Uptake Of HNO3 Research Articles

Heterogeneous uptake of nitric acid on Na‐montmorillonite clay as a function of relative humidity

Atmospheric mineral aerosol is a potentially important reactive surface that may provide a heterogeneous sink for gas phase species such as nitric acid (HNO3). We have studied the uptake of HNO3 on Na‐montmorillonite, a swelling clay mineral, at low temperatures as a function of relative humidity (RH), HNO3 pressure and clay mass. Condensed phase products were probed with transmission Fourier transform infrared spectroscopy while the loss of HNO3 from the gas phase was simultaneously monitored with mass spectrometry. We find that below 16% RH, uptake of HNO3 on Na‐montmorillonite is below our detection limit. However, at 29% RH the lower limit to the uptake coefficient for loss of HNO3 on Na‐montmorillonite is γ = 8 × 10−5 as calculated using the BET surface area. This value increases to γ = 4 × 10−4 at 44% RH. The HNO3 content, water content and γ all increase with increasing RH, but are independent of temperature from 210 to 232 K and independent of pressure from 1 × 10−5 to 3 × 10−4 torr HNO3. Surprisingly, at 44% RH, Na‐montmorillonite can contain approximately 20% water and 30% HNO3 by weight. The results of this study suggest that swelling clays can impact the partitioning of gas phase HNO3 when sufficient water vapor is available and may serve as a potentially important cloud condensation nucleus in the troposphere.

Effect of humidity on nitric acid uptake to mineral dust aerosol particles

Abstract. This study presents the first laboratory observation of HNO3 uptake by airborne mineral dust particles. The model aerosols were generated by dry dispersion of Arizona Test Dust (ATD), SiO2, and by nebulizing a saturated solution of calcium carbonate. The uptake of 13N-labeled gaseous nitric acid was observed in a flow reactor on the 0.2–2 s reaction time scale at room temperature and atmospheric pressure. The amount of nitric acid appearing in the aerosol phase at the end of the flow tube was found to be a linear function of the aerosol surface area. SiO2 particles did not show any significant uptake, while the CaCO3 aerosol was found to be more reactive than ATD. Due to the smaller uncertainty associated with the reactive surface area in the case of suspended particles as compared to bulk powder samples, we believe that we provide an improved estimate of the rate of uptake of HNO3 to mineral dust. The fact that the rate of uptake was smaller at a concentration of 1012 than at 1011 was indicative of a complex uptake mechanism. The uptake coefficient averaged over the first 2 s of reaction time at a concentration of 1012 molecules cm-3 was found to increase with increasing relative humidity, from 0.022±0.007 at 12% RH to 0.113±0.017 at 73% RH , which was attributed to an increasing degree of solvation of the more basic minerals. The extended processing of the dust by higher concentrations of HNO3 at 85% RH led to a water soluble coating on the particles and enhanced their hygroscopicity.

Nitric acid in cirrus clouds

Uptake of nitric acid (HNO3) in Arctic cirrus ice crystals was observed on 11 February 2003 by in‐situ instruments onboard the M55 Geophysica aircraft. The cirrus cloud with a mean ice water content of 5.4 mg m−3 covered northern Scandinavia for several hours and extended up to the thermal tropopause at 12.3 km. Within the cirrus region, on average 9% of the total HNO3 measured as reactive nitrogen (NOy) is present in ice particles, increasing to 19% at temperatures below 205 K. In contrast to previous studies, we discuss the HNO3 uptake in ice in terms of HNO3/H2O molar ratios in ice crystals. The HNO3 content of the ice increases with increasing gas phase HNO3 concentrations and decreasing temperatures. Enhanced uptake of HNO3 in ice and heterogeneous chemistry on cold cirrus clouds may disturb the upper tropospheric ozone budget.

The impact of ice uptake of nitric acid on atmospheric chemistry

Abstract. The potential impact of the uptake of HNO3 on ice on the distribution of NOy species, ozone and OH has been assessed using the global scale chemistry-transport model MATCH-MPIC. Assuming equilibrium uptake according to dissociative Langmuir theory results in significant reductions of gas phase HNO3. Comparison to a large set of observations provides support that significant uptake of HNO3 on ice is occurring, but the degree of the uptake cannot be inferred from this comparison alone. Sensitivity simulations show that the uncertainties in the total amount of ice formation in the atmosphere and the actual expression of the settling velocity of ice particles only result in small changes in our results. The largest uncertainty is likely to be linked to the actual theory describing the uptake process and the value of the initial uptake coefficient. The inclusion of non-methane hydrocarbon chemistry partially compensates for the absence of HNO3 uptake on ice when this is neglected in the model. The calculated overall effect on upper tropospheric ozone concentrations and the tropospheric methane lifetime are moderate to low. These results support a shift in the motivation for future experimental and theoretical studies of HNO3-ice interaction towards the role of HNO3 in hydrometeor surface physics.

Nitric acid partitioning in cirrus clouds: the role of aerosol particles and relative humidity

Owing to the potential of cirrus clouds to vertically redistribute HNO3 in the upper troposphere, the uptake of HNO3 in ice particles is at the focus of recent research. Here, we investigate whether HNO3 residing in freezing aerosol particles could be a relevant source of HNO3 in ice clouds. To this end, model studies on the sensitivity of the uptake of HNO3 in aerosol particles to temperature, relative humidity with respect to ice (RHice), particle composition and amount of available HNO3 were performed. Combining the model results with the history of RHice during cirrus formation and comparison with field measurements indicates that at temperatures > 200 K a considerable part of the HNO3 in ice may originate from freezing particles containing HNO3.

Global impacts of gas‐phase chemistry‐aerosol interactions on direct radiative forcing by anthropogenic aerosols and ozone

We present here a first global modeling study on the influence of gas‐phase chemistry/aerosol interactions on estimates of anthropogenic forcing by tropospheric O3 and aerosols. Concentrations of gas‐phase species and sulfate, nitrate, ammonium, black carbon, primary organic carbon, secondary organic carbon, sea salt, and mineral dust aerosols in the preindustrial, present‐day, and year 2100 (IPCC SRES A2) atmospheres are simulated online in the Goddard Institute for Space Studies general circulation model II' (GISS GCM II'). With fully coupled chemistry and aerosols, the preindustrial, present‐day, and year 2100 global burdens of tropospheric ozone are predicted to be 190, 319, and 519 Tg, respectively. The burdens of sulfate, nitrate, black carbon, and organic carbon are predicted respectively to be 0.32. 0.18, 0.01, 0.33 Tg in preindustrial time, 1.40, 0.48, 0.23, 1.60 Tg in present‐day, and 1.37, 1.97, 0.54, 3.31 Tg in year 2100. Anthropogenic O3 is predicted to have a globally and annually averaged present‐day forcing of +0.22 W m−2 and year 2100 forcing of +0.57 W m−2 at the top of the atmosphere (TOA). Net anthropogenic TOA forcing by internally mixed sulfate, nitrate, organic carbon, and black carbon aerosols is estimated to be virtually zero in the present‐day and +0.34 W m−2 in year 2100, whereas it is predicted to be −0.39 W m−2 in present‐day and −0.61 W m−2 in year 2100 if the aerosols are externally mixed. Heterogeneous reactions are shown to be important in affecting anthropogenic forcing. When reactions of N2O5, NO3, NO2, and HO2 on aerosols are accounted for, TOA anthropogenic O3 forcing is less by 20–45% in present‐day and by 20–32% in year 2100 at mid to high latitudes in the Northern Hemisphere, as compared with values predicted in the absence of heterogeneous gas‐aerosol reactions. Mineral dust uptake of HNO3 and O3 is shown to have practically no influence on anthropogenic O3 forcing. Heterogeneous reactions of N2O5, NO3, NO2, and HO2 are predicted to have noticeable impacts on anthropogenic aerosol forcing over industrialized areas, leading to 0–2 W m−2 more anthropogenic aerosol cooling in present‐day and 2–8 W m−2 more cooling in year 2100 in these areas as compared with forcings calculated in the absence of heterogeneous reactions. Sea salt uptake of SO2 reduces the magnitude of TOA aerosol cooling by 0.5–1 W m−2 over the oceans around 60°N in the present‐day and year 2100 scenarios. Near dust sources, mineral dust uptake of SO2 and HNO3 leads to less anthropogenic aerosol cooling by 0.5–1 W m−2 in the present‐day and 1–2 W m−2 in year 2100.

Water, sulfur dioxide and nitric acid adsorption on calcium carbonate: A transmission and ATR-FTIR study

Calcium carbonate (CaCO3) is a reactive component of mineral dust aerosol as well as buildings, statues and monuments. In this study, attenuated total reflection (ATR) and transmission Fourier transform infrared spectroscopy (FTIR) have been used to study the uptake of water, sulfur dioxide and nitric acid on CaCO3 particles at 296 K. Under atmospheric conditions, CaCO3 particles are terminated by a Ca(OH)(CO3H) surface layer. In the presence of water vapor between 5 and 95% relative humidity (RH), water molecularly adsorbs on the Ca(OH)(CO3H) surface resulting in the formation of an adsorbed thin water film. The adsorbed water film assists in the enhanced uptake of sulfur dioxide and nitric acid on CaCO3 in several ways. Under dry conditions (near 0% RH), sulfur dioxide and nitric acid react with the Ca(OH)(CO3H) surface to form adsorbed carbonic acid (H2CO3) along with sulfite and nitrate, respectively. Adsorbed carbonic acid is stable on the surface under vacuum conditions. Once the surface saturates with a carbonic acid capping layer, there is no additional uptake of gas-phase sulfur dioxide and nitric acid. However, upon adsorption of water, carbonic acid dissociates to form gaseous carbon dioxide and there is further uptake of sulfur dioxide and nitric acid. In addition, adsorbed water increases the mobility of the ions at the surface and enhances uptake of SO2 and HNO3. In the presence of adsorbed water, CaSO3 forms islands of a crystalline hydrate whereas Ca(NO3)2 forms a deliquescent layer or micropuddles. Thus adsorbed water plays an important and multi-faceted role in the uptake of pollutant gases on CaCO3.

A kinetic model for uptake of HNO3 and HCl on ice in a coated wall flow system

A simple model of gas flow and surface exchange with a single site Langmuir mechanism has been developed to describe effects of adsorption and desorption on trace gas concentrations at the outflow from a coated wall flow tube reactor. The model was tested by simulating experimental results for the uptake of HNO3 and HCl on ice films at temperatures and gas concentrations corresponding to the ice stability region in the upper troposphere. The experimental time-dependent uptake profiles were best fitted with an additional process involving diffusion of the adsorbed molecules into the ice film. The model allowed true surface coverages to be distinguished from total uptake including transfer to the bulk, leading to more accurate estimates of the Langmuir constant, Keq, for surface adsorption. A revised expression was obtained for the temperature dependence of the Keq=-(4.43 +/- 0.77)x 10(5)T+(10.72 +/- 1.75)x 10(7) hPa-1. Reasonable fits to the desorption profiles observed following cessation of exposure of the film to HNO3 or HCl were obtained at high surface coverage but at low coverage desorption was too slow. The analysis suggested that the ice surface was characterised by sites of different binding energy, some weakly bound sites from which the acid molecules desorbed rapidly, and some strong-binding sites which led to essentially irreversible uptake. Experiments involving competitive co-adsorption of HNO3 and HCl, conducted at relatively high equilibrium surface coverage, were well simulated by the model, as were those where the same surface was repeatedly exposed to gas phase acids.

Inorganic composition of fine particles in mixed mineral dust–pollution plumes observed from airborne measurements during ACE‐Asia

Chemical characteristics of inorganic water‐soluble aerosol particles measured in large Asian springtime dust events during the Asian Pacific Regional Characterization Experiment (ACE‐Asia) were investigated. Three specific flights (flights 6, 7, and 10) in the Yellow Sea boundary layer with high mineral dust concentrations mixed with pollutants from Asian urban centers are presented. Measurements during a similar campaign, Transport and Chemical Evolution over the Pacific (TRACE‐P), in the same region suggested that fine‐particle ammonium sulfate and nitrate salts, and potassium, apparently from biomass burning, are common particle ionic constituents in polluted air. Observations from the ACE campaign show similar characteristics and found that the main component of water‐soluble mineral dust was Mg2+ and Ca2+. Ion charge balances of measured fine and total aerosol suggest that a significant fraction of the Mg2+ and Ca2+ observed were in the form of carbonates. In polluted air mixed with dust that advected directly from large urban regions in roughly half a day to 1 day (flights 6 and 7), much of the fine‐particle nitrate and sulfate (approximately 80%) was apparently associated with ammonium or potassium, the rest likely associated with mineral dust. Only air masses that spent 2–5 days over the Yellow Sea (flight 10) had clear evidence of Cl− depletion. Initial mass accommodation coefficients much less than 0.1 for uptake of SO2 or HNO3 by mineral dust in urban plumes containing fossil fuel and biomass‐burning emissions could explain the observations. The data suggest an accommodation coefficient dependence on relative humidity.

Reactive Uptake of Nitric Acid into Aqueous Sodium Chloride Droplets Using Real-Time Single-Particle Mass Spectrometry

The kinetics and rate-limiting mechanism of reactive uptake of nitric acid into submicron, deliquescent sodium chloride aerosols are determined. The reaction was performed in a flow tube with a real-time single-particle mass spectrometer connected to the outlet to determine the chloride-to-nitrate ratio of the transformed particles. Pseudo-first-order conditions were maintained by keeping the nitric acid pressure constant, as measured with a chemiluminescence analyzer. Experiments were performed with 100−220 nm diameter droplets at ca. 80% relative humidity and nitric acid concentrations between 60 and 380 ppb. Rate constants and uptake coefficients were determined from time-dependent changes in the chloride concentration of individual particles that traversed the reactor. The initial reactive uptake coefficient for 100 nm droplets was found to be 4.9 ± 2.7 × 10-3 and, to a first approximation, independent of the nitric acid concentration. The uptake coefficient also was found to increase linearly with increasing droplet size over the size range studied. These dependencies suggest that transport phenomena (diffusion of HNO3(g) to the droplet surface, accommodation of HNO3 into the droplet, diffusion of HNO3(aq) and HCl(aq) inside the droplet, and transport of HCl across the droplet surface into the gas phase) do not limit the reaction rate. Instead, reactive uptake of HNO3(g) is limited by formation of molecular HCl in the aqueous phasea thermodynamically controlled process. The results are consistent with related measurements that show uniform chloride/nitrate/sodium mole ratios in submicron-size aerosols, a large uptake coefficient for aerosols in the low micron-size range, and decreasing chloride-to-nitrate ratios (because of transport limitations) in supermicron-size aerosols.

Heterogeneous Reaction of Gaseous Nitric Acid on γ-Phase Iron(III) Oxide

The uptake of HNO3 on γ-Fe2O3 particles that model atmospheric mineral dust has been investigated using FT-IR spectroscopy and mass spectrometry to probe the condensed and gas phases, respectively. To accurately calculate the HNO3 saturation coverage (θ) and initial uptake coefficient (γ), the specific surface area of γ-Fe2O3 was measured in situ using water as an adsorbate. The saturation coverage of HNO3 on γ-Fe2O3 was found to be θ = (1.1 ± 0.9) × 1014 molecules/cm2 and the initial uptake coefficient was found to be γ = (1.5 ± 1.0) × 10-5 at 297 K and PHNO3 = 1 × 10-5 Torr. These values were slightly larger at 220 K for the same partial pressure of nitric acid. Spectroscopically, HNO3 was observed to bind to the surface in the form of nitrate ions. The significance of this reaction to tropospheric chemistry is discussed.

Global modeling of heterogeneous chemistry on mineral aerosol surfaces: Influence on tropospheric ozone chemistry and comparison to observations

Mineral aerosols can affect gas phase chemistry in the troposphere by providing reactive sites for heterogeneous reactions. We present here a global modeling study of the influence of mineral dust on the tropospheric photochemical cycle. This work is part of the Mineral Dust and Tropospheric Chemistry (MINATROC) project, which focussed on measurement campaigns, laboratory experiments, and integrative modeling. The laboratory experiments provide uptake coefficients for chemical species on mineral aerosol surfaces, which are used to compute the heterogeneous reaction rates in the model. The field measurements at Mount Cimone, northern Italy, provide trace gas and aerosol measurements during a Saharan dust episode and are used to evaluate the model. The simulations include the reactions between mineral dust aerosols and the gas‐phase species O3, HNO3, NO3, and N2O5. Under the conditions for the year 2000 the model simulates a decrease in global tropospheric ozone mass by about 5% due to the heterogeneous reactions on dust aerosols. The most important heterogeneous reaction is the uptake of HNO3 on the dust surface, whereby the direct uptake of ozone on dust is not important in atmospheric chemistry. The comparison of the model results to observations indicates that the model simulates well the aerosol mass transported into the Mediterranean during the dust events and the arrival of all major dust events that were observed during a 7 month period. The decrease in ozone concentration during dust events is better simulated by the model when the heterogeneous reactions are included.

Asian dust storm events of spring 2001 and associated pollutants observed in New England by the Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) monitoring network

Between 18 April and 13 May 2001, three statistically extreme dust aerosol events were observed across the entire northeastern United States. High levels of bulk aerosol water‐soluble Ca2+ (range = 42–482 pptv) and PM2.5 elemental Ca (range = 19–156 pptv) were observed simultaneously at Atmospheric Investigation, Regional Modeling, Analysis and Prediction (AIRMAP) and Interagency Monitoring of Protected Visual Environments (IMPROVE) stations. On the basis of Ca2+ concentrations, the average bulk dust concentration for all events across all four AIRMAP stations was estimated to be 7.4 μg/m3. There was no evidence of dust outbreaks in North America large enough to explain these events. However, in April 2001, massive dust storms occurred in the Tarim Pendi basin and in the Gobi deserts of southern Mongolia and China. Comparison of elemental ratios of AIRMAP samples to previously reported Asian dust aerosol samples showed that all AIRMAP samples had a chemical composition similar to Asian dust transported over long distances. Within the dust plumes, strong correlations were observed between absorption, scattering, and CO, indicative of an anthropogenic contribution including elemental carbon and SO42− aerosols. Aerosol NO3− was also highly elevated during event days, most likely due to uptake of HNO3 by the dust during transport. A comparison of dust plumes sampled by AIRMAP to those sampled off the Asian coast during the TRACE‐P airborne mission and on the U.S. west coast, strongly suggested entrainment of additional pollutants (e.g., CO, aerosol NO3−, and SO42−) as the dust plumes were transported over North America.

The heterogeneous reaction of HNO3on mineral dust and γ-alumina surfaces: a combined Knudsen cell and DRIFTS study

The kinetics of the interaction of HNO3 with natural mineral dusts (Saharan, Chinese and Arizona dust) and γ-alumina surfaces has been studied at T = 298 K using a Knudsen cell reactor coupled to a mass spectrometer for kinetic studies on the gas uptake as well as DRIFT spectroscopy for studies of the surface products. The uptake of HNO3 on each surface was found to be fast with initial uptake coefficients of γ ≈ 0.1. Nitrate and water have been identified as reaction products. The formation rate of surface nitrate, however, was slower with uptake coefficients ranging from 8 × 10−3 < γ < 5.4 × 10−2 depending on the chemical nature of the surface. From these results a two-step mechanism for the reactive uptake of HNO3 onto mineral oxides, consisting of fast adsorption of gas-phase HNO3 followed by a slower surface reaction of HNO3(ads) with surface OH-groups is inferred. Furthermore, it was found that the reactivity of mineral dust towards HNO3 decreased with increasing exposure. However, the original reactivity could be recovered by water exposure and may therefore be conserved under atmospheric conditions.

Aerosol chemical composition in Asian continental outflow during the TRACE‐P campaign: Comparison with PEM‐West B

Aerosol associated soluble ions and the radionuclide tracers 7Be and 210Pb were quantified in 414 filter samples collected in spring 2001 from the DC‐8 during the Transport and Chemical Evolution over the Pacific (TRACE‐P) campaign. Binning the data into near Asia (flights from Hong Kong and Japan) and remote Pacific (all other flights) revealed large enhancements of NO3−, SO4=, C2O4=, NH4+, K+, Mg2+, and Ca2+ near Asia. The boundary layer and lower troposphere were most strongly influenced by continental outflow, and the largest enhancements were seen in Ca2+ (a dust tracer) and NO3− (reflecting uptake of HNO3 onto the dust). Comparing the TRACE P near Asia bin with earlier results from the same region during PEM‐West B (in 1994) shows at least twofold enhancements during TRACE P in most of the ions listed above. Calcium and NO3− were most enhanced in this comparison as well (more than sevenfold higher in the boundary layer and threefold higher in the lower troposphere). Independent estimation of Asian emissions of gaseous precursors of the aerosol‐associated ions suggest only small changes between the two missions, and precipitation fields do not suggest any significant difference in the efficiency of the primary sink, precipitation scavenging. It thus appears that with the possible exception of dust, the enhancements of aerosol‐associated species during TRACE P cannot be explained by stronger sources or weaker sinks. We argue that the enhancements largely reflect the fact that TRACE P focused on characterizing Asian outflow, and thus the DC‐8 was more frequently flown into regions that were influenced by well‐organized flow off the continent.

Knudsen Cell Studies of the Reaction of Gaseous HNO3 with NaCl Using Less than a Single Layer of Particles at 298 K: A Modified Mechanism

The uptake and reaction of HNO3 with NaCl was studied at 298 K using a Knudsen cell coupled to a quadrupole electron impact mass spectrometer. Experiments were conducted using less than one layer of particles to clearly define the available reactive surface area. The uptake of HNO3 was observed to be faster initially than at longer reaction times. A new model is proposed that incorporates reactions at two different types of sites: (1) steps and edges on the NaCl surface holding surface adsorbed water (SAW) and (2) dry terrace sites. The initial, more rapid uptake is attributed to reaction with both types of sites on a fresh NaCl surface, while the slower uptake at longer reaction times is due only to reaction at the steps and edges where new reaction sites are generated by the SAW-assisted recrystallization of the NaNO3 product. The initial uptake coefficient based on data at short reaction times is γ0 = (2.3 ± 1.9) × 10-3, in agreement within the experimental errors with a value of γ0 = (1.1 ± 0.4) × 10-3 (2s) derived from the dependence of the uptake coefficient on the initial HNO3 concentration. The fraction of the surface area covered by sites holding SAW was estimated to be approximately 50% based on the uptake coefficient, averaged over three cycles of exposure to HNO3, γ = (1.0 ± 0.8) × 10-3 (2s). The data suggest that the reaction of HNO3 with effluoresced sea salt particles is less important than previously thought relative to reactions with N2O5 and ClONO2, which generate chlorine atom precursors.

Atmospheric measurements of gas-phase HNO&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; and SO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; using chemical ionization mass spectrometry during the MINATROC field campaign 2000 on Monte Cimone

Abstract. The EU-project MINATROC (MINeral dust And TROpospheric Chemistry) aims at enabling an estimation of the influence of mineral dust, a major, but to date largely ignored component of tropospheric aerosol, on tropospheric oxidant cycles. Within the scope of this project continuous atmospheric measurements of gas-phase HNO3 and SO2 were conducted in June and July 2000 at the CNR WMO station, situated on Monte Cimone (MTC) (44°11' N --10°42' E, 2165 m asl), Italy. African air transporting dust is occasionally advected over the Mediterranean Sea to the site, thus mineral aerosol emitted from Africa will encounter polluted air masses and provide ideal conditions to study their interactions. HNO3 and SO2 were measured with an improved CIMS (chemical ionization mass spectrometry) system for ground-based measurements that was developed and built at MPI-K Heidelberg. Since HNO3 is a very sticky compound special care was paid for the air-sampling and background-measurement system. Complete data sets could be obtained before, during and after major dust intrusions. For the first time these measurements might provide a strong observational indication of efficient uptake of gas-phase HNO3 by atmospheric mineral-dust aerosol particles.

Fluxes of nitrates between snow surfaces and the atmosphere in the European high Arctic

Abstract. Measurements of atmospheric and snow mixing ratios of nitrates and nitrites and their fluxes above the snow surface were made during two intensive campaigns during spring time 2001 at Ny-Ålesund, Svalbard as part of the EU project "`The NItrogen Cycle and Effects on the oxidation of atmospheric trace species at high latitudes" (NICE). At this coastal site close to the unseasonably unfrozen fjord, of the measured nitrogen species, only HNO3 showed a significant flux on to the snow surface; a mean deposition of -8.7 nmol h-1 m-2 was observed in late April / early May 2001. These fluxes may be due to the reaction of HNO3 with sea salt, and especially NaCl, or may be simply uptake of HNO3 by ice, which is alkaline because of the sea salt in our marine environment. During snowfall periods dry deposition of HNO3 may contribute up to 10% of the N budget in the snow; however, the main source for N is wet deposition in falling snow. The surface snow at Ny-Ålesund showed very complex stratigraphy; the NO3- mixing ratio in snow varied between 65 and 520 ng g-1, the total NO3- content of the snowpack was on the order of 2700 ng cm-2. In comparison the atmospheric boundary layer column showed a NO3- content of only 8 ng cm-2. The limited exchange, however, between the snow and the atmosphere was attributed to low mobility of NO3- in the observed snow. Contrary to other Arctic sites (i.e. Alert, Nunavut or Summit, Greenland) deposition of sea salt and crustal aerosols in this marine environment made the surface snow alkaline; snow NO3- was associated with heavier cations and was not readily available for physical exchange or photochemical reactions.

Quantifying uptake of HNO3 and H2O by alumina particles in Athena‐2 rocket plume

The goal of this study is to quantify uptake of H2O and HNO3 by and estimate their residence time on alumina particles in Athena‐2 rocket plumes. This study uses in situ measurements made in the lower stratosphere with the NASA WB‐57F high‐altitude aircraft on 24 September 1999. Constraining the Atmospheric and Environmental Research, Inc. (AER), plume model with available measurements, we found that (1) H2O uptake coefficient for alumina particles is larger than 3 × 10−4, (2) HNO3 is produced via ClONO2 + HCl → Cl2 + HNO3 on alumina particles and resides on their surfaces for 5–52 min, and (3) alumina particles in the plume are covered by 100–200 monolayers of adsorbed H2O and 0.1–10 monolayers of HNO3 under lower stratospheric conditions. These values are uncertain by at least a factor of 2. We speculate that the H2O coverage remaining on alumina particles accelerates the ClONO2 + HCl → Cl2 + HNO3 reaction, thus leading to a larger than previously thought global ozone loss to solid‐fueled rocket emissions, especially if at least several percent of emitted alumina mass are in submicron particles.

Heterogeneous reactivity of NO and HNO3 on mineral dust in the presence of ozone

The co-adsorption and reaction of NO and O3 on authentic Saharan dust surfaces was investigated in a Knudsen reactor at ≈296 K. NO was consumed on the dust surface in the presence of O3 and thereby partially converted to NO2, which was released to the gas-phase. An empirical expression for the dependence of NO2 production, PNO2, on the O3 and NO concentrations and dust surface area could be formulated, allowing the importance of this process in the atmosphere to be assessed: , where Adust is the dust surface area per cubic centimetre of air, C′a = 1.4 × 109 s−1 cm−2, bO3 = 4.0 × 10−12 cm3, and bNO = 5.4 × 10−13 cm3. Even at high tropospheric dust concentrations, this production rate is too low to significantly supplement that from NO oxidation by O3 and HO2. Experiments to examine chemical ageing of dust by ozone showed that HNO3 uptake was not influenced by the presence of 100 ppb O3 (STP), and HNO3 uptake coefficients were similar to those previously derived.