Size-Resolved Molecular Characterization of Water-Soluble Organic Matter in Atmospheric Particulate Matter from Northern China

Atmospheric particulate matter (PM) affects visibility, climate, biogeochemical cycles and human health. Water-soluble organic matter (WSOM) is an important component of PM. In this study, PM samples with size-resolved measurements at aerodynamic cut-point diameters (Dp) of 0.01-18μm were collected in the rural area of Baoding and the urban area of Dalian, Northern China. Non-targeted analysis was adopted for the characterization of the molecule constitutes of WSOM in different sized particles using Fourier transform-ion cyclotron resonance mass spectrometry. Regardless of the location, the composition of WSOM in Aitken mode particles (aerodynamic diameter < 0.05 μm) was similar. The WSOM in accumulation mode particles (0.05-2 μm) in Baoding was predominantly composed of CHO compounds (84.9%), which were mainly recognized as lignins and lipids species. However, S-containing compounds (64.2%), especially protein and carbohydrates species, accounted for most of the WSOM in the accumulation mode particles in Dalian. The CHO compounds (67.6%-79.7%) contributed the most to the WSOM in coarse mode particles (> 2 μm) from both sites. Potential sources analysis indicated the WSOM in Baoding were mainly derived from biomass burning and oxidation reactions, while the WSOM in Dalian arose from coal combustion, oxidation reactions, and regional transport.

Compositional and optical characteristics of aqueous brown carbon and HULIS in the eastern Indo-Gangetic Plain using a coupled EEM PARAFAC, FT-IR and 1H NMR approach

This study provides insights into the fluorophoric composition of aqueous brown carbon (BrCaq) and chemically-separated humic-like substances (HULIS): neutral HULIS (HULIS-n; at pH = 7) and acidic HULIS (HULIS-a; at pH = 2) on a seasonal and day-night basis in the eastern Indo-Gangetic Plain (IGP), India. A coupled approach including excitation-emission matrix (EEM) fluorescence and parallel factor analysis (PARAFAC) model, Fourier-transformed infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy was employed to understand the links between structural, compositional and fluorophoric characteristics of BrCaq and HULIS fractions. HULIS fluorophores (HULISfluoro) with varying oxidation states transported from the northwest IGP were dominant during biomass burning seasons (post-monsoon and winter), while protein-like fluorophores (PRLISfluoro) from marine emissions showed large contributions during summer. HULIS-n moieties were mostly primary in nature with higher conjugation, while HULIS-a were associated with secondarily formed and aged species with a larger contribution from degradation products. A substantial presence of tyrosine-like proteins in both chemically-separated HULIS fractions indicated that atmospheric HULIS is not entirely humic or fulvic-like in the eastern IGP. Finally, the dominance of H-C-O groups across seasons suggested consistent fossil fuel signatures along with season-specific influence of photodegradable cellulose from marine organisms in the summer and biomass burning in the post-monsoon and winter.

Positive matrix factorization of seasonally resolved organic aerosol at three different central European background sites based on nuclear magnetic resonance Aerosolomics data

Concentration data derived from 1H NMR analysis of the water-soluble organic compounds from fine aerosol (PM2.5) at three Central European background stations, Košetice, Frýdlant (both in the Czech Republic), and Melpitz (Germany), were used for detailed source apportionment analysis. Two winter and two summer episodes (year 2021) with higher organic concentrations and similar wind directions were selected for NMR analyses. The concentration profiles of 61 water-soluble organic compounds were determined by NMR Aerosolomics and a principal component analysis (PCA) was performed on this dataset. Based on the PCA results, 23 compounds were selected for positive matrix factorization (PMF) analysis in order to identify dominant aerosol sources at rural background sites in Central Europe. Both the PCA and the subsequent PMF analyses clearly distinguished the characteristics of winter and summer aerosol particles. In summer, four factors were identified from PMF and were associated with biogenic aerosol (61-78 %), background aerosol (9-15 %), industrial biomass combustion (7-13 %), and residential heating (5-13 %). In winter, only 3 factors were identified - industrial biomass combustion (33-49 %), residential heating (37-45 %) and a background aerosol (8-30 %). The main difference was observed in the winter season with a stronger contribution of emissions from industrial biomass burning at the Czech stations Košetice and Frýdlant (47-49 %) compared to the Melpitz station (33 %). However, in general, there were negligible differences in identified sources between stations in the given seasons, indicating a certain homogeneity in PM2.5 composition within Central Europe at least during the sampling periods.

Controls of Mineral Solubility on Adsorption-Induced Molecular Fractionation of Dissolved Organic Matter Revealed by 21 T FT-ICR MS

Mineral adsorption-induced molecular fractionation of dissolved organic matter (DOM) affects the composition of both DOM and OM adsorbed and thus stabilized by minerals. However, it remains unclear what mineral properties control the magnitude of DOM fractionation. Using a combined technique approach that leverages the molecular composition identified by ultrahigh resolution 21 T Fourier transform ion cyclotron resonance mass spectrometry and adsorption isotherms, we catalogue the compositional differences that occur at the molecular level that results in fractionation due to adsorption of Suwannee River fulvic acid on aluminum (Al) and iron (Fe) oxides and a phyllosilicate (allophane) species of contrasting properties. The minerals of high solubility (i.e., amorphous Al oxide, boehmite, and allophane) exhibited much stronger DOM fractionation capabilities than the minerals of low solubility (i.e., gibbsite and Fe oxides). Specifically, the former released Al3+ to solution (0.05-0.35 mM) that formed complexes with OM and likely reduced the surface hydrophobicity of the mineral-OM assemblage, thus increasing the preference for adsorbing polar DOM molecules. The impacts of mineral solubility are exacerbated by the fact that interactions with DOM also enhance metal release from minerals. For sparsely soluble minerals, the mineral surface hydrophobicity, instead of solubility, appeared to be the primary control of their DOM fractionation power. Other chemical properties seemed less directly relevant than surface hydrophobicity and solubility in fractionating DOM.

Research progress on the characteristics, sources, and environmental and potential health effects of water-soluble organic compounds in atmospheric particulate matter

Water-soluble organic compounds (WSOCs) have received extensive attention due to their indistinct chemical components, complex sources, negative environmental impact, and potential health effects. To the best of our knowledge, until now, there has been no comprehensive review focused on the research progress of WSOCs. This paper reviewed the studies on chemical constituent and characterization, distribution condition, sources, environmental impact, as well as the potential health effects of WSOCs in the past 13 years. Moreover, the main existing challenges and directions for the future research on WSOCs were discussed from several aspects. Because of the complex composition of WSOCs and many unknown individual components that have not been detected, there is still a need for the identification and quantification of WSOCs. As modern people spend more time in indoor environments, it is meaningful to fill the gaps in the component characteristics and sources of indoor WSOCs. In addition, although in vitro cell experiments have shown that WSOCs could induce cellular oxidative stress and trigger the inflammatory response, the corresponding mechanisms of action need to be further explored. The current population epidemiology research of WSOCs is missing. Prospectively, we propose to conduct a comprehensive and simultaneous analysis strategy for concentration screening, source apportionment, potential health effects, and action mechanisms of WSOCs based on high throughput omics coupled with machine learning simulation and prediction.

Does liquid-liquid phase separation impact ice nucleation in mixed polyethylene glycol and ammonium sulfate droplets?

Particles can undergo different phase transitions in the atmosphere including deliquescence, liquid-liquid phase separation (LLPS), melting, and freezing. In this study, phase transitions of particles/droplets containing polyethylene glycol with a molar mass of 400 g mol^-1 (PEG400) and ammonium sulfate (AS), i.e., PEG400-AS particles/droplets, were investigated at different organic-to-inorganic dry mass ratios (OIRs) under typical tropospheric temperatures and water activities (a_w). The investigated droplets (60-100 μm) with or without LLPS in the closed system froze through homogeneous ice nucleation. At temperatures lower than 200 K, multiple ice nucleation events were observed within the same individual droplets at low a_w. Droplets with and without LLPS shared similar lambda values at the same OIR according to the lambda approach indicating they form ice through the same mechanism. A parameterization of lambda values was provided which can be used to predict freezing temperature of aqueous PEG400-AS droplets. We found that adding AS reduces the temperature dependence of a_w in aqueous PEG400 droplets. Assuming incorrectly that a_w is temperature-independent for a constant droplet composition leads to a deviation between the experimental determined ice nucleation rate coefficients for droplets at OIR > 1 and the predicted values by the water-activity-based ice nucleation theory. We proposed a parameterization of temperature dependence of a_w to minimize the deviations of the measured melting temperatures and nucleation rate coefficients from the corresponding predictions for aqueous PEG400-AS system.

1H NMR structural signatures of source and atmospheric organic aerosols in India

Organic aerosols (OA) play significant roles in several atmospheric processes and adversely impact human health. This study examines the key structural units present in water- and methanol-soluble organic carbon (WSOC, MSOC) fraction of OA from emission sources (traffic and biomass cooking) and an urban background location in India. Proton nuclear magnetic resonance (¹H NMR) spectroscopy was employed to assess the distribution of non-exchangeable proton structural groups of the OAs. Organic carbon, elemental carbon, black carbon, and water-soluble organic carbon (WSOC) analyses were also conducted. The ¹H NMR analysis corroborated that the WSOC and MSOC fractions hold similar ¹H structural groups; however, they differ in their relative distribution and absolute concentrations across the ambient locations and source emissions. The relative contribution of the proton structural groups to OA was in the order C-H > H-C-C=> H-C-O > Ar-H. The aliphatic concentration was lower in the morning tunnel entry aerosols when compared to other tunnel aerosols, whereas the unsaturated structures (H-C-C= ) were present in all the tunnel aerosols within a range of 47.2-62.3 μmol/m³. The aromatic groups were the maximum in the firewood aerosols, about 1.4 and 3.7 times higher than the crop residue and the mixed fuel aerosols, respectively. The total functional groups, i.e., the sum of all the observed groups, significantly correlated with C-H (r = 0.96) and WSOC (r = 0.7), suggesting the higher contribution of aliphatic groups in the WSOC fraction. WSOC examined in this study fits well in the established ¹H NMR source identification fingerprints of urban aerosols. However, biomass cooking aerosols do not fit the established biomass burning organic aerosols (BBOAs) boundaries, exhibiting a smaller relative contribution of carbon-oxygen double bonds and a less oxidised character than open-field burning. Our results provide essential insights into the nature of urban atmospheric, near-traffic and biomass cooking OAs in India.

Leaching material from Antarctic seaweeds and penguin guano affects cloud-relevant aerosol production

Within the Southern Ocean, the greatest warming is occurring on the Antarctic Peninsula (AP) where clear cryospheric and biological consequences are being observed. Antarctic coastal systems harbour a high diversity of marine and terrestrial ecosystems heavily influenced by Antarctic seaweeds (benthonic macroalgae) and bird colonies (mainly penguins). Primary sea spray aerosols (SSA) formed by the outburst of bubbles via the sea-surface microlayer depend on the organic composition of the sea water surface. In order to gain insight into the influence of ocean biology and biogeochemistry on atmospheric aerosol, we performed in situ laboratory aerosol bubble chamber experiments to study the effect of different leachates of biogenic material - obtained from common Antarctic seaweeds as well as penguin guano - on primary SSA. The addition of different leachate materials on a seawater sample showed a dichotomous effect depending on the leachate material added - either suppressing (up to 52%) or enhancing (22-88%) aerosol particle production. We found high ice nucleating particle number concentrations resulting from addition of guano leachate material. Given the evolution of upper marine polar coastal ecosystems in the AP, further studies on ocean-atmosphere coupling are needed in order to represent the currently poorly understood climate feedback processes.

Rapid transition of aerosol optical properties and water-soluble organic aerosols in cold season in Fenwei Plain

The Fenwei Plain (FWP) continues to be one of the most polluted regions in China despite the improvement of air quality in recent years. However, our understanding of aerosol optical properties (AOP) and its relationship with aerosol composition particularly in cold season is far from complete. Here we conducted three-month measurements of AOP from November 2020 to January 2021 in the FWP along with fine particle composition and water-soluble organic aerosol (WSOA) measurements. Our results showed rapid transitions in AOP from November to January due to the enhanced primary emissions and the decreased aqueous-phase processing. The single scattering albedo (SSA) decreased from 0.85 to 0.78, while the absorption Ångstrӧm exponent (AAE) increased from 1.41 to 1.60, demonstrating the increasing role of absorbing aerosol and brown carbon in cold season. Further analysis showed that SSA increased significantly with the fraction of secondary inorganic aerosol, while AAE was highly correlated with the fraction of primary OA (POA), highlighting the different impacts of primary and secondary aerosol on AOP. Chemical apportionment showed the dominant contributions of ammonium nitrate (29%) and ammonium sulfate (27%) to particle extinction before heating season, while that of POA increased to 27% during heating season. Although the pollution level showed a clear increase during the heating season, the changes in visibility were small due to the decreased mass extinction efficiency from 3.48 to 2.91 m² g^-1. Positive matrix factorization illustrated a clear transition in WSOA composition from the dominance of secondary OA (SOA) in November to POA in heating season. Compared with the large decrease in water-soluble aqueous-phase SOA, the consistently high concentration of photochemical-related SOA elucidated the presence of strong photochemical processing in cold season. Overall, our results demonstrate the significant transition in primary emissions and secondary formation in cold season, and such changes have affected AOP substantially.

Aerial drone furnished with miniaturized versatile air sampling systems for selective collection of nitrogen containing compounds in boreal forest

A wide variety of nitrogen-containing compounds are present in the environment, which contributes to air pollution and new particle formation, for example. These eventually affect human health and the climate. With all this consideration, there is a growing interest in the development of efficient and reliable methods to determine these compounds in the atmosphere. In this study, titanium hydrogen phosphate-modified Mobil Composition of Matter No. 41 was used as sorbent material for in-tube extraction (ITEX) sampling system, to selectively collect nitrogen-containing compounds from natural air samples. The effect of sampling accessories, based on adsorbent coatings (with Tenax-GR as an adsorbent material) and polytetrafluoroethylene filters, was studied to improve the selectivity of the sampling system and to remove particles. Aerial drone with miniaturized air sampling system was employed for the reliable collection of nitrogen-containing compounds in both gas phase and aerosol particles. A total of 170 air samples were collected in July 2020 at the SMEAR II station, Finland to evaluate nitrogen-containing compounds diurnal patterns and vertical profiles (0.25, 5, 50, and 150 m). More than twenty nitrogen-containing compounds, such as aliphatic amines, imines, imidazoles, and pyridines, were identified, quantified or semi-quantified. The average concentrations of detected aliphatic amines at the altitude of 50 m were up to 40.4 ng m^-3 (dimethylamine) in gas phase and 128 ng m^-3 (ethylamine) in aerosol particles. Among nitrogen-containing compounds detected, pyridine gave the highest average concentration of 746 ng m^-3 in gas phase and 644 ng m^-3 in particle phase.

Water-insoluble carbonaceous components in rainwater over an urban background location in Northern India during pre-monsoon and monsoon seasons

The carbonaceous content of rainwater was investigated in samples collected at an urban background site in northern India. Sampling was performed on an event basis during two seasons: pre-monsoon (PM) and monsoon (MN) season covering May-June and July-August, respectively, in 2016. The concentrations of different fractions of water-insoluble organic carbon (WIOC) and elemental carbon (EC) were precisely determined, and the sources of WIOC and EC were also analysed. The result revealed that the average WIOC and EC concentration in rainwater ranged from 0.4 to 52 mgC/L and from 0.1 to 15.3 mgC/L, respectively. The concentrations of WIOC and EC were found to be ~ 9 times and ~ 12 times higher, respectively, in the PM season than MN season. The WIOC/EC ratio indicated higher variation in PM season as compared to that of the MN season, suggesting divergent emission sources during the PM season. The formation of water-insoluble secondary organic carbon (WISOC) has also been identified as one of the causes for the extensive difference in the WIOC/EC ratio in different seasons. Results showed that the WIOC and its fractions were efficiently scavenged through rain. While EC and its fractions were less significantly scavenged, due to its hydrophobicity and fine size. The atmospheric scavenging coefficients of selected carbonaceous components were found significantly correlated with rain intensity (RI) during both the seasons. Higher rain intensity caused greater rates of carbonaceous component wash-out and decreasing concentrations of carbonaceous components in the rain.

Direct noninvasive 1 H NMR analysis of stream water DOM: Insights into the effects of lyophilization compared with whole water

NMR spectroscopy is widely used in the field of aquatic biogeochemistry to examine the chemical structure of dissolved organic matter (DOM). Most aquatic DOM analyzed by proton NMR (¹ H NMR) is concentrated mainly by freeze-drying prior to analysis to combat low concentrations, frequently <100 μM C, and eliminate interference from water. This study examines stream water with low dissolved organic carbon content by ¹ H NMR with a direct noninvasive analysis of whole water using a water-suppression technique. Surface waters, collected from the headwaters of the Rio Tempisquito, Costa Rica, were examined directly, and the spectral characteristics were compared with those of the traditional preanalysis freeze-drying approach revealing significant differences in the relative intensity of peaks between the whole water and freeze-dried DOM. The freeze-dried DOM required less time to obtain quality spectra, but several peaks were missing compared with the spectra of whole water DOM; notably the most dominant peak in the spectrum constituting roughly 10% of the DOM. The stream water DOM showed an increase in the relative intensity of aliphatic methyl and methylene groups and a decrease in carbonyl, carboxyl, and carbohydrate functionalities after freeze-drying. The results of this study show that freeze-drying alters the original composition of DOM and thus freeze-dried DOM may not represent the original DOM. The information gained from whole water analysis of stream water DOM in a noninvasive fashion outweighs the attraction of reduced analysis times for preconcentrated samples, particularly for studies interested in investigating the low molecular weight fraction of DOM.

Characteristics and sources of water-soluble organic aerosol in a heavily polluted environment in Northern China

Water-soluble organic aerosol (WSOA) in fine particles (PM_2.5) collected during wintertime in a polluted city (Handan) in Northern China was characterized using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS). Through comparing with real-time measurements from a collocated Aerosol Chemical Speciation Monitor (ACSM), we determined that WSOA on average accounts for 29% of total organic aerosol (OA) mass and correlates tightly with secondary organic aerosol (SOA; Pearson's r = 0.95). The mass spectra of WSOA closely resemble those of ambient SOA, but also show obvious influences from coal combustion and biomass burning. Positive matrix factorization (PMF) analysis of the WSOA mass spectra resolved a water-soluble coal combustion OA (WS-CCOA; O/C = 0.17), a water-soluble biomass burning OA (WS-BBOA; O/C = 0.32), and a water-soluble oxygenated OA (WS-OOA; O/C = 0.89), which account for 10.3%, 29.3% and 60.4% of the total WSOA mass, respectively. The water-solubility of the OA factors was estimated by comparing the offline AMS analysis results with the ambient ACSM measurements. OOA has the highest water-solubility of 49%, consistent with increased hygroscopicity of oxidized organics induced by atmospheric aging processes. In contrast, CCOA is the least water soluble, containing 17% WS-CCOA. The distinct characteristics of WSOA from different sources extend our knowledge of the complex aerosol chemistry in the polluted atmosphere of Northern China and the water-solubility analysis may help us to understand better aerosol hygroscopicity and its effects on radiative forcing in this region.

Molecular Speciation of Size Fractionated Particulate Water-Soluble Organic Carbon by Two-Dimensional Nuclear Magnetic Resonance (NMR) Spectroscopy

Particulate matter is associated with increased morbidity and mortality; its effects depend on particle size and chemical content. It is important to understand the composition and resultant toxicological profile of particulate organic compounds, the largest and most complex fraction of particulate matter. The objective of the study was to delineate the nuclear magnetic resonance (NMR) spectral fingerprint of the biologically relevant water-soluble organic carbon (WSOC) fraction of size fractionated urban aerosol. A combination of one and two-dimensional NMR spectroscopy methods was used. The size distribution of particle mass, water-soluble extract, non-exchangeable organic hydrogen functional types and specific biomarkers such as levoglucosan, methane sulfonate, ammonium and saccharides indicated the contribution of fresh and aged wood burning emissions, anthropogenic and biogenic secondary aerosol for fine particles as well as primary traffic exhausts and pollen for large particles. Humic-like macromolecules in the fine particle size range included branched carbon structures containing aromatic, olefinic, keto and nitrile groups and terminal carboxylic and hydroxyl groups such as terpenoid-like polycarboxylic acids and polyols. Our study show that 2D-NMR spectroscopy can be applied to study the chemical composition of size fractionated aerosols.

Aerosol Toxins Emitted by Harmful Algal Blooms Susceptible to Complex Air-Sea Interactions

Critical research is needed regarding harmful algal blooms threatening ecosystem and human health, especially through respiratory routes. Additional complexity comes from the poorly understood factors involved in the physical production of marine aerosols coupled with complex biogeochemical processes at ocean surfaces. Here-by using a marine aerosol generation tank-five bubble-bursting experiments (with contrasting incubation times and, likely, physiological microalgal states) were run to investigate simultaneously the concentrations of the toxins, synthesized by a natural Ostreopsis cf. ovata bloom, in suspension in the water and in the atmosphere. The first two experiments (EXP1-2) were run with moderate levels of O. cf. ovata cell numbers (ca. 10⁵ cells·L^-1) and total toxin in suspension (4 × 10⁶ pg·L_water^-1) obtained at an early phase of the bloom. After 0.75-4 h incubation, toxin concentration in the aerosols accounted for 49-69 pg·L_air^-1. By striking contrast, three experiments (EXP3-5)-conducted with samples collected two weeks later with higher cell abundances and higher toxin concentration in the seston (respectively, about 1 × 10⁶ cells·L^-1 and 2 × 10⁸ pg·L_water^-1) and incubated for 21 h-showed about 15-fold lower atmospheric concentrations (3-4 pg·L_air^-1), while important foam accumulation was observed in the water surface in the tank. Offline spectroscopic analysis performed by proton-nuclear magnetic resonance spectroscopy showed that the particulate organic carbon in the water was drastically different from that of bubble-bursting aerosols from the tank experiments-suggesting a selective transfer of organic compounds from seawater into the atmosphere. Overall, the results suggest that aerosol production and diffusion of marine toxins in the atmosphere are regulated by complex interactions between biological processes and air-sea aerosol production dynamics.

Fluorescence characteristics of water-soluble organic carbon in atmospheric aerosol☆

Fluorescence spectroscopy is a commonly used technique to analyze dissolved organic matter in aquatic environments. Given the high sensitivity and non-destructive analysis, fluorescence has recently been used to study water-soluble organic carbon (WSOC) in atmospheric aerosols, which have substantial abundance, various sources and play an important role in climate change. Yet, current research on WSOC characterization is rather sparse and limited to a few isolated sites, making it challenging to draw fundamental and mechanistic conclusions. Here we presented a review of the fluorescence properties of atmospheric WSOC reported in various field and laboratory studies, to discuss the current advances and limitations of fluorescence applications. We highlighted that photochemical reactions and relevant aging processes have profound impacts on fluorescence properties of atmospheric WSOC, which were previously unnoticed for organic matter in aquatic environments. Furthermore, we discussed the differences in sources and chemical compositions of fluorescent components between the atmosphere and hydrosphere. We concluded that the commonly used fluorescence characteristics derived from aquatic environments may not be applicable as references for atmospheric WSOC. We emphasized that there is a need for more systematic studies on the fluorescence properties of atmospheric WSOC and to establish a more robust reference and dataset for fluorescence studies in atmosphere based on extensive source-specific experiments.

Sources and atmospheric processing of brown carbon and HULIS in the Indo-Gangetic Plain: Insights from compositional analysis

We present here spectroscopic compositional analysis of brown carbon (BrC) and humic-like substances (HULIS) in the Indian context under varying conditions of source emissions and atmospheric processing. To this end, we study bulk water-soluble organic matter (WSOM), neutral- and acidic-HULIS (HULIS-n and HULIS-a), and high-polarity (HP)-WSOM collected in the eastern Indo-Gangetic Plain (IGP) with respect to UV-Vis, fluorescence, FT-IR, ¹H NMR and ¹³C characteristics under three aerosol regimes: photochemistry-dominated summer, aged biomass burning (BB)-dominated post-monsoon, and fresh BB-dominated winter. Absorption coefficients (b_{abs_365 nm}; Mm^-1) of WSOM and HULIS fractions increase by a factor of 2-9 during winter as compared to summer, with HULIS-n dominating total HULIS + HP-WSOM absorption (73-81%). Fluorophores in HULIS-n appear to contain near-similar levels of aromatic and unsaturated aliphatic conjugation across seasons, while HULIS-a exhibits distinctively smaller-chain structures in summer and post-monsoon. FT-IR spectra reveals, among others, strong signatures of aromatic phenols in winter WSOM suggesting a BB-related origin. ¹H NMR-based source attribution coupled with back trajectory analysis indicate the presence of secondary and BB-related organic aerosol (SOA and BBOA) in the post-monsoon and winter, and marine-derived OA (MOA) in the summer, which is supported by ¹³C measurements. Overall, these observations uncover a complex interplay of emissions and atmospheric processing of carbonaceous aerosols in the IGP.

Global Importance of Hydroxymethanesulfonate in Ambient Particulate Matter: Implications for Air Quality

Sulfur compounds are an important constituent of particulate matter, with impacts on climate and public health. While most sulfur observed in particulate matter has been assumed to be sulfate, laboratory experiments reveal that hydroxymethanesulfonate (HMS), an adduct formed by aqueous phase chemical reaction of dissolved HCHO and SO2, may be easily misinterpreted in measurements as sulfate. Here we present observational and modeling evidence for a ubiquitous global presence of HMS. We find that filter samples collected in Shijiazhuang, China, and examined with ion chromatography within 9 days show as much as 7.6 μg m-3 of HMS, while samples from Singapore examined 9-18 months after collection reveal ~0.6 μg m-3 of HMS. The Shijiazhuang samples show only minor traces of HMS 4 months later, suggesting that HMS had decomposed over time during sample storage. In contrast, the Singapore samples do not clearly show a decline in HMS concentration over 2 months of monitoring. Measurements from over 150 sites, primarily derived from the IMPROVE network across the United States, suggest the ubiquitous presence of HMS in at least trace amounts as much as 60 days after collection. The degree of possible HMS decomposition in the IMPROVE observations is unknown. Using the GEOS-Chem chemical transport model, we estimate that HMS may account for 10% of global particulate sulfur in continental surface air and over 25% in many polluted regions. Our results suggest that reducing emissions of HCHO and other volatile organic compounds may have a co-benefit of decreasing particulate sulfur.

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.

A Significant Portion of Water-Soluble Organic Matter in Fresh Biomass Burning Particles Does Not Contribute to Hygroscopic Growth: An Application of Polarity Segregation by 1-Octanol-Water Partitioning Method

The importance of water-soluble organic matter (WSOM) on the hygroscopic growth of particles is recognized, yet roles of different categories of WSOM are under debate. We segregated WSOM from Indonesian biomass burning particles by the 1-octanol-water partitioning method. The method is based on the 1-octanol-water partition coefficient (K_OW), which correlates with water solubility. The segregated WSOM was analyzed using the humidified tandem differential mobility analyzer (HTDMA) and time-of-flight aerosol chemical speciation monitor (ToF-ACSM). Both the hygroscopicity parameter κ and the fractional contribution of m/z 44 (f₄₄), which serves as a metric for degree of oxygenation, increased with polarity. This result experimentally evidenced that highly polar/water-soluble OM is highly hygroscopic/oxygenated. Positive matrix factorization (PMF) identified three factors from the ToF-ACSM data. Deconvolution of κ by PMF factors demonstrated that the less polar fractions, which occupy approximately 20-60% of WSOM dependent on the biomass type, almost do not contribute to water uptake under subsaturated conditions. This result highlights that categorization of WSOM will be needed to understand how hygroscopic growth of aerosol particles is regulated.

Polarity-Dependent Chemical Characteristics of Water-Soluble Organic Matter from Laboratory-Generated Biomass-Burning Revealed by 1-Octanol-Water Partitioning

Polarity distribution of water-soluble organic matter (WSOM) is an important factor in determining the hygroscopic and cloud nucleation abilities of organic aerosol particles. We applied a novel framework to quantitatively classify WSOM based on the 1-octanol-water partition coefficient (K_OW), which often serves as a proxy of polarity. In this study, WSOM was generated in a laboratory biomass-burning experiment by smoldering of Indonesian peat and vegetation samples. The fractionated WSOM was analyzed using a UV-visible spectrophotometer, spectrofluorometer, and time-of-flight aerosol chemical speciation monitor. Several deconvolution methods, including positive matrix factorization, parallel factor analysis, and least-squares analysis, were applied to the measured spectra, resulting in three classes of WSOM. The highly polar fraction of WSOM, which predominantly exists in the range of log K_OW < 0, is highly oxygenated and exhibits similar optical properties as those of light-absorbing humic-like substances (HULIS, termed after the humic substances due to the similarity in chemical characteristics). WSOM in the least-polar fraction, which mainly distributes in log K_OW > 1, mostly consists of hydrocarbon-like and high molecular weight species. In between the most- and least-polar fraction, WSOM in the marginally polar fraction likely contains aromatic compounds. The analyses have also suggested the existence of HULIS with different polarities. Comparison with previous studies indicates that only WSOM in the highly polar fraction (log K_OW < 0) likely contributes to water uptake.

Cloud droplet activation of organic-salt mixtures predicted from two model treatments of the droplet surface

The droplet surface plays important roles in the interaction between organic aerosols with clouds and climate. Surface active organic compounds can partition to the droplet surface, depleting the solute from the droplet bulk or depressing the droplet surface tension. This may in turn affect the shape of the droplet growth curve, threshold of aerosol activation into cloud droplets, activated droplet size distributions, and cloud radiative effects. In this work, a new monolayer model along with a traditional Gibbs adsorption isotherm model was used in conjunction with equilibrium Köhler theory to predict cloud condensation nuclei (CCN) activation of both simple and complex surface active model aerosol systems. For the surface active aerosol considered, the monolayer droplet model produces similar results to the Gibbs model as well as comparable results to CCN measurements from the literature, even for systems where specific molecular identities and aqueous properties are unknown. The monolayer model is self-contained and fully prognostic, and provides a versatile, conceptually simple, yet physically based model for understanding the role of organic surfactants in cloud droplet formation.

Atmospheric HULIS and its ability to mediate the reactive oxygen species (ROS): A review

Atmospheric humic-like substances (HULIS) are not only an unresolved mixture of macro-organic compounds but also powerful chelating agents in atmospheric particulate matters (PMs); impacting on both the properties of aerosol particles and health effects by generating reactive oxygen species (ROS). Currently, the interests of HULIS are intensively shifting to the investigations of HULIS-metal synergic effects and kinetics modeling studies, as well as the development of HULIS quantification, findings of possible HULIS sources and generation of ROS from HULIS. In light of HULIS studies, we comprehensively review the current knowledge of isolation and physicochemical characterization of HULIS from atmospheric samples as well as HULIS properties (hygroscopic, surface activity, and colloidal) and possible sources of HULIS. This review mainly highlights the generation of reactive oxygen species (ROS) from PMs, HULIS and transition metals, especially iron. This review also summarized the mechanism of iron-organic complexation and recent findings of OH formation from HULIS-metal complexes. This review will be helpful to carry out the modeling studies that concern with HULIS-transition metals and for further studies in the generation of ROS from HULIS-metal complexes.

Role of ammonium ion and transition metals in the formation of secondary organic aerosol and metallo-organic complex within fog processed ambient deliquescent submicron particles collected in central part of Indo-Gangetic Plain

In this study we observed the role of ammonium ion (NH₄⁺) and transition metals (Fe, Mn, Cr, and Cu) present in ambient submicron particles in stabilizing and enhancing the yield of water soluble organic carbon (WSOC). A good correlation of WSOC with transition metals and NH₄⁺ was found (R² = 0.87 and 0.71), respectively within foggy episode collected ambient PM₁ (particles having aerodynamic diameter ≤1.0 μm) suggesting plausibleness of alternate oxidation (primarily various carbonyls into their respective organic acids, esters and other derivatives.) and aging mechanisms. Molar concentration of ammonium ion was observed to be exceeded over and above to require in neutralizing the sulphate and nitrate which further hints its role in the neutralization, stabilization and enhancement of subset of WSOC such as water soluble organic acids. Transition metals were further apportioned using enrichment factor analysis. The source of Fe, Mn, and Cr was found to be crustal and Cu was tagged to anthropogenic origin. This study also described the plausible role of significant predictors (Fe and Cu) in the secondary organic aerosol (SOA) formation through effect of Fenton chemistry. Mass-to-charge ratio of identified oxalic acid from our published recent field study (carried out from same sampling location) was used for understanding the possible metallo-organic complex with Fe supports the substantial role of Fe in SOA formation in the deliquescent submicron particles facilitated by aqueous-phase chemistry.

Two-Dimensional Offline Chromatographic Fractionation for the Characterization of Humic-Like Substances in Atmospheric Aerosol Particles

Organic carbon in atmospheric particles comprises a large fraction of chromatographically unresolved compounds, often referred to as humic-like substances (HULIS), which influence particle properties and impact climate, human health, and ecosystems. To better understand its composition, a two-dimensional (2D) offline method combining size-exclusion (SEC) and reversed-phase liquid chromatography (RP-HPLC) using a new spiked gradient profile is presented. It separates HULIS into 55 fractions of different size and polarity, with estimated ranges of molecular weight and octanol/water partitioning coefficient (log P) from 160-900 g/mol and 0.2-3.3, respectively. The distribution of HULIS within the 2D size versus polarity space is illustrated with heat maps of ultraviolet absorption at 254 nm. It is found to strongly differ in a small example set of samples from a background site near Leipzig, Germany. In winter, the most intense signals were obtained for the largest molecules (>520 g/mol) with low polarity (log P ∼ 1.9), whereas in summer, smaller (225-330 g/mol) and more polar (log P ∼ 0.55) molecules dominate. The method reveals such differences in HULIS composition in a more detailed manner than previously possible and can therefore help to better elucidate the sources of HULIS in different seasons or at different sites. Analyzing Suwannee river fulvic acid as a common HULIS surrogate shows a similar polarity range, but the sizes are clearly larger than those of atmospheric HULIS.

Chemical characterization of humic-like substances (HULIS) in PM2.5 in Lanzhou, China

Evaporative light scattering detection (ELSD) was applied to quantify HULIS (humic-like substances) for the first time in 2012 winter and 2013 summer at an urban site in Lanzhou. Water soluble organic carbon (WSOC), water soluble inorganic ions, and carbonaceous species (OC/EC) were also analyzed. The results show that OM (Organic Matter=OC×1.6, constituting 45.8% to PM_2.5) was the most abundant species, followed by SNA (SO₄^2-+NO₃^-+NH₄⁺, constituting 23.4% to PM_2.5). The chemical species were in the order of: OC>EC>SO₄^2->NO₃^->NH₄⁺>Cl^->Ca²⁺>K⁺. The annual average concentration of HULIS was 4.70μg/m^-3 and HULISc (carbon content of HULIS) contributed 6.19% to PM_2.5 and 45.6% to WSOC, indicating that HULIS was the most important components of WSOC. The concentration of HULIS was 2.14±0.80μg/m³ in summer and 7.24±2.77μg/m³ in winter, respectively. The concentrations of HULIS were relatively low and stable in summer, while high and varied dramatically in winter. The abundance of HULISc in WSOC shows a more concentrated distribution in Lanzhou, with a range between 0.28-0.57. The ratios of HULIS/K⁺ were 6.25±1.41 and 6.14±1.96 in summer and winter, respectively, suggesting there were other significant sources in addition to biomass burning emissions. HULIS and WSOC exhibited similar seasonal variation and had a strong positive correlation. In addition to the good relationship (0.89) between HULIS and Cl^- in winter, the great enhancement of HULIS with significantly high Cl^- and relatively low K⁺ in winter indicated that residential coal burning was probably an important HULIS source in winter. Correlation and back trajectory analysis suggested that biomass burning and secondary formation were also important HULIS sources and the contribution of HULIS from dust could be neglected. Adverse meteorological conditions were also important factors for the accumulation of HULIS in winter.

Airborne particulate matter pollution in urban China: a chemical mixture perspective from sources to impacts

Rapid urban and industrial development has resulted in severe air-pollution problems in developing countries such as China, especially in highly industrialized and populous urban clusters. Dissecting the complex mixtures of airborne particulate matter (PM) has been a key scientific focus in the last two decades, leading to significant advances in understanding physicochemical compositions for comprehensive source apportionment. However, identifying causative components with an attributable link to population-based health outcomes remains a huge challenge. The microbiome, an integral dimension of the PM mixture, is an unexplored frontier in terms of identities and functions in atmospheric processes and human health. In this review, we identify the major gaps in addressing these issues, and recommend a holistic framework for evaluating the sources, processes and impacts of atmospheric PM pollution. Such an approach and the knowledge generated will facilitate the formulation of regulatory measures to control PM pollution in China and elsewhere.

Water uptake of multicomponent organic mixtures and their influence on hygroscopicity of inorganic salts

The hygroscopic behaviors of atmospherically relevant multicomponent water soluble organic compounds (WSOCs) and their effects on ammonium sulfate (AS) and sodium chloride were investigated using a hygroscopicity tandem differential mobility analyzer (HTDMA) in the relative humidity (RH) range of 5%-90%. The measured hygroscopic growth was compared with predictions from the Extended-Aerosol Inorganics Model (E-AIM) and Zdanovskii-Stokes-Robinson (ZSR) method. The equal mass multicomponent WSOCs mixture containing levoglucosan, succinic acid, phthalic acid and humic acid showed gradual water uptake without obvious phase change over the whole RH range. It was found that the organic content played an important role in the water uptake of mixed particles. When organic content was dominant in the mixture (75%), the measured hygroscopic growth was higher than predictions from the E-AIM or ZSR relation, especially under high RH conditions. For mass fractions of organics not larger than 50%, the hygroscopic growth of mixtures was in good agreement with model predictions. The influence of interactions between inorganic and organic components on the hygroscopicity of mixed particles was related to the salt type and organic content. These results could contribute to understanding of the hygroscopic behaviors of multicomponent aerosol particles.

Size distribution and sources of humic-like substances in particulate matter at an urban site during winter

This study investigates the size distribution and possible sources of humic-like substances (HULIS) in ambient aerosol particles collected at an urban site in Gwangju, Korea during the winter of 2015. A total of 10 sets of size-segregated aerosol samples were collected using a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI), and the samples were analyzed to determine the mass as well as the presence of ionic species (Na(+), NH4(+), K(+), Ca(2+), Mg(2+), Cl(-), NO3(-), and SO4(2-)), water-soluble organic carbon (WSOC) and HULIS. The separation and quantification of the size-resolved HULIS components from the MOUDI samples was accomplished using a Hydrophilic-Lipophilic Balanced (HLB) solid phase extraction method and a total organic carbon analyzer, respectively. The entire sampling period was divided into two periods: non-Asian dust (NAD) and Asian dust (AD) periods. The contributions of water-soluble organic mass (WSOM = 1.9 × WSOC) and HULIS (=1.9 × HULIS-C) to fine particles (PM1.8) were approximately two times higher in the NAD samples (23.2 and 8.0%) than in the AD samples (12.8 and 4.2%). However, the HULIS-C/WSOC ratio in PM1.8 showed little difference between the NAD (0.35 ± 0.07) and AD (0.35 ± 0.05) samples. The HULIS exhibited a uni-modal size distribution (@0.55 μm) during NAD and a bimodal distribution (@0.32 and 1.8 μm) during AD, which was quite similar to the mass size distributions of particulate matter, WSOC, NO3(-), SO4(2-), and NH4(+) in both the NAD and AD samples. The size distribution characteristics and the results of the correlation analyses indicate that the sources of HULIS varied according to the particle size. In the fine mode (≤1.8 μm), the HULIS composition during the NAD period was strongly associated with secondary organic aerosol (SOA) formation processes similar to those of secondary ionic species (cloud processing and/or heterogeneous reactions) and primary emissions during the biomass burning period, and during the AD period, it was only associated with SOA formation. In the coarse mode (3.1-10 μm), it was difficult to identify the HULIS sources during the NAD period, and during the AD period, the HULIS was most likely associated with soil-related particles [Ca(NO3]2 and CaSO4) and/or sea-salt particles (NaNO3 and Na2SO4).

Characterization of PM2.5 and PM10 fugitive dust source profiles in the Athabasca Oil Sands Region

Geological samples were collected from 27 representative locations in the Athabasca Oil Sands Region (AOSR) in Alberta, Canada. These samples were resuspended onto filter substrates for PM2.5 and PM10 size fractions. Samples were analyzed for 229 chemical species, consisting of elements, ions, carbon, and organic compounds. These chemical species are normalized to gravimetric mass to derive individual source profiles. Individual profiles were grouped into six categories typical of those used in emission inventories: paved road dust, unpaved road dust close to and distant from oil sand operations, overburden soil, tailings sands, and forest soils. Consistent with their geological origin, the major components are minerals, organic and elemental carbon, and ions. The sum of five major elements (i.e., Al, Si, K, Ca, and Fe) and their oxidized forms account for 25-40% and 45-82% of particulate matter (PM) mass, respectively. Si is the most abundant element, averaging 17-18% in the Facility (oil sand operations) and 23-27% in the Forest profiles. Organic carbon is the second most abundant species, averaging 9-11% in the Facility and 5-6% in the Forest profiles. Elemental carbon abundance is 2-3 times higher in Facility than Forest profiles. Sulfate abundance is ~7 times higher in the Facility than in the Forest profiles. The ratios of cation/anion and base cation (sum of Na+, Mg2+, K+, and Ca2+)/nitrogen- and sulfur-containing ions (sum of NH4+, NO2-, NO3-, and SO4(2-)) exceed unity, indicating that the soils are basic. Lead (Pb) isotope ratios of facility soils are similar to the AOSR stack and diesel emissions, while those of forest soils have much lower 206Pb/207Pb and 208Pb/207Pb ratios. High-molecular-weight n-alkanes (C25-C40), hopanes, and steranes are more than an order of magnitude more abundant in Facility than Forest profiles. These differences may be useful for separating anthropogenic from natural sources of fugitive dust at receptors.

IMPLICATIONS

Several organic compounds typical of combustion emissions and bitumen are enriched relative to forest soils for fugitive dust sources near oil sands operations, consistent with deposition uptake by biomonitors. AOSR dust samples are alkaline, not acidic, indicating that potential acid deposition is neutralized. Chemical abundances are highly variable within emission inventory categories, implying that more specific subcategories can be defined for inventory speciation.

Decreasing Aerosol Water Is Consistent with OC Trends in the Southeast U.S

Water is a ubiquitous and abundant component of atmospheric aerosols. It influences light scattering, the hydrological cycle, atmospheric chemistry, and secondary particulate matter (PM) formation. Despite the critical importance of aerosol liquid water, mass concentrations are not well-known. Using speciated ion and meteorological data from the Southeastern Aerosol Research and Characterization network, we employ the thermodynamic model ISORROPIAv2.1 to estimate water mass concentrations and evaluate trends from 2001 to 2012 in urban and rural locations. The purpose of this study is to better understand the historical trends of aerosol liquid water in the southeast U.S. in the context of improved air quality and recently noted reductions in particulate organic carbon (OC). Aerosol water mass concentrations decrease by ∼79% from 2001 to 2012 in the region. Decreases are more prominent in rural than in urban areas. Fractional contribution of water to PM also decreases during the same time period, and this is consistent with recently noted improvements in visibility. These findings agree with the hypotheses that aerosol liquid water facilitates formation of biogenic secondary organic aerosol (SOA) and that biogenically derived SOA is modulated in the presence of anthropogenic perturbations.

Measurements of the HO2 uptake coefficients onto single component organic aerosols

Measurements of HO2 uptake coefficients (γ) were made onto a variety of organic aerosols derived from glutaric acid, glyoxal, malonic acid, stearic acid, oleic acid, squalene, monoethanol amine sulfate, monomethyl amine sulfate, and two sources of humic acid, for an initial HO2 concentration of 1 × 10(9) molecules cm(-3), room temperature and at atmospheric pressure. Values in the range of γ < 0.004 to γ = 0.008 ± 0.004 were measured for all of the aerosols apart from the aerosols from the two sources of humic acid. For humic acid aerosols, uptake coefficients in the range of γ = 0.007 ± 0.002 to γ = 0.09 ± 0.03 were measured. Elevated concentrations of copper (16 ± 1 and 380 ± 20 ppb) and iron (600 ± 30 and 51 000 ± 3000 ppb) ions were measured in the humic acid atomizer solutions compared to the other organics that can explain the higher uptake values measured. A strong dependence upon relative humidity was also observed for uptake onto humic acid, with larger uptake coefficients seen at higher humidities. Possible hypotheses for the humidity dependence include the changing liquid water content of the aerosol, a change in the mass accommodation coefficient or in the Henry's law constant.

Dissolved organic matter in urban stormwater runoff at three typical regions in Beijing: chemical composition, structural characterization and source identification

Chemical composition, structural characterization and source identification of DOM in urban stormwater runoff collected from three typical regions in Beijing were investigated.

Photosensitised humic-like substances (HULIS) formation processes of atmospheric significance: a review

Photosensitised reactions can produce compounds that closely resemble the humic-like substances (HULIS) occurring in atmospheric aerosols. The relevant processes have been observed in the laboratory, in both gas-solid systems and the aqueous phase. They involve triplet sensitisers (such as benzophenones, anthraquinones and nitroaromatic compounds, which yield reactive triplet states after sunlight absorption) or photogenerated oxidants like (•)OH, in the presence of substrates that undergo oligomerisation reactions upon oxidation. Formation of higher molecular weight compounds, modification of the wettability properties of organic films and photoproduction of substances with humic-like fluorescence properties have been observed as a consequence of the photosensitised reactions. Ozone plays an important but still not completely clear role in gas-solid systems.

Nuclear magnetic resonance spectroscopy for determining the functional content of organic aerosols: a review

The knowledge deficit of organic aerosol (OA) composition has been identified as the most important factor limiting our understanding of the atmospheric fate and implications of aerosol. The efforts to chemically characterize OA include the increasing utilization of nuclear magnetic resonance spectroscopy (NMR). Since 1998, the functional composition of different types, sizes and fractions of OA has been studied with one-dimensional, two-dimensional and solid state proton and carbon-13 NMR. This led to the use of functional group ratios to reconcile the most important sources of OA, including secondary organic aerosol and initial source apportionment using positive matrix factorization. Future research efforts may be directed towards the optimization of experimental parameters, detailed NMR experiments and analysis by pattern recognition methods to identify the chemical components, determination of the NMR fingerprints of OA sources and solid state NMR to study the content of OA as a whole.

Method for characterization of low molecular weight organic acids in atmospheric aerosols using ion chromatography mass spectrometry

The structural composition of PM2.5 monitored in the atmosphere is usually divided by the analysis of organic carbon, black (also called elemental) carbon, and inorganic salts. The characterization of the chemical composition of aerosols represents a significant challenge to analysts, and studies are frequently limited to determination of aerosol bulk properties. To better understand the potential health effects and combined interactions of components in aerosols, a variety of measurement techniques for individual analytes in PM2.5 need to be implemented. The method developed here for the measurement of organic acids achieves class separation of aliphatic monoacids, aliphatic diacids, aromatic acids, and polyacids. The selective ion monitoring capability of a triple quadropole mass analyzer was frequently capable of overcoming instances of incomplete separations. Standard Reference Material (SRM) 1649b Urban Dust was characterized; 34 organic acids were qualitatively identified, and 6 organic acids were quantified.

On the water-soluble organic nitrogen concentration and mass size distribution during the fog season in the Po Valley, Italy

The study of organic nitrogen gained importance in recent decades due to its links with acid rain, pollution, and eutrophication. In this study, aerosol and fog water samples collected from two sites in Italy during November 2011 were analyzed to characterize their organic nitrogen content. Organic nitrogen contributed 19-25% of the total soluble nitrogen in the aerosol and around 13% in fog water. The largest water soluble organic nitrogen concentrations in the PM1.2 fraction occurred during the diurnal period with mean values of 2.03 and 2.16 μg-N m(-3) (154 and 145 nmol-N m(-3)) at Bologna and San Pietro Capofiume (SPC), respectively. The mean PM10 WSON concentration during diurnal periods at SPC was 2.30 μg-N m(-3) (164 nmol-N m(-3)) while it was 1.34 and 0.82 μg-N m(-3) (95.7 and 58.5 nmol-N m(-3)) in the night and fog water samples, respectively. Aerosol mass distribution profiles obtained during fog changed significantly with respect to those estimated in periods without fog periods due to fog scavenging, which proved to be over 80% efficient. Linear correlations suggested secondary processes related to combustion and, to a lesser extent, biomass burning, as plausible sources of WSON. Regarding the inorganic nitrogen fraction, the results showed that ammonium was the largest soluble inorganic nitrogen component in the samples.

Sources and characteristics of carbonaceous aerosols at Agra "World heritage site" and Delhi "capital city of India"

Agra, one of the oldest cities "World Heritage site", and Delhi, the capital city of India are both located in the border of Indo-Gangetic Plains (IGP) and heavily loaded with atmospheric aerosols due to tourist place, anthropogenic activities, and its topography, respectively. Therefore, there is need for monitoring of atmospheric aerosols to perceive the scenario and effects of particles over northern part of India. The present study was carried out at Agra (AGR) as well as Delhi (DEL) during winter period from November 2011 to February 2012 of fine particulate (PM₂.₅: d < 2.5 μm) as well as associated carbonaceous aerosols. PM₂.₅ was collected at both places using medium volume air sampler (offline measurement) and analyzed for organic carbon (OC) and elemental carbon (EC). Also, simultaneously, black carbon (BC) was measured (online) at DEL. The average mass concentration of PM₂.₅ was 165.42 ± 119.46 μg m(-3) at AGR while at DEL it was 211.67 ± 41.94 μg m(-3) which is ~27% higher at DEL than AGR whereas the BC mass concentration was 10.60 μg m(-3). The PM₂.₅ was substantially higher than the annual standard stipulated by central pollution control board and United States Environmental Protection Agency standards. The average concentrations of OC and EC were 69.96 ± 34.42 and 9.53 ± 7.27 μm m(-3), respectively. Total carbon (TC) was 79.01 ± 38.98 μg m(-3) at AGR, while it was 50.11 ± 11.93 (OC), 10.67 ± 3.56 μg m(-3) (EC), and 60.78 ± 14.56 μg m(-3) (TC) at DEL. The OC/EC ratio was 13.75 at (AGR) and 5.45 at (DEL). The higher OC/EC ratio at Agra indicates that the formation of secondary organic aerosol which emitted from variable primary sources. Significant correlation between PM₂.₅ and its carbonaceous species were observed indicating similarity in sources at both sites. The average concentrations of secondary organic carbon (SOC) and primary organic carbon (POC) at AGR were 48.16 and 26.52 μg m(-3) while at DEL it was 38.78 and 27.55 μg m(-3), respectively. In the case of POC, similar concentrations were observed at both places but in the case of SOC higher over AGR by 24 in comparison to DEL, it is due to the high concentration of OC over AGR. Secondary organic aerosol (SOA) was 42% higher at AGR than DEL which confirms the formation of secondary aerosol at AGR due to rural environment with higher concentrations of coarse mode particles. The SOA contribution in PM₂.₅ was also estimated and was ~32 and 12% at AGR and DEL respectively. Being high loading of fine particles along with carbonaceous aerosol, it is suggested to take necessary and immediate action in mitigation of the emission of carbonaceous aerosol in the northern part of India.

Functional characterization of the water-soluble organic carbon of size-fractionated aerosol in the southern Mississippi Valley

The chemical content of water-soluble organic carbon (WSOC) as a function of particle size was characterized in Little Rock, Arkansas in winter and spring 2013. The objectives of this study were to (i) compare the functional characteristics of coarse, fine and ultrafine WSOC and (ii) reconcile the sources of WSOC for periods when carbonaceous aerosol was the most abundant particulate component. The WSOC accounted for 5 % of particle mass for particles with δ_p > 0.96 μm and 10 % of particle mass for particles with δ_p < 0.96 μm. Non-exchangeable aliphatic (H-C), unsaturated aliphatic (H-C-C=), oxygenated saturated aliphatic (H-C-O), acetalic (O-CH-O) and aromatic (Ar-H) protons were determined by proton nuclear magnetic resonance (¹H-NMR). The total non-exchangeable organic hydrogen concentrations varied from 4.1 ± 0.1 nmol m^-3 for particles with 1.5 < δ_p < 3.0 μm to 73.9 ± 12.3 nmol m^-3 for particles with δ_p < 0.49 μm. The molar H/C ratios varied from 0.48 ± 0.05 to 0.92 ± 0.09, which were comparable to those observed for combustion-related organic aerosol. The R-H was the most abundant group, representing about 45 % of measured total non-exchangeable organic hydrogen concentrations, followed by H-C-O (27 %) and H-C-C= (26 %). Levoglucosan, amines, ammonium and methanesulfonate were identified in NMR fingerprints of fine particles. Sucrose, fructose, glucose, formate and acetate were associated with coarse particles. These qualitative differences of ¹H-NMR profiles for different particle sizes indicated the possible contribution of biological aerosols and a mixture of aliphatic and oxygenated compounds from biomass burning and traffic exhausts. The concurrent presence of ammonium and amines also suggested the presence of ammonium/aminium nitrate and sulfate secondary aerosol. The size-dependent origin of WSOC was further corroborated by the increasing δ¹³C abundance from -26.81 ± 0.18 ‰ for the smallest particles to -25.93 ± 0.31 ‰ for the largest particles and the relative distribution of the functional groups as compared to those previously observed for marine, biomass burning and secondary organic aerosol. The latter also allowed for the differentiation of urban combustion-related aerosol and biological particles. The five types of organic hydrogen accounted for the majority of WSOC for particles with δ_p > 3.0 μm and δ_p < 0.96 μm.

Comparative study for separation of atmospheric humic-like substance (HULIS) by ENVI-18, HLB, XAD-8 and DEAE sorbents: elemental composition, FT-IR, 1H NMR and off-line thermochemolysis with tetramethylammonium hydroxide (TMAH)

Humic-like substances (HULIS) are significant constituents of aerosols, and the isolation and characterization of HULIS by solid-phase extraction methods are dependent on the sorbents used. In this study, we used the following five methods: ENVI-18, HLB-M, HLB-N, XAD-8 and DEAE, to isolate atmospheric HULIS at an urban site. Then we conducted a comparative investigation of the HULIS chemical characteristics by means of elemental analysis, Fourier transform infrared spectroscopy, (1)H nuclear magnetic resonance spectroscopy and off-line thermochemolysis with tetramethylammonium hydroxide. The results indicate that HULIS isolated using different methods show many similarities in chemical composition and structure. Some differences were however also observed between the five isolated HULIS: HULISHLB-M contains a relatively high content of OCH group, compared to HULISENVI-18 and HULISXAD-8; HULISXAD-8 contains a relatively high content of hydrophobic and aromatic components, compared to HULISENVI-18 and HULISHLB-M; HULISDEAE contains the highest content of aromatic functional groups, as inferred by (1)H NMR spectra, but a great amount of salts generally present in the HULISDEAE and thereby limited the choices for characterizing the materials (i.e., elemental analysis and TMAH thermochemolysis); HULISHLB-N has relatively high levels of H and N, a high N/C atomic ratio, and includes N-containing functional groups, which suggests that it has been altered by 2% ammonia introduced in the eluents. In summary, we found that ENVI-18, HLB-M, and XAD-8 are preferable methods for isolation and characterization of HULIS in atmospheric aerosols. These results also suggest that caution is required when applying DEAE and HLB-N isolating methods for characterizing atmospheric HULIS.

Measurement of humic-like substances in aerosols: a review

Aerosol-phase humic-like substances (HULIS) have received increasingly attention due to their universal ambient presence, active participation in atmospheric chemistry and important environmental and health effects. In last decade, intensive field works have promoted development of quantification and analysis method, unearthed spatio-temporal variation, and proved evidence for source identification of HULIS. These important developments were summarized in this review to provide a global perspective of HULIS. The diverse operational HULIS definitions were gradually focused onto several versions. Although found globally in Europe, Asia, Australasia and North America, HULIS are far more typical in continental and near-ground aerosols. HULIS concentrations varied from <1 μg/m(3) to >13 μg/m(3), with their carbon fraction making up 9%-72% of water soluble organic carbon. Dominant HULIS source was suggested as secondary processes and biomass burning, with the detailed formation pathways suggested and verified in laboratory works.

Atmospheric aerosol water-soluble organic carbon measurement: a theoretical analysis

The measurement of Water-Soluble Organic Carbon (WSOC) in atmospheric aerosol is usually carried out by sample collection on filters, extraction in ultrapure water, filtration, and measurement of the total organic carbon. This paper investigates the role of different conditions of sampling and extraction as well as the range of solubilities of the organic compounds that contribute to the WSOC. The sampling and extraction of WSOC can be described by a single parameter, P, expressing the ratio of water used per volume of air sampled on the analyzed filter. Two cases are examined in order to bound the range of interactions of the various organic aerosol components with each other. In the first we assume that the organic species form an ideal solution in the particle and in the second that the extraction of a single compound is independent of the presence of the other organics. The ideal organic solution model predicts that species with water solubility as low as 10(-4) g L(-1) contribute to the measured WSOC. In the other end, the independent compounds model predicts that low-solubility (as low as 10(-7) g L(-1)) compounds are part of the WSOC. Studies of the WSOC composition are consistent with the predictions of the ideal organic solution model. A value of P = 0.1 cm(3) m(-3) is proposed for the extraction of WSOC for typical organic aerosol concentrations (1-10 μg m(-3)). WSOC measurements under high concentration conditions often used during source sampling will tend to give low WSOC values unless higher P values are used.

Seasonal and air mass trajectory effects on dissolved organic matter of bulk deposition at a coastal town in south-western Europe

Rainwater contains a complex mixture of organic compounds which may influence climate, terrestrial and maritime ecosystems and thus human health. In this work, the characteristics of DOM of bulk deposition at a coastal town on the southwest of Europe were assessed by UV-visible and three-dimensional excitation-emission matrix fluorescence spectroscopies and by dissolved organic carbon (DOC) content. The seasonal and air mass trajectory effects on dissolved organic matter (DOM) of bulk deposition were evaluated. The absorbance at 250 nm (UV(250 nm)) and integrated fluorescence showed to be positively correlated with each other, and they were also positively correlated to the DOC in bulk deposition, which suggest that a constant fraction of DOM is likely to fluoresce. There was more chromophoric dissolved organic matter (CDOM) present in summer and autumn seasons than in winter and spring. Bulk deposition associated with terrestrial air masses contained a higher CDOM content than bulk deposition related to marine air masses, thus highlighting the contribution of terrestrial/anthropogenic sources.

First spectroscopic study on the structural features of dissolved organic matter isolated from rainwater in different seasons

The complexity of rainwater dissolved organic matter (DOM) and the large percentage considered uncharacterized has made it difficult to determine the role of rainwater DOM in regional and global carbon budgets. Recent studies have concentrated on determining the structural characteristics of the bulk DOM in rainwater, but a comparison between the structural characteristics of rainwater DOM from different seasons is lacking. In this work, DOM was extracted from rainwater collected in different seasons by a procedure based on adsorption onto DAX-8 resin and a comparison between the spectroscopic characteristics of extracted DOM was performed using UV-visible, excitation-emission matrix (EEM) fluorescence and (1)H NMR spectroscopies. Similar structural characteristics were observed for extracted DOM from the different seasons: high content of aliphatic structures, hydroxy and alkoxy groups, carbonyl groups and unsaturated carbon atoms, and low content of aromatic structures when compared with aliphatic structures. The obtained results suggest a model of chemical structures for the extracted DOM from rainwater, as consisting mainly of aliphatic chains, with COOH, -CH(2)OH, -COCH(3), or -CH(3) terminal groups, and with only a minor aromatic component. Moreover, this study suggests that the DOM extracted from rainwater has higher aliphatic character and lower aromatic content than aquatic humic substances. Thus, the chemical characteristics of aquatic humic substances may not be good models for DOM extracted from rainwater.