Flow reactor and triple quadrupole mass spectrometer investigations of negative ion reactions involving nitric acid: Implications for atmospheric HNO3 detection by chemical ionization mass spectrometry

Atmospheric nitric acid measurements by ACIMS (Active Chemical Ionization Mass Spectrometry) are based on ion-molecule reactions of CO₃ ^-(H₂O) _n and NO₃ ^-(H₂O) _n with HNO₃. We have studied these reactions in the laboratory using a flow tube apparatus with mass spectrometric detection of reactant and product ions. Both product ion distributions and rate coefficients were measured. All reactions were investigated in an N₂-buffer (1–3 hPa) at room temperature. The reaction rate coefficients of OH^-, O₂ ^-, O₃ ^-, CO₄ ^-, CO₃ ^-, CO₃ ^-H₂O, NO₃ ^-, and NO₃ ^-H₂O were measured relative to the known rate k=3.0×10^-9 cm³ s^-1 for the reaction of O^- with HNO₃. The main product ion of the reaction of CO₃ ^-H₂O with HNO₃ was found to be (CO₃HNO₃)^- supporting a previous suggestion made on the basis of balloon-borne ACIMS measurements. For the reaction of bare CO₃ ^- with HNO₃ three product ions were observed, namely NO₃ ^-, (NO₃OH)^-, and (CO₃HNO₃)^-. The reaction rate coefficients for CO₃ ^-H₂O (1.7×10^-9 cm³ s^-1) and NO₃ ^-H₂O (1.6×10^-9 cm³ s^-1) were found to be close to the collision rate. The measured k values for bare CO₃ ^- (1.3×10^-9 cm³ s^-1) and NO₃ ^- (0.7×10^-9 cm³ s^-1) are somewhat smaller. The collisional dissociations of CO₃ ^-(H₂O) _n , NO₃ ^-(H₂O) _n (n=1, 2), (CO₃HNO₃)^- and (NO₃HNO₃)^-, occasionally influencing ACIMS measurements, were also studied. Fragment ion distributions were measured using a triple quadrupole mass spectrometer. The results showed that previous stratospheric nitric acid measurements were unimpaired from collisional dissociation processes whereas these processes played a major role during previous tropospheric measurements leading to an underestimation of nitric acid concentrations. Previous ACIMS HNO₃ detection was also affected by the conversion of CO₃ ^-(H₂O) _n to NO₃ ^-(H₂O) _n due to ion source-produced neutral radicals. A novel ACIMS ion source was developed in order to avoid these problems and to improve the ACIMS method.     

Characterization of organic aerosols in Beijing using an aerodyne high-resolution aerosol mass spectrometer

Fine particle of organic aerosol(OA), mostly arising from pollution, are abundant in Beijing. To achieve a better understanding of the difference in OA in summer and autumn, a high-resolution time-of-flight aerosol mass spectrometer(HRTo F-AMS, Aerodyne Research Inc., USA) was deployed in urban Beijing in August and October 2012. The mean OA mass concentration in autumn was 30 ± 30 μg m-3, which was higher than in summer(13 ± 6.9 μg m-3). The elemental analysis found that OA was more aged in summer(oxygen-to-carbon(O/C) ratios were 0.41 and 0.32 for summer and autumn,respectively). Positive matrix factorization(PMF) analysis identified three and five components in summer and autumn, respectively. In summer, an oxygenated OA(OOA), a cooking-emission-related OA(COA), and a hydrocarbon-like OA(HOA)were indentified. Meanwhile, the OOA was separated into LV-OOA(low-volatility OOA) and SV-OOA(semi-volatile OOA);and in autumn, a nitrogen-containing OA(NOA) was also found. The SOA(secondary OA) was always the most important OA component, accounting for 55% of the OA in the two seasons. Back trajectory clustering analysis found that the origin of the air masses was more complex in summer. Southerly air masses in both seasons were associated with the highest OA loading, while northerly air masses were associated with the lowest OA loading. A preliminary study of OA components,especially the POA(primary OA), in different periods found that the HOA and COA all decreased during the National Day holiday period, and HOA decreased at weekends compared with weekdays.     

Determination of heterogeneous reaction probability using deposition profile measurement in an annular reactor: Application to the N2O5/H2O reaction

A method for the estimation of the reaction probability of the heterogeneous N₂O₅+H₂O 2HNO₃ reaction using the deposition profile in a laminar flow tube, in which the walls are coated with the condensed aqueous phase of interest, is presented. The production of gas phase nitric acid on the surface followed by its absorption complicates the deposition profiles and hence the calculation of the reaction probability. An estimation of the branching ratio for this process enables a more appropriate calculation to be carried out. Reaction probabilities of N₂O₅ on substances including some normally constituting atmospheric aerosols, NaCl, NH₄HSO₄, as well as Na₂CO₃ are estimated and found to depend on relative humidity and characteristics of the coating used. These fell within the range (0.04–2.0)×10^–2.     

Ensemble reconstruction of the atmospheric column from surface pressure using analogues

We present a statistical method to reconstruct continuous atmospheric fields on various pressure levels, given a constraint at the surface. The method is based on analogues of circulation and taking into consideration the time sequence of the analogues. The method is tested on the 2001–2011 period, with an emphasis on the year 2010. We base the atmospheric reconstruction on reanalysis data from 1948 to 2000, and use a constraint of sea-level pressure for 2001–2011. The pattern correlation scores appear to be significant most of the time, although score flaws are occasionally detected. Those flaws are mainly due to the time continuity constraint that is imposed on the reconstruction, which lowers the possibility of finding matching analogues. This method offers an ensemble of atmospheric reconstructions, and presents a computationally cheap alternative to data assimilation for a climate model, although with lower scores.     

Analysis of atmospheric flow over a surface protrusion using the turbulence kinetic energy equation

Flow over surface obstructions can produce significantly large wind shears such that adverse flying conditions can occur for aeronautical systems (helicopters, STOL vehicles, etc.) Atmospheric flow fields resulting from a semi-elliptical surface obstruction in an otherwise horizontally homogeneous statistically stationary flow are modelled with the boundary-layer / Boussinesq-approximation of the governing equation of fluid mechanics. The turbulence kinetic energy equation is used to determine the dissipative effects of turbulent shear on the mean flow. Mean-flow results are compared with those given in a previous paper where the same problem was attacked using a Prandtl mixing-length hypothesis. The diffusion and convection of turbulence kinetic energy not accounted for in the Prandtl mixing-length concept cause departures of the mean wind profiles from those previously computed, primarily in the regions of strong pressure gradients. Iso-lines of turbulence kinetic energy and turbulence intensity are plotted in the plane of the flow. They highlight regions of high turbulence intensity in the stagnation zone and sharp gradients in intensity along the transition from adverse to favourable pressure gradient.     

The atmospheric chemistry of dimethylsulfoxide (DMSO) kinetics and mechanism of the OH+DMSO reaction

We have employed a pulsed laser photolysis-pulsed laser induced fluorescence technique to study the kinetics and mechanism of the reaction of OH with dimethylsulfoxide and its deuterated analogue. A rate coefficient of (1.0±0.3)×10^-10 cm³ molecule^-1 s^-1 was obtained ar room temperature. The rate coefficient was independent of pressure over the range 25–700 Torr, showed no dependence on the nature of the buffer gas and showed no kinetic isotope effect. A limited study of the temperature dependence indicated that the reaction displays a negative activation energy. The gas phase ultraviolet absorption spectrum was obtained at room temperature and showed a strong absorption feature in the far ultraviolet. The absolute absorption cross-section at 205 nm, the absorption peak, is (1.0±0.3)×10^-17 cm², where the large uncertainty results from experimental difficulties associated with the low vapor pressure and stickiness of DMSO.     

Relative-rate study of the gas-phase reaction of hydroxy radicals with difunctional organic nitrates at 298 K and atmospheric pressure

Rate coefficients for the reactions of difunctional nitrates with atmospherically important OH radicals are not currently available in the literature. This study represents the first determination of rate coefficients for a number of C(3) and C(4) carbonyl nitrates and dinitrates with OH radicals in a 38 l glass reaction chamber at 1000 mbar total pressure of synthetic air by 298±2 K using a relative kinetic technique.The following rate coefficients (in units of 10^-12 cm³ molecule^-1 s^-1) were obtained: 1,2-propandiol dinitrate, <0.31; 1,2-butandiol dinitrate, 1.70±0.32; 2,3-butandiol dinitrate, 1.07±0.26; -nitrooxyacetone, <0.43; 1-nitrooxy-2-butanone, 0.91±0.16; 3-nitrooxy-2-butanone, 1.27±0.14; 1,4-dinitrooxy-2-butene, 15.10±1.45; 3,4-dinitrooxy-1-butene, 10.10±0.50.The possible importance of reaction of OH as an atmospheric sink for the compounds compared to other loss processes is considered.     

Assessment of regional seasonal rainfall predictability using the CPTEC/COLA atmospheric GCM

This is a study of the annual and interannual variability of regional rainfall produced by the Center for Weather Forecasts and Climate Studies/Center for Ocean, Land and Atmospheric Studies (CPTEC/COLA) atmospheric global climate model. An evaluation is made of a 9-member ensemble run of the model forced by observed global sea surface temperature (SST) anomalies for the 10-year period 1982–1991. The Brier skill score and, Relative Operating Characteristics (ROC) are used to assess the predictability of rainfall and to validate rainfall simulations, in several regions world wide. In general, the annual cycle of precipitation is well simulated by the model for several continental and oceanic regions in the tropics and mid latitudes. Interannual variability of rainfall during the peak rainy season is realistically simulated in Northeast Brazil, Amazonia, central Chile, and southern Argentina–Uruguay, Eastern Africa, and tropical Pacific regions, where the model shows good skill. Some regions, such as northwest Peru–Ecuador, and southern Brazil exhibit a realistic simulation of rainfall anomalies associated with extreme El Niño warming conditions, while in years with neutral or La Niña conditions, the agreement between observed and simulated rainfall anomalies is not always present. In the monsoon regions of the world and in southern Africa, even though the model reproduces the annual cycle of rainfall, the skill of the model is low for the simulation of the interannual variability. This is indicative of mechanisms other than the external SST forcing, such as the effect of land–surface moisture and snow feedbacks or the representation of sub-grid scale processes, indicating the important role of factors other than external boundary forcing. The model captures the well-known signatures of rainfall anomalies of El Niño in 1982–83 and 1986–87, indicating its sensitivity to strong external forcing. In normal years, internal climate variability can affect the predictability of climate in some regions, especially in monsoon areas of the world.     

Enhanced response of an atmospheric flow to a line-type heat sink in the presence of a critical level

Summary Response of the atmosphere to a line-type heat sink, which represents a cold pool induced by evaporative cooling in falling precipitation, is investigated. Two-dimensional, steady-state, linear perturbations forced by the diabatic cooling in the presence of a critical level are solved analytically. The ambient flow is assumed to have a three-layer structure which is the same as that in Lindzen and Tung (1976, denoted as LT hereafter) except that an isolated diabatic cooling is specified in the lower layer. The shear layer with a critical level is assumed to be either dynamically stable or unstable. A steady-state solution is possible even for a dynamically unstable flow in the middle layer because the wave energy is allowed to propagate to infinity in the upper layer.Thermally induced wave response near the critical level depending on the stability and wind shear in terms of the Richardson number exhibits the same behavior as the eigenvalue problem solved by Jones (1967) and LT because the source mechanism does not change the critical level behavior. That is, when the shear layer is dynamically stable, almost all of the wave energy is absorbed near the critical level, while for dynamically unstable case waves can be partially-or over-reflected from the critical level depending on the Richardson number. Waves can be over-reflected and over-transmitted simultaneously as they travel through the critical level in the process of the energy extraction from the unstable mean shear flow.Using the duct condition proposed by LT, it is found that the magnitude of the perturbation vertical velocity in the lower layer is 6 times larger than that for a nonducting case with the same cooling rate. This implies that under a proper choice of the critical level height and stability profile, the response of the atmosphere to a line-type heat sink can be significantly enhanced through the over-reflection process.With 7 Figures     

Observed generation of an atmospheric gravity wave by shear instability in the mean flow of the planetary boundary layer

Observations of a single boundary-layer event — the generation of an atmospheric gravity wave by an unstable shear flow at Haswell, Colorado on November 12, 1971 — are briefly described and discussed. The observations were made using: (a) an acoustic echo sounder, (b) anemometers mounted at two fixed levels on a 150-m tower, (c) an anemometer and a thermometer mounted on a movable carriage on the tower, and (d) a microbarograph array, including one microbarograph mounted atop the tower. The wave phase velocity (–3.5–4.0 m s^–1) was found to equal the wind velocity in the middle of the shear flow, as assumed by other authors. The wave-associated vertical fluxes of momentum and energy measured just above the wave critical layer were estimated to be –5 dyn cm^–2 and –800 erg cm^–2 s^–1, respectively. These are large values. The annual average vertical flux of momentum at temperate and high latitudes is –0.25 dyn cm^–2, while the average kinetic energy dissipation rate in a unit column of atmosphere is –5 × 10³ erg cm^–2 s^–1. If the region of wave generation was itself propagating horizontally, its propagation velocity was large compared with the horizontal phase speed of the small-scale waves generated. Wave generation appeared to occur over an area large compared with the size of the microbarograph array (i.e., 2 km).     

An analysis of wind velocity fluctuations in the atmospheric surface layer using an orthonormal wavelet transform

A wavelet analysis can supply information of both the location (time) and the scale of fluctuations. This method is applied to the fluctuations of the natural wind and the turbulent transport of momentum in the atmospheric surface layer. The shapes of both the wavelet spectra and the Fourier spectra of the three components of the wind velocity fluctuations are similar to each other. The quadrant representation of momentum transport shows the scale difference of the transport. The large-scale fluctuations mainly contribute to the downward transport of momentum.     

Is the recent build-up of atmospheric CO2 over Europe reproduced by models. Part 2: an overview with the atmospheric mesoscale transport model CHIMERE

In this issue, Ramonet et al. revealed a positive trend in European, atmospheric CO₂ concentrations relative to a marine, North Atlantic reference baseline, for the years 2001–2006. The observed build up mainly occurred during the cold season where it reaches a 0.8 ppm yr⁻¹ at low-altitude stations to a 0.3 ppm yr⁻¹ at mid-altitude stations. We explore the cause of this build-up using the mesoscale model CHIMERE. We first model the observed trends, using interannually varying fluxes and transport, then suppress the interannual variability in fluxes or aspects of transport to elucidate the cause. The run with no interannual variability in fluxes still matches observed trends suggesting that transport is the major cause. Separate runs varying either boundary layer height or winds show that changes in boundary layer height explain the trends at low-altitude stations within the continents while changes in wind regimes drive changes elsewhere.