978 research outputs found
Changing aerosol chemistry is redefining HONO sources
No full textAbstract Heterogeneous reactions of NO2 on particulate matter have been considered an important source of HONO (Nitrous acid) in the troposphere, whereas its contribution is controversial due to the lack of uptake coefficient of NO2 (γNO2) on the surfaces of ambient particulate matter (PM). Here we investigate the the γNO2 to form HONO and its evolution based on long-term comprehensive field observations (2019–2023) in Beijing and a random forest model with Shapley additive explanations. The γNO2 on ambient PM is on the order of 10−6, decreasing markedly from 3.07 ± 5.99 × 10−6 in 2019 to 1.43 ± 3.22 × 10−6 in 2023. This decrease is driven by the increase in aerosol pH, linked to increased ratio of NH4NO3 to (NH4)2SO4, resulting from an unbalanced desulfurization and denitrification. This study implies that the role of the heterogeneous reaction of NO2 on aerosol surfaces in HONO production is declining in Beijing, providing valuable insights into the atmospheric chemistry in urban environments
Generation and 355 nm laser photodissociation of nitrous acid (HONO) and HONO-water clusters
No full textA stable source for the continuous production of high concentrations of gaseous nitrous acid (HONO) up to 5000 ppm has been developed, characterized, and employed for a study of the near-UV photodissociation of HONO and HONO-water clusters in a continuous supersonic free-jet expansion. The source consists of a flow reactor fed with aqueous reagent solutions purged by an inert carrier gas at flow rates up to 1 L/min. The dynamics of the photodissociation of jet-cooled HONO and HONO-water clusters at 355 nm have been studied by measuring the rotational distribution of the nascent NO (?? = 2) photofragment using the laser-induced fluorescence (LIF) technique. Distinctly bimodal rotational distributions have been observed for the nascent, vibrationally excited NO, which are well described by the sum of two components: a Gaussian distribution at high J and a 170 K Boltzmann distribution in the low-J range reflecting photodissociation of bare HONO , HONO-H2O complexes, and small HONO water clusters.</p
Four years of ground-based MAX-DOAS observations of HONO and NO2 in the Beijing area
No full textGround-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements of nitrous acid (HONO) and its precursor NO2 (nitrogen dioxide) as well as aerosols have been performed daily in Beijing city centre (39.98° N, 116.38° E) from July 2008 to April 2009 and at the suburban site of Xianghe (39.75° N, 116.96° E) located ~60 km east of Beijing from March 2010 to December 2012. This extensive dataset allowed for the first time the investigation of the seasonal cycle of HONO as well as its diurnal variation in and in the vicinity of a megacity. Our study was focused on the HONO and NO2 near-surface concentrations (0–200 m layer) and total vertical column densities (VCDs) and also aerosol optical depths (AODs) and extinction coefficients retrieved by applying the Optimal Estimation Method to the MAX-DOAS observations. Monthly averaged HONO near-surface concentrations at local noon display a strong seasonal cycle with a maximum in late fall/winter (~0.8 and 0.7 ppb at Beijing and Xianghe, respectively) and a minimum in summer (~0.1 ppb at Beijing and 0.03 ppb at Xianghe). The seasonal cycles of HONO and NO2 appear to be highly correlated, with correlation coefficients in the 0.7–0.9 and 0.5–0.8 ranges at Beijing and Xianghe, respectively. The stronger correlation of HONO with NO2 and also with aerosols observed in Beijing suggests possibly larger role of NO2 conversion into HONO in the Beijing city center than at Xianghe. The observed diurnal cycle of HONO near-surface concentration shows a maximum in the early morning (about 1 ppb at both sites) likely resulting from night-time accumulation, followed by a decrease to values of about 0.1–0.4 ppb around local noon. The HONO / NO2 ratio shows a similar pattern with a maximum in the early morning (values up to 0.08) and a decrease to ~0.01–0.02 around local noon. The seasonal and diurnal cycles of the HONO near-surface concentration are found to be similar in shape and in relative amplitude to the corresponding cycles of the HONO total VCD and are therefore likely driven mainly by the balance between HONO sources and the photolytic sink, whereas dilution effects appear to play only a minor role. The estimation of OH radical production from HONO and O3 photolysis based on retrieved HONO near-surface concentrations and calculated photolysis rates indicate that in the 0–200 m altitude range, HONO is by far the largest source of OH radicals in winter as well as in the early morning at all seasons, while the contribution of O3 dominates in summer from mid-morning until mid-afternoon.Geoscience & Remote SensingCivil Engineering and Geoscience
Reactive Uptake of HONO to TiO2 Surface: “Dark” Reaction
No full textInternational audienceThe interaction of HONO with TiO2 solid films was studied under dark conditions using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to TiO2 was studied as a function of HONO concentration ([HONO)0 = (0.3–3.3) × 1012 molecules cm–3), water concentration (RH = 3 × 10–4 to 13%), and temperature (T = 275–320 K). TiO2 surface deactivation upon exposure to HONO was observed. The measured initial uptake coefficient of HONO on TiO2 surface was independent of the HONO concentration and showed slight negative temperature dependence (activation factor = −1405 ± 110 K). In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ0 = 1.8 × 10–5 (RH)-0.63 (calculated using BET surface area, 40% uncertainty) at T = 300 K. NO2 and NO were observed as products of the HONO reaction with TiO2 surface with sum of their yields corresponding to nearly 100% of the nitrogen mass balance. The yields of the NO and NO2 products were found to be 42 ± 7% and 60 ± 9%, respectively, independent of relative humidity, temperature, and concentration of HONO under experimental conditions used. The contribution of aerosol to the total HONO loss in the boundary layer (calculated with initial uptake data for HONO on TiO2 surface) showed the unimportance of this process in the atmosphere. In addition, the diffusion coefficient of HONO in He was determined to be DHONO-He = 490 ± 50 Torr cm2 s–1 at T = 300 K
Reactive uptake of HONO on aluminium oxide surface
No full textInternational audienceKinetics and products of the interaction of HONO with solid films of Al2O3 were investigated under dark and UV irradiation conditions using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The reactive uptake of HONO to Al2O3 was studied as a function of HONO concentration ([HONO]0 = (0.6–3.5) × 1012 molecule cm−3), relative humidity (RH = 1.4 × 10−4 to 35.4%), temperature (T = 275–320 K) and UV irradiation intensity (JNO2=0.002–0.012 s−1JNO2=0.002–0.012 s−1). The measured reactive uptake coefficient was independent of the HONO concentration and temperature. In contrast, the relative humidity (RH) was found to have a strong impact on the uptake coefficient: γ = 4.8 × 10−6 (RH)−0.61 and γ = 1.7 × 10−5 (RH)−0.44 under dark conditions and on irradiated surface (JNO2=0.012 s−1JNO2=0.012 s−1), respectively (γ calculated with BET surface area, 30% conservative uncertainty). NO2 and NO were observed as products of the HONO reaction with Al2O3 surface with yields of 40 ± 6 and 60 ± 9%, respectively, independent of relative humidity, temperature, concentration of HONO and UV irradiation intensity under experimental conditions used. The HONO uptake on mineral aerosol (calculated with uptake data for HONO on Al2O3 surface) appears to be of minor importance compared with other HONO loss processes in the boundary layer of the earth atmosphere
Modeling of daytime HONO vertical gradients during SHARP 2009
No full textNitrous acid (HONO) acts as a major precursor of the hydroxyl radical (OH) in the urban atmospheric boundary layer in the morning and throughout the day. Despite its importance, HONO formation mechanisms are not yet completely understood. It is generally accepted that conversion of NO2 on surfaces in the presence of water is responsible for the formation of HONO in the nocturnal boundary layer, although the type of surface on which the mechanism occurs is still under debate. Recent observations of higher than expected daytime HONO concentrations in both urban and rural areas indicate the presence of unknown daytime HONO source(s). Various formation pathways in the gas phase, and on aerosol and ground surfaces have been proposed to explain the presence of daytime HONO. However, it is unclear which mechanism dominates and, in the cases of heterogeneous mechanisms, on which surfaces they occur. Vertical concentration profiles of HONO and its precursors can help in identifying the dominant HONO formation pathways. In this study, daytime HONO and NO2 vertical profiles, measured in three different height intervals (20–70, 70–130, and 130–300 m) in Houston, TX, during the 2009 Study of Houston Atmospheric Radical Precursors (SHARP) are analyzed using a one-dimensional (1-D) chemistry and transport model. Model results with various HONO formation pathways suggested in the literature are compared to the the daytime HONO and HONO/NO2 ratios observed during SHARP. The best agreement of HONO and HONO/NO2 ratios between model and observations is achieved by including both a photolytic source of HONO at the ground and on the aerosol. Model sensitivity studies show that the observed diurnal variations of the HONO/NO2 ratio are not reproduced by the model if there is only a photolytic HONO source on aerosol or in the gas phase from NO2* + H2O. Further analysis of the formation and loss pathways of HONO shows a vertical dependence of HONO chemistry during the day. Photolytic HONO formation at the ground is the major formation pathway in the lowest 20 m, while a combination of gas-phase, photolytic formation on aerosol, and vertical transport is responsible for daytime HONO between 200–300 m a.g.l. HONO removal is dominated by vertical transport below 20 m and photolysis between 200–300 m a.g.l
The ALMA-PILS survey: First detection of nitrous acid (HONO) in the interstellar medium
No full textInternational audienceNitrogen oxides are thought to play a significant role as a nitrogen reservoir and to potentially participate in the formation of more complex species. Until now, only NO, N2O, and HNO have been detected in the interstellar medium. We report the first interstellar detection of nitrous acid (HONO). Twelve lines were identified towards component B of the low-mass protostellar binary IRAS 16293–2422 with the Atacama Large Millimeter/submillimeter Array, at the position where NO and N2O have previously been seen. A local thermodynamic equilibrium model was used to derive the column density (∼9 × 1014 cm−2 in a 0 .″5 beam) and excitation temperature (∼100 K) of this molecule. HNO, NO2, NO+, and HNO3 were also searched for in the data, but not detected. We simulated the HONO formation using an updated version of the chemical code Nautilus and compared the results with the observations. The chemical model is able to reproduce satisfactorily the HONO, N2O, and NO2 abundances, but not the NO, HNO, and NH2OH abundances. This could be due to some thermal desorption mechanisms being destructive and therefore limiting the amount of HNO and NH2OH present in the gas phase. Other options are UV photodestruction of these species in ices or missing reactions potentially relevant at protostellar temperatures
Kinetics of the gas phase reaction OH+NO(+M)->HONO(+M) and the determination of the UV absorption cross sections of HONO
No full textThe reaction OH + NO(+ M) --> HONO(+ M) with M = SF6 as a third body has been employed as a clean source for recording the near-ultraviolet absorption spectrum of HONO without interference from other absorbing species. The reaction was initiated by the pulse radiolysis of SF6/H2O/NO mixtures with total pressures in the range 10-1000 mbar at 298 K. The pressure dependence of the rate coefficient was studied by time-resolved UV and IR spectroscopy. By analysis of the fall-off curve we have derived a value for the limiting low pressure rate constant k(0)/[SF6] = (1.5 +/- 0.1) X 10(-30) cm(6) molecule(-2) s(-1) at 298 K, using the values of k(infinity) = (3.3 +/- 0.3) X 10(-11) cm(3) molecule(-1) s(-1) and F-cent = 0.81 reported by Tree and co-workers. The UV spectrum of HONO was recorded in the range 320-400 nm and an absolute absorption cross section of sigma = (5.02 +/- 0.76) X 10(-19) cm(2) molecule(-1) has been determined for the strongest band of HONO located at 354.2 nm. Differential absorption cross sections to be used for field measurements of HONO were also investigated. (C) 1997 Elsevier Science B.V
HONO and NO<sub>2</sub> evolution from irradiated nitrate-doped ice and frozen nitrate solutions
No full textInternational audienceNitrate photolysis in the wavelength range 250?1200 nm was studied on ice in a controlled laboratory experiment. Monolayer coverage of nitrate was achieved by dosing well-known amounts of HNO3 from the gas phase onto a frozen water surface. Fluxes of HONO and NO2 into the gas phase with time were quantified at temperatures between 193 K and 258 K and as a function of illumination wavelength in the range: 250?345 nm. Whereas HONO release showed a strong temperature dependence at colder temperatures, attributed to reversible adsorption processes, NO2 fluxes were independent of temperature. The observed fluxes of HONO and NO2 at high temperature were not affected by diffusion or adsorption processes, and could be used to estimate a quantum yield for HONO formation of (3.8±0.6)×10?4. A different wavelength dependence for HONO and NO2 fluxes indicates that additional reactions besides nitrate photolysis and subsequent release of the products contribute to the emission of nitrogen oxides
Measurements of the HONO photodissociation constant
No full textMeasurements of the photodissociation constant for nitrous acid (j HONO) were made at an urban site in Toronto, Canada, during the months of May–July 2005, using an optically thin actinometer. Operating details of the j HONO monitor are reported, along with laboratory tests. Measurements of j HONO were obtained for solar zenith angles ranging from 20–75∘, under clear and cloudy skies. Maximum error estimates on j HONO under clear skies range from 11% at sunrise, to 4% at solar noon, with a minimum detection limit of 5.7 × 10−4/sec for our actinometer. Measured clear-sky values of j HONO were compared with values calculated by a four-stream discrete ordinate radiative transfer (RT) model (ACD TUV version 4.1), and were found to be within better than 10% agreement for solar zenith angles < 65∘. For conditions of scattered cloud, enhancement and suppression of the j HONO values occurred by as much as 16%–70%, and 59%–80%, respectively. The integrated band area of the nπ∗ transition for gas-phase nitrous acid yields an oscillator strength, f = (1.06 ± 0.044)×10−3 (based on clear-sky data), 19.1% higher than the value reported by Bongartz et al. (1991)
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