Mechanistic Inside into the Gas-Phase NO3·+HO2· Reaction

The reaction between NO 3 · and HO 2 · is critical in nighttime atmospheric chemistry. This reaction is believed to occur via two channels: one leading to the formation of HNO3 and the other forming OH · . A long-standing question regarding this reaction is whether this reaction occurs through HNO3 path or OH · or both at a time. Some indirect experiments proposed the HNO3 path as the exclusive path, while some suggested the possibility of both the paths. In the present work, using high-level quantum chemical and kinetics calculations, we have tried to shed light on the mechanism of this reaction. We have incorporated full triple excitation and partial quadratic excitation corrections at the coupled-cluster level for our energetics part, whereas a master equation approach has been employed to obtain the rate constants within 213-400 K. Our investigation suggests that it is only the OH · path through which the reaction takes place.

Rapid aqueous-phase dark reaction of phenols with nitrosonium ions: Novel mechanism for atmospheric nitrosation and nitration at low pH

Dark aqueous-phase reactions involving the nitrosation and nitration of aromatic organic compounds play a significant role in the production of light-absorbing organic carbon in the atmosphere. This process constitutes a crucial aspect of tropospheric chemistry and has attracted growing research interest, particularly in understanding the mechanisms governing nighttime reactions between phenols and nitrogen oxides. In this study, we present new findings concerning the rapid dark reactions between phenols containing electron-donating groups and inorganic nitrite in acidic aqueous solutions with pH levels <3.5. This reaction generates a substantial amount of nitroso- and nitro-substituted phenolic compounds, known for their light-absorbing properties and toxicity. In experiments utilizing various substituted phenols, we demonstrate that their reaction rates with nitrite depend on the electron cloud density of the benzene ring, indicative of an electrophilic substitution reaction mechanism. Control experiments and theoretical calculations indicate that the nitrosonium ion (NO+) is the reactive nitrogen species responsible for undergoing electrophilic reactions with phenolate anions, leading to the formation of nitroso-substituted phenolic compounds. These compounds then undergo partial oxidation to form nitro-substituted phenols through reactions with nitrous acid (HONO) or other oxidants like oxygen. Our findings unveil a novel mechanism for swift atmospheric nitrosation and nitration reactions that occur within acidic cloud droplets or aerosol water, providing valuable insights into the rapid nocturnal formation of nitrogen-containing organic compounds with significant implications for climate dynamics and human health.

Nitrous Acid (HONO) Dissociation on the Water and Ice Surface: An Ab Initio Molecular Dynamics Study

In the atmosphere, the photodissociation of HONO is a significant source of OH radicals after ozone. In the present study, using Born-Oppenheimer molecular dynamics, we showed that HONO can dissociate on ice and water surfaces without light. In addition, the dissociation time of HONO is found to be much less on the ice surface compared to the same time on the water droplets.

Deciphering the role of LiNO3 additives in Li-S batteries

The ultrahigh theoretical energy density of lithium-sulfur (Li-S) batteries has attracted intensive research interest. However, most of the long-term cycling performance parameters are strongly dependent on the utilization of the electrolyte, which is considered as an indispensable component in Li-S batteries. Over the past few decades, numerous research studies around LiNO₃ as an electrolyte additive have been carried out and have been confirmed to significantly upgrade the electrochemical performance of Li-S batteries, but the mechanism of performance improvement is still not well-understood. In this minireview, we revisit the controversial issues surrounding LiNO₃ based on recent representative studies, provide a comprehensive understanding of the role of LiNO₃ in the Li-S battery system, and specifically discuss what the panoramic view of the solid electrolyte interface film formed by LiNO₃ on the surface of Li metal anodes looks like. Finally, we present general conclusions and unique insights into the future development of Li-S batteries. This minireview aims to provide a tutorial reference for researchers who are ready to enter or are active in the field of Li-S batteries.

Anthropogenic control over wintertime oxidation of atmospheric pollutants

During winter in the mid-latitudes, photochemical oxidation is significantly slower than in summer and the main radical oxidants driving formation of secondary pollutants, such as fine particulate matter and ozone, remain uncertain, owing to a lack of observations in this season. Using airborne observations, we quantify the contribution of various oxidants on a regional basis during winter, enabling improved chemical descriptions of wintertime air pollution transformations. We show that 25-60% of NO_x is converted to N₂O₅ via multiphase reactions between gas-phase nitrogen oxide reservoirs and aerosol particles, with ~93% reacting in the marine boundary layer to form >2.5 ppbv ClNO₂. This results in >70% of the oxidizing capacity of polluted air during winter being controlled, not by typical photochemical reactions, but from these multiphase reactions and emissions of volatile organic compounds, such as HCHO, highlighting the control local anthropogenic emissions have on the oxidizing capacity of the polluted wintertime atmosphere.

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.

Atmospheric chemistry of benzyl alcohol: kinetics and mechanism of reaction with OH radicals

The atmospheric oxidation of benzyl alcohol has been investigated using smog chambers at ICARE, FORD, and EUPHORE. The rate coefficient for reaction with OH radicals was measured and an upper limit for the reaction with ozone was established; kOH = (2.8 ± 0.4) × 10(-11) at 297 ± 3 K (averaged value including results from Harrison and Wells) and kO(3) < 2 × 10(-19) cm(3) molecule(-1) s(-1) at 299 K. The products of the OH radical initiated oxidation of benzyl alcohol in the presence of NOX were studied. Benzaldehyde, originating from H-abstraction from the -CH(2)OH group, was identified using in situ FTIR spectroscopy, HPLC-UV/FID, and GC-PID and quantified in a yield of (24 ± 5) %. Ring retaining products originating from OH-addition to the aromatic ring such as o-hydroxybenzylalcohol and o-dihydroxybenzene as well as ring-cleavage products such as glyoxal were also identified and quantified with molar yields of (22 ± 2)%, (10 ± 3)%, and (2.7 ± 0.7)%, respectively. Formaldehyde was observed with a molar yield of (27 ± 10)%. The results are discussed with respect to previous studies and the atmospheric oxidation mechanism of benzyl alcohol.

Determination of inlet transmission and conversion efficiencies for in situ measurements of the nocturnal nitrogen oxides, NO3, N2O5 and NO2, via pulsed cavity ring-down spectroscopy

Pulsed cavity ring-down spectroscopy is a highly sensitive method for direct absorption spectroscopy that has been applied to in situ detection of NO3, N2O5 and NO2 in the atmosphere from a variety of platforms, including ships, aircraft, and towers. In this paper, we report the development of schemes to significantly improve the accuracy of these measurements. This includes the following: (1) an overall improvement in the inlet transmission efficiencies (92 +/- 2% for NO3 and 97 +/- 1% for N2O5) achieved primarily through a reduction in the inlet residence time; and (2) the development of a calibration procedure that allows regular determination of these efficiencies in the field by addition of NO3 or N2O5 to the inlet from a portable source followed by conversion of NO3 to NO2. In addition, the dependence of the instrument's sensitivity and accuracy to a variety of conditions encountered in the field, including variations in relative humidity, aerosol loading, and VOC levels, was systematically investigated. The rate of degradation of N2O5 transmission efficiency on the inlet and filter system due to the accumulation of inorganic aerosol was determined, such that the frequency of filter changes required for accurate measurements could be defined. In the absence of aerosol, the presence of varying levels of relative humidity and reactive VOC were found to be unimportant factors in the instrument's performance. The 1 sigma accuracy of the NO3, N2O5, and NO2 measured with this instrument are -9/+12, -8/+11, +/- 6%, respectively, where the -/+ signs indicate that the actual value is low/high relative to the measurement. The largest contribution to the overall uncertainty is now due to the NO3 absorption cross section rather than the inlet transmission efficiency.

Kinetic Study of the Gas-Phase Reactions of OH and NO3 Radicals and O3 with Selected Vinyl Ethers

Kinetic studies on the gas-phase reactions of OH and NO3 radicals and ozone with ethyl vinyl ether (EVE), propyl vinyl ether (PVE) and butyl vinyl ether (BVE) have been performed in a 405 L borosilicate glass chamber at 298 +/- 3 K in synthetic air using in situ FTIR spectroscopy to monitor the reactants. Using a relative kinetic method rate coefficients (in units of cm3 molecule(-1) s(-1)) of (7.79 +/- 1.71) x 10(-11), (9.73 +/- 1.94) x 10(-11) and (1.13 +/- 0.31) x 10(-10) have been obtained for the reaction of OH with EVE, PVE and BVE, respectively, (1.40 +/- 0.35) x 10(-12), (1.85 +/- 0.53) x 10(-12) and (2.10 +/- 0.54) x 10(-12) for the reaction of NO3 with EVE, PVE and BVE, respectively, and (2.06 +/- 0.42) x 10(-16), (2.34 +/- 0.48) x 10(-16) and (2.59 +/- 0.52) x 10(-16) for the ozonolysis of EVE, PVE and BVE, respectively. Tropospheric lifetimes of EVE, PVE and BVE with respect to the reactions with reactive tropospheric species (OH, NO3 and O3) have been estimated for typical OH and NO3 radical and ozone concentrations.

Variability in Nocturnal Nitrogen Oxide Processing and Its Role in Regional Air Quality

Nitrogen oxides in the lower troposphere catalyze the photochemical production of ozone (O3) pollution during the day but react to form nitric acid, oxidize hydrocarbons, and remove O3 at night. A key nocturnal reaction is the heterogeneous hydrolysis of dinitrogen pentoxide, N2O5. We report aircraft measurements of NO3 and N2O5, which show that the N2O5 uptake coefficient, g(N2O5), on aerosol particles is highly variable and depends strongly on aerosol composition, particularly sulfate content. The results have implications for the quantification of regional-scale O3 production and suggest a stronger interaction between anthropogenic sulfur and nitrogen oxide emissions than previously recognized.

Atmospheric reactions influence seasonal PAH and nitro-PAH concentrations in the Los Angeles basin

Ambient measurements of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs were carried out during August 2002 and January 2003 in Los Angeles, CA, a source site and in Riverside, CA, a downwind receptor site approximately 90 km to the east of Los Angeles. Atmospheric concentrations of PAHs and nitro-PAHs are of interest because both of these compound classes include potent mutagens and carcinogens. To augment our current understanding of atmospheric formation of nitro-PAHs, four sampling periods were employed to study the diurnal variations of these compounds. The PAH concentrations were highest in Los Angeles during January, as a result of traffic input at this source site undertightwintertime atmospheric inversions. In contrast, nitro-PAH levels were highest in Riverside during August, as a result of enhanced summertime photochemistry. Hydroxyl radical-initiated reactions produced nitro-PAHs in both seasons, while in winter little evidence for nitrate radical chemistry was seen. For the August samples, nitrate radical-initiated formation of nitro-PAHs is suggested by nitro-PAH isomer profiles not only at the downwind location as anticipated, but also atthe source site. In southern California, the contribution of atmospheric formation through gas-phase radical-initiated PAH reactions to the ambient burden of nitro-PAHs is dominant, with the semi-volatile nitro-PAHs being the most abundant and 2-nitrofluoranthene being the major particle-associated nitro-PAH.

Prototype for in situ detection of atmospheric NO3 and N2O5 via laser-induced fluorescence

We describe a prototype designed for in situ detection of the nitrate radical (NO3) by laser-induced fluorescence (LIF) and of N2O5 by thermal dissociation followed by LIF detection of NO3. An inexpensive 36 mW continuous wave multi-mode diode laser at 662 nm is used to excite NO3 in the B2E'(0000) <-- X2A'2(0000) band. Fluorescence is collected from 700 to 750 nm. The prototype has a sensitivity to NO3 of 76 ppt for a 60 s integration with an accuracy of 8%. Although this sensitivity is adequate for studies of N205 in many environments, it is much less sensitive (about 300 times) than expected based on a comparison of previously measured photophysical properties of NO2 and NO3. This implies much stronger nonradiative coupling of electronic states in NO3 than in NO2.

Rate constants for the gas-phase reactions of a series of alkylnaphthalenes with the nitrate radical

Naphthalene and its methyl-, ethyl-, and dimethyl-derivatives are semivolatile polycyclic aromatic hydrocarbons expected to be in the gas phase in ambient atmospheres and are subject to nighttime degradation by gas-phase reactions with the nitrate (NO3) radical. Using a relative rate method, rate constants for the gas-phase reactions of NO3 radicals with a series of alkylnaphthalenes have been measured at 298 +/- 2 K and atmospheric pressure of air. The compounds studied were 1- and 2-methylnaphthalene (1- and 2-MN), 1- and 2-ethylnaphthalene (1- and 2-EN), and the 10 dimethylnaphthalene isomers (1,2-, 1,3-, 1,4-,1,5-, 1,6-, 1,7-, 1,8-, 2,3-, 2,6-, and 2,7-DMN). Sampling in Riverside, CA showed that these alkylnaphthalenes were readily detected in ambient air, with the exception of 1,8-DMN. The reactions of naphthalene and the alkylnaphthalenes with NO3 radicals proceed by initial addition of the radical to form an aromatic-NO3 adduct (with rate constant k(a)) which either decomposes back to reactants (with rate constant kb) or reacts with NO2 to form products (with rate constant k(c). Using naphthalene as the reference compound, the values of (k(a)k(c)/k(b)) obtained for the NO3 radical reactions (in units of 10(-28) cm(6) molecule(-2) S(-1), indicated errors are two least-squares standard deviations) were as follows: 1-MN, 7.15 +/- 0.37; 2-MN, 10.2 +/- 1.0; 1-EN, 9.82 +/- 0.69; 2-EN, 7.99 +/- 0.99; 1,2-DMN, 64.0 +/- 2.3; 1,3-DMN, 21.3 +/- 1.2; 1,4-DMN, 13.0 +/- 0.5; 1,5-DMN, 14.1 +/- 1.3; 1,6-DMN, 16.5 +/- 1.8; 1,7-DMN, 13.5 +/- 0.7; 1,8-DMN, 212 +/- 59; 2,3-DMN, 15.2 +/- 0.5; 2,6-DMN, 21.2 +/- 1.6; 2,7-DMN, 21.0 +/- 1.5.