Compounds In Atmospheric Aerosols Research Articles

Unambiguous Analysis and Systematic Mapping of Oxygenated Aromatic Compounds in Atmospheric Aerosols Using Ultrahigh-Resolution Mass Spectrometry.

Compositional analysis of organic aerosols (OAs) at the molecular level has been a long-standing challenge in field and laboratory studies. In this work, we applied different extraction protocols to aerosol samples collected from the ambient atmosphere and biomass burning sources, followed by Orbitrap mass spectrometric analysis with a soft electrospray ionization source operating in both positive and negative ionization modes. To systematically map the distribution of mono- and dioxygenated aromatic compounds (referred to as aromatic CHO1 and CHO2 formulas) in OA, we developed a unique two-dimensional Kendrick mass defect (2D KMD) framework. Our analysis unveiled a total of (76, 64, 70) aromatic CHO1 formulas and (103, 110, 106) CHO2 formulas, corresponding to samples obtained from ambient air, rice straw burning, and sugarcane leaf burning, respectively. These results reveal a significant number of additional distinct formulas exclusively present in ambient samples, suggesting a significant chemical transformation of OAs in the atmosphere. The analytical approach can be further extended to incorporate multiple layers of 2D KMD, enabling systematic mapping of the unexplored chemical space for complex environmental samples.

Characteristics of bacterial and fungal communities and their associations with sugar compounds in atmospheric aerosols at a rural site in northern China

Abstract. Bioaerosols play significant roles in causing health and climate effects. Sugar compounds in air have been widely used to trace the source of bioaerosols. However, knowledge about the association of sugar molecules and the microbial community at taxonomic levels in atmospheric aerosols remains limited. Here, microbial community compositions and sugar molecules in total suspended particles collected from a typical rural site, Gucheng, in the North China Plain were investigated by gas chromatography–mass spectrometry and high-throughput gene sequencing, respectively. Results show that fungal community structure exhibited distinct diurnal variation with largely enhanced contribution of Basidiomycota at night, while bacterial community structure showed no obvious difference between daytime and night. SourceTracker analysis revealed that fungi and bacteria were mainly from plant leaves and unresolved sources (presumably human-related emissions and/or long-distance transport). All the detected anhydrosugars and sugar alcohols and trehalose showed diurnal variations with lower concentrations in the daytime and higher concentrations at night, which may be affected by enhanced fungal emissions at night, while primary sugars (except trehalose) showed an opposite trend. Mantel's test showed that more sugar compounds exhibited significant associations with fungal community structure than bacterial community structure. Co-occurrence analysis revealed the strong associations between sugar compounds and a few saprophytic fungal genera with low relative abundances, e.g., Hannaella, Lectera, Peniophora, Hydnophlebia, Sporobolomyces and Cyphellophora. This study suggests that the entire fungal community, rather than specific fungal taxa, likely greatly contributes to sugar compounds in rural aerosols, while the contribution of bacteria is limited.

Molecular characteristics and stable carbon isotope compositions of dicarboxylic acids and related compounds in wintertime aerosols of Northwest China

Dicarboxylic acids are one of the important water-soluble organic compounds in atmospheric aerosols, causing adverse effects to both climate and human health. More attention has therefore been paid to organic acids in aerosols. In this study, the molecular distribution and diurnal variations of wintertime dicarboxylic acids in a rural site of Guanzhong Plain, Northwest China, were explored. Oxalic acid (C2, day: 438.9 ± 346.8 ng m−3, night: 398.8 ± 392.3 ng m−3) is the most abundant compound followed by methylglyoxal (mGly, day: 207.8 ± 281.1 ng m−3, night: 222.9 ± 231.0 ng m−3) and azelaic (C9, day: 212.8 ± 269.1 ng m−3, night: 211.4 ± 136.7 ng m−3) acid. The ratios of C9/C6 and C9/Ph indicating that atmospheric dicarboxylic acids in winter in the region mainly come from biomass burning. Furthermore, secondary inorganic ions (NO3−, SO42−, and NH4+), relative humidity, liquid water content, and in-situ pH of aerosols are highly linearly correlated with C2, suggesting that liquid phase oxidation is an important pathway for the formation of dicarboxylic acids. The δ13C analysis of C2 suggested that lighter carbon isotope compositions tend to be oxidized to form aqueous-phase secondary organic aerosols (aqSOA), leading to the decay of 13C in aqSOA products rather than aerosol aging. This study provides a theoretical basis for the mechanism of formation of dicarboxylic acid.

Enhanced Nitrite Production from the Aqueous Photolysis of Nitrate in the Presence of Vanillic Acid and Implications for the Roles of Light-Absorbing Organics.

A prominent source of hydroxyl radicals (•OH), nitrous acid (HONO) plays a key role in tropospheric chemistry. Apart from direct emission, HONO (or its conjugate base nitrite, NO2-) can be formed secondarily in the atmosphere. Yet, how secondary HONO forms requires elucidation, especially for heterogeneous processes involving numerous organic compounds in atmospheric aerosols. We investigated nitrite production from aqueous photolysis of nitrate for a range of conditions (pH, organic compound, nitrate concentration, and cation). Upon adding small oxygenates such as ethanol, n-butanol, or formate as •OH scavengers, the average intrinsic quantum yield of nitrite [Φ(NO2-)] was 0.75 ± 0.15%. With near-UV-light-absorbing vanillic acid (VA), however, the effective Φ(NO2-) was strongly pH-dependent, reaching 8.0 ± 2.1% at a pH of 8 and 1.5 ± 0.39% at a more atmospherically relevant pH of 5. Our results suggest that brown carbon (BrC) may greatly enhance the nitrite production from the aqueous nitrate photolysis through photosensitizing reactions, where the triplet excited state of BrC may generate solvated electrons, which reduce nitrate to NO2 for further conversion to nitrite. This photosensitization process by BrC chromophores during nitrate photolysis under mildly acidic conditions may partly explain the missing HONO in urban environments.

Nuclear Magnetic Resonance Aerosolomics: A Tool for Analysis of Polar Compounds in Atmospheric Aerosols.

Nuclear magnetic resonance aerosolomics was proposed as a new approach to the analysis of the water-soluble organic compound fraction in aerosol particulate matter. The identification of individual compounds is based on a comparison of precise chemical shifts in the 1H NMR spectrum with the signals in the standards library. For this purpose, Chenomx metabolomics software and a comprehensive spectra library of 150 compounds known from chemistry of aerosols were used. This approach enabled the identification of 60 compounds in real aerosol samples collected at a suburban site in Prague. Using the metabolomic spectra library, three new compounds were identified in aerosols for the first time, and an association of four other compounds to the atmospheric particulate matter was confirmed. The obtained concentration profiles of all identified chemical individuals were subsequently subjected to advanced statistical analysis. NMR aerosolomics clearly differentiates between summer and winter aerosol samples via multivariate statistical analysis and revealed some interesting trends in composition, according to aerosol particle size. Furthermore, the univariate statistical analysis was applied to highlight compounds responsible for the group separation, and possible sources of these compounds were suggested.

Characterization of benzene polycarboxylic acids and polar nitroaromatic compounds in atmospheric aerosols using UPLC-MS/MS.

The molecular characterization of water-soluble organic compounds (WSOC), a large fraction of the organic mass found in the atmospheric aerosols, is important to better understand emissions and atmospheric processes influencing the particulate pollution in most urban areas. This study deals with the development of a routine method using ultrahigh pressure liquid chromatography-electrospray ionization-triple quadrupole mass spectrometry (UPLC-ESI-MS/MS) for rapid analysis of primary and secondary organic compounds distributed among three classes: (i) benzene polycarboxylic acids; (ii) nitroaromatic acids and (iii) nitrophenols in ambient particles. Using an UPLC HSS T3 column with a mobile phase consisting of formic acid/acetonitrile under gradient elution, all target analytes were eluted within a total time of 12min. Although some targeted analytes with different m/z were not resolved, a quantitation of these compounds was carried by distinct multiple reaction monitoring (MRM) transitions. Quality parameters of the method were established. The method was proven to be sensitive with limits of detection ranged from 0.02 to 0.89ng/mL. Together with a simple sample preparation and the use of labeled internal standards, the method was confirmed to be robust and reliable to determine a large number of organic tracers in atmospheric particulate matter samples. The analytical procedure was also applied to assess the abundance and characteristics of target analytes in PM2.5 emitted from diesel and gasoline-powered engines, and Urban Dust and Diesel Particulate Matter Standard Reference Materials (SRM 1649b and SRM 1650b, respectively). The obtained results suggest that trimellitic, 4-hydroxyphthalic and 4-nitrophthalic acids may be used as potential tracers for diesel engine emissions. Clear differences in distribution of target species were observed between urban PM2.5 affected by the traffic and biomass burning emissions.

Hygroscopicity of amino acids and their effect on the water uptake of ammonium sulfate in the mixed aerosol particles

Amino acids are important water-soluble nitrogen-containing compounds in atmospheric aerosols. They can be involved in cloud formation due to their hygroscopicity and have significant influences on the hygroscopicity of inorganic compounds, which have not yet been well characterized. In this work, the hygroscopic properties of three amino acids, including aspartic acid, glutamine, and serine, as well as their mixtures with ammonium sulfate (AS) were investigated using a hygroscopicity tandem differential mobility analyzer (HTDMA) system. The gradual water uptake of aspartic acid, glutamine and serine particles indicates that they exist as liquid phase at low RH. When mixing either aspartic acid or glutamine with AS by mass ratio of 1:3, we observed a clear phase transition but with a lower deliquescence relative humidity (DRH) with respect to that of pure AS. This suggests the crystallization of AS in the presence of each of these two amino acids. However, as the mass fractions of these two amino acids increased in the mixed particles, the deliquescence transition process was not obvious. In contrast, the crystallization of AS was efficiently hampered even at low content (i.e., 25% by mass) of serine in the mixed particles. The Zdanovskii-Stokes-Robinson (ZSR) method in general underestimated the hygroscopic growth of any mixtures at RH below 79% (prior to AS deliquescence), suggesting both amino acid and the partially dissolved AS contributed the overall hygroscopicity at RH in this range. Relatively good agreements were reached between the measurements and model predictions using the Extended Aerosol Inorganic Model (E-AIM) assuming solid state AS in the mixed particles for 1:3 aspartic acid-AS and glutamine-AS systems. However, the model failed to simulate the water uptake behaviors of any other systems. It demonstrates that the interactions between components within the aerosols have a significant effect on the phase state of the mixed particles.

Composition and source apportionment of saccharides in aerosol particles from an agro-industrial zone in the Indo-Gangetic Plain.

The characterization of saccharidic compounds in atmospheric aerosols is important in order to retrieve information about organic carbon sources and their transport pathways through the atmosphere. In this study, composition and sources of saccharides in PM10 were determined in a South Asian megacity (Faisalabad) during the year2015-2016. PM10 sampled on quartz filters was analyzed by anion exchange chromatography for the selected saccharidic compounds. The average PM10 concentration was found to be 744 ± 392μgm-3, exceeding the daily limits proposed by Pak-EPA (150μgm-3), US-EPA (150μgm-3), and WHO (50μgm-3). The average total saccharidic concentration was found to be 2820 ± 2247ngm-3. Among the different saccharidic categories, anhydrosugars were the most abundant in concentration followed by primary sugars and sugar alcohols. The correlation and principal component analysis indicated emissions from biomass combustion, soil suspensions from areas such as farmlands having high microorganism activity, and biogenic emissions such as airborne fungal spores and vegetation detritus as major sources of saccharides in the aerosol samples.

Mutual Impact of Mineral and Organic Components in Atmospheric Aerosol

The effect of ammonium sulfate ((NH4)2SO4) on the condensation of low-volatile organic compounds in atmospheric aerosol is considered. Using the UNIFAC model, a physicochemical analysis has been conducted for the condensation of ISNP—a product of photochemical transformations of isoprene and α-pinene in the atmosphere. The variability of the mass content of ISNP, mass concentration of aerosol particles, and their phase state at different temperatures (T) and relative humidities (RH) have been calculated. Transition of the organic component into the aqueous phase of ammonium sulfate particles is observed only at certain combinations of T and RH. In comparison with condensation in the absence of ammonium sulfate, the ISNP content at given T and RH can be lower or higher. The results of calculations indicate that the newly forming particles of mixed composition are characterized by a higher hygroscopicity and a higher capacity to be converted into drops (miscible liquid phase) at an air humidity lower than for particles that contain only ammonium sulfate.

Pollution Characteristics and Source Analysis of n-alkanes and Saccharides in PM2.5 During the Winter in Liaocheng City

To investigate molecular composition, mass concentrations, and sources of n-alkanes and sugars which are adsorbed in ambient particulate matters in Liaocheng City during winter, PM2.5 samples were collected from January 17 to February 15, 2017 at Liaocheng University. 19 kinds (C18-C36) of n-alkanes and 10 kinds of sugars were determined using GC-MS. The identification of n-alkane and sugar sources were investigated using principal component analysis (PCA). The results showed that the mass concentrations of total n-alkanes in PM2.5 during the winter were (456.9±252.5) ng·m-3. During the haze period, the concentrations of n-alkanes were two times higher than those on clear days. Additionally, the concentrations of n-alkanes during fireworks event I and fireworks event Ⅱ were 0.9 times and 1.2 times higher than those on clear days. During the sampling period, the Carbon preference index (CPI) was 1.2±0.1, and the contribution from plant wax concentrations for n-alkanes (% Wax Cn) was between 3.1%~36.0%, indicating that fossil fuels were the major source of n-alkanes in Liaocheng City during the winter. The mass concentrations of saccharides in PM2.5 during the winter were (415.5±213.8) ng·m-3. Levoglucosan was the most abundant species, followed by galactosan and mannosan, which accounted for more than 91.6% of total saccharides, indicating that biomass burning was much more significant in Liaocheng City. PCA further suggested that n-alkane and saccharide compounds in atmospheric aerosol during the winter in Liaocheng City were primarily derived from fossil fuel and biomass burning.

Changes in Light Absorptivity of Molecular Weight Separated Brown Carbon Due to Photolytic Aging.

Brown carbon (BrC) consists of those organic compounds in atmospheric aerosols that absorb solar radiation and may play an important role in planetary radiative forcing and climate. However, little is known about the production and loss mechanisms of BrC in the atmosphere. Here, we study how the light absorptivity of BrC from wood smoke and secondary BrC generated from the reaction of ammonium sulfate with methylglyoxal changes under photolytic aging by UVA radiation in the aqueous phase. Owing to its chemical complexity, BrC is separated by molecular weight using size exclusion chromatography, and the response of each molecular weight fraction to aging is studied. Photolytic aging induced significant changes in the light absorptivity of BrC for all molecular weight fractions; secondary BrC was rapidly photoblenched, whereas for wood smoke BrC, both photoenhancement and photobleaching were observed. Initially, large biomass burning BrC molecules were rapidly photoenhanced, followed by slow photolysis. As a result, large BrC molecules dominated the total light absorption of aged biomass burning BrC. These experimental results further support earlier observations that large molecular weight BrC compounds from biomass burning can be relatively long-lived components in atmospheric aerosols, thus more likely to have larger impacts on aerosol radiative forcing and could serve as biomass burning tracers.

Towards the isolation and estimation of elemental carbon in atmospheric aerosols using supercritical fluid extraction and thermo-optical analysis

Air-starved combustion of biomass and fossil fuels releases aerosols, including airborne carbonaceous particles, causing negative climatic and health effects. Radiocarbon analysis of the elemental carbon (EC) fraction can help apportion sources of its emission, which is greatly constrained by the challenges in isolation of EC from organic compounds in atmospheric aerosols. The isolation of EC using thermo-optical analysis is however biased by the presence of interfering compounds that undergo pyrolysis during the analysis. EC is considered insoluble in all acidic, basic, and organic solvents. Based on the property of insolubility, a sample preparation method using supercritical CO2 and methanol as co-solvent was developed to remove interfering organic compounds. The efficiency of the method was studied by varying the density of supercritical carbon dioxide by means of temperature and pressure and by varying the methanol content. Supercritical CO2 with 10% methanol by volume at a temperature of 60 °C, a pressure of 350 bar and 20 min static mode extraction were found to be the most suitable conditions for the removal of 59 ± 3% organic carbon, including compounds responsible for pyrolysis with 78 ± 16% EC recovery. The results indicate that the method has potential for the estimation and isolation of EC from OC for subsequent analysis methods and source apportionment studies.

High abundances of dicarboxylic acids, oxocarboxylic acids, and α-dicarbonyls in fine aerosols (PM2.5) in Chengdu, China during wintertime haze pollution.

Daytime and nighttime fine aerosol (PM2.5) samples were collected during a haze episode in January 2013 within the urban area of Chengdu, southwest China. Aerosol samples were analyzed for low-molecular-weight homologous dicarboxylic acids, oxocarboxylic acids and α-dicarbonyls, as well as organic carbon and elemental carbon. Concentration ranges of diacids, oxoacids, and α-dicarbonyls were 1,400-5,250, 272-1,380, and 88-220ngm(-3), respectively. Molecular distributions of diacids (mean 3,388 ± 943ngm(-3)) were characterized by a predominance of oxalic acid (C2; 1,373 ± 427ngm(-3)), followed by succinic (C4), terephthalic (tPh), and phthalic (Ph) acids. Such high levels of tPh and Ph were different from those in other Asian cities where malonic acid (C3) is the second or third highest species, mostly owing to significant emissions from coal combustion and uncontrolled waste incineration. High contents of diacids, oxoacids, and α-dicarbonyls were detected on hazy days, suggesting an enhanced emission and/or formation of these organics during such a weather condition. Concentrations of unsaturated aliphatic diacids (e.g., maleic acid) and phthalic acids were higher in nighttime than in daytime. Good positive correlations of C2 with C3, C4, ketomalonic (kC3), pyruvic (Pyr), and glyoxylic (ɷC2) acids in daytime suggest secondary production of C2 via the photooxidation of longer chain diacids and ɷC2. This study demonstrated that both primary emissions and secondary production are important sources of dicarboxylic acids and related compounds in atmospheric aerosols in the Sichuan Basin.

Analysis of organic sulfur compounds in atmospheric aerosols at the HKUST supersite in Hong Kong using HR-ToF-AMS.

Organic sulfur compounds have been identified in ambient secondary organic aerosols, but their contribution to organic mass is not well quantified. In this study, using a high-resolution time-of-flight aerosol mass spectrometer (AMS), concentrations of organic sulfur compounds were estimated based on the high-resolution fragmentation patterns of methanesulfonic acid (MSA), and organosulfates (OS), including alkyl, phenyl, and cycloalkyl sulfates, obtained in laboratory experiments. Mass concentrations of MSA and minimum mass concentrations of OS were determined in a field campaign conducted at a coastal site of Hong Kong in September 2011. MSA and OS together accounted for at least 5% of AMS detected organics. MSA is of marine origin with its formation dominated by local photochemical activities and enhanced by aqueous phase processing. OS concentrations are better correlated with particle liquid water content (LWC) than with particle acidity. High-molecular-weight OS were detected in the continental influenced period probably because they had grown into larger molecules during long-range transport or they were formed from large anthropogenic precursors. This study highlights the importance of both aqueous-phase processing and regional influence, i.e., different air mass origins, on organic sulfur compound formation in coastal cities like Hong Kong.

Size-resolved characterisation of organic compounds in atmospheric aerosols collected at Welgegund, South Africa

The organic fraction of atmospheric aerosols is 20 to 90 % of which only a small percentage has been chemically characterised. Two-dimensional gas chromatography with a time-of-flight mass spectrometer (GCxGC-TOFMS) is a powerful instrument used to chemically characterise organic compounds. Size-resolved characterisation and semi-quantification of ambient organic aerosol compounds were performed with a GCxGC-TOFMS for the first time in South Africa. Twenty-four-hour samples were collected for 1 year for three different size ranges. A combined total of 1056 different organic compounds could be tentatively characterised. The largest number of organic compounds tentatively identified was PM2.5–1 (particles in the size range 1–2.5 μm), while this size fraction also had the highest total number of normalised response factors (∑NRF). On average, 52, 26, 6, 13 and 3 % of species tentatively identified were oxygenated species, hydrocarbons, halogenated compounds, N-containing compounds and S-containing compounds, respectively. Oxygenated compounds were the most abundant species. Alkane and mono-aromatic species were the largest number of hydrocarbons tentatively identified with the highest ∑NRFs. The largest number of oxygenated species tentatively characterised were carboxylic acids and esters, while ether compounds had the highest ∑NRFs. Most of the halogenated compounds tentatively identified were chlorinated species with the highest ∑NRFs in two size fractions. Iodate species had a significantly higher ∑NRF in the PM2.5–1 size fraction. The largest number of N-containing species tentatively characterised with the highest ∑NRFs were amines. A small number of S-containing compounds with low ∑NRFs were tentatively identified. The major sources of organic compounds measured at Welgegund were considered to be biomass burning and air masses moving over the anthropogenically impacted source regions.

Polar organic marker compounds in atmospheric aerosol in the Po Valley during the Supersito campaigns — Part 2: Seasonal variations of sugars

Four intensive experimental campaigns were conducted in the Po Valley (Northern Italy) in different seasons through the years 2012 and 2013, in the framework of the “Supersito” project. As a part of a study on polar tracers in atmospheric PM2.5, the present paper describes the abundances and temporal variations of sugars, as primary biogenic biomarkers, being the major form of photosynthetically assimilated carbon in the biosphere. The study includes primary saccharides (glucose, sucrose, arabinose, galactose and mycose), sugar alcohols (arabitol and mannitol) and anhydrosugars (levoglucosan, galactosan and mannosan).Strong seasonality was observed with total sugars concentration nearly 10 times higher in the cold seasons (mean 377 ng m−3) than in summer/spring (mean 36 ng m−3). Also sugar composition profiles varied seasonally, being dominated by anhydrosugars in fall and winter, i.e., levoglucosan (mean 271 ng m−3), followed by mannosan (mean 53 ng m−3) and galactosan (mean 29 ng m−3). These data indicate that in the cold seasons the biomass combustion for domestic heating is the main sugar source representing nearly 94% of the total saccharides mass measured in PM2.5. Accordingly, glucose, arabinose and galactose show the highest concentrations, since these saccharides are also emitted during the burning process as uncombusted biomass materials. In spring/summer the primary saccharides are dominant in PM2.5, with mannitol as the most abundant, followed by mycose, glucose and ribitol that are emitted by the terrestrial biomass, reflecting the higher sugar production and utilization by the ecosystem in the warm seasons.These results were confirmed by investigating other molecular markers, such as low-molecular-weight carboxylic acids and n-alkane homologs. Principal Component Analysis was applied to the data to extract three PCs that may be attributed to different saccharide sources, such as biomass burning and primary bio aerosol.

Nitrogen and Sulfur Compounds in Atmospheric Aerosols: A New Parametrization of Polarized Molecular Orbital Model Chemistry and Its Validation against Converged CCSD(T) Calculations for Large Clusters.

The parametrization of the polarized molecular orbital (PMO) method, which is a neglect-of-diatomic-differential-overlap (NDDO) semiempirical method that includes polarization functions on hydrogens, is extended to include the constituents that dominate the nucleation of atmospheric aerosols, including ammonia, sulfuric acid, and water. The parametrization and validation are based mainly on CCSD(T)/CBS results for atmospheric clusters composed of sulfuric acid, dimethylamine, and ammonia and on M06-2X exchange-correlation functional calculations for other constituents of the atmospheric aerosols. The resulting model, called PMO2a, is parametrized for molecules containing any type of H, C, or O, amino or ammonium N, and S atoms bonded to O. The new method gives greatly improved electric polarization compared to any other member of the family of NDDO methods. In addition, PMO2a is shown to outperform previous NDDO methods for atomization energies and atmospheric aerosol reaction energies; therefore, its use can be recommended for realistic simulations.

Comparison of abundances, compositions and sources of elements, inorganic ions and organic compounds in atmospheric aerosols from Xi'an and New Delhi, two megacities in China and India

Wintertime TSP samples collected in the two megacities of Xi'an, China and New Delhi, India were analyzed for elements, inorganic ions, carbonaceous species and organic compounds to investigate the differences in chemical compositions and sources of organic aerosols. The current work is the first time comparing the composition of urban organic aerosols from China and India and discussing their sources in a single study. Our results showed that the concentrations of Ca, Fe, Ti, inorganic ions, EC, PAHs and hopanes in Xi'an are 1.3–2.9 times of those in New Delhi, which is ascribed to the higher emissions of dust and coal burning in Xi'an. In contrast, Cl−, levoglucosan, n-alkanes, fatty alcohols, fatty acids, phthalates and bisphenol A are 0.4–3.0 times higher in New Delhi than in Xi'an, which is attributed to strong emissions from biomass burning and solid waste incineration. PAHs are carcinogenic while phthalates and bisphenol A are endocrine disrupting. Thus, the significant difference in chemical compositions of the above TSP samples may suggest that residents in Xi'an and New Delhi are exposed to environmental hazards that pose different health risks.Lower mass ratios of octadecenoic acid/octadecanoic acid (C18:1/C18:0) and benzo(a)pyrene/benzo(e)pyrene (BaP/BeP) demonstrate that aerosol particles in New Delhi are photochemically more aged. Mass closure reconstructions of the wintertime TSP indicate that crustal material is the most abundant component of ambient particles in Xi'an and New Delhi, accounting for 52% and 48% of the particle masses, respectively, followed by organic matter (24% and 23% in Xi'an and New Delhi, respectively) and secondary inorganic ions (sulfate, nitrate plus ammonium, 16% and 12% in Xi'an and New Delhi, respectively).

Polar organic marker compounds in atmospheric aerosol in the Po Valley during the Supersito campaigns — Part 1: Low molecular weight carboxylic acids in cold seasons

In the framework of the “Supersito” project, three intensive experimental campaigns were conducted in the Po Valley (Northern Italy) in cold seasons, such as late autumn, pre-winter and deep-winter, over three years from 2011 to 2013. As a part of a study on polar marker compounds, including carboxylic acids, sugar derivatives and lignin phenols, the present study reports a detailed discussion on the atmospheric concentrations of 14 low molecular weight carboxylic acids, mainly dicarboxylic and oxo-hydroxy carboxylic acids, as relevant markers of primary and secondary organic aerosols.PM2.5 samples were collected in two monitoring sites, representing urban and rural background stations. The total quantities of carboxylic acids were 262, 167 and 249 ng m−3 at the urban site and 308, 115, 248 ng m−3 at the rural site in pre-winter, fall and deep-winter, respectively. These high concentrations can be explained by the large human emission sources in the urbanized region, combined with the stagnant atmospheric conditions during the cold seasons that accumulate the organic precursors and accelerate the secondary atmospheric reactions.The distribution profiles of the investigated markers suggest the dominant contributions of primary anthropogenic sources, such as traffic, domestic heating and biomass burning. These results are confirmed by comparison with additional emission tracers, such as anhydro-saccharides for biomass burning and fatty acids originated from different anthropogenic sources. In addition, some secondary constituents were detected in both sites, as produced by in situ photo-chemical reactions from both biogenic (e.g. pinonic acid) and anthropogenic precursors (e.g. phthalic and adipic acids).The impact of different sources from human activities was elucidated by investigating the week pattern of carboxylic and fatty acid concentrations. The weekly trends of analytes during the warmer campaign (fall 2012; mean temperature: 12 °C) may be related to emissions from motor vehicle traffic and industrial activities. Otherwise, the random pattern of the markers suggests the prevalent contribution of primary emissions from residential heating in the colder deep-winter (mean temperature: 5 °C).

Time-resolved variations in the distributions of inorganic ions, carbonaceous components, dicarboxylic acids and related compounds in atmospheric aerosols from Sapporo, northern Japan during summertime

To better understand time-resolved variations of water-soluble organic aerosols in the atmosphere, we collected atmospheric particles (TSP) every 3 h during summertime (8–10 August, 2005) in Sapporo, northern Japan. We measured inorganic ions, carbonaceous components, dicarboxylic acids, ketoacids and α-dicarbonyls in TSP. SO42− was found as the most abundant ionic species (57 ± 9% of total ions determined) followed by NH4+ and NO3−. However, none of the ionic species showed any diurnal trend throughout the campaign. Organic carbon (OC) ranged from 2.1 to 12.1 μg m−3 whereas elemental carbon (EC) was negligible in most of the samples (0.31 ± 0.56 μg m−3). Oxalic (C2) acid was the most abundant diacid species, followed by malonic (C3) and succinic (C4) acids. Water-soluble OC (WSOC), water-insoluble OC (WIOC) and OC as well as dominant diacids (C2–C4), total diacids, ketoacids and α-dicarbonyls did not show diurnal trend on 8 August, but they showed clear diurnal distributions during 9–10 August following the changes in ambient temperature (and radiation). Detailed analyses of time-resolved aerosols demonstrate that diurnal variations of organic aerosol compositions are caused by local in situ photochemical production, but are significantly superimposed by long-range atmospheric transport of aerosols, particularly when the air masses are enriched with emissions from higher plants and/or biomass burning, and their photochemical processing during the transport.