Nitrated Polycyclic aromatic hydrocarbons (NPAHs) widely exist in atmospheric aerosol particles are important constituents of brown carbon. Naphthalene and other polycyclic aromatic hydrocarbons (PAHs) are vital precursors of NPAHs. The NPAHs components of secondary organic aerosol (SOA) generated by the photooxidation of naphthalene under different concentrations of NO2 in chamber are on-line measured using synchrotron radiation vacuum ultraviolet photoionization aerosol mass spectrometer (VUV-PIMS) and verified off-line with optical spectrometry in this study. The results demonstrate that NO2 can promote the generation of NPAHs and formation of SOA. Using VUV-PIMS on-line detection, and combined with off-line UV-Vis and infrared spectroscopy verification, it is determined that carboxyls and naphthols are main components of naphthalene SOA particles without NO2, and nitro-naphthalene, dinitro-naphthalene, nitro-naphthol and dinitro-naphthol via the nitration of OH-naphthalene adduct and naphthol products of naphthalene are identified as principal constituents of SOA with NO2. The increase of strong chromophore of N = O of nitro group in NPAHs strengthens the absorbing ability of naphthalene SOA particles. The averaged mass absorption coefficient (< MAC>) over 200–600 nm of naphthalene SOA particles is increases gradually with the increasing concentration of NO2. The < MAC > of naphthalene SOA particles with 1000 ppb NO2 is 688 cm2/g, which is close to to that of biomass burning organic aerosol particles. These results offer the reference for exploring the formation mechanism and optical properties of NPAHs under the background of high concentration of NOx in urban atmosphere.
Research Article
Characterization of nitrated polycyclic aromatic hydrocarbons in secondary organic aerosol derived from photooxidation of naphthalene in the presence of NO2
https://doi.org/10.21203/rs.3.rs-1969205/v1
This work is licensed under a CC BY 4.0 License
Version 1
posted
You are reading this older preprint version
Nitrated polycyclic aromatic hydrocarbons
Naphthalene
Secondary organic aerosol
Laser desorption/ ionization
Reaction mechanisms
Nitrated polycyclic aromatic hydrocarbons (NPAHs) generated by the substitution of one or more hydrogen atoms in the aromatic ring of polycyclic aromatic hydrocarbons (PAHs) with nitro group (-NO2) are a common type of organic nitrogen compounds in aerosol particles (Bandowe and Meusel 2017; Lammel et al. 2020; Wietzoreck et al. 2022). Apart from the primary emission sources such as incomplete combustion of coal, petroleum and biomass (Zhao et al. 2017; Nežiková et al. 2021; Zhang et al. 2021), NPAHs can also be generated through the oxidation of PAHs by OH or NO3 radical in the atmosphere. OH or NO3 radicals are added to aromatic ring of PAHs to yield hydroxycyclohexadienyl or nitrooxycyclohexadienyl radicals, which reacted with NO2 or O2 to form NPAHs. These gaseous products can engender secondary organic aerosol (SOA) through self-condensation and gas/particle partitioning process (Keyte et al. 2013; Jariyaposit et al. 2014; Yan et al. 2021). NPAHs have strong stimulating effect, can cause mutagenicity, carcinogenicity, which seriously endanger human health (Besis et al. 2022; Sun et al. 2022). In addition, NPAHs contain strong chromophore of -NO2 group are the principal constituents of brown carbon (BrC) with strong light absorption capacity, which can absorb sunlight and reduce visibility. It is the culprit of haze pollution and has gradually become the driving factor of regional climate change (Laskin et al. 2015; Bandowe and Meusel 2017; Yan et al. 2021). The research on the formation mechanism and optical properties of NPAHs has become the hot spot in atmospheric chemistry.
The chemical composition and formation mechanism of NPAHs have been studied by smog chamber simulation. Nishino et al. (2008), Zimmermann et al. (2012, 2013), Jariyasopit et al. (2014) have carried out the chamber experiments of SOA generated by the photooxidation PAHs with NOx. SOA particles are collected by filter, extracted by methanol or other organic solvents, and NPAHs such as 2-nitronaphthalene and dimethylnitronaphthalene are measured by liquid chromatography/mass spectrometry. Xie et al. (2017) have carried out the photooxidation of naphthalene and found that nitro-naphthol and hydroxyl-nitro- naphthol dominated in SOA with NOx. Compared to SOA in the absence of NOx, SOA particles with NOx exhibit stronger light absorption, and NPAHs have the largest average contribution to light absorption at 365 nm. However, these experiments often use chromatographic column to separate NPAHs products, which require a long separation time and cumbersome procedures. In addition, filtration collection and ultrasonic extraction destroy the original state of SOA particles, and secondary reactions and loss of some components occure during the treatment process, so that NPAHs cannot be accurately analyzed (Sun et al. 2020), which affecte the research on the detection and formation mechanism of NPAHs.
The on-line aerosol mass spectrometry technology developed in recent years has provided the new opportunity to measure aerosol particles in real-time. Among them, Aerodyne aerosol mass spectrometer (AMS) and aerosol laser time-of-flight mass spectrometer (ALTOFMS) are often utilized for measurement of aerosol particles in real-time (Pratt and Prather 2018). However, AMS utilizes high-energy electron bombardment ionization, while, ALTOFMS uses high-intensity UV laser for desorption ionization, resulting in the generation of more fragment ions, which increases the difficulty of identification the components of aerosol particles (Laskin et al. 2018). Recently, vacuum ultraviolet photoionization aerosol mass spectrometer (VUV-PIMS) uses synchrotron radiation with high photon density as photoionization source, and can realize single photon ionization in vacuum ultraviolet region. This method is “soft ionization”, which obtains molecular ion peaks and produces less ionized fragments, is conducive to the analysis and identification of aerosol particle components in real-time (Dang et al. 2022). Our group has used VUV-PIMS to measure the photooxidation products of isoprene in real-time, and methacrolein, methyl vinyl ketone, glyoxal and other organics are detected (Pan et al. 2012). So, VUV-PIMS is used to on-line measure SOA particles generated by photooxidation of naphthalene with different concentrations of NO2, UV-Vis spectrophotometer and attenuated total reflection Fourier transformed infrared spectroscopy (ATR-FTIR) are used to perform off-line measurement verification in this study. Also, the averaged mass absorption coefficient (< MAC>) over 200–600 nm of naphthalene SOA is acquired, and the influence of NO2 on < MAC > of naphthalene SOA is determined. This will help to study the compoments and optics of NPAHs in urban atmosphere.
2.1 Materials
Naphthalene (> 99%), hydrogen peroxide (30%), 1,4-naphthoquinone (97%), 1-naphthol (99.0%), phthalaldehyde (97%), 2-nitro-naphthalene (99%), 2-nitro-1-naphthol (≥ 95%) and methanol (> 99%) are obtained from Sigma-Aldrich Chemical Company. NO2 (> 99.9%) is purchased from Nanjing Special Gas Factory.
2.2 Naphthalene SOA formation without and with NO2
Formation of SOA derived from the photooxidation of naphthalene without and with different concentration of NO2 is carried out in homemade chamber (Huang et al. 2018; Lu et al. 2020). After flushing the chamber, about 300 L clean air is added to the Teflon bag firstly, then a certain volume of naphthalene and hydrogen peroxide are injected into vaporization bottle with the temperature of 50℃ and filled to chamber with clean air. Also, a certain amount of NO2 is added into the chamber via Teflon lines. Finally, the Teflon bag is filled with the clean air to full volume. The chamber’s relative humidity and temperature are controlled at ~ 37% and 298 K in all experiments. 4 UV lamps with peak intensity at 254 nm are utilized to irradiate H2O2 to generate OH radicals (Thornton et al. 2020), which initiate the oxidation of naphthalene to form SOA particles. As displayed in Fig. 1, the concentrations of NOx, naphthalene and SOA are detected using NO-NO2-NOx analyzer (TEI model 42i), GC-FID (Agilent 7820A) and scanning mobility particle sizer (SMPS, TSI 3080L DMA, TSI 3775 CPC). While, the components of naphthalene SOA particles are on-line measured by VUV-PIMS. The concentrations of hydrogen peroxide and naphthalene in all experiments are controlled to 5000 ppb and 1000 ppb. 8 experiments are carried out without and with 125, 250, 500, 750, 1000, 1250 and 1500 ppb NO2, respectively. Each experiment is conducted 3 times, and the averaged result is used for data analysis.
2.3 On-line and off-line characterization the components of naphthalene SOA
The VUV-PIMS of the atomic and molecular experimental station (U14-A) of Hefei National Synchrotron Radiation Laboratory is utilized to on-line measure SOA particles (Fang et al. 2011; Pan et al. 2012). As shown in Fig. 1, naphthalene SOA particles are entered into the aerodynamic lenses to shape the collimated particle beam. The beam is volatilized on a metal plate with the temperature of 150 ℃ and transfers into the vacuum ionization chamber. It is ionized after being vertically crossed with synchrotron radiation in the ionization chamber. The ion signal is collected by reflective time-of-flight mass spectrometry. After the signal is amplified by the pre-amplifier, the data is taken by the ultrafast data acquisition card to obtain the mass peak information such as the molecular ion peak of carbonyls and NPAHs products (Fang et al. 2011; Pan et al. 2012). After illumination, naphthalene SOA particles are collected onto the polytetrafluoroethylene membrane filter (Sigma-Aldrich Chemistry Corporation, 47 mm, 0.20 mm pore size). Then, the filter is sonicated for 30 minutes to extract the components of SOA into 2% methanol solution (Feng et al. 2019; Lu et al. 2020). The UV-6100S spectrophotometer (Mapada Instruments, China) and ATR-FTIR (Thermo Nicolet iS 10, Thermo Fisher Scientific, USA) are utilized to verify the carbonyls and NPAHs components in extraction of naphthalene SOA particles.
2.4 Characterization of optical property of naphthalene SOA
Mass absorption coefficient (MAC) is commonly used to represent the light absorption property of aerosols. Particles are collected with filter, and components are extracted by organic solvent. The attenuation of light passing through the extract solution is measured by UV-Vis spectrometer to obtain the absorbance. MAC parameter can be determined with optical path length and the organic carbon concentration in extract solution (Updyke et al. 2012; Powelson et al. 2014):
In the formula (1), b is optical path, Asolution is absorbance of the extract solution at λ, and Cmass is organic carbon concentration in extract solution. On the basis of formula (2), the averaged MAC (< MAC>) is calculated by integrating within the range of λ1-λ2. The UV-6100S spectrophotometer and total organic carbon analyzer (TOC-L, Shimadzu, Japan) are used to determine the absorbance (Asolution) from 200 to 600 nm and organic carbon of extract solution, respectively. The optical path length used in this study is 1 cm. Based on the measured Asolution and Cmass, the < MAC > over 200–600 nm of naphthalene SOA is obtained according to formulas (1) and (2) (Updyke et al. 2012; Powelson et al. 2014).
3.1 Influence of NO2 on the formation of naphthalene SOA
For the mixture of 5000 ppb hydrogen peroxide and 1000 ppb naphthalene, the concentration of the formed SOA is measured with SPMS in every 15 minutes, and wall effect correction is carried out according to the procedure provided in our previous studies (Huang et al. 2013; Lu et al. 2020). The corrected mass concentration of SOA with irradiation time is displayed in Fig. 2. A small amount of particles (5 µg/m3) are detected by SMPS after 15 minutes of illumination. OH radicals react with naphthalene to yield semi- and non-volatile products, which condensed to generate SOA particles when the saturated vapor pressure is reached. Only a certain amount of naphthalene reacted, the gaseous product condensed to produce SOA particles when it reaches its saturated vapor pressure. Therefore, the concentration of SOA particles is low during the first 15 minutes of illumination. Thereafter, more OH radicals react with naphthalene to generate more products to participate in the process of gas/particle partitioning, and the concentration of SOA particles increases gradually (Jathar et al. 2016). Naphthalene is not detected by GC-FID after 210 minutes of illumination, and the corrected concentration of SOA reaches the maximum value of 235 µg/m3. Since then, no naphthalene participates in the reaction to form particles, the concentration of SOA particles corrected for the wall effect remain nearly unchanged as shown in Fig. 2.
The concentration of naphthalene SOA particles with NO2 in the concentration of 125, 250, 500, 750, 1000, 1250 and 1500 ppb are measured subsequently. Similar to the situation without NO2 illustrated in Fig. 2, the wall effect corrected mass concentration of SOA with 1000 ppb NO2 gradually increases with the illumination time. When irradiated for 210 minutes, the corrected maximum concentration of naphthalene SOA reaches 362 µg/m3, which was 54% larger than that without NO2. The mass concentration curves of naphthalene SOA under different concentration of NO2 with reaction time is similar to the situation without NO2 displayed in Fig. 2. The corrected maximum mass concentration formed from 5000 ppb hydrogen peroxide and 1000 ppb naphthalene with different concentrations of NO2 as shown in Fig. 3 is about 270–362 µg/m3, which is greater than that of naphthalene SOA formed without NO2 (235 µg/m3). These indicate that NO2 can promote the generation of naphthalene SOA. When the concentration of NO2 is larger than 1000 ppb, the corrected maximum concentration of naphthalene SOA dose not continues to increase. For characterizing the components of naphthalene SOA without and with different concentrations of NO2, on-line VUV-PIMS and off-line measurements are performed.
3.2 Characterize the components of naphthalene SOA without NO2
In order to confirm whether the VUV-PIMS can be utilized to measure organic compounds, the photoionization mass spectra of naphthalene, 1,4-naphthoquinone, 1-naphthol, phthalaldehyde, 2-nitro- naphthalene and 2-nitro-1-naphthol are measured firstly. A certain amount of the above organic is dissolved in 100 mL of 2% methanol aqueous solution to obtain 0.1mM organic standard solution, respectively, and then transferred to TSI 9302 atomizer in turn to obtain particles with the size in range of 0.1 ~ 2 µm. After drying via silica gel tube, the aerosol particles are detected by VUV-PIMS via aerodynamic lens to shape the collimated particle beam. The particle beam is volatilized on the heating plate at 150°C and transferred into the vacuum ionization chamber, and is ionized after perpendicularly intersecting with the synchrotron radiation (Fig. 1). Organics are ionized by synchrotron radiation ultraviolet with 10.6 eV, which is commonly used commercial at present (Dang et al. 2022). The generated ions are detected with reflective time-of-flight mass spectrometer, and the single photon ionization mass spectra of organics are shown in Fig. 4.
As shown in Fig. 4 (a) and (b), there is only one mass peak in the single photon ionization mass spectrum of naphthalene and 1,4-naphthoquinone, with m/z of 128 and 158 respectively. The mass-charge-ratio of these two peaks are the same as the molecular weight (Mw) of naphthalene and 1,4-naphthoquinone, which are the molecular ion peaks of naphthalene (C10H8+) and 1,4-naphthoquinone (C10H6O2+). The single photon ionization mass spectra of phthalaldehyde, 1-naphthol and 2-nitro- naphthalene are found to have two mass peaks. The mass-to-charge ratios of the mass peaks at m/z of 134, 144 and 173 shown in Fig. 4(c)-(e) are the same as their molecular weights, which are the molecular ion peaks of phthalaldehyde (C8H6O2+), 1-naphthol (C10H7OH+) and 2-nitro-naphthalene (C10H7NO2+), respectively. The mass peak of m/z 77 presented in Fig. 4(c) is identified as the benzene ion peak (C6H5+) produced by the cracking of C-O bond in phthalaldehyde molecular ion peak followed by the loss of aldehyde group. Figure 4(d) shows a weak mass spectrum peak with m/z of 127, which corresponds to the naphthalene related molecular ion peak ([M-H]+, C10H7+) formed from the loss of hydroxyl group in 1-naphthol molecular ion. While, the mass peak of m/z 127 in Fig. 4(e) is the naphthalene related molecular ion peak m/z of 127 ([M-H]+, C10H7+), which is formed from the fragmentation of C-N bond in 2-nitro-naphthalene molecular ion peak to loss of the nitro group. Similarly, the mass-charge-ratio of the mass peak at 189 in the single photon ionization mass spectrum of 2-nitro-1-naphthol displayed in Fig. 4(f) is equal to the molecular weight of 2-nitro-1-naphthol, which is its molecular ionization peak (C10H6OHNO2+). The mass peak with m/z of 143 may correspond to the naphthol related molecular ion peak (C10H6OH+) generated by the fragmentation of C-O bond in 2-nitro-1-naphthol molecular ion peak to lose the nitro group. The mass peak at 126 is identified as the naphthalene related molecular ion peak ([M-2H]+, C10H6+) (Mysak et al. 2005; Dang et al. 2022).
Silva and Prather (2002) and have measured the mass spectrum of naphthalene, resorcinol, 4-nitro- phenol and other organic particles by ALTOFMS. Organic particles are ionized by the Nd:YAG laser with 266 nm, yielding positive ion mass spectra similar to those obtained using 70 eV electron bombardment ionization. However, the use of high-intensity ultraviolet laser for desorption and ionization is easy to cause molecular ions, benzene ring and other structures to break and produce carbon ions or hydrocarbon ions, resulting in low molecular ion peak intensity and more fragment ion peaks, which increases the difficulty of component identification. Compared to the mass spectra of organics reported by Silva and Prather (2002), the molecular ion peaks in single photon mass spectrum shown in Fig. 4 are still similar. Also, the single photon mass spectrum produced by synchrotron radiation ultraviolet light with 10.6 eV nm have strong intensity of molecular ion peak and few ionized fragment peaks, which is conducive to the identification of organic compounds.
Based on the single photon mass spectra of naphthalene, 1,4-naphthoquinone and 1-naphthol, SOA particles formed from the photooxidation of naphthalene without NO2 are measured on-line subsequently, and the obtained mass spectrum is shown in Fig. 5. Since naphthalene SOA is mixture, mass peaks with m/z of 58, 77, 127, 134, 144 and 158 appear in the mass spectrum. Compared with the mass spectrum shown in Fig. 4, m/z = 127 in the single photon mass spectrum is the naphthalene related molecular ion peak ([M-H]+, C10H7+), and the mass peak at m/z = 144, its mass-to-charge ratio is equal to naphthol’s molecular weight, is the molecular ion peak of naphthol, indicating that naphthol SOA particles contain naphthol component. While, m/z = 77 is the benzene ion peak (C6H5+), the mass peak at m/z = 134 may correspond to the phthalaldehyde molecular ion peak (C8H6O2+, the mass-to-charge ratio is equal to its molecular weight). It can be inferred that naphthalene reacts with OH radical to generate phthalaldehyde. In addition, the mass peaks at m/z = 158 and 58 are identified as the molecular ion peaks of 1,4-naphthoquinone (C10H6O2+) and glyoxal (C2H2O2+), as their mass-to-charge ratios are equal to their molecular weight (Mysak et al. 2005; Dang et al. 2022). These mass spectral information demonstrate that naphthol, phthalaldehyde, 1,4- naphthoquinone and glyoxal are the products for the reaction of naphthalene with OH radicals. Compared to other mass peaks, the peak at m/z = 134 has the highest intensity, indicating that phthalaldehyde is the main component of naphthalene SOA.
The OH-initiated photooxidation of naphthalene mainly generates C1- or C2-OH–naphthalene adducts through OH addition (Keyte et al. 2013; Shiroudi et al. 2014). As shown in Fig. 6, the C1-OH–naphthalene adduct can react with O2 leading to the generation of 1-naphthol. The formed 1-naphthol can react with HO2 radical and O2 to yield a diol intermediate which rearranged to form 1,4-naphthoquinone followed by loss of H2. Also, O2 is expected to attack the C1-OH–naphthalene adduct forming energy-rich peroxy radical intermediates, which decomposes to generate phthaldialdehyde and glyoxal (Nishino et al. 2009). Thus, carboxyls and naphthols are principal constituents of SOA without NO2. These are authenticated by UV-Vis and IR spectra of extraction solution for naphthalene SOA particles without NO2 displayed in Fig. 7 and Fig. 8.
The UV-Vis absorption spectrum of extraction solution for naphthalene SOA particles without NO2 shown in Fig. 7 has no obvious peak in 400–600 nm, but an absorption band at 205 nm in ultraviolet region. The experimental results of Carlton et al. (2007) have confirmed that this absorption band is the characteristic absorption produced by the n→π* transition of the carbonyl group. In the infrared spectrum of extraction solution for naphthalene SOA particles without NO2 displayed in Fig. 8, the peak at 2978 cm− 1 is identified as the stretching vibration of the C-H on benzene ring, and the peak at 1657 cm− 1 is the stretching vibration of C = O. While, the peak at 892 cm− 1 is the characteristic absorption peak of C-H bending vibration outside the plane of aldehydes (Liu et al. 2015). Based on these mass and absorption spectrum information, it can be confirmed that the naphthalene SOA particles contain carbonyl compounds such as phthalaldehyde, glyoxal and 1,4-naphthoquinone. In addition, the UV-Vis absorption spectrum of extraction solution has an obvious absorption peak near 277 nm. According to the results of Marković and Tošović (2015), this absorption peak is the characteristic absorption peak generated by the n → π * transition between the lone pair electron of oxygen atom in the hydroxyl group in phenols and the double bond on the benzene ring. In the infrared spectrum of extraction solution, there are stretch vibration absorption peaks of -OH group and C-O bond of phenolic substances at 3667 cm− 1, 1249 cm− 1 and 1060 cm− 1 (Liu et al. 2015) (Fig. 8), demonstrating that naphthol compounds exist in naphthalene SOA particles.
3.3 Characterize NPAHs of naphthalene SOA with NO2
The naphthalene SOA particles with 1000 ppb NO2 are detected by VUV-PIMS after photooxidation, and the measured single photon mass spectrum is illustrated in Fig. 9. In addition to the mass peaks with m/z of 58 (C2H2O2+), 127 (C10H7+), 134 (C8H6O2+), 144 (C10H7OH+), there are also new mass peaks at m/z of 173, 188, 218 and 234, indicating the formation of new products. Comparing the mass spectrum shown in Fig. 9, referring to the mass spectrum of related organic compounds provided by the NIST database and the possible reaction mechanisms, the analysis of m/z = 127, 173 and 218 mass peaks shows that, m/z = 127 is the naphthalene related molecular ion peak ([M-H]+, C10H7+), m/z = 173 is 46 larger than m/z = 127, it is speculated that this mass peak corresponds to the molecular ion peak of nitro-naphthalene (C10H7NO2+) generated by replacing the hydrogen atom of naphthalene by nitro group. The mass peak of m/z = 218 is 45 larger than that of m/z = 173, which is presumed to be the molecular ion peak of dinitro-naphthalene (C10H6N2O4+) formed from the substitution of hydrogen atom on nitro-naphthalene molecule by nitro group. Similarly, m/z = 144 is the molecular ion peak of naphthol (C10H7OH+), and the mass peak of m/z = 189 is 45 larger than that of m/z = 144, which is identified as the molecular ion peak of nitro-naphthol (C10H6OHNO2+) produced by replacing the hydrogen atom of naphthol by nitro group. The mass peak of m/z = 244 is 45 larger than that of m/z = 189, which may identify as the molecular ion peak of dinitro-naphthol (C10H5OHN2O4+) formed from the substitution of hydrogen atom on the nitro-naphthol molecule with nitro group (Mysak et al. 2005; Dang et al. 2022). Compared with other mass peaks, the mass peaks at m/z = 173, 188, 218 and 234 have higher intensity, indicating that nitro-naphthalene, dinitro-naphthalene, nitro- naphthol and dinitro-naphthol are the main components of naphthalene SOA with 1000 ppb NO2.
The UV-Vis absorption spectrum of extraction solution for naphthalene SOA particles with1000 ppb NO2 is different from that in the absence of NO2 as shown in Fig. 7. There are obvious strong peaks at 220 and 362 nm. The peak at 220 nm is the characteristic absorption peak of the conjugated double bond of the naphthalene ring (Mondal et al. 2014). Xie et al. (2017) have detected a strong absorption peak at 365 nm when measuring the UV-Vis spectrum of extraction solution for naphthalene SOA particles with NOx. They proposed that this absorption band is the characteristic absorption peak generated by the n→π* transition of the nitro group in nitroaromatic compound. The absorption peak at 362 nm detected in this study is similar to the absorption peak measured by Xie et al. (2017), indicating that the extract solution contains NPAHs. The UV-Vis absorption spectrum of extraction solution contains both the characteristic absorption peaks of the conjugated double bond in naphthalene ring and the nitro group, which confirms that NPAHs are principal constituents of the naphthalene SOA particles in the presence of NO2. In addition to the stretch vibration absorption peaks of -OH group and C-O bond of phenolic substances at 3667 cm− 1, 1250 cm− 1 and 1060 cm− 1, the stretching vibration of the C-H bond on benzene ring at 2978 cm− 1, there are new peaks at 1503 and 1340 cm− 1 appeared in the infrared spectrum of extraction solution for naphthalene SOA particles with1000 ppb NO2 displayed Fig. 10. Referring to the results of Liu et al. (2015), these two absorption peaks are identified as the symmetric and antisymmetric stretching vibration absorption peaks of N = O in nitro group. This once again confirms that NPAHs are principal constituents of naphthalene SOA particles with1000 ppb NO2.
According to the research results of Nishino et al. (2008) and Zimmermann et al. (2012), the C1 and C2 OH-naphthalene adduct can undergo a competitive decomposition with O2 and NO2. As shown in Fig. 11, the N atom of NO2 can attack the OH-naphthalene adduct leading to the formation of 2-nitronaphthalene by dehydration. As reviewed by Keyte et al. (2013), 2-nitro-naphthalene can be transformed into 4-nitro- naphthalene through isomerization. The generated 2-nitro-naphthalene or 4-nitro-naphthalene further react with OH radical and NO2 to formed 2,4-dinitro-naphthalene. Also, the naphthol products react with OH radical and NO2 to generate NPAHs. OH radical extracts the hydrogen atom of phenolic hydroxyl group in1-naphthol to yield oxy-naphthyl radical. In the presence of NO2, oxy-naphthyl radical continues to react with NO2 to generate 2-nitro-1-naphthol (Nishino et al. 2008; Zimmermann et al. 2012). As suggested by Keyte et al. (2013), nitro-naphthol can also be formed from naphthol by further addition of OH and NO2 and the loss of H2O. As shown in Fig. 11, OH radical adds to C3 of 1-naphthol to form 1,3- hydroxycyclohexadienyl adduct, NO2 attacks C2 or C4 of the adduct leading to the formation of 2-nitro-1- naphthol or 4-nitro-1-naphthol by dehydration. The formed 2-nitro-1-naphthol or 4-nitro-1-naphthol further reacts with OH radical and NO2 to generate 2,4-dinitro-1-naphthol. Since the formed OH-naphthalene adduct and naphthol products immediately nitrated by OH radical and NO2, NPAHs are the main constituents of naphthalene SOA particles with NO2. The formed NPAHs have low volatility, which can quickly condense to form particles. Therefore, NO2 can promote the generation of SOA particles as illustrated in Fig. 3.
3.4 Characterization the < MAC > of naphthalene SOA
Aerosol particles affect the visibility of the atmosphere by absorbing solar radiation, and the < MAC > is commonly uesd to quantify particles’ light-absorbing properties (Updyke et al. 2012; Powelson et al. 2014). The absorbance (Asolution) from 200 to 600 nm and organic carbon mass concentration (Cmass) of naphthalene SOA extract solution is measured using UV-Vis spectrophotometer and total organic carbon analyzer. The < MAC > over 200–600 nm of naphthalene SOA without and with 125, 250, 500, 750, 1000, 1250 and 1500 ppb NO2 is achived base on the formula (1) and (2), respectively. As displayed in Fig. 12, the < MAC > of naphthalene SOA without NO2 is 295 cm2/g, which is slightly less than that of anthropogenic SOA particles measured by Updyke et al. (2012) (300 cm2/g). According to the previous measurement results, the main components of naphthalene SOA without NO2 are naphthol and carbonyls. These compounds only contain C = C and C = O, without strong chromophores and auxiliary groups (Laskin et al. 2015). Therefore, in the absence of NO2, naphthalene SOA particles have weak light absorbing ability.
The extract solutions of naphthalene SOA particles with NO2 show light-yellow to brownish-yellow. While, the measured < MAC > of naphthalene SOA particles shown in Fig. 12, is increases gradually with the increasing concentration of NO2. The < MAC > of naphthalene SOA particles with 1000 ppb NO2 is 688 cm2/g, which is slightly less than the < MAC > of biomass burning organic aerosol (BBOA) (700 cm2•g− 1) reported by Chakrabarty et al. (2010), and is 133% larger than that of naphthalene SOA particles without NO2 (295 cm2/g), indicating that naphthalene SOA particles with 1000 ppb NO2 had strong light absorption ability. This is mainly due to that NPAHs are the major components of naphthalene SOA particles with 1000 ppb NO2. The N = O chromophore in the NPAHs molecule strengthened the absorbing ability of naphthalene SOA particles. High concentration of NO2 is favorable for nitrification of OH-naphthalene adduct and naphthol products. Therefore, NPAHs components and < MAC > of naphthalene SOA particles increases with the increasing concentration of NO2. But in each experiment, the concentration of hydrogen peroxide and naphthalene are kept constant for each experiment, and the generated OH-naphthalene adducts and naphthol products are nearly unchanged. When NO2 increases to a certain concentration (1000 ppb), all the OH-naphthalene adducts and naphthol products are completely converted to NPAHs, and then the concentration of NO2 continues to increase, and the production of NPAHs dose not increase. Therefore, as shown in Fig. 12, when NO2 exceeds 1000 ppb, the < MAC > of naphthalene SOA particles basically remaines unchanged.
Compared with the previous photoxidaion experiments of naphthalene, biphenyl and dimethylnaphthalene with NOx (Nishino et al. 2008; Zimmermann et al. 2012, 2013; Jariyasopit et al. 2014), the NPAHs components of naphthalene SOA particles with different NO2 concentrations are characterized by on-line and off-line technologies in current study. The < MAC > of naphthalene SOA in the range of 200–600 nm is detected by total organic carbon analyzer and UV-Vis absorption spectrometer. From the measurement of VUV-PIMS and verification with UV-Vis and ATR-FTIR, it is confirmed that nitro-naphthalene, dinitro-naphthalene, nitro-naphthol and dinitro-naphthol are the major NPAHs products of naphthalene SOA particles with NO2. The < MAC > of naphthalene SOA particles with 1000 ppb NO2 is 688 cm2/g, which comparable to that of BBOA (700 cm2/g). The increase of strong chromophore of N = O of nitro group in NPAHs strengthenes the absorbing ability of naphthalene SOA particles. Since the formation rate of anthropogenic SOA particles is higher than that of organic aerosol particles generated by biomass combustion (Hallquist et al. 2009), SOA particles generated by photooxidation of PAHs under the background of high concentration of NOx may play a vital contributor to climate forcing.
SOA particles formed from photoxidation of PAHs under the background of high NOx concentration are considered to be an important contributor to NPAHs components in brown carbon. The NPAHs in naphthalene SOA are on-line detected using VUV-PIMS, and off-line verified by UV-Vis and ATR-FTIR in this study. Different from the naphthols and carboxyls measured in naphthalene SOA without NO2, nitro-naphthalene, dinitro-naphthalene, nitro-naphthol and dinitro-naphthol via the nitration of OH-naphthalene adduct and naphthol products of naphthalene are identified as major components of SOA with NO2. Also, the < MAC > over 200–600 nm of naphthalene SOA particles are measured by UV-Vis spectrophotometer and total organic carbon analyzer, and the obtained < MAC > of naphthalene SOA particles is gradually increases with the increasing concentration of NO2. The < MAC > of naphthalene SOA particles with 1000 ppb NO2 is 688 cm2/g, which comparable to that of BBOA. The increase of strong chromophore of N = O of nitro group in NPAHs strengthenes the absorbing ability of naphthalene SOA particles. Thus, anthropogenic SOA particles generate under the background of high concentration of NOx may contribute to the climate forcing. Nevertheless, this study focuses on measuring the NPAHs and < MAC > of naphthalene SOA particles, and does not involve on-line measurement of optical properties. The aerosol albedometer can be utilized to measure the optics of naphthalene SOA in follow-up experiments.
Funding
This work is supported by the National Natural Science Foundation of China (No. 41575118), the Key Project of Natural Science Foundation of Fujian Province of China (No.2020J02044), the Natural Science Foundation of Fujian Province of China (No.2021J01987), and the Youth Science and Technology Project of Fujian Provincial Department of Education (No. JAT200340).
Conflicts of interest
We declare that we have no financial and personal relatioships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled.
Availability of data and material
Not applicable.
Code availability
Not applicable.
Authors' contributions
Mincong Zhu: Investigation, data curation, writing-original draft preparation, funding acquisition. Mingqiang Huang: Conceptualization, validation, writing-review and editing, project administration, funding acquisition. Weichao Wang: Data curation, software. Xiaobin Shan: Software, resources. Liusi Sheng: Supervision, resources, validation. Weixiong Zhao: Formal analysis, resources. Xuejun Gu: Methodology, software. Weijun Zhang: Supervision, resources, validation. All authors reviewed and commented on the manuscript.
- Bandowe, B.A.M., Meusel, H.: Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) in the environment – A review. Sci. Total Environ. 581-582, 237–257 (2017)
- Besis, A., Gallou, D., Avgenikou, A., Serafeim, E., Samara, C.: Size-dependent in vitro inhalation bioaccessibility of PAHs and O/N PAHs - Implications to inhalation risk assessment. Environ. Pollut. 301, 119045 (2022)
- Carlton, A.G., Turpin, B.J., Altieri, K.E., Seitzinger, S., Reff, A., Lim, H.J., Ervens, B.: Atmospheric oxalic acid and SOA production from glyoxal: results of aqueous photooxidation experiments. Atmos. Environ. 41, 7588–7602 (2007)
- Chakrabarty, R.K., Moosmller, H., Chen, L.W.A., Lewis, K., Arnott, W.P., Mazzoleni, C., Dubey, M.K., Wold, C.E., Hao, W.M., Kreidenweis, S.M.: Brown carbon in tar balls from smoldering biomass combustion. Atmos.Chem. Phys. 10, 6363–6370 (2010)
- Dang, M., Liu, R.D., Dong, F.S., Liu, B., Hou, K.Y.: Vacuum ultraviolet photoionization on-line mass spectrometry: Instrumentation developments and applications. TrAC Trends Anal. Chem. 149, 116542 (2022).
- Fang, W.Z., Gong, L., Shan, X.B., Liu, F.Y., Wang, Z.Y., Sheng, L.S.: Thermal desorption/ tunable vacuum–ultraviolet time-of-flight photoionization aerosol mass spectrometry for investigating secondary organic aerosols in chamber experiments. Anal. Chem. 83, 9024–9032 (2011)
- Feng, Z.Z., Huang, M.Q., Cai, S.Y., Xu, X.Z., Yang, Z.L., Zhao, W.X., Hu, C.J., Gu, X.J., Zhang, W.J.: Characterization of single scattering albedo and chemical components of aged toluene secondary organic aerosol. Atmos. Pollut. Res. 10, 1736–1744 (2019)
- Hallquist, M., Wenger, J., Baltensperger, U., Rudich, Y., Simpson, D., Claeys, M., Dommen, J., Donahue, N., George, C., Goldstein, A.: The formation, properties and impact of secondary organic aerosol: current and emerging issues. Atmos. Chem. Phys. 9, 5155–5236 (2009)
- Huang, M.Q., Hao, L.Q., Gu, X.J., Hu, C.J., Zhao, W.X., Wang, Z.Y., Fang, L., Zhang, W.J.: Effects of inorganic seed aerosols on the growth and chemical composition of secondary organic aerosol formed from OH-initiated oxidation of toluene. J. Atmos. Chem. 70, 151–164 (2013)
- Huang, M.Q., Xu, J., Cai, S.Y., Liu, X.Q., Zhao, W.X., Hu, C.J., Gu, X.J., Fang, L. Zhang, W.J.: Characterization of brown carbon constituents of benzene secondary organic aerosol aged with ammonia. J. Atmos. Chem. 75, 205–218 (2018)
- Jariyasopit, N., McIntosh, M., Zimmermann, K., Arey, J., Atkinson, R., Cheong, P.H.Y., Carter, R.G., Yu, T.W., Dashwood, R.H., Simonich, S.L.N.: Novel nitro-PAH formation from heterogeneous reactions of PAHs with NO2, NO3/N2O5, and OH radicals: Prediction, laboratory studies, and mutagenicity. Environ. Sci. Technol. 48, 412–419 (2014).
- Jathar, S.H., Mahmud, A., Barsanti, K.C., Asher, W.E., Pankow, J.F., Kleeman, M.J.: Water uptake by organic aerosol and its influence on gas/particle partitioning of secondary organic aerosol in the United States. Atmos. Environ. 129, 142–154 (2016)
- Keyte, I.J., Harrisson, R.M., Lammel, G.: Chemical reactivity and long-range transport potential of polycyclic aromatic hydrocarbons - a review. Chem. Soc. Rev. 42, 9333–9391 (2013)
- Laskin, A., Laskin, J., Nizkorodov, S.A.: Chemistry of atmospheric brown carbon. Chem. Rev. 115, 4335–4382 (2015)
- Laskin, J., Laskin, A., Nizkorodov, S.A.: Mass spectrometry analysis in atmospheric chemistry. Anal. Chem. 90, 166–189 (2018)
- Lammel, G., Kitanovski, Z., Kukučka, P., Novák, J., Arangio, A.M., Codling, G.P., Filippi, A., Hovorka, J., Kuta, J., Leoni, C., Příbylová, P., Prokeš, R., Sáňka, O., Shahpoury, P., Tong, H.J., Wietzoreck, M.: Oxygenated and nitrated polycyclic aromatic hydrocarbons in ambient air- levels, phase partitioning, mass size distributions, and inhalation bioaccessibility. Environ. Sci. Technol. 54, 2615–2625 (2020)
- Lin, P., Liu, J., Shilling, J.E., Kathmann, S.M.,Laskin, J., Laskin, A.: Molecular characterization of brown carbon (BrC) chromophores in secondary organic aerosol generated from photo- oxidation of toluene. Phys. Chem. Chem. Phys. 17, 23312–23325 (2015)
- Liu, Y., Liggio, J., Staebler, R., Li, S.M.: Reactive uptake of ammonia to secondary organic aerosols: kinetics of organonitrogen formation. Atmos. Chem. Phys. 15, 13569–13584 (2015)
- Lu, T.T., Huang, M.Q., Zhao, W.X., Hu, C.J., Gu, X.J., Zhang, W.J.: Influence of ammonium sulfate seed particle on optics and compositions of toluene derived organic aerosol in photochemistry. Atmosphere 11, 961 (2020)
- Marković, S., Tošović, J.: Application of time-dependent density functional and natural bond orbital theories to the UV–vis absorption spectra of some phenolic compounds. J. Phys. Chem. A 119, 9352–9362 (2015)
- Mondal, K., Bhattacharyya, S., Sharma, A.: Photocatalytic degradation of naphthalene by electrospun mesoporous carbon-doped anatase TiO2 nanofiber mats. Ind. Eng. Chem. Res. 53, 18900–18909 (2014)
- Mysak, E.R., Wilson, K.R., Jimenez-Cruz, M., Ahmed, M., Baer, T.: Synchrotron radiation based aerosol time-of-flight mass spectrometry for organic constituents. Anal. Chem. 77, 5953–5960 (2005)
- Nežiková, B., Degrendele, C., Bandowe, B.A.M., Šmejkalová, A.H., Kukučka, P., Martiník, J., Mayer, L., Prokeš, R., Přibylová, P., Klánová, J., Lammel, G.: Three years of atmospheric concentrations of nitrated and oxygenated polycyclic aromatic hydrocarbons and oxygen heterocycles at a central European background site. Chemosphere. 269,128738 (2021)
- Nishino, N., Atkinson, R., Arey, J.: Formation of nitro products from the gas-phase OH radical-initiated reactions of toluene, naphthalene and biphenyl: Effect of NO2 concentration. Environ. Sci. Technol. 42, 9203–9209 (2008)
- Nishino, N.; Arey, J.; Atkinson, R. Yields of glyoxal and ring-cleavage co-products from the OH radical initiated reactions of naphthalene and selected alkylnaphthalenes. Environ. Sci. Technol. 43, 8554–8560 (2009)
- Pan, G., Hu, C.J., Huang, M.Q., Wang, Z.Y., Cheng, Y., Liu, Z., Gu, X.J., Zhao, W.X., Zhang, W.J., Chen, J., Liu, F.Y., Shan, X.B., Sheng, L.S.: A VUV photoionization mass spectrometric study on the OH-initiated photooxidation of isoprene with synchrotron radiation. J. Environ. Sci. 24, 2075–2082 (2012)
- Powelson, M.H., Espelien, B.M., Hawkins, L.N., Galloway, M.M., De Haan, D.O.: Brown carbon formation by aqueous-phase carbonyl compound reactions with amines and ammonium sulfate. Environ. Sci. Technol. 48, 985–993 (2014)
- Pratt, K.A., Prather, K.A.: Mass spectrometry of atmospheric aerosols-Recent developments and applications. Part II: On-line mass spectrometry techniques. Mass Spectrom. Rev. 31, 1–16 (2011)
- Shiroudi, A., Deleuze, M.S., Canneaux, S.: Theoretical study of the oxidation mechanisms of naphthalene initiated by hydroxyl radicals: The OH-addition pathway. J. Phys. Chem. A 118, 4593–4610 (2014)
- Silva, P.J., Prather, K.A.: Interpretation of mass spectra from organic compounds in aerosol time-of-flight mass spectrometry. Anal. Chem. 72, 3553–3562 (2002).
- Sun, C.J., Qu, L.L., Wu, L., Wu, X., Sun, R., Li, Y.X.: Advances in analysis of nitrated polycyclic aromatic hydrocarbons in various matrices. TrAC Trend Anal. Chem. 127, 115878 (2020)
- Sun, J., Shen, Z.X., Zhang, T., Kong, S.F., Zhang, H.A., Zhang, Q., Niu, X.Y., Huang, S.S., Xu, H.M., Ho, K.F. Cao, J.F.: A comprehensive evaluation of PM2.5-bound PAHs and their derivative in winter from six megacities in China: Insight the source-dependent health risk and secondary reactions. Environ. Int. 165, 107344 (2022)
- Thornton, J.A., Shilling, J.E., Shrivastava, M., D’Ambro, E.L., Zawadowicz, M.A., Liu, J.M.: A near-explicit mechanistic evaluation of isoprene photochemical secondary organic aerosol formation and evolution: Simulations of multiple chamber experiments with and without added NOx. ACS Earth Space Chem. 4, 1161–1181 (2020)
- Updyke, K.M., Nguyen, T.B., Nizkorodov, S.A.: Formation of brown carbon via reactions of ammonia with secondary organic aerosols from biogenic and anthropogenic precursors. Atmos. Environ. 63, 22–31 (2012)
- Wietzoreck, M., Kyprianou, M., Musa Bandowe, B. A., Celik, S., Crowley, J. N., Drewnick, F., Eger, P., Friedrich, N., Iakovides, M., Kukučka, P., Kuta, J., Nežiková, B., Pokorná, P., Přibylová, P., Prokeš, R., Rohloff, R., Tadic, I., Tauer, S., Wilson, J., Harder, H., Lelieveld, J., Pöschl, U., Stephanou, E. G., and Lammel, G.: Polycyclic aromatic hydrocarbons (PAHs) and their alkylated, nitrated and oxygenated derivatives in the atmosphere over the Mediterranean and Middle East seas. Atmos. Chem. Phys. 22, 8739–8766 (2022)
- Xie, M.J., Chen, X., Hays, M.D., Lewandowski, M., Offenberg, J., Kleindienst, T.E., Holder, A.L.: Light absorption of secondary organic aerosol: Composition and contribution of nitroaromatic compounds. Environ. Sci. Technol. 51, 11607–11616 (2017)
- Yan, J.P., Wang, X.P., Gong, P., Wang, C.F.: Nitrated polycyclic aromatic compounds in the atmospheric environment: A review. Crit. Rev. Environ. Sci. Technol. 55, 1159–1185 (2021)
- Zhang, Y., Shen, Z.X., Sun, J., Zhang, L.M., Zhang, B., Zou, H.J., Zhang, T., Ho, S.S.H., Chang, X.J., Xu, H.M., Wang, T., Cao, J.J.: Parent, alkylated, oxygenated and nitrated polycyclic aromatic hydrocarbons in PM2.5 emitted from residential biomass burning and coal combustion: A novel database of 14 heating scenarios. Environ. Pollut. 268, 115881 (2021)
- Zhao, T., Yang, L.X., Huang, Q., Zhang, W., Duan, S.F., Gao, H.L., Wang, W.X.: PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) and nitrated-PAHs (NPAHs) emitted by gasoline vehicles: Characterization and health risk assessment. Sci. Total Environ. 727, 138631 (2017)
- Zimmermann, K., Atkinson, R., Arey, J.: Effect of NO2 concentration on dimethylnitronaphthalene yields and isomer distribution patterns from the gas-phase OH radical-initiated reactions of selected dimethylnaphthalenes. Environ. Sci. Technol. 46, 7535–7542 (2012)
- Zimmermann, K., Jariyasopit, N., Simonich, S.L.N., Tao, S., Atkinson, R., Arey, J.: Formation of Nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/ NO2. Environ. Sci. Technol. 47, 8434–8442 (2013)
No competing interests reported.