Measurement of phase-distributed nitrophenols in Rome ambient air

The role of nitroaromatic compounds (NACs) in constraining BrC absorption in the Indo-Gangetic Plain (IGP)

We present here the first measurements of nitroaromatic compounds (NACs) including nitrophenols (NPs), nitrocatechols (NCs) and nitrosalicylic acids (NSAs) from the Indian subcontinent and their role in constraining brown carbon (BrC) absorption. NACs at a rural receptor site in the eastern Indo-Gangetic Plain (IGP) (annual average: 185 ± 94 ng m-3) was dominated by NSAs (135 ± 77 ng m-3), followed by NPs (29 ± 11 ng m-3) and NCs (17 ± 16 ng m-3), with notable enrichments during nighttime and during the biomass burning seasons. An equilibrium absorption partitioning model estimated that >90 % of NSAs and NCs were in the particle-phase, suggesting lower degradation rates via oxidation and photolysis potentially due to year-round high relative humidity. While the contribution of NACs to organic aerosol mass was only 0.42 ± 0.23 %, their contribution to BrC absorption in the 300-450 nm range was higher by an order of magnitude (8 ± 4 %), with NCs and NSAs contributing almost equally in the low-visible (400-450 nm) range as at 365 nm. Despite having mass concentrations lower than NPs by factors of ∼2, contribution of NCs to BrC absorption at λ ≥ 400 nm was comparable to that by NPs, indicating the importance of the absorption efficiency of chromophores. The receptor model positive matrix factorization (PMF) quantified three major NAC sources: fossil fuel combustion (49 ± 15 %; annual average), secondary formation (40 ± 12 %), and biomass burning (11 ± 9 %), with variable contributions on seasonal and day-night bases. In summary, the study uncovered the significant role of NACs in constraining BrC absorption in the IGP, which stresses the importance for molecular-level characterization of BrC chromophores.

Comprehensive understanding on sources of high levels of fine particulate nitro-aromatic compounds at a coastal rural area in northern China

Nitro-aromatic compounds (NACs) are among the major components of brown carbon (BrC) in the atmosphere, causing negative impacts on regional climate, air quality, and ecological health. Due to the extensive origins, it is still a challenge to figure out the contributions and originating regions for different sources of atmospheric NACs. Here, field observations on fine particulate NACs were conducted at a coastal rural area in Qingdao, China in the winter of 2018 and 2019. The mean total concentrations of fine particulate nitro-aromatic compounds were 125.0 ± 89.5 and 27.7 ± 21.1 ng/m3 in the winter of 2018 and 2019, respectively. Among the measured eleven NACs, nitrophenols and nitrocatechols were the most abundant species. Variation characteristics and correlation analysis showed that humidity and anthropogenic primary emissions had significant influences on the NAC abundances. In this study, two tracing methods of the improved spatial concentration weighted trajectory (SCWT) model and the receptor model of positive matrix factorization (PMF) were combined to comprehensively understand the origins of NACs in fine particles at coastal Qingdao. Four major sources were identified, including coal combustion, biomass burning, vehicle exhaust, and secondary formation. Surprisingly, coal combustion was responsible for about half of the observed nitro-aromatic compounds, followed by biomass burning (∼30%). The results by SCWT demonstrated that the coal combustion dominated NACs mainly originated from the Shandong peninsula and the areas to the north and southwest, while those dominated by biomass burning primarily came from local Qingdao and the areas to the west.

Source apportionment of gaseous Nitrophenols and their contribution to HONO formation in an urban area

Nitrophenols (NPs) have significant impacts on human health, climate, and atmospheric chemistry. Despite numerous measurements of particulate NPs, still little is known about their gaseous atmospheric abundances, sources, and fate. Here, four gaseous NPs [2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), and 2-Methyl-4-nitrophenol (2-Me-4-NP)] were continuously monitored during late Spring at an urban site in Houston, Texas. Among the four NPs, 4-NP showed the highest abundance, followed by 2-Me-4-NP, 2-NP, and 2,4-DNP with average concentrations of 1.07 ± 0.19 ppt, 0.47 ± 0.12 ppt, 0.41 ± 0.16 ppt, and 0.27 ± 0.09 ppt, respectively. The positive matrix factorization (PMF) model identified seven sources: industrial NPs, secondary formation, phenol sources, acetonitrile source, natural gas/crude oil, traffic, and petrochemical industries/oil refineries. A zero-dimensional photochemical box model was used to simulate the observed 2-NP and 2,4-DNP. A 50.0% and 70.0% jNO2 was found to be consistent with the measured 2-NP and 2,4-DNP. This yields a nitrous acid (HONO) production of 7.5 ± 2.5 ppt/h from 06:00 to 18:00 Central Standard Time (CST) from both NPs. An extrapolation including other known NPs suggests a maximum HONO formation of 13.8 ppt/h. The results of this study suggest that using PMF analysis supplemented by photochemical box model provides identification of the NPs sources and their atmospheric implication to HONO formation.

Photolysis frequency of nitrophenols derived from ambient measurements

Nitrophenols, a class of important intermediate products from the oxidation of aromatics, can participate in photochemistry and influence the atmospheric oxidative capacity. However, the reported photolysis frequencies of nitrophenols show considerable discrepancies. Here, measurements of nitrophenol, and methyl nitrophenol using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) at both urban and regional sites in southern China are used to constrain photolysis frequencies of nitrophenols. Considerable concentrations with a campaign average of 58 ± 32 ppt for nitrophenol and 97 ± 59 ppt for methyl nitrophenol were observed at the regional site. Based on the in-situ measurement dataset, a steady-state calculation was performed along with a zero-dimensional box model to analyze the budgets of nitrophenols. The result indicates that both primary emission and photolysis have significant impacts on nitrophenols. Primary emission contributes up to 88 % of the total nitrophenols production while photolysis accounts for up to 98 % of the total removal rate. The dominant sink of nitrophenols is photolysis with a rate of about 3.5 % ± 1.3 % of j_NO2 for nitrophenol and 2.4 % ± 1.0 % of j_NO2 for methyl nitrophenol. The results of this study suggest that using advanced mass spectrometry to accurately measure ambient nitrophenols, supplemented by an observation-based box model for budget analysis, provides an important indication for determining photolysis rate constants of nitrophenols.

Revealing Internal Rotation and 14N Nuclear Quadrupole Coupling in the Atmospheric Pollutant 4-Methyl-2-nitrophenol: Interplay of Microwave Spectroscopy and Quantum Chemical Calculations

The structure and interactions of oxygenated aromatic molecules are of atmospheric interest due to their toxicity and as precursors of aerosols. Here, we present the analysis of 4-methyl-2-nitrophenol (4MNP) using chirped pulse and Fabry-Pérot Fourier transform microwave spectroscopy in combination with quantum chemical calculations. The rotational, centrifugal distortion, and ¹⁴N nuclear quadrupole coupling constants of the lowest-energy conformer of 4MNP were determined as well as the barrier to methyl internal rotation. The latter has a value of 106.4456(8) cm^-1, significantly larger than those from related molecules with only one hydroxyl or nitro substituent in the same para or meta positions, respectively, as 4MNP. Our results serve as a basis to understand the interactions of 4MNP with atmospheric molecules and the influence of the electronic environment on methyl internal rotation barrier heights.

Characterization of nitrated aromatic compounds in fine particles from Nanjing, China: Optical properties, source allocation, and secondary processes

Recently, nitrated aromatic compounds (NACs) have received much attention due to their role as key chromophores of brown carbon (BrC) and their impact on human health and the climate. In this study, a method for detection of 12 NACs in the atmosphere was developed and applied to the detection of 191 atmospheric samples in the northern suburbs of Nanjing in 2017. The average concentration of total NACs in Nanjing was 26.48 ng m^-3, which was lower than that in North China. The total NACs also showed obvious seasonal variation, with the highest concentration in winter (51.99 ng m^-3) and the lowest concentration in summer (11.26 ng m^-3). Moreover, the contribution of subcomponents of NACs also changed with the seasons. Nitrophenols (NPs) and nitrocatechols (NCs) were most abundant in winter, while nitrosalicylic acids (NSAs) were more abundant in summer, accounting for 30%, 27%, and 85%, respectively. The reason for this result may be due to the different sources of dominance of NACs in different seasons. The light absorption of NACs to water-soluble BrC was mainly concentrated in the 300-400 nm range, and its contribution reached the maximum at 310 nm. NPs and NCs had the highest contribution to BrC among all NACs in winter, with a range of 25-54% and 3-59%, respectively. The Positive Matrix Factorization (PMF) was used to analyze the main sources of NACs in different seasons. Secondary generation was the largest source in summer, accounting for 43.5%, and biomass combustion contributed the most in autumn, accounting for 36.7%. NACs are affected by temperature, especially in summer, and the subcomponents vary in temperature dependence. The secondary generation process of NACs is affected by NO₂ and O₃, especially when NO₂ is greater than 40 μg m^-3 and O₃ is less than 220 μg m^-3.

Secondary Formation and Impacts of Gaseous Nitro-Phenolic Compounds in the Continental Outflow Observed at a Background Site in South China

Nitro-phenolic compounds (NPs) have attracted increasing attention because of their health risks and impacts on visibility, climate, and atmospheric chemistry. Despite many measurements of particulate NPs, the knowledge of their gaseous abundances, sources, atmospheric fates, and impacts remains incomplete. Here, 18 gaseous NPs were continuously measured with a time-of-flight chemical ionization mass spectrometer at a background site in South China in autumn and winter. Abundant NPs were observed in the continental outflows from East Asia, with a total concentration up to 122.1 pptv. Secondary formation from the transported aromatics dominated the observed NPs, with mono-NPs exhibiting photochemical daytime peaks and nighttime enrichments of di-NPs and Cl-substituted NPs. The budget analysis indicates that besides the •OH oxidation of aromatics, the NO₃• oxidation also contributed significantly to the daytime mono-NPs, while the further oxidation of mono-NPs by NO₃• dominated the nocturnal formation of di-NPs. Photolysis was the main daytime sink of NPs and produced substantial HONO, which would influence atmospheric oxidation capacity in downwind and background regions. This study provides quantitative insights on the formation and impacts of gaseous NPs in the continental outflow and highlights the role of NO₃• chemistry in the secondary nitro-aromatics production that may facilitate regional pollution.

Cytotoxicity and oxidative stress induced by atmospheric mono-nitrophenols in human lung cells

Nitrophenols (NPs) are hazardous pollutants found in various environmental matrices, including ambient fine particulate matter (PM_2.5), agricultural residues, rainwater, wildfires, and industrial wastes. This study showed for the first time the effect of three pure nitrophenols and their mixture on human lung cells to provide basic understanding of the NP influence on cell elements and processes. We identified NPs in ambient PM_2.5 and secondary organic aerosol (SOA) particles generated from the photooxidation of monocyclic aromatic hydrocarbons in the U.S. EPA smog chamber. We assessed the toxicity of identified NPs and their equimolar mixture in normal bronchial epithelial (BEAS-2B) and alveolar epithelial cancer (A549) lung cell lines. The inhibitory concentration-50 (IC₅₀) values were highest and lowest in BEAS-2B cells treated with 2-nitrophenol (2NP) and 4-nitrophenol (4NP), respectively, at 24 h of exposure. The lactate dehydrogenase (LDH) assay showed that 4NP, the most abundant NP we identified in PM_2.5, was the most cytotoxic NP examined in both cell lines. The annexin-V/fluorescein isothiocyanate (FITC) analysis showed that the populations of late apoptotic/necrotic BEAS-2B and A549 cells exposed to 3NP, 4NP, and NP equimolar mixture increased between 24 and 48 h. Cellular reactive oxygen species (ROS) buildup led to cellular death post exposure to 3NP, 4NP and the NP mixtures, while 2NP induced the lowest ROS buildup. An increased mitochondrial ROS signal following NP exposure occurred only in BEAS-2B cells. The tetramethylrhodamine, methyl ester, perchlorate (TMRM) assay showed that exposed cells exhibited collapse of the mitochondrial membrane potential. TMRM signals decreased significantly only in BEAS-2B cells, and most strongly with 4NP exposures. Our results suggest that acute atmospheric exposures to NPs may be toxic at high concentrations, but not at ambient PM_2.5 concentrations. Further chronic studies with NP and NP-containing PM_2.5 are warranted to assess their contribution to lung pathologies.

Pollution levels and deposition processes of airborne organic pollutants over the central Adriatic area: Temporal variabilities and source identification

First data on polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatic compounds (NACs) in aerosols as well as of PAHs, polychlorinated biphenyls (PCBs) and NACs in bulk and wet atmospheric deposition samples were simultaneously obtained during 6-month-long field campaign at the costal central Adriatic area. Special attention was given to open-fire biomass burning episodes as extreme events common for the overall Mediterranean coastal area in order to gain a better understanding of the atmospheric variabilities and potential sources of trace organic pollutants in coastal environments. Diesel and gasoline combustion related to land and maritime traffic as well as occasional open-fire episodes (forest fires) were found to be the dominant pollution sources of PAHs in PM₁₀ particles. NACs were determined almost exclusively in samples affected by biomass burning episodes. Open-fire episodes had a strong contribution to the overall NACs atmospheric deposition fluxes. Several chlorinated congeners of PCBs were predominantly contributed in deposition samples.

Secondary Production of Gaseous Nitrated Phenols in Polluted Urban Environments

Nitrated phenols (NPs) are important atmospheric pollutants that affect air quality, radiation, and health. The recent development of the time-of-flight chemical ionization mass spectrometer (ToF-CIMS) allows quantitative online measurements of NPs for a better understanding of their sources and environmental impacts. Herein, we deployed nitrate ions as reagent ions in the ToF-CIMS and quantified six classes of gaseous NPs in Beijing. The concentrations of NPs are in the range of 1 to 520 ng m^-3. Nitrophenol (NPh) has the greatest mean concentration. Dinitrophenol (DNP) shows the greatest haze-to-clean concentration ratio, which may be associated with aqueous production. The high concentrations and distinct diurnal profiles of NPs indicate a strong secondary formation to overweigh losses, driven by high emissions of precursors, strong oxidative capacity, and high NO_x levels. The budget analysis on the basis of our measurements and box-model calculations suggest a minor role of the photolysis of NPs (<1 ppb h^-1) in producing OH radicals. NPs therefore cannot explain the underestimated OH production in urban environments. Discrepancies between these results and the laboratory measurements of the NP photolysis rates indicate the need for further studies aimed at understanding the production and losses of NPs in polluted urban environments.

One-year measurements of secondary organic aerosol (SOA) markers in the Paris region (France): Concentrations, gas/particle partitioning and SOA source apportionment

Twenty-five biogenic and anthropogenic secondary organic aerosol (SOA) markers have been measured over a one-year period in both gaseous and PM₁₀ phases in the Paris region (France). Seasonal and chemical patterns were similar to those previously observed in Europe, but significantly different from the ones observed in America and Asia due to dissimilarities in source precursor emissions. Nitroaromatic compounds showed higher concentrations in winter due to larger emissions of their precursors originating from biomass combustion used for residential heating purposes. Among the biogenic markers, only isoprene SOA marker concentrations increased in summer while pinene SOA markers did not display any clear seasonal trend. The measured SOA markers, usually considered as semi-volatiles, were mainly associated to the particulate phase, except for the nitrophenols and nitroguaiacols, and their gas/particle partitioning (GPP) showed a low temperature and OM concentrations dependency. An evaluation of their GPP with thermodynamic model predictions suggested that apart from equilibrium partitioning between organic phase and air, the GPP of the markers is affected by processes suppressing volatility from a mixed organic and inorganic phase, such as enhanced dissolution in aerosol aqueous phase and non-equilibrium conditions. SOA marker concentrations were used to apportion secondary organic carbon (SOC) sources applying both, an improved version of the SOA-tracer method and positive matrix factorization (PMF) Total SOC estimations agreed very well between both models, except in summer and during a highly processed Springtime PM pollution event in which systematic underestimation by the SOA tracer method was evidenced. As a first approach, the SOA-tracer method could provide a reliable estimation of the average SOC concentrations, but it is limited due to the lack of markers for aged SOA together with missing SOA/SOC conversion fractions for several sources.

Effects of P-nitrophenol exposure on the testicular development and semen quality of roosters

The widespread use of P-nitrophenol (PNP) as a raw material in pesticides, medicines and dyes has led to environmental pollution. PNP is a well-known endocrine disruptor in mammals and quails. This study investigated the effects of long-term PNP exposure on the testicular development and semen quality of roosters. Pubescent and postpubescent animals were given drinking water supplemented with (0 mg/L, 1 mg/L, 10 mg/L, or 100 mg/L) PNP for eight weeks or sixteen weeks. The relative testis weight, antioxidant index, serum hormone concentration, morphological changes, semen quality and expression of major steroidogenic genes were measured. The results showed that eight weeks of PNP exposure decreased CAT activity and increased H₂O₂ level in serum and testes in the 10 mg/L and 100 mg/L PNP-treated groups. Detached sperm cells were also found in the testicular tissues of the 100 mg/L PNP-treated group. After sixteen weeks of PNP exposure, daily weight gain, sperm motility, serum testosterone concentration and 3β1-hydroxysteroid dehydrogenase (HSD3β1) mRNA expression were decreased in the 100 mg/L PNP-treated group. Some vacuoles in the seminiferous epithelium in the testicular tissues were found in the 10 mg/L and 100 mg/L PNP-treated groups. In conclusion, as an endocrine disruptor, PNP exposure impaired antioxidant capacity, reduced testosterone synthesis, caused morphological changes in testes, and ultimately decreased semen quality in the roosters. The reproductive damage of PNP to roosters depended on the length of exposure time and the administered dose.

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

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

Nitrated phenols and the phenolic precursors in the atmosphere in urban Jinan, China

Nitrated phenols are a major class of brown carbon in the atmosphere and have adverse effects on human and plants health. They are emitted from combustion sources or produced by oxidation of phenolic precursors. In this study, fine particulates, total suspended particulates, and gas-phase samples were collected in urban Jinan in winter, spring, and summer, and UHPLC-MS analysis was used to determine 8 phenolic compounds and 12 nitrated phenols in these samples. The seasonal average concentrations of total phenolic compounds and total nitrated phenols were in the ranges of 2.6-18.7 ng m^-3 and 13.5-105.4 ng m^-3, respectively. The concentrations of phenolic compounds and nitrated phenols were highest in winter, followed (in decreasing order) by spring, and summer. Phenol and salicylic acid were the most abundant phenolic species in both gaseous and particulate samples. 4-Nitrophenol was the most abundant nitrated phenols in particulate matters, followed by 4-nitrocatechol and 5-nitrosalicylic acid, while 4-nitrophenol and 2,4-dinitrophenol were the dominant species in the gas phase. The distributions of phenolic compounds and nitrated phenols in fine and coarse particles and in gas and particle phases were largely dependent on the aerosol size distribution, the ambient temperature, and the compound volatility. More of them were distributed in fine particles and gas-phase in summer than in spring. It was found that phenol, catechol, methyl-catechols, 4-nitrophenol, and methyl-nitrophenols mainly derived from coal combustion, while biomass burning was the main source of cresols, 2,6-dimethyl-4-nitrophenol, 4-nitrocatechol, and methyl-nitrocatechols. In addition, secondary formation contributed the largest fraction of nitrosalicylic acids and vehicle exhaust was the major source of cresols, 2,6-dimethyl-4-nitrophenol, and 4-methyl-2,6-dinitrophenol. Further correlation analysis revealed positive correlations between nitrated phenols and corresponding phenolic precursors, indicating the important roles that phenolic precursors played in the secondary formation and abundance of nitrated phenols in the atmosphere.

Seasonal variation and sources of derivatized phenols in atmospheric fine particulate matter in North China Plain

Qualitative and quantitative analyses of derivatized phenols in Beijing and in Xinglong were performed from 2016 to 2017 using gas chromatography-mass spectrometry. The results showed substantially more severe pollution in Beijing. Of the 14 compounds detected, the total average concentration was 100 ng/m³ in Beijing, compared with 11.6 ng/m³ in Xinglong. More specifically, concentration of nitro-aromatic compounds (NACs) (81.9 ng/m³ in Beijing and 8.49 ng/m³ in Xinglong) was the highest, followed by aromatic acids (14.6 ng/m³ in Beijing and 2.42 ng/m³ in Xinglong) and aromatic aldehydes (3.62 ng/m³ in Beijing and 0.681 ng/m³ in Xinglong). In terms of seasonal variation, the highest concentrations were found for 4-nitrocatechol in winter in Beijing (79.1 ± 63.9 ng/m³) and 4-nitrophenol in winter in Xinglong (9.72 ± 8.94 ng/m³). The analysis also revealed diurnal variations across different seasons. Most compounds presented higher concentrations at night in winter because of the decreased boundary layer height and increased heating intensity. While some presented higher levels during the day, which attributed to the photo-oxidation process for summer and more biomass burning activities for autumn. Higher concentrations appeared in winter and autumn than in spring and summer, which resulted from more coal combustions and adverse meteorological conditions. The significant correlations among NACs indicated similar sources of pollution. Higher correlations presented within each subgroup than those between the subgroups. Good correlations between levoglucosan and nitrophenols, nitrocatechols, nitrosalicylic acids, with correlation coefficients (r) of 0.66, 0.69 and 0.69, respectively, indicating an important role of biomass burning among primary sources.

Emissions of fine particulate nitrated phenols from various on-road vehicles in China

Nitrated phenols are receiving increasing attention due to their adverse impacts on the environment and human health. Previous measurements have revealed the non-ignorable contribution of vehicle exhaust to atmospheric nitrated phenols in urban areas. However, there is a lack of comprehensive understanding of the emission characteristics and the total emission of nitrated phenols from current on-road traffic. This study investigated the emissions from eight passenger vehicles, eight trucks, and two taxis, with fuel types including diesel, gasoline, and compressed natural gas. Exhaust emissions were collected and measured using a mobile measurement system on two testing routes. Twelve nitrated phenols in the collected fine particulate matter were detected using ultrahigh performance liquid chromatography-mass spectrometry. Overall, the emission profiles of fine particulate nitrated phenols varied with vehicle load and fuel type. The 4-nitrophenol and its methyl derivatives were dominant nitrated phenol species emitted by the vehicles with proportions of 38.4%-68.0%, which is significantly different from the proportions of nitrated phenols emitted from biomass burning and coal combustion. The emission factors also exhibited large variations across vehicle type, fuel type, and emission standards, with relatively low values for gasoline vehicles and taxis fueled by compressed natural gas and high values for diesel vehicles. Based on the emission factors of nitrated phenols from different vehicles, the estimated total emission of nitrated phenols from on-road vehicles in China was 58.9 Mg (-86%-85% within 95% confidence interval), with diesel trucks contributing the most substantial fractions. This work highlights the very high level of emissions of nitrated phenols from diesel vehicles and provides an essential basis for atmospheric modeling and effective pollution control.

Environmental persistence, hazard, and mitigation challenges of nitroaromatic compounds

Nitroaromatic compounds (NACs) are extensively used in different industries and are synthesized in large quantity due to their heavy demand worldwide. The broad use of NACs poses a serious pollution threat. The treatment processes used for the removal of NACs are not effective and sustainable, leading to their release into the environment. The nitro group attached to benzene ring makes the compounds recalcitrant due to which they persist in the environment. Being hazardous to human as well as other living organisms, NACs are listed in the USEPA's priority pollutant group. This review provides updated information on the sources of NACs, prevalence in different environmental matrices, and recent developments in methods of their detection, with emphasis on current trends as well as future prospects. The harmful effects of NACs due to exposure through different routes are also highlighted. Further, the technologies reported for the treatment of NACs, including physico-chemical and biological methods, and the challenges faced for their effective implementation are discussed. Thus, the review discusses relevant issues in detail making suitable recommendations, which can be helpful in guiding further research in this subject.

Emissions of fine particulate nitrated phenols from the burning of five common types of biomass

Nitrated phenols are among the major constituents of brown carbon and affect both climates and ecosystems. However, emissions from biomass burning, which comprise one of the most important primary sources of atmospheric nitrated phenols, are not well understood. In this study, the concentrations and proportions of 10 nitrated phenols, including nitrophenols, nitrocatechols, nitrosalicylic acids, and dinitrophenol, in fine particles from biomass smoke were determined under three different burning conditions (flaming, weakly flaming, and smoldering) with five common types of biomass (leaves, branches, corncob, corn stalk, and wheat straw). The total abundances of fine nitrated phenols produced by biomass burning ranged from 2.0 to 99.5 μg m^-3. The compositions of nitrated phenols varied with biomass types and burning conditions. 4-nitrocatechol and methyl nitrocatechols were generally most abundant, accounting for up to 88-95% of total nitrated phenols in flaming burning condition. The emission ratios of nitrated phenols to PM_2.5 increased with the completeness of combustion and ranged from 7 to 45 ppmm and from 239 to 1081 ppmm for smoldering and flaming burning, respectively. The ratios of fine nitrated phenols to organic matter in biomass burning aerosols were comparable to or lower than those in ambient aerosols affected by biomass burning, indicating that secondary formation contributed to ambient levels of fine nitrated phenols. The emission factors of fine nitrated phenols from flaming biomass burning were estimated based on the measured mass fractions and the PM_2.5 emission factors from literature and were approximately 0.75-11.1 mg kg^-1. According to calculations based on corn and wheat production in 31 Chinese provinces in 2013, the total estimated emission of fine nitrated phenols from the burning of corncobs, corn stalks, and wheat straw was 670 t. This work highlights the apparent emission of methyl nitrocatechols from biomass burning and provides basic data for modeling studies.

Molecular composition of organic aerosols at urban background and road tunnel sites using ultra-high resolution mass spectrometry

Organic aerosol composition in the urban atmosphere is highly complex and strongly influenced by vehicular emissions which vary according to the make-up of the vehicle fleet. Normalized test measurements do not necessarily reflect real-world emission profiles and road tunnels are therefore ideal locations to characterise realistic traffic particle emissions with minimal interference from other particle sources and from atmospheric aging processes affecting their composition. In the current study, the composition of fine particles (diameter ≤2.5 μm) at an urban background site (Elms Road Observatory Site) and a road tunnel (Queensway) in Birmingham, UK, were analysed with direct infusion, nano-electrospray ionisation ultrahigh resolution mass spectrometry (UHRMS). The overall particle composition at these two sites is compared with an industrial harbour site in Cork, Ireland, with special emphasis on oxidised mono-aromatics, polycyclic aromatic hydrocarbons (PAHs) and nitro-aromatics. Different classification criteria, such as double bond equivalents, aromaticity index and aromaticity equivalent are used and compared to assess the fraction of aromatic components in the approximately one thousand oxidized organic compounds at the different sampling locations.

FT-IR product study of the reactions of NO3 radicals with ortho-, meta-, and para-cresol

Product analyses of the NO3 radical-initiated oxidation of ortho-, meta-, and para-cresol have been performed in large-volume chamber systems at the University of Wuppertal (1080 L quartz glass reactor: QUAREC) and the European Photoreactor (EUPHORE), Valencia, Spain. The reaction of O3 with NO2 was used for the in situ generation of NO3 radicals in both QUAREC and EUPHORE. In the QUAREC experiments the gas-phase reaction of ortho-cresol isomer with NO3 yielded (11.5 ± 0.8) % 6-methyl-2-nitrophenol (6M2NP), (4.4 ± 0.3) % methyl-1,4-benzoquinone (MQUIN) and (77.2 ± 6.3) % HNO3. The reaction of NO3 radicals with meta-cresol yielded (21.2 ± 1.4) % 3-methyl-2-nitrophenol (3M2NP), (22.8 ± 1.8) % 3-methyl-4-nitrophenol (3M4NP), (23.5 ± 1.8) % 5-methyl-2-nitrophenol (5M2NP), (4.2 ± 0.7) % MQUIN and (72.3 ± 6.4) % HNO3. In the reaction of NO3 radicals with para-cresol, 4-methyl-2-nitrophenol (4M2NP) and HNO3 were identified as products with yields of (41.3 ± 3.7) % and (85.0 ± 10.2) %, respectively. In the EUPHORE chamber not all products were formed at levels above the detection limit, however, in cases where detection was possible similar product yields were observed. The product formation yields determined in both chambers are compared with available literature data and a gas-phase mechanism is proposed to explain the formation of the products observed from the reaction of NO3 and with cresol isomers.

Contribution of nitrated phenols to wood burning brown carbon light absorption in Detling, United Kingdom during winter time

We show for the first time quantitative online measurements of five nitrated phenol (NP) compounds in ambient air (nitrophenol C6H5NO3, methylnitrophenol C7H7NO3, nitrocatechol C6H5NO4, methylnitrocatechol C7H7NO4, and dinitrophenol C6H4N2O5) measured with a micro-orifice volatilization impactor (MOVI) high-resolution chemical ionization mass spectrometer in Detling, United Kingdom during January-February, 2012. NPs absorb radiation in the near-ultraviolet (UV) range of the electromagnetic spectrum and thus are potential components of poorly characterized light-absorbing organic matter ("brown carbon") which can affect the climate and air quality. Total NP concentrations varied between less than 1 and 98 ng m(-3), with a mean value of 20 ng m(-3). We conclude that NPs measured in Detling have a significant contribution from biomass burning with an estimated emission factor of 0.2 ng (ppb CO)(-1). Particle light absorption measurements by a seven-wavelength aethalometer in the near-UV (370 nm) and literature values of molecular absorption cross sections are used to estimate the contribution of NP to wood burning brown carbon UV light absorption. We show that these five NPs are potentially important contributors to absorption at 370 nm measured by an aethalometer and account for 4 ± 2% of UV light absorption by brown carbon. They can thus affect atmospheric radiative transfer and photochemistry and with that climate and air quality.

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.

Development of a liquid chromatographic method based on ultraviolet-visible and electrospray ionization mass spectrometric detection for the identification of nitrocatechols and related tracers in biomass burning atmospheric organic aerosol

RATIONALE

Studying the chemical composition of biomass burning aerosol (BBA) is very important in order to assess their impact on the climate and the biosphere. In the present study, we focus on the characterization of some newly recognized biomass burning aerosol tracers including methyl nitrocatechols, nitroguaiacols and 4-nitrocatechol, but also on nitrophenols, methyl nitrophenols and nitrosalicylic acids, using liquid chromatography tandem mass spectrometry.

METHODS

For the purpose of their separation and detection in atmospheric aerosol, a new chromatographic method was initially developed based on reversed-phase chromatography coupled with ultraviolet/visible (UV/Vis) detection. The method was afterwards transferred to a liquid chromatography/electrospray ionization linear ion trap mass spectrometry (LC/ESI-LITMS) system in order to identify the targeted analytes in winter aerosol from the city of Maribor, Slovenia, using their chromatographic retention times and characteristic (-)ESI product ion (MS(2) ) spectra.

RESULTS

The fragmentation patterns of analytes obtained with LITMS are presented. Additional nitro-aromatic compounds (m/z 168 and 182) closely related to the targeted nitrocatechols and nitroguaiacols were detected in the aerosol. According to their MS(2) spectra these compounds could be attributed to methyl homologues of methyl nitrocatechols and nitroguaiacols.

CONCLUSIONS

The proposed LC/MS method results in a better separation and specificity for the targeted analytes. Several nitro-aromatic compounds were detected in urban BBA. The LC/MS peak intensity of the newly detected methyl nitrocatechols and nitroguaiacols is comparable to that of the methyl nitrocatechols, which also qualifies them as suitable molecular tracers for secondary biomass burning aerosol.

Phenol and nitrophenols in the air and dew waters of Santiago de Chile

Phenol, nitrophenols and dinitrophenols were measured in air and dews in downtown Santiago de Chile. In both systems, phenol, 2-nitrophenol (2-NP), and 4-nitrophenol (4-NP) were the compounds found in higher concentrations and with major frequency. Temporal profiles in air were compatible with a significant direct incorporation from mobile sources. The data can be explained in terms of a faster removal of 2-NP than 4-NP, with the former predominating in fresh air masses and 4-NP in more aged samples. All these compounds, as well as dinitrophenols, were found in dew waters. Simultaneous measurements in air and dew indicate that phenol present in dew exceeds that expected in equilibrated samples, while the opposite occurs with 4-NP. This last result is associated to mass transfer limitations for the highly water soluble nitroderivative.

On the effect of pH in aromatic photonitration upon nitrate photolysis

This paper studies the pH effect on the photonitration of catechol, 1-naphthol, naphthalene, and benzene. The pH trend is influenced by the generation of HNO(2) and peroxynitrous acid (HOONO) upon nitrate photolysis. HNO(2) can be involved in a direct and an indirect nitration process. Direct nitration follows the pH distribution of HNO(2) (flexus around 3). Indirect nitration, possibly involving nitrosation+oxidation, would be highest around pH3. HOONO can be involved in electrophilic nitration, where the initial formation rate of the nitroderivatives is proportional to [H(+)], or take part in nitration directly, in which case a less important pH effect in photonitration is observed. The relative importance of the various nitration pathways for each substrate determines the resulting pH effect in photonitration upon nitrate photolysis.