Thermal degradation of 18 amino acids during pyrolytic processes

Biomass pyrolysis greatly impacts climates, ecosystem dynamics, air quality, human health, global carbon and nitrogen cycle. The emissions of nitrogen-containing compounds from biomass pyrolysis highly depend on the protein nitrogen existing in biomass. However, the quantitative kinetic information, including the rate constant and apparent activation energy of individual amino acid induced by pyrolysis are still yet to be well-constrained. Towards this, we performed a series of controlled pyrolysis experiments where 18 equimolar free amino acids standard mixtures were pyrolyzed under ambient oxygen at temperatures between 160 and 240 °C. Additionally, straw samples were pyrolyzed to understand the mechanism of combined amino acids in protein liberation to free amino acids during pyrolytic processes. Our observations indicated that an increase in heating duration and temperature promote the degradation of free amino acids. Further, the heating stability of the 18 examined amino acids varied, which could be related to the length and functional groups present in their side chains. Our result shows that the degradation processes of all examined 18 amino acids followed irreversible first-order reaction kinetics in air within the given temperature range, with their activation energy ranging from 88.5 to 137.44 kJ mol-1. The distinct distribution patterns of both combined and free amino acids in aerosol samples from straw pyrolytic processes were obtained. The kinetic information of amino acids garnered herein helps to elucidate the transformation mechanisms of nitrogenous compounds during biomass burning.

Peatland Wildfires Enhance Nitrogen-Containing Organic Compounds in Marine Aerosols over the Western Pacific

Peatland wildfires contribute significantly to the atmospheric release of light-absorbing organic carbon, often referred to as brown carbon. In this study, we examine the presence of nitrogen-containing organic compounds (NOCs) within marine aerosols across the Western Pacific Ocean, which are influenced by peatland fires from Southeast Asia. Employing ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) in electrospray ionization (ESI) positive mode, we discovered that NOCs are predominantly composed of reduced nitrogenous bases, including CHN+ and CHON+ groups. Notably, the count of NOC formulas experiences a marked increase within plumes from peatland wildfires compared to those found in typical marine air masses. These NOCs, often identified as N-heterocyclic alkaloids, serve as potential light-absorbing chromophores. Furthermore, many NOCs demonstrate pyrolytic stability, engage in a variety of substitution reactions, and display enhanced hydrophilic properties, attributed to chemical processes such as methoxylation, hydroxylation, methylation, and hydrogenation that occur during emission and subsequent atmospheric aging. During the daytime atmospheric transport, aging of aromatic N-heterocyclic compounds, particularly in aliphatic amines prone to oxidation and reactions with amine, was observed. The findings underscore the critical role of peatland wildfires in augmenting nitrogen-containing organics in marine aerosols, underscoring the need for in-depth research into their effects on marine ecosystems and regional climatic conditions.

Characteristics and source apportionment of water-soluble organic nitrogen (WSON) in PM2.5 in Hong Kong: With focus on amines, urea, and nitroaromatic compounds

Water-soluble organic nitrogen (WSON) is ubiquitous in fine particulate matter (PM2.5) and poses health and environmental risks. However, there is limited knowledge regarding its comprehensive speciation and source-specific contributions. Here, we conducted chemical characterization and source apportionment of WSON in 65 PM2.5 samples collected in Hong Kong during a 1-yr period. Using various mass-spectrometry-based techniques, we quantified 22 nitrogen-containing organic compounds (NOCs), including 17 nitroaromatics (NACs), four amines, and urea. The most abundant amine and NACs were dimethylamine and 4-nitrocatechol, respectively. Two secondary (i.e., secondary formation and secondary nitrate) and five primary sources (i.e., sea salt, fugitive dust, marine vessels, vehicle exhaust, and biomass burning) of WSON and these three categories of NOCs were identified. Throughout the year, secondary sources dominated WSON formation (69.0%), while primary emissions had significant contributions to NACs (77.1%), amines (75.9%), and urea (83.7%). Fugitive dust was the leading source of amines and urea, while biomass burning was the main source of NACs. Our multi-linear regression analysis revealed the significant role of sulfate, NO3, nitrate, liquid water content, and particle pH on WSON formation, highlighting the importance of nighttime NO3 processing and heterogeneous and aqueous-phase formation of NOCs in the Hong Kong atmosphere.

Mixing states and secondary formation processes of organic nitrogen-containing single particles in Guangzhou, China

Organic nitrogen (ON) compounds play a significant role in the light absorption of brown carbon and the formation of organic aerosols, however, the mixing state, secondary formation processes, and influencing factors of ON compounds are still unclear. This paper reports on the mixing state of ON-containing particles based on measurements obtained using a high-performance single particle aerosol mass spectrometer in January 2020 in Guangzhou. The ON-containing particles accounted for 21% of the total detected single particles, and the particle count and number fraction of the ON-containing particles were two times higher at night than during the day. The prominent increase in the content of ON-containing particles with the enhancement of NOx mainly occurred at night, and accompanied by high relative humidity and nitrate, which were associated with heterogeneous reactions between organics and gaseous NOx and/or NO3 radical. The synchronous decreases in ON-containing particles and the mass absorption coefficient of water-soluble extracts at 365 nm in the afternoon may be associated with photo-bleaching of the ON species in the particles. In addition, the positive matrix factorization analysis found five factors dominated the formation processes of ON particles, and the nitrate factor (33%) mainly contributed to the production of ON particles at night. The results of this study provide unique insights into the mixing states and secondary formation processes of the ON-containing particles.

Dissecting the contributions of organic nitrogen aerosols to global atmospheric nitrogen deposition and implications for ecosystems

Atmospheric deposition of particulate organic nitrogen (ONp) is a significant process in the global nitrogen cycle and may be pivotally important for N-limited ecosystems. However, past models largely overlooked the spatial and chemical inhomogeneity of atmospheric ONp and were thus deficient in assessing global ONp impacts. We constructed a comprehensive global model of atmospheric gaseous and particulate organic nitrogen (ON), including the latest knowledge on emissions and secondary formations. Using this model, we simulated global atmospheric ONp abundances consistent with observations. Our estimated global atmospheric ON deposition was 26 Tg N yr-1, predominantly in the form of ONp (23 Tg N yr-1) and mostly from wildfires (37%), oceans (22%) and aqueous productions (17%). Globally, ONp contributed as much as 40% to 80% of the total N deposition downwind of biomass-burning regions. Atmospheric ONp deposition thus constituted the dominant external N supply to the N-limited boreal forests, tundras and the Arctic Ocean, and its importance may be amplified in a future warming climate.

Abundance and sources of organic nitrogen in fine (PM2.5) and coarse (PM2.5-10) particulate matter in urban Hong Kong

Organic nitrogen (ON) in atmospheric particles is much less monitored compared to inorganic nitrogen (IN), despite its significant contribution to atmospheric N deposition budget. In this study, we expanded a newly developed instrumental method for IN and ON in PM2.5 samples to PM10 samples. We determined the quantities of ON and IN for paired PM2.5 and PM10 samples collected at an urban coastal site in Hong Kong, southern China over a year. These measurements also allowed the determination of IN and ON abundance in the coarse PM (i.e., PM2.5-10) by taking the difference between PM10 and PM2.5. The measurement results show that ON accounted for 27.6 % and 21.1 % of total N in fine and coarse particles, respectively, and was mainly (87.7 %) distributed in the fine mode at the site. The seasonal variation of ON/total N was relatively small in PM2.5 (23.6-30.4 %) while considerably larger in coarse PM (4.3-42.1 %). Analysis aided by concurrently measured source indicators revealed that sea spray, biological particle emissions, and dust mixed with anthropogenic pollutants are potentially significant sources of ON in coarse particles. Positive matrix factorization (PMF) source apportionment further revealed that industrial emissions/coal combustion (43.6 %), soil dust emission (16.3 %), fresh sea salt emission (15.2 %), and aged sea salt (24.9 %) are major sources of PMcoarse-bound ON at the site. The contributions of industrial emissions/coal combustion and soil dust emission to ON were significantly higher in autumn and winter. Fresh sea salt emissions contributed greater proportions to ON in spring and summer, while ON associated with the aged sea salt source was higher in spring and autumn. These findings have advanced our quantitative understanding of the sources of PMcoarse-bound ON, which was scarcely determined in the past. Furthermore, the ON measurement data in fine and coarse particles helps estimate ON deposition, which has been previously under-evaluated.

Seasonal source identification and formation processes of marine particulate water soluble organic nitrogen over an offshore island in the East China Sea

Water soluble organic nitrogen (WSON) had great influences on the aerosol chemistry, hygroscopicity, marine primary productivity, as well as nitrogen biogeochemical cycles. Aerosol sampling was conducted over an offshore island in the East China Sea in four seasons of 2019, aiming to reveal the seasonal sources and secondary formation processes of marine WSON. The annual mean WSON concentration reached 1.05 ± 1.72 μg/m³ with a mean WSON/WSTN fraction of 27 %. In spring, WSON was associated with combustion emissions. The liquid-phase reaction of NH₃/NH₄⁺ with VOCs was a potential secondary formation process of WSON. In summer, WSON was mainly formed through the gaseous phase oxidation of marine biogenic precursors. In autumn, WSON showed miscellaneous sources from agricultural activities, biomass burning, and fossil fuel combustion. In addition to the contribution from primary urea, WSON could be also affected by the oxidation of biological proteinaceous matters. This explained the highest WSON concentrations and WSON/WSOC ratios in autumn. In winter, WSON was probably emitted from sea spray aerosols via the bubble-bursting processes. This study indicated that the sources of WSON over the coastal waters in the East China Sea were quite diverse, highlighting the need of more detailed characterization of marine WSON at the molecular level.

Computational chemistry of cluster: Understanding the mechanism of atmospheric new particle formation at the molecular level

New particle formation (NPF), which exerts significant influence over human health and global climate, has been a hot topic and rapidly expands field of research in the environmental and atmospheric chemistry recent years. Generally, NPF contains two processes: formation of critical nucleus and further growth of the nucleus. However, due to the complexity of the atmospheric nucleation, which is a multicomponent process, formation of critical clusters as well as their growth is still connected to large uncertainties. Detection limits of instruments in measuring specific gaseous aerosol precursors and chemical compositions at the molecular level call for computational studies. Computational chemistry could effectively compensate the deficiency of laboratory experiments as well as observations and predict the nucleation mechanisms. We review the present theoretical literatures that discuss nucleation mechanism of atmospheric clusters. Focus of this review is on different nucleation systems involving sulfur-containing species, nitrogen-containing species and iodine-containing species. We hope this review will provide a deep insight for the molecular interaction of nucleation precursors and reveal nucleation mechanism at the molecular level.

Dwindling aromatic compounds in fine aerosols from chunk coal to honeycomb briquette combustion

With the implementation of clean coal policy in China, the chunk coal has been gradually replaced by honeycomb briquette in domestic energies. In this study, the molecular composition of fine particles (PM_2.5) from chunk coal and honeycomb briquette combustion is characterized using the Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS). More than 6000 molecular formulae were detected in each PM_2.5 sample. A remarkable decrease in unsaturation and aromatic compounds was found from chunk coal to honeycomb briquette derived aerosols. Around 73.6% of the unique CHON compounds in chunk coal are considered to have aromatic structures, while it decreased to 7.3% in honeycomb briquette. Most of these nitroaromatics detected only in chunk coal are highly carcinogenic and mutagenic with 4-6 rings. Moreover, the aromatic compounds in sulfur-containing compounds also showed a significant decrease. Meanwhile, because of the perforated shape and the additives added during the production of honeycomb briquettes, there are more heteroatoms-containing molecules released from honeycomb briquette combustion, which are highly functional compounds with high molecular weight, high degree of oxidation, and low volatility. Our results provide molecular level evidence that the transformation from chunk coal to honeycomb briquette can effectively reduce the emission of aromatic compounds, which is beneficial to assessing and reducing the impacts to climate change as well as human health.

High time-resolved variations of proteins in PM2.5 during haze pollution periods in Xi'an, China

Proteinaceous matter is an important component of PM_2.5, which can cause adverse health effects and also influence the air quality and climate change. However, there is little attention to high time-resolved variations and potential role of aerosol proteins during haze pollution periods. In this study, PM_2.5 samples were first collected by a medium flow sampler in autumn and winter in Xi'an, China. Then three high time-resolved monitoring campaigns during haze pollution periods were conducted to determine the evolving characteristics of total protein concentration and explore the interactive relationship between protein and other chemical compositions. The results showed that the average protein concentration in PM_2.5 in Xi'an (5.46 ± 3.32 μg m^-3) was higher than those in most cities of China, and varied by seasons and air pollution conditions. In particular, the protein concentration in PM_2.5 increased with the increase of air quality index (AQI). The continuous variations of aerosol proteins during the haze pollution periods further showed that PM_2.5, atmospheric humidity and long-distance air mass transport exerted the significant impacts on the protein components in aerosols. Based on the present observation, it is suggested that aerosol proteins might affect the generation of secondary aerosols under haze weather conditions. The present results may provide a new possible insight into the variations and the role of aerosol proteinaceous matter during the formation and development of haze pollution.

Aerosol Proteinaceous Matter in Coastal Okinawa, Japan: Influence of Long-Range Transport and Photochemical Degradation

The characteristics, sources, and atmospheric oxidation processes of marine aerosol proteinaceous matter (APM), including total proteins and free amino acids (FAAs), were investigated using a set of 1 year total suspended particulate (TSP) samples collected in the coastal area of Okinawa Island in the western North Pacific rim. The concentrations of APM at this site (total proteins: 0.16 ± 0.10 μg m^-3 and total FAAs: 9.7 ± 5.6 ng m^-3, annual average) are comparable to those of marine APM. The major FAA species of APM are also similar to previously reported marine APM with glycine as the dominant species (31%). Based on the different seasonal trends and weak correlations of total proteins and FAAs, we found that they were contributed by different sources, especially with the influence of long-range transport from the Asian continent of northern China and Mongolia and the oceanic area of the Bohai Sea, Yellow Sea, and East China Sea. The photochemical oxidation processes of high-molecular-weight proteins releasing FAAs (especially glycine) were also considered as an important factor influencing the characteristics of APM at this site. In addition, we propose a degradation process based on the correlation with ozone and ultraviolet radiation, emphasizing their roles in the degradation of proteins. Our findings help to deepen the understanding of atmospheric photochemical reaction processes of organic aerosols.

Source and formation process impact the chemodiversity of rainwater dissolved organic matter along the Yangtze River Basin in summer

Rainwater dissolved organic matter (DOM) plays an important role in the biogeochemical cycle and evolution of organic matter in the land-atmosphere interface. To better understand their sources and molecular composition in the atmosphere, rainwater samples were collected at six different locations along the Yangtze River Basin. Based on the application of a combined approach including excitation-emission matrix (EEM) fluorescence and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), various sources (terrestrial, anthropogenic, and autochthonous sources) of rainwater DOM were revealed. Results show that the derivatives of biogenic volatile organic compounds were widely distributed and contributed to rainwater DOM along the Yangtze River Basin. In the up-river city Batang, rainwater DOM was affected by the long-range atmospheric transport due to the Indian summer monsoon. Lijiang, a city on the southeastern edge of Tibetan plateau, was related to strong local biomass burning. The industrial cities of Panzhihua and Luzhou showed large differences in organic composition due to distinct industrial types. Fuling, a district in Chongqing Municipality, was significantly contributed by aged organics from biomass burning. While rainwater DOM in Shanghai, a coastal megacity, contained a high fraction of sea spray organics. Further, more than 70% of rainwater DOM molecules are associated with 36 typical transformation mechanisms during rainwater-scavenging processes, e.g., oxidation reactions, dealkylation and decarboxylation. Our study demonstrates that local natural and anthropogenic emissions and climatic conditions strongly shaped the chemodiversity and possible precursor-product pairs of rainwater DOM along the Yangtze River Basin, which helps to better understand the biogeochemical cycles of organic matter in a large-scale watershed under the influence of human activities.

Simultaneous Determination of Aerosol Inorganic and Organic Nitrogen by Thermal Evolution and Chemiluminescence Detection

Inorganic nitrogen (IN) and organic nitrogen (ON) molecules constitute a significant part of atmospheric aerosol. Unlike IN, the total ON quantity remains largely unquantified due to a lack of a simple and direct measurement method. This analytical deficiency hinders the quantitative assessment of the various environmental and health effect impacts by aerosol ON. In this work, we developed an analyzer system that utilizes programmed thermal evolution of carbonaceous and nitrogenous aerosols and chemiluminescence detection coupled with the multivariate curve resolution data treatment to achieve simultaneous quantification of IN and ON. The system is capable of detecting IN and ON as low as 96 ng N per sample on a small filter aliquot (1 cm²) without any pretreatment. This method breakthrough opens the door to quantifying an important pool of aerosol N that was analytically inaccessible in the past and holds the promise to quantifying IN and ON in other environmental samples. As a demonstration, quantification of aerosol ON at an urban site in Hong Kong, China, in samples spanning over a year reveals ON constituting a significant fraction (9-52%) of the total aerosol nitrogen and having major source origins in both secondary formation and primary emissions.

A review of efflorescence kinetics studies on atmospherically relevant particles

The efflorescence transitions of aerosol particles have been intensively investigated due to their critical impacts on global climate and atmospheric chemistry. In the present study, we present a critical review of efflorescence kinetics focusing on three key issues: the efflorescence relative humidity (ERH) and the influence factors for aerosol ERH (e.g. particle sizes, and temperature); efflorescence processes of mixed aerosols, concerning the effect of coexisting inorganic and organic components on the efflorescence of inorganic salts; homogeneous and heterogeneous nucleation rates of pure and mixed aerosols. Among the previous studies, there are significant discrepancies for measured aerosol ERH under even the same conditions. Moreover, the interactions between organic and inorganic components remain largely unclear, causing efflorescence transition behaviours and chemical composition evolutions of certain mixed systems to be debatable. Thus, it is important to better understand efflorescence to gain insights into the physicochemical properties and characterize observed efflorescence characteristics of atmospheric particles, as well as guide further studies on aerosol hygroscopicity and reactivity.

Charge State Dependence of Amino Acid Propensity at Water Surface: Mechanisms Elucidated by Molecular Dynamics Simulations

Atmospheric aerosols contain a variety of compounds, among them free amino acids and salt ions. The pH of the aerosol droplets depends on their origin and environment. Consequently, compounds like free amino acids found in the droplets will be at different charge states, since these states to a great extent depend on the surrounding pH condition. In droplets of marine origin, amino acids are believed to drive salt ions to the water surface and a pH-dependent amino acid surface propensity will, therefore, indirectly affect many processes in atmospheric chemistry and physics such as for instance cloud condensation. To understand the surface propensity of glycine, valine, and phenylalanine at acidic, neutral, and basic pH, we used molecular dynamics (MD) simulations to investigate them at three different charge states in water. Their respective surface propensities were obtained by the means of a potential of mean force (PMF) in an umbrella sampling approach. Glycine was found to have no preference for the surface, while both valine and phenylalanine showed high propensities. Among the charge states of the surface-enriched ones, the cation, representing the amino acids at low pH, was found to have the highest affinity. Free energy decomposition revealed that the driving forces depend strongly on the nature of the amino acid and its charge state. In phenylalanine, the main factor was found to be a substantial entropy gain, likely related to the side chain, whereas in valine, hydrogen bonding to the functional groups leads to favorable energies and, in turn, affects the surface propensity. A significant gain in water-water enthalpy was seen for both valine and phenylalanine.

The Air and Sewage Pollutants from Biological Waste Treatment

The mechanical-biological waste treatment plants (MBTP), which include the municipal waste biogas plants, have an important role in sustainable urban development. Some plants are equipped with a sewage pre-treatment plant, which is then directed to the sewerage system and the treatment plant. Others, on the other hand, have only a non-drainage tank. The parameters of technological sewage (TS) or processing technology could reduce sewage contamination rates. In addition to the quality of sewage from waste treatment plants, the emission of odours is also an important problem, as evidenced by the results obtained over the sewage pumping station tank. The conducted statistical analysis shows a significant positive correlation between odour concentration (cod) and volatile organic compounds (VOCs). Analysing the individual compounds, a high positive correlation was also found—the strongest being between H2S, NH3 and VOCs. In the case of sewage compounds, the insignificant correlation between P total and other parameters was found. For the rest of the compounds, the highest positive correlation was found between COD and BOD and N-NO2 and N-NH3 as well as COD and N-NO2. The dilution of sewage is only an ad hoc solution to the problem. Further work should be aimed at reducing sewage pollution rates. The obtained results indicate large pollution of technological sewage and a high level of odour and odorants concentration. The novelty and scientific contribution presented in the paper are related to analyses of various factors on technological sewage parameters and odour and odorant emission from TS tank at biogas plant processing municipal waste, which may be an important source of knowledge on the management of TS, its disposal and minimisation of emitted compound emissions.

A Quantitative Method to Measure and Speciate Amines in Ambient Aerosol Samples

Ambient reactive nitrogen is a mix of nitrogen-containing organic and inorganic compounds. These various compounds are found in both aerosol- and gas-phases with oxidized and reduced forms of nitrogen. Aerosol-phase reduced nitrogen is predominately thought to include ammonium and amines. In ambient samples, the ammonium concentration is routinely determined, but the contribution of amines is not. We developed a method to discretely measure amines from ambient aerosol samples. It employs ion chromatography using a Thermo Scientific IonPac Dionex CS-19 column with conductivity detection and a three-step separation using a methanesulfonic acid eluent. This method allows for the quantification of 18 different amines, including the series of methylamines and the different isomers of butylamine. Almost all amines quantifiable by this technique were measured regularly when applying this method to ambient filter samples collected in Rocky Mountain National Park (RMNP) and Greeley, CO. The sum of the amines was ~0.02 µg m−3 at both sites. This increased to 0.04 and 0.09 µg m−3 at RMNP and Greeley, respectively, at the same time they were impacted by smoke. Analysis of separate, fresh biomass burning source samples, however, suggests that smoke is likely a minor emission source of amines in most environments.

Abiotic and Biological Degradation of Atmospheric Proteinaceous Matter Can Contribute Significantly to Dissolved Amino Acids in Wet Deposition

Atmospheric proteinaceous matter is characterized by ubiquity and potential bioavailability. However, little is known about the origins, secondary production processes, and biogeochemical role of proteinaceous matter in wet deposition. Precipitation samples were collected in suburban Guiyang (southwestern China) over a 1 year period to investigate their chemical components, mainly including dissolved combined amino acids (DCAAs), dissolved free AAs (DFAAs), and nonleachable particulate AAs (PAAs). Glycine was most abundant in the DFAAs, while the dominant species in DCAAs and PAAs was glutamic acid (including deaminated glutamine). The total DCAA, DFAA, and PAA concentrations peaked on average in spring (min. in summer). On average, the contribution of DCAA-nitrogen (median of 3.44%) to dissolved organic nitrogen was 5-fold higher than that of DFAA-nitrogen (median of 0.60%). Correlation analyses of AAs with ozone, nitrogen dioxide, and the quantitative degradation index suggest that DC(/F)AAs are linked with both abiotic and biological degradation of proteinaceous matter. Moreover, the high FAA scavenging ratios indicate the presence of postdepositional degradation of atmospheric proteinaceous matter. Further, the positive matrix factorization results suggest that the degradation of atmospheric proteinaceous matter markedly contributes to DCAAs and DFAAs in precipitation. Overall, the results suggest that the secondary processes involved in the degradation of atmospheric proteinaceous matter significantly promote direct bioavailability of AA-nitrogen.

Potential Increased Risk of Trisomy 18 Observed After a Fertilizer Warehouse Fire in Brazos County and TX

Background: In this paper, we aimed to investigate the potential impacts of a fire accident in a fertilizer warehouse on chromosomal anomalies, including Trisomy 21 (T21) and Trisomy (T18) among pregnancies in Brazos County, Texas. We conducted an observational study in Brazos County, TX, with all patients of T18 and T21 cases in the live births in Brazos County between 2005–2014. The prevalence of T18 and T21 before, during, and after the accident in Brazos County were calculated and compared. The Standardized Morbidity Ratio (SMR) was applied to compare the prevalence of T18 and T21 in Brazos County to the statewide prevalence in Texas after adjusting for maternal race and age. Compared with statewide risk, the risk of T18 during the impacted years in Brazos county was found to be significantly higher (SMR = 5.0, 95% Confidence Interval(CI): 2.19–9.89), while there was no significant difference before (SMR = 0.77, 0.13–2.54) and after the accident (SMR = 0.71, 0.12–2.36). However, the prevalence of T21 during the impacted years was not significantly different from those before or after the accident. This study conclusively suggests that this fertilizer fire may be related to the increased prevalence of T18 in Brazos County, though the findings warrant further investigation.

Aerosol Liquid Water Promotes the Formation of Water-Soluble Organic Nitrogen in Submicrometer Aerosols in a Suburban Forest

Water-soluble organic nitrogen (WSON) affects the formation, chemical transformations, hygroscopicity, and acidity of organic aerosols as well as biogeochemical cycles of nitrogen. However, large uncertainties exist in the origins and formation processes of WSON. Submicrometer aerosol particles were collected at a suburban forest site in Tokyo in summer 2015 to investigate the relative impacts of anthropogenic and biogenic sources on WSON formations and their linkages with aerosol liquid water (ALW). The concentrations of WSON (ave. 225 ± 100 ngN m^-3) and ALW exhibited peaks during nighttime, which showed a significant positive correlation, suggesting that ALW significantly contributed to WSON formation. Further, the thermodynamic predictions by ISORROPIA-II suggest that ALW was primarily driven by anthropogenic sulfate. Our analysis, including positive matrix factorization, suggests that aqueous-phase reactions of ammonium and reactive nitrogen with biogenic volatile organic compounds (VOCs) play a key role in WSON formation in submicrometer particles, which is particularly significant in nighttime, at the suburban forest site. The formation of WSON associated with biogenic VOCs and ALW was partly supported by the molecular characterization of WSON. The overall result suggests that ALW is an important driver for the formation of aerosol WSON through a combination of anthropogenic and biogenic sources.

Characterising Particulate Organic Nitrogen at A Savannah-Grassland Region in South Africa

Although atmospheric organic N compounds are considered to be important, especially in new particle formation and their contribution to brown carbon, these species are not that well understood. This can be partially attributed to their chemical complexity. Therefore, the aim of this study was to assess the characteristics of organic N compounds utilising comprehensive two-dimensional gas chromatography coupled with a time-of-flight mass spectrometer (GCxGC-TOFMS) in aerosol samples that were collected at a savanna-grassland background region and to determine the possible sources. 135 atmospheric organic N compounds were tentatively characterised and semi-quantified, which included amines, nitriles, amides, urea, pyridine derivatives, amino acids, nitro-and nitroso compounds, imines, cyanates and isocyanates, and azo compounds. Amines contributed to 51% of the semi-quantified concentrations, while nitriles, pyridine derivatives, and amides comprised 20%, 11%, and 8%, respectively, of the semi-quantified concentrations. Amines, nitriles, amides, and pyridine derivatives concentrations were higher during the dry season, which were attributed to meteorology and open biomass burning. Anthropogenic sources impacting air masses measured at Welgegund, as well as regional agricultural activities, were considered as the major sources of amines, while the regional influence of household combustion was most likely the main source of nitriles, amides, and pyridine derivatives. The other organic N species were most likely related to the influence of local and regional agricultural activities.

Occurrence of Aerosol Proteinaceous Matter in Urban Beijing: An Investigation on Composition, Sources, and Atmospheric Processes During the "APEC Blue" Period

Aerosol proteinaceous matter is comprised of a substantial fraction of bioaerosols. Its origins and interactions in the atmosphere remain poorly understood. We present observations of total proteins, combined, and free amino acids (CAAs and FAAs) in fine particulate matter (PM_2.5) samples in urban Beijing before and during the 2014 Asia-Pacific Economic Cooperation (APEC) summit. The decreases in proteins, CAAs and FAAs levels were observed after the implementation of restrictive emission controls. Significant changes were observed for the composition profiles in FAAs with the predominance of valine before the APEC and glycine during the APEC, respectively. These variations could be attributed to the influence of sources, atmospheric processes, and meteorological conditions. FAAs (especially valine and glycine) were suggested to be released by the degradation of high molecular weight proteins/polypeptides by atmospheric oxidants (i.e., ozone and free radicals) and nitrogen dioxide. Besides daytime reactions, nighttime chemistry was found to play an important role in the atmospheric formation of valine during the nights, suggesting the possible influence of NO₃ radicals. Our findings provide new insights into the significant impacts of atmospheric oxidation capacity on the occurrence and transformation of aerosol proteinaceous matter which may affect its environmental, climate and health effects.

Free and combined L- and D-amino acids in Arctic aerosol

Aerosol samples were collected with a high-volume cascade impactor with a 10 day sampling frequency at the Gruvebadet observatory, close to Ny-Ålesund (Svalbard Islands). A total of 42 filters were analyzed for free and combined amino acids, as they are key components of bio-aerosol. This article provides the first investigation of free and combined L- and d-amino acids in Arctic atmospheric particulate matter. The main aim of this study was to determine how these compounds are distributed in size-segregated aerosols after short-range and long-range atmospheric transport and understand the possible sources of amino acids. The total load of free amino acids ranged from 2.0 to 10.8 pmol m^-3, while combined amino acids ranged from 5.5 to 18.0 pmol m^-3. At these levels amino compounds could play a role in the chemistry of cloud condensation nuclei and fine particles, for example by influencing their buffering capacity and basicity. Free and combined amino acids were mainly found in the fine aerosol fraction (<0.49 μm) and their concentrations could be affect by several sources, the most important of which were biological primary production and biomass burning.

Characterization of the water soluble fraction in ultrafine, fine, and coarse atmospheric aerosol

Water soluble organic carbon significantly contributes to aerosol's carbon mass and its chemical composition is poorly characterized due to the huge number of species. In this study, we determined 94 water-soluble compounds: inorganic ions (Cl^-, Br^-, I^-, NO₃^-, SO₄^2-,K⁺, Mg⁺, Na⁺, NH₄⁺, Ca²⁺), organic acids (methanesulfonic acid and C₂-C₇ carboxylic acids), monosaccharides, alcohol-sugars, levoglucosan and its isomers, sucrose, phenolic compounds, free l- and d-amino acids and photo-oxidation products of α-pinene (cis-pinonic acid and pinic acid). The sampling was conducted using a micro-orifice uniform deposit impactor (MOUDI) at the urban area of Mestre-Venice from March to May 2016. The main aim of this work is to identify the source of each detected compound, evaluating its particle size distribution. Clear differences in size distributions were observed for each class of analyzed compounds. The positive matrix factorization (PMF) model was used to identify six factors related to different sources: a) primary biogenic aerosol particles with particle size > 10 μm; b) secondary sulfate contribution; c) biomass burning; d) primary biogenic aerosol particles distributed between 10 and 1 μm; e) an aged sea salt input and f) SOA pinene. Each factor was also characterized by different composition in waters soluble compounds and different particles size distribution.

Photochemical Cloud Processing of Primary Wildfire Emissions as a Potential Source of Secondary Organic Aerosol

We investigated the gas-phase chemical composition of biomass burning (BB) emissions and their role in aqueous secondary organic aerosol (aqSOA) formation through photochemical cloud processing. A high-resolution time-of-flight chemical ionization mass spectrometer using iodide reagent ion chemistry detected more than 100 gas-phase compounds from the emissions of 30 different controlled burns during the 2016 Fire Influence on Regional and Global Environments Experiment (FIREX) at the Fire Science Laboratory. Compounds likely to partition to cloudwater were selected based on high atomic oxygen-to-carbon ratio and abundance. Water solubility was confirmed by detection of these compounds in water after mist chamber collection during controlled burns and analysis using ion chromatography and electrospray ionization interfaced to high-resolution time-of-flight mass spectrometry. Known precursors of aqSOA were found in the primary gaseous BB emissions (e.g., phenols, acetate, and pyruvate). Aqueous OH oxidation of the complex biomass burning mixtures led to rapid depletion of many compounds (e.g., catechol, levoglucosan, methoxyphenol) and formation of others (e.g., oxalate, malonate, mesoxalate). After 150 min of oxidation (approximatively 1 day of cloud processing), oxalate accounted for 13-16% of total dissolved organic carbon. Formation of known SOA components suggests that cloud processing of primary BB emissions forms SOA.

High fire-derived nitrogen deposition on central African forests

Atmospheric nitrogen (N) deposition is an important determinant of N availability for natural ecosystems worldwide. Increased anthropogenic N deposition shifts the stoichiometric equilibrium of ecosystems, with direct and indirect impacts on ecosystem functioning and biogeochemical cycles. Current simulation data suggest that remote tropical forests still receive low atmospheric N deposition due to a lack of proximate industry, low rates of fossil fuel combustion, and absence of intensive agriculture. We present field-based N deposition data for forests of the central Congo Basin, and use ultrahigh-resolution mass spectrometry to characterize the organic N fraction. Additionally, we use satellite data and modeling for atmospheric N source apportionment. Our results indicate that these forests receive 18.2 kg N hectare-1 years-1 as wet deposition, with dry deposition via canopy interception adding considerably to this flux. We also show that roughly half of the N deposition is organic, which is often ignored in N deposition measurements and simulations. The source of atmospheric N is predominantly derived from intensive seasonal burning of biomass on the continent. This high N deposition has important implications for the ecology of the Congo Basin and for global biogeochemical cycles more broadly.

Free amino acids in the Arctic snow and ice core samples: Potential markers for paleoclimatic studies

The role of oceanic primary production on climate variability has long been debated. Defining changes in past oceanic primary production can help understanding of the important role that marine algae have in climate variability. In ice core research methanesulfonic acid is the chemical marker commonly used for assessing changes in past primary production. However, other organic compounds such as amino acids, can be produced and emitted into the atmosphere during a phytoplankton bloom. These species can be transported and deposited onto the ice cap in polar regions. Here we investigate the correlation between the concentration of chlorophyll-a, marker of marine primary production, and amino acids present in an ice core. For the first time, free l- and d-amino acids in Arctic snow and firn samples were determined by a sensitive and selective analytical method based on liquid chromatography coupled with tandem mass spectrometry. The new method for the determination of free amino acids concentrations was applied to firn core samples collected on April 2015 from the summit of the Holtedahlfonna glacier, Svalbard (N 79'08.424, E 13'23.639, 1120m a.s.l.). The main results of this work are summarized as follows: (1) glycine, alanine and proline, were detected and quantified in the firn core samples; (2) their concentration profiles, compared with that of the stable isotope δ¹⁸O ratio, show a seasonal cycling with the highest concentrations during the spring and summer time; (3) back-trajectories and Greenland Sea chlorophyll-a concentrations obtained by satellite measurements were compared with the amino acids profile obtained from ice core samples, this provided further insights into the present results. This study suggests that the amino acid concentrations in the ice samples collected from the Holtedahlfonna glaciers could reflect changes in oceanic phytoplankton abundance.

Water soluble organic aerosols in indo gangetic plain (IGP): Insights from aerosol mass spectrometry

Filter samples collected during winter of 2015-16 from two polluted urban locations (Allahabad and Kanpur) residing within Indo-Gangetic plain (IGP) showed high levels of water-soluble organic aerosols (WSOA). Total organic aerosols (OA) in submicron fraction, measured at Kanpur in real time via Aerosol Mass Spectrometer also showed substantially high concentration levels. WSOA to OA contribution in Kanpur was found to be very high (around 55%) indicating significant contributions from secondary OA (SOA). On average, WSOA oxidation ratio (O/C) was found to be higher (15-20%) in Kanpur than at Allahabad. WSOA from Allahabad was found to be following a much shallower slope (-0.38) in Van Krevelen diagram (H/C vs O/C plot) than Kanpur (-0.58). These differences suggest different composition and chemistry of WSOA at these two different locations. O/C ratios of WSOA were found to be much higher (~40%) than that of OA and independent of WSOA loading. Higher OA loadings were found to be associated with less oxidized primary OAs (POA) and culminated into lower WSOA/OA ratios. The presence of organo sulfate in filter samples from both locations indicate a significant amount of aqueous processing of organics. Concentrations and characteristics of water insoluble OA (WIOA) in Kanpur revealed that although they are present in significant quantity, their oxidation levels are much (almost 3 times) lower than that of WSOA. This finding indicates that less oxidized OAs are less soluble in line with the conventional wisdom. This study provides the first insight into oxidation levels and evolution of WSOA from India and also explores the interplay between WSOA and OA characteristics based on AMS measurements.

Chemical Constituents of Carbonaceous and Nitrogen Aerosols over Thumba Region, Trivandrum, India

Aerosol filter samples collected at a tropical coastal site Thumba over Indian region were analysed for water-soluble ions, total carbon and nitrogen, organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon/nitrogen and their sources for different seasons of the year. For the entire study period, the order of abundance of ions showed the dominance of secondary ions, such as SO₄^2-, NO₃^-, and NH₄⁺. On average, Mg²⁺ (56%), K⁺ (11%), SO₄^2- (8.8%), and Ca²⁺ (8.1%) contributions were from maritime influence. There was significant chloride depletion due to enhanced levels of inorganic acids, such as SO₄^2- and NO₃^-. Total carbon contributed 21% of the aerosol total suspended particulate matter in which 85% is organic carbon. Primary combustion-generated carbonaceous aerosols contributed 41% of aerosol mass for the entire study period. High average ratios of OC/EC (5.5 ± 1.8) and WSOC/OC (0.38 ± 0.11) suggest that organic aerosols are predominantly comprised of secondary species. In our samples, major fraction (89 ± 9%) was found to be inorganic nitrate in total nitrogen (TN). Good correlations (R ² ≥ 0.82) were observed between TN with NO₃^- plus NH₄⁺, indicating that nitrate and ammonium ions account for a significant portion of TN. The temporal variations in the specific carbonaceous aerosols and air mass trajectories demonstrated that several pollutants and/or their precursor compounds are likely transported from north western India and the oceanic regions.

Proteins and Amino Acids in Fine Particulate Matter in Rural Guangzhou, Southern China: Seasonal Cycles, Sources, and Atmospheric Processes

Water-soluble proteinaceous matter including proteins and free amino acids (FAAs) as well as some other chemical components was analyzed in fine particulate matter (PM_2.5) samples collected over a period of one year in rural Guangzhou. Annual averaged protein and total FAAs concentrations were 0.79 ± 0.47 μg m^-3 and 0.13 ± 0.05 μg m^-3, accounting for 1.9 ± 0.7% and 0.3 ± 0.1% of PM_2.5, respectively. Among FAAs, glycine was the most abundant species (19.9%), followed by valine (18.5%), methionine (16.1%), and phenylalanine (13.5%). Both proteins and FAAs exhibited distinct seasonal variations with higher concentrations in autumn and winter than those in spring and summer. Correlation analysis suggests that aerosol proteinaceous matter was mainly derived from intensive agricultural activities, biomass burning, and fugitive dust/soil resuspension. Significant correlations between proteins/FAAs and atmospheric oxidant (O₃) indicate that proteins/FAAs may be involved in O₃ related atmospheric processes. Our observation confirms that ambient FAAs could be degraded from proteins under the influence of O₃, and the stoichiometric coefficients of the reactions were estimated for FAAs and glycine. This finding provides a possible pathway for the production of aerosol FAAs in the atmosphere, which will improve the current understanding on atmospheric processes of proteinaceous matter.

Molecular Characterization of Nitrogen-Containing Organic Compounds in Humic-like Substances Emitted from Straw Residue Burning

The molecular composition of humic-like substances (HULIS) in different aerosol samples was analyzed using an ultrahigh-resolution mass spectrometer to investigate the influence of biomass burning on ambient aerosol composition. HULIS in background aerosols were characterized with numerous molecular formulas similar to biogenic secondary organic aerosols. The abundance of nitrogen-containing organic compounds (NOC), including nitrogen-containing bases (N-bases) and nitroaromatics, increased dramatically in ambient aerosols affected by crop residue burning in the farm field. The molecular distribution of N-bases in these samples exhibited similar patterns to those observed in smoke particles freshly emitted from lab-controlled burning of straw residues but were significantly different with those observed from wood burning. Signal intensity of the major N-bases correlated well with the atmospheric concentrations of potassium and levoglucosan. These N-bases can serve as molecular markers distinguishing HULIS from crop residue burning with from wood burning. More nitroaromatics were detected in ambient aerosols affected by straw burning than in fresh smoke aerosols, indicating that many of them are formed in secondary oxidation processes as smoke plumes evolve in the atmosphere. This study highlights the significant contribution of crop residue burning to atmospheric NOC. Further study is warranted to evaluate the roles of NOC on climate and human health.

Five primary sources of organic aerosols in the urban atmosphere of Belgrade (Serbia)

Biomass burning and primary biological aerosol particles (PBAPs) represent important primary sources of organic compounds in the atmosphere. These particles and compounds are able to affect climate and human health. In the present work, using HPLC-orbitrapMS, we determined the atmospheric concentrations of molecular markers such as anhydrosugars and phenolic compounds that are specific for biomass burning, as well as the concentrations of sugars, alcohol sugars and d- and l-amino acids (D-AAs and L-AAs) for studying PBAPs in Belgrade (Serbia) aerosols collected in September-December 2008. In these samples, high levels of all these biomarkers were observed in October. Relative percentages of vanillic (V), syringic compounds (S) and p-coumaric acid (PA), as well as levoglucosan/mannosan (L/M) ratios, helped us discriminate between open fire events and wood combustion for domestic heating during the winter. L-AAs and D-AAs (1% of the total) were observed in Belgrade aerosols mainly in September-October. During open fire events, mean D-AA/L-AA (D/L) ratio values of aspartic acid, threonine, phenylalanine, alanine were significantly higher than mean D/L values of samples unaffected by open fire. High levels of AAs were observed for open biomass burning events. Thanks to four different statistical approaches, we demonstrated that Belgrade aerosols are affected by five sources: a natural source, a source related to fungi spores and degraded material and three other sources linked to biomass burning: biomass combustion in open fields, the combustion of grass and agricultural waste and the combustion of biomass in stoves and industrial plants. The approach employed in this work, involving the determination of specific organic tracers and statistical analysis, proved useful to discriminate among different types of biomass burning events.

Marine biogenic source of atmospheric organic nitrogen in the subtropical North Atlantic

Global models estimate that the anthropogenic component of atmospheric nitrogen (N) deposition to the ocean accounts for up to a third of the ocean's external N supply and 10% of anthropogenic CO2 uptake. However, there are few observational constraints from the marine atmospheric environment to validate these findings. Due to the paucity of atmospheric organic N data, the largest uncertainties related to atmospheric N deposition are the sources and cycling of organic N, which is 20-80% of total N deposition. We studied the concentration and chemical composition of rainwater and aerosol organic N collected on the island of Bermuda in the western North Atlantic Ocean over 18 mo. Here, we show that the water-soluble organic N concentration ([WSON]) in marine aerosol is strongly correlated with surface ocean primary productivity and wind speed, suggesting a marine biogenic source for aerosol WSON. The chemical composition of high-[WSON] aerosols also indicates a primary marine source. We find that the WSON in marine rain is compositionally different from that in concurrently collected aerosols, suggesting that in-cloud scavenging (as opposed to below-cloud "washout") is the main contributor to rain WSON. We conclude that anthropogenic activity is not a significant source of organic N to the marine atmosphere over the North Atlantic, despite downwind transport from large pollution sources in North America. This, in conjunction with previous work on ammonium and nitrate, leads to the conclusion that only 27% of total N deposition to the global ocean is anthropogenic, in contrast to the 80% estimated previously.

Chemical speciation and source apportionment of fine particulate matter in Santiago, Chile, 2013

Santiago is one of the largest cities in South America and has experienced high fine particulate matter (PM2.5) concentrations in fall and winter months for decades. To better understand the sources of fall and wintertime pollution in Santiago, PM2.5 samples were collected for 24 h every weekday from March to October 2013 for chemical analysis. Samples were analyzed for mass, elemental carbon (EC), organic carbon (OC), water soluble organic carbon (WSOC), water soluble nitrogen (WSTN), secondary inorganic ions, and particle-phase organic tracers for source apportionment. Selected samples were analyzed as monthly composites for organic tracers. PM2.5 concentrations were considerably higher in the coldest months (June-July), averaging (mean ± standard deviation) 62±15 μg/m(3) in these two months. Average fine particle mass concentration during the study period was 40±20 μg/m(3). Organic matter during the peak winter months was the major component of fine particles comprising around 70% of the particle mass. Source contributions to OC were calculated using organic molecular markers and a chemical mass balance (CMB) receptor model. The four combustion sources identified were wood smoke, diesel engine emission, gasoline vehicles, and natural gas. Wood smoke was the predominant source of OC, accounting for 58±42% of OC in fall and winter. Wood smoke and nitrate were the major contributors to PM2.5. In fall and winter, wood smoke accounted for 9.8±7.1 μg/m(3) (21±15%) and nitrate accounted for 9.1±4.8 μg/m(3) (20±10%) of fine PM. The sum of secondary inorganic ions (sulfate, nitrate, and ammonium) represented about 30% of PM2.5 mass. Secondary organic aerosols contributed only in warm months, accounting for about 30% of fine PM during this time.

Heterogeneous oxidation of nitrite anion by gas-phase ozone in an aqueous droplet levitated by laser tweezers (optical trap): is there any evidence for enhanced surface reaction?

Optical trapping of micron-sized droplet morphology and heterogeneous kinetics with gas-phase ozone with nitrite in a wall-less apparatus.

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.

A seasonal nitrogen deposition budget for Rocky Mountain National Park

Nitrogen deposition is a concern in many protected ecosystems around the world, yet few studies have quantified a complete reactive nitrogen deposition budget including all dry and wet, inorganic and organic compounds. Critical loads that identify the level at which nitrogen deposition negatively affects an ecosystem are often defined using incomplete reactive nitrogen budgets. Frequently only wet deposition of ammonium and nitrate are considered, despite the importance of other nitrogen deposition pathways. Recently, dry deposition pathways including particulate ammonium and nitrate and gas phase nitric acid have been added to nitrogen deposition budgets. However, other nitrogen deposition pathways, including dry deposition of ammonia and wet deposition of organic nitrogen, still are rarely included. In this study, a more complete seasonal nitrogen deposition budget was constructed based on observations during a year-long study period from November 2008 to November 2009 at a location on the east side of Rocky Mountain National Park (RMNP), Colorado, USA. Measurements included wet deposition of ammonium, nitrate, and organic nitrogen, PM2.5 (particulate matter with an aerodynamic diameter less than 2.5 microm, nitrate, and ammonium) concentrations of ammonium, nitrate, and organic nitrogen, and atmospheric gas phase concentrations of ammonia, nitric acid, and NO2. Dry deposition fluxes were determined from measured ambient concentrations and modeled deposition velocities. Total reactive nitrogen deposition by all included pathways was found to be 3.65 kg N x ha(-1) yr(-1). Monthly deposition fluxes ranged from 0.06 to 0.54 kg N x ha(-1)yr(-1), with peak deposition in the month of July and the least deposition in December. Wet deposition of ammonium and nitrate were the two largest deposition pathways, together contributing 1.97 kg N x ha(-1)yr(-1) or 54% of the total nitrogen deposition budget for this region. The next two largest deposition pathways were wet deposition of organic nitrogen and dry deposition of ammonia; combined they contributed 1.37 kg N x ha(-1)yr(-1) or 37% of the total nitrogen deposition budget. To better understand the nitrogen cycle and key interactions between the atmosphere and biosphere we need to include as many sources and types of nitrogen as possible and understand their variability throughout the year. Here we examine the components of the nitrogen deposition budget to better understand the factors that influence the different deposition pathways and their seasonal variations.

The cycling of organic nitrogen through the atmosphere

Atmospheric organic nitrogen (ON) appears to be a ubiquitous but poorly understood component of the atmospheric nitrogen deposition flux. Here, we focus on the ON components that dominate deposition and do not consider reactive atmospheric gases containing ON such as peroxyacyl nitrates that are important in atmospheric nitrogen transport, but are probably not particularly important in deposition. We first review the approaches to the analysis and characterization of atmospheric ON. We then briefly summarize the available data on the concentrations of ON in both aerosols and rainwater from around the world, and the limited information available on its chemical characterization. This evidence clearly shows that atmospheric aerosol and rainwater ON is a complex mixture of material from multiple sources. This synthesis of available information is then used to try and identify some of the important sources of this material, in particular, if it is of predominantly natural or anthropogenic origin. Finally, we suggest that the flux of ON is about 25 per cent of the total nitrogen deposition flux.

Liquid chromatography tandem mass spectrometry method for characterization of monoaromatic nitro-compounds in atmospheric particulate matter

Nitrogen-containing organic compounds in the atmosphere have drawn attention owing to their impact on aerosol chemistry and physics and their potential adverse effects on the biosphere. Among them, nitrocatechols and their homologs have recently been associated with biomass burning. In the present study, nitrocatechols, nitrophenols, nitroguaiacols and nitrosalicylic acids (NSAs) were simultaneously quantified for the first time by using a new analytical method based on liquid chromatography/tandem mass spectrometry, which was systematically optimized and validated. Several analyte specific issues regarding the sample preparation and chromatographic analysis were addressed in order to ensure method sensitivity, precision, and accuracy. Sample matrix effects were thoroughly investigated in order to ensure method specificity. The method was found to be sensitive with limits of detection ranging from 0.1 to 1.0 μg L(-1), and with accuracy generally between 90 and 104%. The relative standard deviations for repeatability and intermediate precision were better than 4% and 9%, respectively. The method was applied to the analysis of winter and summer PM(10) samples from the city of Ljubljana, Slovenia. Aerosol concentrations as high as 152 and 134 ng m(-3) were obtained for the major aerosol nitro-aromatics: 4-nitrocatechol (4NC) and methyl-nitrocatechols (MNCs), respectively. Up to 500-times higher concentrations of 4NC and MNCs were found in winter compared to summer aerosols. The correlation analysis for winter samples showed that 4NC, MNCs, and NSAs are strongly inter-correlated (R(2)=0.84-0.96). Significant correlations between these analytes and anhydrosugars support their proposed origin from biomass burning. The studied nitro-aromatics were found to constitute a non-negligible fraction (around 1%) of the organic carbon.

Elemental composition of HULIS in the Pearl River Delta Region, China: results inferred from positive and negative electrospray high resolution mass spectrometric data

The HUmic-LIke Substances (HULIS) fraction isolated from aerosol samples collected at a rural location of the Pearl River Delta Region (PRD), China, during the harvest season was analyzed by both positive and negative mode electrospray ionization (ESI) coupled with an ultrahigh resolution mass spectrometer (UHRMS). With the remarkable resolving power and mass accuracy of ESI-UHRMS, thousands of elemental formulas were identified. Formulas detected in the positive (ESI+) and the negative (ESI-) mode complement each other due to differences in the ionization mechanism, and the use of both provides a more complete characterization of HULIS. Compounds composed of C, H, and O atoms were preferentially detected in ESI- by deprotonation, implying their acidic properties. Tandem MS and Kendrick Mass Defect analysis implies that carboxyl groups are abundant in the CHO compounds. This feature is similar to those of natural fulvic acids, but relatively smaller molecular weights are observed in the HULIS samples. A greater number of reduced nitrogen organic compounds were observed in the ESI+ compared to ESI-. Compounds with biomass burning origin including alkaloids, amino acids, and their derivatives are their probable constituents. Sulfur-containing species were dominantly detected in ESI-. The presence of sulfate fragments in the MS/MS spectra of these species and their high O/S ratios implies that they are mainly organosulfates. Organosulfates and nitrooxy-organosulfates were often the most intensive peaks in the ESI- spectra. They are believed to be products of reactive uptake of photooxidation products of reactive volatile organic compounds by acidic sulfate particles. The elemental compositions deduced from the UHRMS analysis confirm the conclusion from our previous study that biomass burning and SOA formation are both important sources of HULIS in the PRD region.

Urea: An important piece of Water Soluble Organic Nitrogen (WSON) over the Eastern Mediterranean

The role of atmospheric urea on the biogeochemical cycle of Water Soluble Organic Nitrogen (WSON) in the Eastern Mediterranean was assessed by collecting and analyzing wet and dry deposition samples and size segregated aerosols during a one year period (2006). In rain water volume weighted mean (VWM) concentration of urea was found equal to 5.5μM. In atmospheric particles the average concentration of urea in coarse and fine mode was 0.9±1.9nmol N m(-3) (median 0.0nmol N m(-3)) and 2.2±3.0nmol N m(-3) (median 1.1nmol N m(-3)), respectively. The percentage contribution of urea to WSON fraction was 0% and 20% in coarse and fine particles respectively. On an annual basis 0.81mmol m(-2) and 1.78mmol m(-2) of urea were deposited via wet and dry deposition, contributing to WSON by 10% and 11% respectively. Regression analysis of urea with the main ions and trace metals measured in parallel suggest that soil and anthropogenic activities significantly contribute to atmospheric urea. Comparison of dry deposition of urea using size segregated deposition velocities with urea collected on a glass bead collector suggested the existence of significant fraction of urea in the gas phase.

Atmospheric nitrogen deposition: revisiting the question of the importance of the organic component

The organic component of atmospheric reactive nitrogen plays a role in biogeochemical cycles, climate and ecosystems. Although its deposition has long been known to be quantitatively significant, it is not routinely assessed in deposition studies and monitoring programmes. Excluding this fraction, typically 25-35%, introduces significant uncertainty in the determination of nitrogen deposition, with implications for the critical loads approach. The last decade of rainwater studies substantially expands the worldwide dataset, giving enough global coverage for specific hypotheses to be considered about the distribution, composition, sources and effects of organic-nitrogen deposition. This data collation and meta-analysis highlights knowledge gaps, suggesting where data-gathering efforts and process studies should be focused. New analytical techniques allow long-standing conjectures about the nature and sources of organic N to be investigated, with tantalising indications of the interplay between natural and anthropogenic sources, and between the nitrogen and carbon cycles.