environment.

Seasonal Variations in PM10 and Associated Chemical Species in Jiuxian Mountain in Fujian Province

PM10 samples were collected at the top of Jiuxian Mountain in Fujian Province from March 2011 to January 2012 and were analyzed for inorganic water-soluble ions and dicarboxylic acids to investigate their seasonal variations and sources. The results showed that PM10 and its associated species exhibited much higher levels in the spring than those in other seasons but the total contribution of the nine species of dicarboxylic acids to PM10 (0.51%±0.41%) was significantly lower than that of the water-soluble ions (18.07%±8.73%). The water-soluble ions were characterized by the highest concentrations of SO42- and NO3-, followed by Na+ and NH4+. Significant positive correlations were observed between cation and anion equivalents, as well as between NH4+ and SO42- or NO3- equivalents. Individual dicarboxylic acid showed a monotonically decreasing trend with increasing carbon number in which oxalic acid accounted for approximately 75% of the total dicarboxylic acids. Characteristic ratios of malonic acid to succinic acid and adipic acid to azelaic acid, MODIS fire spots, and backward trajectories showed that dicarboxylic acids mainly originated from secondary reactions in the atmosphere and that the direct contributions of open biomass burning to dicarboxylic acid concentrations were negligible.

Compositions and Sources of Summertime Dicarboxylic Acids and Related SOA in PM2.5 from Mt. Taishan

To identify the compositions and sources of dicarboxylic acids and related SOA in Mt. Taishan, PM2.5 samples were collected from July to August, 2004, and analyzed for dicarboxylic acids and related compounds, the tracers of biogenic secondary organic aerosol (SOA) (Isopene, α-/β-Pinene and β-caryophyllene SOA tracers), water-soluble organic carbon (WSOC) and inorganic ions. The results showed that total dicarboxylic acids were (376±189) ng·m-3, and C2 was the most abundant dicarboxylic acid, followed by C3, C4 and C9. The concentrations of diacids were more abundant than those in marine regions, but lower than those in urban and other mountainous areas, indicating that the atmosphere in Mt. Taishan was less influenced by anthropogenic pollution. C2/C4, C3/C4 and F/M ratios indicated that diacids were mostly produced by more intensive photochemical oxidation. The relative abundance of C9 to the total diacids, C9/C6 and C9/Ph ratios were higher than those in urban, marine and mountainous regions, further suggesting that SOA in Mt. Taishan atmosphere were mostly derived from biogenic sources rather than anthropogenic sources. Compared to the budgets of model and correlation analysis, it suggested that diacids and related SOA in Mt. Taishan were mostly derived from photochemical oxidation of local biogenic sources.

Quantitative analysis of glycerol in dicarboxylic acid-rich cutins provides insights into Arabidopsis cutin structure

Cutin is an extracellular lipid polymer that contributes to protective cuticle barrier functions against biotic and abiotic stresses in land plants. Glycerol has been reported as a component of cutin, contributing up to 14% by weight of total released monomers. Previous studies using partial hydrolysis of cuticle-enriched preparations established the presence of oligomers with glycerol-aliphatic ester links. Furthermore, glycerol-3-phosphate 2-O-acyltransferases (sn-2-GPATs) are essential for cutin biosynthesis. However, precise roles of glycerol in cutin assembly and structure remain uncertain. Here, a stable isotope-dilution assay was developed for the quantitative analysis of glycerol by GC/MS of triacetin with simultaneous determination of aliphatic monomers. To provide clues about the role of glycerol in dicarboxylic acid (DCA)-rich cutins, this methodology was applied to compare wild-type (WT) Arabidopsis cutin with a series of mutants that are defective in cutin synthesis. The molar ratio of glycerol to total DCAs in WT cutins was 2:1. Even when allowing for a small additional contribution from hydroxy fatty acids, this is a substantially higher glycerol to aliphatic monomer ratio than previously reported for any cutin. Glycerol content was strongly reduced in both stem and leaf cutin from all Arabidopsis mutants analyzed (gpat4/gpat8, att1-2 and lacs2-3). In addition, the molar reduction of glycerol was proportional to the molar reduction of total DCAs. These results suggest “glycerol-DCA-glycerol” may be the dominant motif in DCA-rich cutins. The ramifications and caveats for this hypothesis are presented.

Dicarboxylic Acid Excretion in Normal Formula-Fed and Breastfed Infants.

Infant formulas are often supplemented with medium-chain triglycerides (MCTs) to optimize calories for small for gestational age or preterm infants. High amounts of MCTs have been associated with an increase in dicarboxylic acid (DCA) in the urine. Elevated DCA in the urine is also a clinical indicator for fatty acid metabolism disorders. The purpose of this study was to identify if there is an amount of MCTs that can be provided without elevating urinary DCA excretion. A metabolic screening laboratory provided urinary DCA excretion data for 175 infants. It was verified that no infants were diagnosed with metabolic disorders and therefore were considered "metabolically normal." All infants were either formula fed or breastfed at the time of screening. The type and volume of formula provided at the time of urine screening was documented. The exact amount of MCTs provided to each infant was calculated. The mean age of the infants was 3.09 months. The mean total DCA was determined for both the breastfeeding and formula groups. Within the formula group, the means were 32.07, 13.36, and 5.77 mmol/mol creatinine for adipic, suberic, and sebacic acids, respectively. Spearman correlation coefficient indicated correlations of r = 0.0693, r = 0.0166, and r = -0.0128 between percent MCT and adipic, suberic, and sebacic acids, respectively. No value was statistically significant. DCA excretion amounts did not vary between breastfed and formula-fed infants. Our data suggest that clinicians should not expect elevated dicarboxylic aciduria in infants who are fed a standard formula without added MCT oil.

Atmospheric dry plus wet deposition and wet-only deposition of dicarboxylic acids and inorganic compounds in a coastal suburban environment

This study investigated the chemical properties and composition sources of dicarboxylic organic acids and inorganic salts in dry plus wet deposition (DWD) and wet-only deposition at a coastal suburban area in southern Taiwan in 2008. DWD is the accumulation of dry deposition and wet deposition from the beginning of each new rain event, while wet-only deposition is the wet deposition from the beginning of each new rain event only. A total of 60 samples were collected during the period of study. The wet-only deposition samples were slightly more acidic (pH 5.01–5.50) than the DWD samples (pH 5.51–6.00). The total volume-weighted mean (VWM) equivalent ionic concentration of 784.3 ± 431.1 μeq L−1 in DWD was higher than that of 682.2 ± 392.4 μeq L−1 in wet-only deposition. In both types of deposition the major cation species were Ca2+, Na+ and NH4+, and the major anion species were HCO3−, Cl− and non-sea salt (nss) nss-SO42−. Total dicarboxylic acids contributed only 0.60% and 0.45% of the total ionic equivalent concentration in DWD and wet-only deposition, respectively, and oxalic and malonic acids were the major dicarboxylic acid species. DWD to wet-only deposition species concentration ratios (DWD/W ratios) were always higher than 1.0. DWD contained more water-soluble inorganic salts and dicarboxylic acids than wet-only deposition, with DWD/W ratios of the dust-bound species K+, Mg2+ and Ca2+ as large as 1.6–1.8 and those from photochemical species nss-SO42− and NH4+ of 1.36 and 1.29, respectively. These ratios show that the dry deposition flux of dust is greater than that of photochemical particles. In addition, the 1.81 ratio for oxalic acid shows that oxalic acid is easier to remove from the atmosphere via dry deposition than malonic and succinic acids. Probable deposition composition sources for both DWD and wet-only deposition, investigated using principal component analysis, were marine spray, photochemical inorganic products, and terrestrial origin and photochemical organic products. As the study site is close to the coast, marine spray deposits as dry deposition, and the anthropogenic dicarboxylic acids deposit together with resuspended crustal materials.

Atmospheric oxalic acid and related secondary organic aerosols in Qinghai Lake, a continental background site in Tibet Plateau

Summertime PM2.5 aerosols collected from Qinghai Lake (3200 m a.s.l.), a remote continental site in the northeastern part of Tibetan Plateau, were analyzed for dicarboxylic acids (C2–C11), ketocarboxylic acids and α-dicarbonyals. Oxalic acid (C2) is the dominant dicarboxylic acid in the samples, followed by malonic, succinic and azelaic acids. Total dicarboxylic acids (231 ± 119 ng m−3), ketocarboxylic acids (8.4 ± 4.3 ng m−3), and α-dicarbonyls (2.7 ± 2.1 ng m−3) at the Tibetan background site are 2–5 times less than those detected in lowland areas such as 14 Chinese megacities. Compared to those in other urban and marine areas enhancements in relative abundances of C2/total diacids and diacids-C/WSOC of the PM2.5 samples suggest that organic aerosols in the region are more oxidized due to strong solar radiation. Molecular compositions and air mass trajectories demonstrate that the above secondary organic aerosols in the Qinghai Lake atmosphere are largely derived from long-range transport. Ratios of oxalic acid, glyoxal and methylglyoxal to levoglucosan in PM2.5 aerosols emitted from household burning of yak dung, a major energy source for Tibetan in the region, are 30–400 times lower than those in the ambient air, which further indicates that primary emission from biomass burning is a negligible source of atmospheric oxalic acid and α-dicarbonyls at this background site.

Seasonal variations of water-soluble organic carbon, dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls in Central Himalayan aerosols

Abstract. Aerosol samples were collected from a high elevation mountain site (Nainital, India; 1958 m a.s.l.) in the central Himalayas, a location that provides an isolated platform above the planetary boundary layer to better understand the composition of the remote continental troposphere. The samples were analyzed for water-soluble dicarboxylic acids (C2-C12) and related compounds (ketocarboxylic acids and α-dicarbonyls), as well as organic carbon, elemental carbon and water soluble organic carbon. The contributions of total dicarboxylic acids to total aerosol carbon during wintertime were 1.7% and 1.8%, for day and night, respectively whereas they were significantly smaller during summer. Molecular distributions of diacids revealed that oxalic (C2) acid was the most abundant species followed by succinic (C4) and malonic (C3) acids. The average concentrations of total diacids (433±108 ng m−3), ketoacids (48±23 ng m−3), and α-dicarbonyls (9±4 ng m−3) were similar to those from large Asian cities such as Tokyo, Beijing and Hong Kong. During summer most of the organic species were several times more abundant than in winter. Phthalic acid, which originates from oxidation of polycyclic aromatic hydrocarbons such as naphthalene, was found to be 7 times higher in summer than winter. This feature has not been reported before in atmospheric aerosols. Based on molecular distributions and air mass backward trajectories, we conclude that dicarboxylic acids and related compounds in Himalayan aerosols are derived from anthropogenic activities in the highly populated Indo-Gangetic plain areas.

Summer and winter variations of dicarboxylic acids, fatty acids and benzoic acid in PM<sub>2.5</sub> in Pearl Delta River Region, China

Abstract. Ground-based PM2.5 samples collected at four different sites in Pearl River Delta region (PRD) during winter and summer (from 14 December 2006 to 28 January 2007 in winter and from 4 July to 9 August 2007 in summer) were analyzed for 30 water-soluble organic species, including dicarboxylic acids, ketocarboxylic acids and dicarbonyls, nine fatty acids, and benzoic acid. Molecular distributions of dicarboxylic acids demonstrated that oxalic acid (C2) was the most abundant species followed by phthalic acid (Ph) in PRD region. The concentrations of total dicarboxylic acids ranged from 99 to 1340 ng m−3, with an average of 438 ± 267 ng m−3 in PRD. The concentrations of total ketocarboxylic acids ranged from 0.6 to 207 ng m−3 (43 ± 48 ng m−3 on average) while the concentrations of total α-dicarbonyls, including glyoxal and methylglyoxal, ranged from 0.2 to 89 ng m−3, with an average of 11 ± 18 ng m−3 in PRD. The total quantified water-soluble compounds (TQWOC) (organic carbon) accounted for 3.4 ± 2.2% of OC and 14.3 ± 10.3% of water-soluble OC (WSOC). Hexadecanoic acid (C16:0), octadecanoic acid (C18:0) and oleic acid (C18:1) were the three most abundant fatty acids in PRD. The distributions of fatty acids were characterized by a strong even carbon number predominance with a maximum (Cmax) at hexadecanoic acid (C16:0). Ratio of C18:1 to C18:0 acts as an indicator for aerosol aging. In PRD, an average of C18:1/C18:0 ratio was 0.53 ± 0.39, suggesting an enhanced photochemical degradation of unsaturated fatty acid. Moreover, the concentrations of benzoic acid ranged from 84 to 306 ng m−3, (165 ± 48 ng m−3 on average), which can be emitted as primary pollutant from motor vehicles exhaust, or formed from photochemical degradation of aromatic hydrocarbons. Seasonal variations of the organic specie concentrations were found in the four sampling cities. Higher concentrations of TQWOC were observed in winter (598 ± 321 ng m−3) than in summer (372 ± 215 ng m−3). However, the abundances of TQWOC in OC mass were higher in summer (0.9–12.4%, 4.5 ± 2.7% on average) than in winter (1.1–5.7, 2.5 ± 1.2% on average), being consistent with enhanced secondary production of dicarboxylic acids in warmer weather. Spatial variations of water-soluble dicarboxylic acids were characterized by higher concentrations in Hong Kong and lower concentrations in Guangzhou (GZ)/Zhaoqing (ZQ) during winter whereas the highest concentrations were observed in GZ/ZQ during summer. These spatial and seasonal distributions are consistent with photochemical production and the subsequent accumulation under different meteorological conditions.

Molecular distributions of dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls in biomass burning aerosols: implications for photochemical production and degradation in smoke layers

Abstract. Aerosols in the size class <2.5 μm (6 daytime and 9 nighttime samples) were collected at a pasture site in Rondônia, Brazil, during the intensive biomass burning period of 16–26 September 2002 as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia – Smoke, Aerosols, Clouds, Rainfall and Climate (LBA-SMOCC). Homologous series of dicarboxylic acids (C2–C11) and related compounds (ketocarboxylic acids and α-dicarbonyls) were identified using gas chromatography (GC) and GC/mass spectrometry (GC/MS). Among the species detected, oxalic acid was found to be the most abundant, followed by succinic, malonic and glyoxylic acids. Average concentrations of total dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls in the aerosol samples were 2180, 167 and 56 ng m−3, respectively. These are 2–8, 3–11 and 2–16 times higher, respectively, than those reported in urban aerosols, such as in 14 Chinese megacities. Higher ratios of dicarboxylic acids and related compounds to biomass burning tracers (levoglucosan and K+) were found in the daytime than in the nighttime, suggesting the importance of photochemical production. On the other hand, higher ratios of oxalic acid to other dicarboxylic acids and related compounds normalized to biomass burning tracers (levoglucosan and K+) in the daytime provide evidence for the possible degradation of dicarboxylic acids (≥C3) in this smoke-polluted environment. Assuming that these and related compounds are photo-chemically oxidized to oxalic acid in the daytime, and given their linear relationship, they could account for, on average, 77% of the formation of oxalic acid. The remaining portion of oxalic acid may have been directly emitted from biomass burning as suggested by a good correlation with the biomass burning tracers (K+, CO and ECa) and organic carbon (OC). However, photochemical production from other precursors could not be excluded.

Size distributions of nano/micron dicarboxylic acids and inorganic ions in suburban PM episode and non-episodic aerosol

The distribution of nano/micron dicarboxylic acids and inorganic ions in size-segregated suburban aerosol of southern Taiwan was studied for a PM episode and a non-episodic pollution period, revealing for the first time the distribution of these nanoscale particles in suburban aerosols. Inorganic species, especially nitrate, were present in higher concentrations during the PM episode. A combination of gas-to-nuclei conversion of nitrate particles and accumulation of secondary photochemical products originating from traffic-related emissions was likely a crucial cause of the PM episode. Sulfate, ammonium, and oxalic acid were the dominant anion, cation, and dicarboxylic acid, respectively, accounting for a minimum of 49% of the total anion, cation or dicarboxylic acid mass. Peak concentrations of these species occurred at 0.54 μm in the droplet mode during both non-episodic and PM episode periods, indicating an association with cloud-processed particles. On average, sulfate concentration was 16–17 times that of oxalic acid. Oxalic acid was nevertheless the most abundant dicarboxylic acid during both periods, followed by succinic, malonic, maleic, malic and tartaric acid. The mass median aerodynamic diameter (MMAD) of oxalic acid was 0.77 μm with a bi-modal presence at 0.54 μm and 18 nm during non-episodic pollution and an MMAD of 0.67 μm with mono-modal presence at 0.54 μm in PM episode aerosol. The concomitant formation of malonic acid and oxalic acid was attributed to in-cloud processes. During the PM episode in the 5–100 nm nanoscale range, an oxalic acid/sulfate mass ratio of 40.2–82.3% suggested a stronger formation potential for oxalic acid than for sulfate in the nuclei mode. For total cations (TC), total inorganic anions (TIA) and total dicarboxylic acids (TDA), major contributing particles were in the droplet mode, with least in the nuclei mode. The ratio of TDA to TIA in the nuclei mode increased greatly from 8.40% during the non-episodic pollution period to 28.08% during the PM episode, favoring dicarboxylic acid formation in the nuclei mode. The evidence suggests stronger formation strength and contribution potential exists for dicarboxylic acids than for inorganic salts in nanoscale particles, especially in PM episode aerosol.

Oxalic acid in clear and cloudy atmospheres: Analysis of data from International Consortium for Atmospheric Research on Transport and Transformation 2004

Oxalic acid is often the leading contributor to the total dicarboxylic acid mass in ambient organic aerosol particles. During the 2004 International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) field campaign, nine inorganic ions (including SO42−) and five organic acid ions (including oxalate) were measured on board the Center for Interdisciplinary Remotely Piloted Aircraft Studies (CIRPAS) Twin Otter research aircraft by a particle‐into‐liquid sampler (PILS) during flights over Ohio and surrounding areas. Five local atmospheric conditions were studied: (1) cloud‐free air, (2) power plant plume in cloud‐free air with precipitation from scattered clouds overhead, (3) power plant plume in cloud‐free air, (4) power plant plume in cloud, and (5) clouds uninfluenced by local pollution sources. The aircraft sampled from two inlets: a counterflow virtual impactor (CVI) to isolate droplet residuals in clouds and a second inlet for sampling total aerosol. A strong correlation was observed between oxalate and SO42− when sampling through both inlets in clouds. Predictions from a chemical cloud parcel model considering the aqueous‐phase production of dicarboxylic acids and SO42− show good agreement for the relative magnitude of SO42− and oxalate growth for two scenarios: power plant plume in clouds and clouds uninfluenced by local pollution sources. The relative contributions of the two aqueous‐phase routes responsible for oxalic acid formation were examined; the oxidation of glyoxylic acid was predicted to dominate over the decay of longer‐chain dicarboxylic acids. Clear evidence is presented for aqueous‐phase oxalic acid production as the primary mechanism for oxalic acid formation in ambient aerosols.

Dicarboxylic acids, ketocarboxylic acids and dicarbonyls in the urban roadside area of Hong Kong

Homologous dicarboxylic acids (C 2–C 12), ketocarboxylic acids (ωC 2–ωC 9, pyruvic acid) and dicarbonyls (glyoxal and methylglyoxal) have been studied in the urban aerosol samples (PM 2.5) collected from the Hong Kong roadside atmosphere during winter and summer of 2003 using a capillary GC and GC-MS method. The concentrations of total dicarboxylic acids, ketocarboxylic acids, and α-dicarbonyls were higher in winter than in summer (except for some species like phthalic acid, Ph). Oxalic (C 2) acid was found as the most abundant species in summer, followed by Ph. Oxalic (C 2) acid was also found as the most abundant species in winter, but followed by malonic (C 3) acid. The C 2 diacid comprised 28–66% of the total diacid concentrations. The diacids with higher carbon numbers were less abundant, although C 9 diacid was relatively abundant (2%). Glyoxylic acid (ωC 2) and methylglyoxal were found as the most abundant ketocarboxylic acid and dicarbonyl in both seasons, respectively. The concentrations of the total diacids, total ketoacids and total dicarbonyls ranged from 224 to 1381 ng m −3, 10 to 89 ng m −3 and 5 to 21 ng m −3, respectively. Their relative abundances in PM 2.5 mass were 1.18%, 0.06% and 0.02%, respectively. High concentrations of toluene (winter: 33.8 μg m −3; summer: 41.3 μg m −3) and naphthalenes (winter: 1.2 μg m −3; summer: 1.9 μg m −3) observed were one possible source for the abundant phthalic and also methylmaleic acids detected.

Atmospheric year‐round records of dicarboxylic acids and sulfate at three French sites located between 630 and 4360 m elevation

An atmospheric year‐round study of C2–C5 dicarboxylic acids (oxalic, malonic, succinic, malic, and glutaric) and sulfate was conducted in 2002 and 2003 at three remote western Europe continental sites located at different elevations (from 630 to 4360 m asl). Whatever the site and the season, oxalic acid is always the dominant diacid (average 64% of total dicarboxylic acids) followed by malonic acid (15% of total dicarboxylic acids). High correlation coefficients are observed between C3 (malonic), C4 (malic and succinic), and C5 (glutaric) acids and oxalic acid. These strong relationships between C2–C5 diacids support the hypothesis of a common production of these diacids through the aqueous phase chemistry of glutaric acid. Data gained at different elevations are here useful to compare the mass formation rates of sulfate and dicarboxylic acids. It is shown that in summer the decrease of the sum of dicarboxylic acids with height is far less pronounced than the decrease of sulfate (a factor of 2 instead of 6.8 from 630 to 4360 m asl). That demonstrates that the production of dicarboxylic acids occurs at up to 4300 m elevation while the production of sulfate from SO2 mainly takes place between the boundary layer and 3000 m elevation. With respect to summer 2002 the sum of dicarboxylic acids was enhanced in summer 2003 (from 136 to 331 ng m−3 STP at 2870 m asl, for instance) whereas a weaker increase is observed for sulfate (from 1700 to 2500 ng m−3 STP at 2870 m asl). These changes are attributed to the particular summer 2003 conditions which led to enhanced level of oxidants (strengthened secondary productions) and warmer temperatures (enhanced emissions of biogenic precursors of diacids).

Screening method for organic aciduria by spectrofluorometric measurement of total dicarboxylic acids in human urine based on intramolecular excimer-forming fluorescence derivatization

A simple screening method of organic aciduria by spectrofluorometric measurement of total dicarboxylic acids in human urine is described. This method is based on an intramolecular excimer-forming fluorescence derivatization with a pyrene reagent, 4-(1-pyrene)butanoic acid hydrazide (PBH). Dicarboxylic acids in urine were converted to the corresponding dipyrene-labeled derivatives by reaction with PBH in the presence of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and pyridine, and the derivatives afforded intramolecular excimer fluorescence (420–540 nm) which can clearly be discriminated from the normal fluorescence (360–420 nm) emitted from reagent blanks. The technique is so selective that it permits spectrofluorometric measurement of total amount of dicarboxylic acids by the direct derivatization of diluted urine samples. The same reaction mixture has also served as a liquid chromatographic (LC) sample for the separative determination of individual dicarboxylic acids. The spectrofluorometric data did not contradict with the LC data. These methods were usefully applied to preliminary screening test of glutaric aciduria. In conclusion, the present derivatization method allows rapid and direct determination of total amount of dicarboxylic acids in human urine samples.

Identification of dicarboxylic acids and aldehydes of PM10 and PM2.5 aerosols in Nanjing, China

In this study aerosol samples of PM10 and PM2.5 collected from 18 February 2001 to 1 May 2001 in Nanjing, China were analyzed for their water-soluble organic compounds. A series of homologous dicarboxylic acids (C 2–10) and two kinds of aldehydes (methylglyoxal and 2-oxo-malonaldehyde) were detected by GC and GC/MS. Among the identified compounds, the concentration of oxalic acid was the highest at all the five sites, which ranged from 178 to 1423 ng/m 3. The second highest concentration of dicarboxylic acids were malonic and succinic acids, which ranged from 26.9 to 243 ng/m 3. Higher level of azelaic acid was also observed, of which the maximum was 301 ng/m 3. As the highest fraction of dicarboxylic acids, oxalic acid comprised from 28% to 86% of total dicarboxylic acids in PM10 and from 41% to 65% of total dicarboxylic acids in PM2.5. The dicarboxylic acids (C 2, C 3, C 4) together accounted for 38–95% of total dicarboxylic acids in PM10 and 59–87% of dicarboxylic acids in PM2.5. In this study, the total dicarboxylic acids accounted for 2.8–7.9% of total organic carbon (TOC) of water-soluble matters for PM10 and 3.4–11.8% of TOC for PM2.5. All dicarboxylic acids detected in this study together accounted for about 1% of particle mass. The concentration of azelaic acid was higher at one site than others, which may be resulted from higher level of volatile fat used for cooking. The amounts of dicarboxyic acids (C 2,3,4,9) and 2-oxo-malonaldehyde of PM2.5 were higher in winter and lower in spring. Compared with other major metropolitans in the world, the level of oxalic acid concentration of Nanjing is much higher, which may be contributed to higher level of particle loadings, especially for fine particles.

Massive Production of Farnesol-Derived Dicarboxylic Acids in Mice Treated with the Squalene Synthase Inhibitor Zaragozic Acid A

The zaragozic acids are potent inhibitors of squalene synthase.In vivostudies in mice confirmed our earlier observations that inhibition of squalene synthase by zaragozic acid A was accompanied by an increase in the incorporation of label from [3H]mevalonate into farnesyl-diphosphate (FPP)-derived isoprenoic acids (J. D. Bergstromet al.,1993,Proc. Natl. Acad. Sci. USA90, 80–84). Farnesyl-diphosphate-derived metabolites appear transiently in the liver. We were unable to detect any farnesol formation in the zaragozic acid-treated animals which indicates that FPP is readily converted to farnesoic acid and dicarboxylic acids in the liver. These metabolites were found to be produced only in the liver and not in the kidney.trans-3,7-Dimethyl-2-octaen-1,8-dioic acid and 3,7-dimethyloctan-1,8-dioic acid were identified as the major end products of farnesyl-diphosphate metabolism in the urine of mice treated with zaragozic acid A. Quantitative analysis of these FPP-derived dicarboxylic acids by gas–liquid chromatography revealed that approximately 11 mg of total dicarboxylic acids is excreted per day into the urine of a mouse after 3 days of treatment with zaragozic acid A.