Chloride Aerosol Research Articles

Performance of respiratory filters and surgical masks against bacterial aerosols

A laboratory test system has been designed and built to measure the efficiency of filter material from several commonly used respirator filter cartridges, approved disposable dust masks, nuisance dust masks, single-use surgical procedure masks and a resuscitation mask against aerosols of the bacteria Bacillus subtilis subspecies globigii, Micrococcus luteus and Pseudomonas alcaligenes. All tests were carried out at a flow rate of 301min−1. The same materials were also tested with monodisperse urea aerosols in the size range 1.5–9 μm and with the British Standard BS 4400 sodium chloride aerosol, which has a mass geometric mean diameter of 0.6 μm and a geometric standard deviation of 2.3. One type of surgical mask allowed penetration of up to 83% of a microbiological aerosol and 87% of a non-biological aerosol, and nuisance dust masks allowed penetrations of up to effectively 100% for a microbiological aerosol and 91% for a non-biological aerosol. The materials of the other surgical masks and the resuscitation mask, all of which were electrically charged, performed better against all the test aerosols. Penetration of microbiological aerosols through the respirator filter materials was no greater than 0.88%, and penetration of non-biological aerosols no greater than 1.72%. The results for microbiological aerosols generally corresponded to those for the non-biological aerosols in the same size range.

ADSORPTION OF WATER ON NaCl

Surface Review and LettersVol. 04, No. 04, pp. 757-770 (1997) ReviewsNo AccessADSORPTION OF WATER ON NaClGEORGE E. EWING and STEVEN J. PETERSGEORGE E. EWINGDepartment of Chemistry, Indiana University, Bloomington, IN 47405, USA and STEVEN J. PETERSDepartment of Chemistry, Indiana University, Bloomington, IN 47405, USAhttps://doi.org/10.1142/S0218625X97000742Cited by:17 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail FiguresReferencesRelatedDetailsCited By 17Nanoparticle-assisted acceleration of laser-irradiated low-density He ionsEva Klimešová, Olena Kulyk, Laura Dittrich, Jakob Andreasson and Maria Krikunova27 December 2021 | Physical Review A, Vol. 104, No. 6Adsorption Capacities of Hygroscopic Materials Based on NaCl-TiO 2 and NaCl-SiO 2 Core/Shell ParticlesMarie Bermeo, Nabil El Hadri, Florent Ravaux, Abdelali Zaki and Linda Zou et al.13 Feb 2020 | Journal of Nanotechnology, Vol. 2020Influence of stearic acid coating of the NaCl surface on the reactivity with NO 2 under humidityS. Sobanska, J. Barbillat, M. Moreau, N. Nuns and I. De Waele et al.1 January 2015 | Physical Chemistry Chemical Physics, Vol. 17, No. 16Impacts of Surface Adsorbed Catechol on Tropospheric Aerosol Surrogates: Heterogeneous Ozonolysis and Its Effects on Water UptakeLaurie A. Woodill, Erinn M. O’Neill and Ryan Z. Hinrichs1 July 2013 | The Journal of Physical Chemistry A, Vol. 117, No. 27Interfacial Dushman-like Chemistry in Hydrated KIO 3 Layers Grown on KIMatthew A. Brown, Paul D. Ashby, Maria J. Krisch, Zhi Liu and B. Simon Mun et al.29 July 2010 | The Journal of Physical Chemistry C, Vol. 114, No. 33A critical assessment of theoretical methods for finding reaction pathways and transition states of surface processesJiří Klimeš, David R Bowler and Angelos Michaelides3 February 2010 | Journal of Physics: Condensed Matter, Vol. 22, No. 7Bromine Enrichment in the Near-Surface Region of Br-Doped NaCl Single Crystals Diagnosed by Rutherford Backscattering SpectrometryM. Hess, U. K. Krieger, C. Marcolli, T. Huthwelker and M. Ammann et al.27 April 2007 | The Journal of Physical Chemistry A, Vol. 111, No. 20Influence of multiple reflections on transmission through a stack of platesW. L. Schaich, George E. Ewing and Robert L. Karlinsey20 September 2006 | Applied Optics, Vol. 45, No. 27Surface Adsorbed Water on NaCl and Its Effect on Nitric Acid Reactivity with NaCl PowdersSutapa Ghosal and John C. Hemminger24 August 2004 | The Journal of Physical Chemistry B, Vol. 108, No. 37Thin Film Water on Insulator SurfacesGeorge E. Ewing, Michelle Foster, Will Cantrell and Vlad Sadtchenko1 Jan 2003Adsorption of water on the NaCl(001) surface. II. An infrared study at ambient temperaturesMichelle C. Foster and George E. Ewing15 Apr 2000 | The Journal of Chemical Physics, Vol. 112, No. 15Water content and morphology of sodium chloride aerosol particlesDavid D. Weis and George E. Ewing1 September 1999 | Journal of Geophysical Research: Atmospheres, Vol. 104, No. D17Water adsorption by hydrophobic organic surfaces: Experimental evidence and implications to the atmospheric properties of organic aerosolsElan Thomas, Yinon Rudich, Sofia Trakhtenberg and Rachel Ussyshkin1 July 1999 | Journal of Geophysical Research: Atmospheres, Vol. 104, No. D13The Reaction of Nitrogen Dioxide with Sea Salt AerosolDavid D. Weis and George E. Ewing9 June 1999 | The Journal of Physical Chemistry A, Vol. 103, No. 25Effect of Water on the HNO 3 Pressure Dependence of the Reaction between Gas-Phase HNO 3 and NaCl SurfacesSutapa Ghosal and John C. Hemminger9 June 1999 | The Journal of Physical Chemistry A, Vol. 103, No. 25Measurements of the H 2 SO 4 mass accommodation coefficient onto polydisperse aerosolA. Jefferson, F. L. Eisele, P. J. Ziemann, R. J. Weber and J. J. Marti et al.1 August 1997 | Journal of Geophysical Research: Atmospheres, Vol. 102, No. D15H2O on NaCl: From Single Molecule, to Clusters, to Monolayer, to Thin Film, to DeliquescenceGeorge E. Ewing Recommended Vol. 04, No. 04 Metrics Downloaded 18 times History Received 14 November 1996 PDF download

Thermodynamic and optical properties of mixed‐salt aerosols of atmospheric importance

Extensive water activity, density, and refractive index data at 25°C are reported for mixed‐salt solutions, NaCl‐KCl, NaCl‐NaNO3, NaCl‐Na2SO4, Na2SO4‐NaNO3, and (NH4)2SO4‐Na2SO4. The data are obtained from hydration experiments using the single‐particle levitation technique developed recently for measuring the thermodynamic and optical properties of microdroplets. These data, covering the whole concentration range from dilute solutions to high supersaturations, provide an opportunity to explore the light‐scattering properties of both internal and external mixtures of the chloride, sulfate, and nitrate aerosols of atmospheric importance. It is shown that for sulfate and nitrate aerosols as solution droplets, the light‐scattering properties do not differ appreciably among all mixture types and compositions, as long as the dry‐salt aerosols have the same particle‐size distribution. However, for mixed‐salt aerosols containing NaCl, the light‐scattering properties do depend upon the composition and particle‐size distribution, although not so much on the mixture type.

Real-Time Monitoring of the Surface and Total Composition of Aerosol Particles

ABSTRACT Laser desorption ionization is used to characterize the products of an aerosol reaction in real time. Sodium chloride aerosols are mixed with vapor phase ammonia and nitric acid to produce an ammonium nitrate surface layer. The product aerosols are sampled directly into a mass spectrometer where the surface and total compositions are distinguished by laser desorption ionization. With a low laser irradiance, only material near the particle surface is desorbed and ionized. In this case, the mass spectra are independent of the amount of ammonium nitrate deposited, and simply indicate a nitrate-enriched surface layer. With a higher laser irradiance, both the surface layer and core are ablated. The relative intensities of ions originating from the surface layer and core reflect the total composition. That is, the relative intensities of ions produced from the ammonium nitrate surface layer increase with increasing surface layer thickness. The laser irradiance dependences of the mass spectra allow the ...

Chemical and size effects of hygroscopic aerosols on light scattering coefficients

The extensive thermodynamic and optical properties recently reported [Tang and Munkelwitz, 1994a] for sulfate and nitrate solution droplets are incorporated into a visibility model for computing light scattering by hygroscopic aerosols. The following aerosol systems are considered: NH4HSO4, (NH4)2SO4, (NH4)3H(SO4), NaHSO4, Na2SO4, NH4NO3, and NaNO3. In addition, H2SO4 and NaCl are included to represent freshly formed sulfate and background sea‐salt aerosols, respectively. Scattering coefficients, based on 1 μg dry salt per cubic meter of air, are calculated as a function of relative humidity for aerosols of various chemical compositions and lognormal size distributions. For a given size distribution the light scattered by aerosol particles per unit dry‐salt mass concentration is only weakly dependent on chemical constituents of the hygroscopic sulfate and nitrate aerosols. Sulfuric acid and sodium chloride aerosols, however, are exceptions and scatter light more efficiently than all other inorganic salt aerosols considered in this study. Both internal and external mixtures exhibit similar light‐scattering properties. Thus for common sulfate and nitrate aerosols, since the chemical effect is outweighed by the size effect, it follows that observed light scattering by the ambient aerosol can be approximated, within practical measurement uncertainties, by assuming the aerosol being an external mixture. This has a definite advantage for either visibility degradation or climatic impact modeling calculations, because relevant data are now available for external mixtures but only very scarce for internal mixtures.

Response of a grassland ecosystem to air pollutants. IV. The chemical climate: Concentrations of relevant non-criteria pollutants (trace gases and aerosols)

The concentrations of sulphur dioxide, nitric acid, nitrous acid, hydrogen chloride, ammonia and sulphate, nitrate, chloride and ammonium in aerosols were measured continuously for two years at the rural site of Rotenkamp near Braunschweig in south-east Lower Saxony. The level of air pollution registered is typical for rural areas near industrial areas in Central Europe. Long-range transport of polluted air masses from Saxony-Anhalt and Saxony affects air quality when high-pressure areas over Eastern Europe result in easterly winds and reduced vertical exchange due to low inversion layers.

Growth of salt and acid aerosol particles in humid air

Aerosols of industrial significance like ammonium chloride, hydrochloric acid and sulphuric acid aerosols have been generated with particle number concentrations between 10 6 and 10 8 cm −3 and particle sizes between 0.1 and 0.5μmn (NH 4Cl), 0.8–1.5 μm (HCI) and 0.2–0.5 μm (H 2SO 4 ). The influence of the generating conditions on the size and the concentration of the aerosol particles have been investigated. After the generation, the particles were exposed to atmospheres of different relative humidity. If a certain level of relative humidity is exceeded, the solid salt particles dissolute and become droplets. The particle diameter of the salt and acid droplets increases if the relative humidity is raised. The particle diameters and concentrations were measured to show the dependence on the generating conditions and the relative humidity by a laseroptical extinction technique. The results of the measurements were compared with growth models. There was a very good agreement between the experimental data and the growth models for salt and acid aerosols. It is therefore possible to evaluate the limit of the growth by pure water vapour saturation, which is especially useful for the design of particle separators.

Mechanism of induction of asthmatic attacks initiated by the inhalation of particles generated by airbag system deployment.

We have previously demonstrated that inhalation of the dust produced by dual frontal airbag deployment can result in significant bronchospasm in approximately 40% of mild to moderate asthmatics. This study was performed to determine the cause of the asthmatic response. Controlled laboratory study. Asthmatics who were previously tested for their response to airbag effluents were exposed for twenty minutes to either 1) airbag effluents from airbag systems in which the airbag was insulated from the hot deployment module; 2) non-sulfur containing airbag effluents; 3) sodium chloride aerosol; or 4) sodium carbonate-bicarbonate aerosol (pH 10). Pre-exposure, post-exposure, and 2 hour post exposure pulmonary spirometry and mechanics were measured. Subject's filled out symptoms questionnaires before exposure, 2, 4, 8, 12, and 19 minutes into the exposure, immediately post-exposure, and 2 hours post-exposure. Prevention of the pyrolysis of the passenger-side bag as it rested on the hot module after deployment did not diminish the asthmatic response. Removal of sulfur-containing oxidants from the airbag pyrotechnic chemistry, which may have led to sulfite production, similarly did not alleviate the asthmatic response to the airbag effluents. Lastly, when asthmatics were exposed to sodium chloride and sodium carbonate-bicarbonate aerosols at approximately the same concentration (approximately 220 mg/m3) as the airbag aerosol concentration that occurred in the in-car tests, they had responses similar to those produced by the airbag exposures. We conclude that the amount of soluble particulate contained in the aerosol discharged into the passenger compartment by dual frontal airbag deployment is largely the cause of the observed evoked asthmatic attacks. The alkaline pH of the airbag and carbonate aerosols may have added an additional degree of provocation.

Sulfuric Acid Aerosol Followed by Ozone Exposure in Healthy and Asthmatic Subjects

These studies evaluated symptom and pulmonary function responses of humans sequentially exposed to sulfuric acid aerosol and ozone. Thirty healthy subjects and 30 allergic asthmatic subjects underwent 3-hr exposures in an environmental chamber to 100 μg/m3 sulfuric acid and sodium chloride (control) aerosols (in random order), followed 24 hr later by 3-hr exposures to ozone (0.08, 0.12, or 0.18 ppm). Each subject was studied four times, receiving each aerosol preexposure followed by two of the three ozone concentrations. For the healthy group, no convincing symptomatic or physiologic effects of exposure to either the aerosol or ozone on lung function were found. For the asthmatic group, preexposure to sulfuric acid altered the pattern of response to ozone in comparison with sodium chloride preexposure and appeared to enhance the small mean decrements in FVC that occurred in response to 0.18 ppm ozone (means ± SE: −3.6 ± 1.5% with sodium chloride preexposure, −6.8 ± 1.7% with sulfuric acid preexposure). Individual responses among asthmatic subjects were quite variable, some demonstrating reductions in FEV1 of more than 35% following ozone exposure. Analysis of variance of changes in FVC revealed evidence for interactions between aerosol and ozone exposure both immediately after (P = 0.005) and 4 hr after (P = 0.030) exposure. Similar effects were seen for FEV1. When normal and asthmatic subjects were combined, four-way analysis of variance revealed an interaction between ozone and aerosol for the entire group (P = 0.0022) and a difference between normal and asthmatic subjects (P = 0.0048). There was no significant effect of exposures on symptoms for either normal or asthmatic subjects. Asthmatic subjects differ from healthy volunteers in their functional responses following sequential exposures to aerosols and ozone and appear to represent a susceptible population.

A theoretical study on the evaporation of dry ammonium chloride and ammonium nitrate aerosols

A theoretical model has been developed to investigate possible mechanisms and parameters which may influence the evaporation behavior of dry ammonium chloride and ammonium nitrate aerosols. The model results compared well with the experimental observations available in the literature. Effects of particle polydispersity, gas-particle interaction, flow pattern of the system, particle number concentration, and accommodation coefficient on the evaporation of dry ammonium chloride and ammonium nitrate were quantitatively determined. The particle size distribution has a significant effect on the overall evaporation rate. A negligence of the size distribution and inappropriate use of the evaporation theory would lead to departures from experimental observations.

Halotherapy for treatment of respiratory diseases.

This work elucidates the questions upon the development of a new drug-free method of a respiratory diseases treatment. Halotherapy (HT)--is mode of treatment in a controlled air medium which simulates a natural salt cave microclimate. The main curative factor is dry sodium chloride aerosol with particles of 2 to 5 mkm in size. Particles density (0.5-9 mg/m3) varies with the type of the disease. Other factors are comfortable temperature- humidity regime, the hypobacterial and allergen-free air environment saturated with aeroions. The effect of HT was evaluated in 124 patients (pts) with various types of respiratory diseases. The control group of 15 pts received placebo. HT course consisted of 10-20 daily procedures of 1 hour. HT resulted in improvements of clinical state in the most of patients. The positive dynamics of flow-volume loop parameters and decrease of bronchial resistance measured by bodyplethysmography were observed. The changes in control group parameters after HT were not statistically significant. The specificity of this method is the low concentration and gradual administration of dry sodium chloride aerosol. Data on healing mechanisms of a specific airdispersive environment of sodium chloride while while treatment the respiratory diseases are discussed.

Contribution of cadmium in cigarettes to lung cancer: an evaluation of risk assessment methodologies.

This investigation concerned the use of quantitative risk assessment for estimating cancer mortality at low-level exposures. We empirically tested whether extrapolating by linear no-threshold models predicted implausible risks at low-level exposures. Cadmium in cigarette smoke was the low-level exposure, and extrapolation was based on potencies estimated from an occupational study and a rodent cancer bioassay. Inhaled cadmium in mainstream and sidestream smoke was estimated from published laboratory experiments. Smoking-specific lung cancer and all-cause mortality rates were estimated from large population-based studies. The mortality rates, amount of inhaled cadmium, and potency values were used to construct life tables for calculating lifetime lung cancer risk with and without a contribution from cadmium in cigarette smoke. The epidemiologic data predicted that 1 to 18 lung cancer deaths per 10,000 smokers may be attributable to inhaled cadmium in cigarette smoke, or approximately 0.2% to 1.6% of smoking-induced lung cancer deaths. Upper 95% bounds on these figures are 7 to 95 lung cancer deaths or 1.6% to 8.8% of smoking-related deaths. The rodent data predicted that 80 to 416 lung cancer deaths per 10,000 smokers (95% upper bounds: 136-707) or 13% to 47% (23-81%) of smoking-induced lung cancer mortality may be attributable to cadmium in cigarette smoke. Linear extrapolation from human data appears to provide plausible estimates of risk at low doses. Considering the large number of carcinogens present in cigarette smoke, the extrapolation from rodents appears to overestimate human risks.(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of the hypertonic saline responsiveness of the airways to exercise induced asthma symptom severity and to histamine or methacholine reactivity.

Conflicting views exist over whether responsiveness of the airways to hypertonic saline relates to non-specific bronchial hyperresponsiveness measured by histamine or methacholine challenge. The bronchoconstrictor responses to exercise and hypertonic saline are reported to be closely related, but the relationship between the symptoms of exercise induced asthma and airway responsiveness to hypertonic saline is not known. In 29 asthmatic patients with a history of exercise induced asthma, the response to an ultrasonically nebulised hypertonic saline (3.6% sodium chloride) aerosol, measured as the volume of hypertonic saline laden air required to produce a fall in forced expiratory volume in one second (FEV1) of > or = 20% (PD20), was compared with the concentration of histamine (PC20; group 1) and methacholine (PC20; group 2) producing a 20% fall in baseline FEV1 and exercise induced asthma symptom severity score (groups 1 and 2). The hypertonic responsiveness was determined in a dose-response manner to a maximum dose of 310 1 and the exercise induced asthma symptom severity was scored on a scale of 0-5. Of the 29 patients, 23 (79%) were responsive to the hypertonic saline, with PD20 values ranging from 9 to 310 1. A significant correlation was found between the PD20 hypertonic saline and the exercise induced asthma symptom score. There was no significant correlation between the PD20 response to hypertonic saline and the histamine PC20 or methacholine PC20. The exclusion of those subjects who failed to respond to hypertonic saline improved the relationship between hypertonic saline and methacholine PC20. No significant correlation was found between the exercise induced asthma symptom score and histamine PC20 or methacholine PC20. These findings suggest that hypertonic saline responsiveness bears a closer relationship to the severity of exercise induced asthma symptoms than to the non-specific bronchial hyperresponsiveness measured by histamine or methacholine reactivity.

23 O 04 Fiber optical detection and analysis of PAHS adsorbed on sodium chloride aerosols by time-resolved fluorescence spectroscopy

23 O 04 Fiber optical detection and analysis of PAHS adsorbed on sodium chloride aerosols by time-resolved fluorescence spectroscopy

MEASUREMENTS OF THE EFFICIENCY OF RESPIRATOR FILTERS AND FILTERING FACEPIECES AGAINST RADON DAUGHTER AEROSOLS

The filtration efficiencies of respirator filters and filtering facepieces have been tested against radon daughters in a fluorspar mine. The test method involved the use of sampling filters exposed to natural radon daughters in air filtered by the test respirators. Respirators with a filtration efficiency high enough for them to be considered suitable for use against toxic dusts generally reduced radon daughter levels by 90% or more, though nuisance dust masks were ineffective. The measured penetration of radon daughters through the former types of filter correlated reasonably well with the penetration of 0.1 microns neutralized monodisperse aerosols, and with that of the BS 4400 sodium chloride aerosol, measured in the laboratory. To simulate exposure in working conditions mine air containing radon daughters was drawn through the test filters for 8 h, but their performance was not affected and they were not measurably radioactive as a result.

The spatial distribution and particle size of some inorganic nitrogen, sulphur and chlorine species over the North Sea

The use of filter packs and a cascade impactor during a series of research cruises in the southern area of the North Sea has yielded detailed spatial distribution patterns of aerosol concentrations, Cl−, NO3−, SO42−1 and NH4+ and gaseous concentrations, HCl, HNO3 and NH3. The overall distribution of the atmospheric concentrations closely parallels published modelled results for metallic species. The chemical transformations of these aerosols and gases are investigated together with their interactions with the seasalt aerosol. Aerosol chloride loss is greatest in the more polluted areas, whilst concentrations products of NH3 with HNO3 and HCl appear insufficient to sustain the existence of NH4NO3 and NH4Cl. Nitrate is associated predominantly with larger particles and appears to be present substantially as a surface coating on marine aerosol. The total dry deposition input for nitrogen species is calculated for the southern sector with extrapolation to the whole of the North Sea, using particle size weighted deposition velocities of 0.63 and 0.21 cm s−1 for NO3−1 and NH4+, respectively, and literature-derived values for the gaseous constituents. Finally the use of air-mass back trajectories illustrates the role of source regions in influencing the chemical composition of the North Sea atmosphere.

Examination of heterogeneous chemical interactions with aerosol surfaces by radiochemical means - first results

Abstract A technique for the investigation of adsorption and desorption processes on particle surfaces by means of short-lived γ-emitting isotopes is presented. Using 136I as an example, the influence of the chemistry of aerosol particle surfaces could be observed. No adsorption of 136I was found on potassium chloride and molybdenum oxide aerosols at room temperature, whereas strong adsorption was observed on carbon and silver aerosols. Temperatures of 300°C and 500°C were needed to desorb the iodine species from carbon and silver aerosols, respectively. These temperatures were used to calculate the desorption enthalpies.

Comparison of the efficiency of respirator filters and filtering facepieces against radon daughter aerosols and laboratory generated aerosols

Respirator filters and filtering facepieces have been tested for filtration efficiency against radon daughters in a flourspar mine. The test method involved the use of sampling filters exposed to natural radon daughters in air filtered by the test respirators. Respirators with a filtration efficiency high enough for them to be considered suitable for use against toxic dusts generally reduced radon daughter levels by 90% or more, though nuisance dust masks were ineffective. The measured penetration of radon daughters through the former types of filter correlated reasonably well with the penetration of 0.1μm neutralised monodisperse aerosol and with that of the BS4400 sodium chloride aerosol, measured in the laboratory. Test filters were exposed to radon daughters in the mine for 8 hours as a simulation of their behaviour during a working shift, but their performance was not altered by this and they did not show measurable radioactivity as a result of it.

Thermophoretic and photophoretic motion of aerosols

Aerosols of various size and composition may be levitated by a light beam. The required intensity agrees well with theoretical predictions. The coagulation rate of sodium chloride aerosols may be influenced by subjecting the particles to a light source. Coagulation rates of the order of 100 times that of Brownian coagulation have been estimated, primarily the result of thermophoretic forces.

Hydrochloric acid: A regional perspective on concentrations and formation in the atmosphere of Southern California

Atmospheric gaseous hydrochloric acid (HCl) concentrations and water-soluble species in the aerosol phase were measured at nine sites in Southern California throughout the year 1986. Annual average HCl concentrations measured by the denuder difference method ranged from 0.39 ppb at an offshore island to 1.25 ppb onshore at Hawthorne, California. An ion balance on the aerosol shows that coarse particle chloride begins as sea salt over the ocean and is depleted relative to aerosol sodium with transport inland. Total chloride and sodium balances show that chloride depletion from the aerosol is matched by a comparable increase in gaseous HCl concentrations, consistent with the proposition that acid gas reactions with sea salt are the principal source of gaseous HCl in the Southern California atmosphere. Fine aerosol chloride exceeds fine particle sodium on a number of occasions, particularly at one inland site known for extraordinarily high NH3 levels. There is evidence that coarse aerosol chloride from sea salt is being processed by atmospheric reactions through HCl to form fine aerosol, possibly NH4Cl.